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Texas pH Evaluation Project
Prepared by:
Texas Institute for Applied Environmental Research
Tarleton State University
Stephenville, Texas
PR0810
November 2008
Texas pH Evaluation Project
Prepared for:
TMDL Program
Texas Commission on Environmental Quality
Austin, Texas
Prepared by:
David Pendergrass
Larry Hauck
Texas Institute for Applied Environmental Research
Tarleton State University
Stephenville, Texas
PR0810
November 2008
Texas pH Evaluation Project
Table of Contents
TABLE OF CONTENTS
LIST OF FIGURES......................................................................................................... iii
LIST OF TABLES .......................................................................................................... iv
SECTION 1 INTRODUCTION ...................................................................................... 1-1
1.1 Context................................................................................................................................ 1-1
1.2 Report Purpose and Organization....................................................................................... 1-1
SECTION 2 BACKGROUND ....................................................................................... 2-1
2.1 Water Quality and pH......................................................................................................... 2-1
2.2 Environmental Influences on Aquatic pH .......................................................................... 2-3
SECTION 3 DEFINITION OF STUDY AREAS AND METHODS OF DATA
ANALYSIS.............................................................................................................. 3-1
3.1 Definition of Study Areas................................................................................................... 3-1
3.2 Methods and Data Analysis................................................................................................ 3-2
SECTION 4 HISTORICAL DATA REVIEW OF IMPAIRED SEGMENTS AND
POTENTIAL SOURCES OF pH IMPAIRMENT...................................................... 4-1
4.1 Segment 0105—Rita Blanca Lake ..................................................................................... 4-1
4.1.1 Historical Data Review ................................................................................................ 4-1
4.1.2 Potential Sources of pH Impairment and Recommendations....................................... 4-3
4.2 Segment 0229—Upper Prairie Dog Town Fork Red River ............................................... 4-5
4.2.1 Historical Data Review ................................................................................................ 4-5
4.2.2 Potential Sources of pH Impairment and Recommendations....................................... 4-5
4.3 Segment 0401—Caddo Lake.............................................................................................. 4-9
4.3.1 Historical Data Review ................................................................................................ 4-9
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Texas pH Evaluation Project
Table of Contents
4.3.2 Potential Sources of pH Impairment and Recommendations..................................... 4-12
4.4 Segment 0402—Big Cypress Creek below Lake O’ the Pines ........................................ 4-13
4.4.1 Historical Data Review .............................................................................................. 4-13
4.4.2 Potential Sources of pH Impairment and Recommendations..................................... 4-13
4.5 Segment 0507—Lake Tawakoni ...................................................................................... 4-15
4.5.1 Historical Data Review .............................................................................................. 4-15
4.5.2 Potential Sources of pH Impairment and Recommendations..................................... 4-17
4.6 Segment 0605—Lake Palestine........................................................................................ 4-19
4.6.1 Historical Data Review .............................................................................................. 4-19
4.6.2 Potential Sources of pH Impairment and Recommendations..................................... 4-21
4.7 Segment 0606—Neches River above Lake Palestine....................................................... 4-23
4.7.1 Historical Data Review .............................................................................................. 4-23
4.7.2 Potential Sources of pH Impairment and Recommendations..................................... 4-25
4.8 Segment 0803—Lake Livingston..................................................................................... 4-25
4.8.1 Historical Data Review .............................................................................................. 4-26
4.8.2 Potential Sources of pH Impairment and Recommendations..................................... 4-26
4.9 Segment 0818—Cedar Creek Reservoir........................................................................... 4-30
4.9.1 Historical Data Review .............................................................................................. 4-32
4.9.2 Potential Sources of pH Impairment and Recommendations..................................... 4-35
4.10 Segment 1212—Lake Somerville................................................................................... 4-36
4.10.1 Historical Data Review ............................................................................................ 4-37
4.10.2 Potential Sources of pH Impairment and Recommendations................................... 4-37
SECTION 5 SUMMARY OF FACTORS CONTRIBUTING TO pH EXCURSIONS IN
LISTED TEXAS WATER BODIES AND RECOMMENDED ACTIONS.................. 5-1
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Texas pH Evaluation Project
Table of Contents
SECTION 6 REFERENCES......................................................................................... 6-1
APPENDIX A CORRELATIONS OF SELECTED ANALYTES FROM IMPAIRED
SEGMENTS........................................................................................................... A-1
LIST OF FIGURES
Figure 2-1
National rainfall pH trends................................................................................... 2-5
Figure 2-2
Average annual precipitation in Texas 1971 – 2000 ........................................... 2-5
Figure 3-1
Map of Texas showing distribution of the eight reservoirs and two streams
considered in this study........................................................................................ 3-3
Figure 4-1
Map of Rita Blanca Lake (Segment 0105) .......................................................... 4-2
Figure 4-2
Satellite image of Rita Blanca Lake, Hartley County, Texas .............................. 4-3
Figure 4-3
Time history of pH for impaired AUs of Rita Blanca Lake, Segment 0105
(data for 1998 – 2006).......................................................................................... 4-4
Figure 4-4
Map of Upper Prairie Dog Town Fork Red River (Segment 0229) .................... 4-6
Figure 4-5
Time history of pH for impaired AUs of Upper Prairie Dog Town Fork Red
River, Segment 0229 (data for 2003 – 2006)....................................................... 4-7
Figure 4-6
Satellite image of Lake Tanglewood dam and Station 18317 of Segment
0229, Randall County, Texas............................................................................... 4-8
Figure 4-7
Map of Caddo Lake and Big Cypress Creek below Lake of the Pines
(Segments 0401 and 0402)................................................................................. 4-10
Figure 4-8
Time history of pH for impaired AUs of Caddo Lake, Segment 0401
(data for 1994 – 2006)........................................................................................ 4-11
Figure 4-9
Time history of pH for impaired AUs of Big Cypress Creek below Lake O’
the Pines, Segment 0401(data for 1994 – 2006) ................................................ 4-14
Figure 4-10
Map of Lake Tawakoni (Segment 0507) ........................................................... 4-16
Figure 4-11
Time history of pH for impaired AUs of Lake Tawakoni, Segment 0507
(data for 1999 – 2006)........................................................................................ 4-18
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Texas pH Evaluation Project
Table of Contents
Figure 4-12
Map of Lake Palestine (Segment 0605) and Neches River above Lake
Palestine (Segment 0606) .................................................................................. 4-20
Figure 4-13
Seasonality of pH in Lake Palestine, assessment units 3, 9, and 10
combined............................................................................................................ 4-21
Figure 4-14
Time history of pH for impaired AUs of Lake Palestine, Segment 0605
(data for 1999 – 2006)........................................................................................ 4-22
Figure 4-15
Time history of pH for impaired AUs of Neches River above Lake Palestine,
Segment 0606(data for 1995 – 2006)................................................................. 4-24
Figure 4-16
Map of Lake Livingston (Segment 0803).......................................................... 4-27
Figure 4-17
Time history of pH for impaired AUs of Lake Livingston, Segment 0803
(data for 1999 – 2006)........................................................................................ 4-28
Figure 4-18
Seasonality of pH in Lake Livingston, assessment units 1 and 6 combined ..... 4-29
Figure 4-19
Map of Cedar Creek Reservoir (Segment 0818)................................................ 4-31
Figure 4-20
Cedar Creek Reservoir chlorophyll-a 17-yr trend (CCWP 2008) ..................... 4-32
Figure 4-21
Time history of pH for Cedar Creek Reservoir, Segment 0803(data for 1997 –
2006) .................................................................................................................. 4-33
Figure 4-22
Cedar Creek Reservoir pH and trend lines for excursions (red) and entire
dataset (black) .................................................................................................... 4-34
Figure 4-23
Time history for pH of impaired AUs of Lake Somerville, Segment 1212
(data for 1997 – 2006)........................................................................................ 4-38
Figure 4-24
Map of Lake Somerville (Segment 1212).......................................................... 4-39
LIST OF TABLES
Table 2-1
Ionic gradients in reservoirs across Texas selected from Ground and Groeger
(1994)................................................................................................................... 2-2
Table 3-1
Segment names, impaired assessment units (AU), pH criteria, year first listed
for pH, and designated uses ................................................................................. 3-4
Table 3-2
Ecoregion descriptions for impaired segments derived from Griffith et al. (2004)
.............................................................................................................................. 3-5
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Texas pH Evaluation Project
Table of Contents
Table 3-3
Screening levels for nutrients and CHLA in Texas freshwater streams and
reservoirs (TCEQ 2008a)..................................................................................... 3-5
Table 3-4
Summary of pH, alkalinity, DO, and specific conductance for each impaired
assessment unit. ND indicates no data................................................................ 3-6
Table 4-1
Watershed pollutant loadings (% contribution) per land use, adapted from
CCWP (2008)..................................................................................................... 4-35
Table 5-1
Summary of Recommendations for pH Impaired Segments Included in the
Study .................................................................................................................... 5-2
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Texas pH Evaluation Project
Table of Contents
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Texas pH Evaluation Project
Table of Contents
List of Acronyms
ALCOA
ASCE
AU
BIC
CCWP
CWA
FWSD
MGD
MUD
NADP
NOAA
NETMWD
OSSF
RRA
SRA
S.U.
SWQMIS
TRWD
TAMU
TAMU-SCL
TCEQ
TIAER
TNRCC
TWDB
TMDL
TRA
TSI
USACE
USEPA
WWTF
WMA
Aluminum Company of America
American Society of Civil Engineers
Assessment Unit
Berner International Corp
Cedar Creek Watershed Partnership
Clean Water Act
Freshwater Supply District
Million Gallons per Day
Municipal Utiility District
National Atmospheric Deposition Program
National Oceanic and Atmospheric Administration
Northeast Texas Municipal Water District
On-Site Sewage Facility
Red River Authority
Sabine River Authority
Standard Units
Surface Water Quality Monitoring Information System
Tarrant Regional Water District
Texas A&M University
Texas A&M University-Soil Characterization Laboratory
Texas Commission on Environmental Quality
Texas Institute for Applied Environmental Research
Texas Natural Resource Conservation Comission
Texas Water Development Board
Total Maximum Daily Load
Trinity River Authority
Trophic State Index
U.S. Army Corp of Engineers
U.S. Environmental Protection Agency
Wastewater Treatment Facility
Wildlife Management Area
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Texas pH Evaluation Project
Table of Contents
List of Chemical and Analyte Abbreviations
Alk
Ca
CaCO3
CHLA
CO2
2-
CO3
DO
DO%sat
EndTime
FeS2
+
H
H2 CO3
H2 SO4
-
HCO3
Na
NaHCO3
NH3 -N
NO3 -N
-
OH
OP
Secchi
SpCond
TP
Alkalinity
Calcium
Calcium carbonate
Chlorophyll-a
Carbon dioxide
Carbonate
Dissolved oxygen
Dissolved oxygen percent saturation
End time of water sample
Pyrite
Hydrogen ion
Carbonic acid
Sulfuric acid
Bicarbonate
Sodium
Sodium bicarbonate
Ammonia-nitrogen
Nitrate-nitrogen
Hydroxl ion
Orthophosphorus
Secchi depth
Specific conductance
Total phosphorus
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Texas pH Evaluation Project
Introduction
SECTION 1
INTRODUCTION
1.1 Context
Section 303(d) of the Clean Water Act (CWA) and U.S. Environmental Protection
Agency (USEPA) Water Quality Planning and Management Regulations (40 Code of Federal
Regulations [CFR] Part 130) require states to develop total maximum daily loads (TMDL) for
water bodies not meeting designated uses where water quality-based controls are in place.
TMDLs establish the allowable loadings of pollutants or other quantifiable parameters for a
water body based on the relationship between pollution sources and in-stream water quality
conditions, so states can implement water quality-based controls to reduce pollution from both
point and nonpoint sources and restore and maintain the quality of its water resources
(USEPA 1991).
As specified in the states’ water quality assessment guidance (e.g., TCEQ 2008a), all
water bodies are assigned to one of five categories ranging from Category 1 (attaining all water
quality standards and no use is threatened) to Category 5 (water body does not meet applicable
water quality standards or is threatened for one or more designated uses by one or more
pollutants). By definition all water bodies on the State of Texas 303(d) list are Category 5 and
are further assigned to one of three subcategories: Category 5a (a TMDL is underway, scheduled,
or will be scheduled), Category 5b (a review of the water quality standards for the water body
will be conducted before a TMDL is scheduled), or Category 5c (additional data and information
will be collected before a TMDL is scheduled).
The State of Texas 2008 303(d) list (TCEQ 2008b) includes numerous water bodies
reported as having pH exceedances, either above or below applicable pH criteria. Texas Surface
Water Quality Standards require a majority of water bodies to maintain a pH range of 6.5-9.0
with a few exceptions (TNRCC 2000a). Most of the water bodies listed for pH have been
assigned to either Category 5b or Category 5c.
1.2 Report Purpose and Organization
The TCEQ is leading an effort to assess the water quality of several classified segments
in Texas reported on the State of Texas 303(d) list for pH impairments. These classified
segments include:
•
Rita Blanca Lake, Segment 0105, Category 5c, first listed in 2004
•
Upper Prairie Dog Town Fork Red River, Segment 0229, Category 5c, first listed in
2006
•
Caddo Lake, Segment 0401, Category 5c, first listed in 1996
•
Big Cypress Creek below Lake of the Pines, Segment 0402, Category 5b, first listed in
2000
•
Lake Tawakoni, Segment 0507, Category 5c, first listed in 2008
•
Lake Palestine, Segment 0605, Category 5c, first listed in 2006
•
Neches River above Lake Palestine, Segment 0606, Category 5c, first listed in 2002
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Texas pH Evaluation Project
•
•
•
Introduction
Lake Livingston, Segment 0803, Category 5c, first listed in 2008
Cedar Creek Reservoir, Segment 0818, Category 5c, first listed in 2002
Lake Somerville, Segment 1212, Category 5c, first listed in 2002
With the exception of Segment 0402, each of these segments is in Category 5c - additional data
and information will be collected before a TMDL is scheduled. The numeric pH criteria will be
addressed on Segment 0402 during the next standards revision.
TCEQ TMDL Program contracted with the Texas Institute for Applied Environmental
Research (TIAER) to (1) acquire historical data and review information necessary to assess
segment listings, (2) evaluate water quality using graphical and statistical methods, and (3) assist
the TCEQ in preparing the justification for further study, listing category changes, standards
adjustments, delisting, or developing TMDLs.
This report is the culmination of a 3-month effort from June through August 2008 to
obtain and analyze data on 10 TCEQ classified segments included in the State of Texas 2008
303(d) list for pH impairments. The report begins with a brief background section on basic pH
principles followed by descriptions of the location of the designated segments and data analysis
methods. These two sections are followed by analysis of each segment including environmental
context, major point and nonpoint sources of nutrient enrichment, historical sampling data,
listing information, and suggestions for future study. The report closes with a summary of
findings and general trends in pH exceedances across the segments.
1-2
Texas pH Evaluation Project
Background
SECTION 2
BACKGROUND
2.1 Water Quality and pH
In the simplest terms, pH is a measure of hydrogen ion concentration:
pH = - log10 [H+]
(Eq. 1)
where [H+] is the hydrogen ion concentration in moles/liter. More specifically, it is a measure of
the relative concentrations of hydrogen (H+) and hydroxyl (OH-) ions and is measured on a log
scale ranging from 1-14, acidic (low) to basic (high). The unit of measurement of pH is standard
units (S.U.), but common practice, as will be employed in this report, is to leave off the units
when reporting numeric pH values. In pure water, both ions are in dynamic equilibrium and the
pH is 7 (neutral). When H+ ions increase and OH- ions correspondingly decrease, water becomes
more acidic and because of the negative logarithmic scale pH values become less than 7.
Alternatively, if OH- is in greater abundance than H+, the water is more basic (i.e., pH > 7).
Most aquatic organisms can tolerate a pH range of 6.0 ─ 9.0 but suffer significant reproductive
and developmental problems, and eventually death, if the water they inhabit becomes too acidic
or basic.
Hydrogen ion concentration in water is directly proportional to aqueous carbon dioxide
(CO2) and inversely proportional to carbonate (CO32-) (Boyd 1990). When CO2 is removed from
a system at equilibrium, carbonate increases then hydrolyzes in the presence of water releasing a
bicarbonate ion and OH- (Eq. 2). This results in more basic water.
CO32- + H2O ↔ HCO3- + OH-
(Eq. 2)
When CO2 is increased, it joins with water to create carbonic acid (H2CO3) which
dissociates to release bicarbonate (HCO3-) and a hydrogen ion (H+) (Eq. 3). This makes water
more acidic.
CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+
(Eq. 3)
Aqueous CO2 is in dynamic equilibrium with atmospheric CO2. This component can be added to
a summary of Equations 2 and 3:
CO2 (air) ↔ CO2 (dissolved) + H2O ↔ H2CO3 ↔ H+ + HCO3- ↔ H+ + CO32-
(Eq. 4)
Photosynthesis and respiration tend to govern the amount of CO2 in water. However,
where bicarbonate is abundant, water is usually resistant to changes in pH caused by biochemical
processes. Wetzel (2001) explains it this way:
An addition of hydrogen ions neutralizes hydroxyl ions formed by the
dissociation of HCO3- and CO32- but more hydroxyl ions are formed
2-1
Texas pH Evaluation Project
Background
immediately by reaction of the carbonate with water. Consequently, the pH
remains essentially unaltered, unless the supply of carbonate or bicarbonate ions
is exhausted. Similarly, when hydroxyl ions are added they react with
bicarbonate ion: HCO3- + OH- ↔ CO32- + H2O.
Alkalinity generally refers to the amount of carbonate or bicarbonate in water. As
demonstrated above, alkaline water tends to be basic and buffered from pH swings because of
reactions with carbonate and bicarbonate. Thus alkalinity has often been used synonymously
with buffering capacity, “basicness” of water, and even hardness [commonly measured as mg/L
of calcium carbonate (CaCO3)], because in natural waters carbonate is often bound with calcium.
In fact, all references to alkalinity in this study are in units of “mg/L as CaCO3”.
Where calcium (Ca) and sodium (Na) are abundant in the soil, carbonate and bicarbonate
can be stored as CaCO3 and sodium bicarbonate (NaHCO3). In productive alkaline waters where
pH is consistently above 8.3, inorganic carbon in the form of dissolved CO2 is rare (CO32becomes the dominant species of inorganic carbon) and algae and phytoplankton assimilate
carbon from alternative sources such as CaCO3 and NaHCO3. As carbonate is hydrolyzed it
releases OH- resulting in even higher pH (Eq. 2). Thus, the Texas Panhandle, which has soils
high in calcium and sodium content (Table 2-1), can be very basic during warm summer
afternoons when photosynthetic assimilation of inorganic carbon is at a maximum. Boyd (1990)
noted that in some eutrophic waters with high levels of sodium and potassium pH can soar to 10
– 12 as photosynthesis uses up CO2 and equilibrium reactions cause the sodium and potassium
carbonate compounds to dissociate.
Table 2-1
Ionic gradients in reservoirs across Texas selected from Ground and Groeger
(1994). Values represent mean values from the individual reservoirs.
Sample n = 15, 44, and 21 for West, Central and East populations,
respectively.
Variable
pH
Total Alkalinity
(mg CaCO3 L-1)
Specific
Conductance
(μS cm -1)
Calcium
(mg L-1)
Sodium
(mg L-1)
Median
Range
Mean
Range
Mean
Range
West
8.2
7.9 – 8.5
129
69 – 180
2444
1138 – 5932
Central
8.2
7.9 – 8.4
134
93 – 206
533
287 – 983
East
7.4
6.6 – 7.9
39
15 – 76
178
89 – 274
Mean
Range
Mean
Range
144
56 – 759
436
48 – 2711
49
24 – 76
41
6 – 128
14
6.5 – 26
15
6.7 – 39
In regions where alkalinity is low, such as East Texas (Table 2-1), buffering capacity is
generally low as well, and large diel swings in dissolved CO2 caused by photosynthesisrespiration cycles can result in large changes in pH during warmer periods. Some natural waters
contain virtually no carbonate and their alkalinity is effectively zero. During peak respiration the
2-2
Texas pH Evaluation Project
Background
pH in these water bodies can reach as low as 4.5. Dips below 4.5 have been recorded in the
Neches River above Lake Palestine (Crowe 2008) but as Boyd (1990) notes, such pH
depressions are attributable to other mineral acids in the soil, such as sulfuric acid (H2SO4), and
not the absence of alkalinity.
2.2 Environmental Influences on Aquatic pH
In reservoirs, eutrophication (high levels of primary production) is typically the dominant
driving force behind pH fluctuations. During summer months when aquatic macrophyte and
phytoplankton production is high, aqueous inorganic carbon (i.e. dissolved CO2) is removed
through photosynthesis and pH rises. This process is especially apparent in deep, open water
where phytoplankton are the dominant primary producers. In contrast, sunlight penetration of
the water column is limited in fluvial and transition zones by turbidity, shading, and heavy
detritus loads, reducing rates of CO2 removal by photosynthesis. In addition, microbial
decomposition of the detritus in these zones can cause the rate of respiration to exceed the rate of
production creating an excess of CO2 and lowering pH. Diel fluctuations in pH also occur in
response to daily peaks and valleys in photosynthetic activity. In a eutrophic reservoir, summer
diel peaks are expected to be higher than winter peaks because of seasonal differences in gross
productivity. Although climate and hydrogeology have a significant influence on pH, in general,
if the gross primary production to community respiration ratio (p:r) is high, pH will increase
(resulting from a net decrease in CO2). If the ratio is small, pH will decrease (resulting from a
net increase in CO2).
Recent research indicates that reservoir eutrophication is primarily an anthropogenic
phenomenon (Smith et al. 2006). In Texas, anthropogenic nutrient inputs to rivers and reservoirs
“dwarf” natural sources according to Ground and Groeger (1994) who also postulated that nearly
all surface waters in the state have been impacted by anthropogenic nutrient loading. The
portion of eutrophication of Texas reservoirs attributable to human development (point and
nonpoint sources), hereafter called cultural eutrophication (sensu Dodds 2006), is of special
significance because it is an unnatural process yet has potential to be reasonably controlled with
improved understanding of its underlying mechanisms. Point source discharges, such as
wastewater treatment facilities (WWTFs), can indirectly alter pH in streams and reservoirs
through nutrient enrichment causing high algal productivity. Nonpoint nutrient contributions
from agriculture are of primary concern in many watersheds with nutrient enriched reservoirs
because agricultural contributions often outpace point source contributions by a large margin
(e.g., McFarland and Hauck 1999 and CCWP 2008). Exceptions to this rule of nonpoint source
dominance apply where the reservoir is relatively small and the primary inflow is from point
sources, such as in Rita Blanca Reservoir in the Texas Panhandle which is largely fed by the City
of Dalhart WWTF (see Section 4.1).
Land use can exert influence on pH within the climatic, geological, and vegetative
context of the region. Impermeable cover in urban areas limits percolation by rainwater and its
interaction with minerals found in soils and bedrock. Mine trailings in the form of pyrite (FeS2),
abundant in east Texas, can increase the H2SO4 content of soil as FeS2 is oxidized; a process
known to depress soil pH for a century after mining operations have ceased (Skousen 1990, Cole
2-3
Texas pH Evaluation Project
Background
1994). Riverine segments are most susceptible to the effects of acidic groundwater discharge,
especially during seasons when groundwater dominates stream inflows (Dodds 2002).
In streams, vegetative cover can affect pH on a seasonal basis, especially where
deciduous trees are abundant. For example, Crowe (2008) found that in the Neches River a large
drop in stream pH in late fall from 6.6 to 4.8 coincided with sap-drop in the local forest. When
trees go dormant during the winter, they draw less moisture from the soil and groundwater flows
more freely, a phenomenon commonly signaled in temperate areas by an increase in stream
discharge. As groundwater flows more freely through the sulfur-bearing soils typical of east
Texas, it forms a dilute sulfuric acid before entering surface flows. Additional leaf fall during
the fall and winter increases the coarse particulate matter loads which further increases the
dissolved CO2 respired by microbes decomposing the leaf litter. These gains in CO2 contribute
to lower surface-water pH (see Eq. 3).
In streams and reservoirs, the severity and direction (acid or basic) of pH fluctuations are
partly functions of regional geology. West and central Texas limestone geology contains
relatively higher amounts of CO32- than east Texas, primarily in the form of calcium carbonate.
Far-east Texas (ecoregion 35, Level III; Griffith et al. 2004) is characterized by acidic sandyloamy soils. This geological difference alone accounts for much of the range of values in several
ionic categories in Texas reservoirs (Ground and Groeger 1994; Table 2-1).
At the continental scale, climate exerts influence on local pH ranges. Rain is naturally
moderately acidic (pH ~ 5.6) because it interacts with atmospheric CO2 and airborne particles
during descent. Upon landing, rain weathers soil and bedrock (to varying degrees) through
physical and chemical action. Dissolved soil components flow with surface runoff and
groundwater and can cause mild to drastic pH fluctuations in surface-water bodies, particularly
streams. Across the continental United States, rainfall pH decreases west to east and this pattern
applies to the large state of Texas that spans approximately 13 degrees of longitude: west Texas
precipitation is consistently above 5.3 while eastern portions regularly receive rain with a pH
under 4.8 (NADP 2008; Figure 2-1). Challenged to address the possible influences of acid rain
on water quality in East Texas, TCEQ commissioned a report published in 2007 (Crowe et al.
2007) that found no classic signals of unnaturally acidic rainfall and thus dismissed
anthropogenic causes as a regional concern. How much precipitation falls is also important to
the mineral weathering processes that impact the pH of runoff and groundwater. Two segments
in this study, Rita Blanca Lake and Upper Prairie Dog Town Fork Red River, are in the
Panhandle where average precipitation totals 18 inches – 22 inches (457 mm – 559 mm)
(TWDB 2007; Figure 2-2). In contrast, the other eight segments in this report are in regions of
east Texas that receive 42 inches – 50 inches (1,067 mm – 1,270 mm) of precipitation per year.
2-4
Texas pH Evaluation Project
Background
Figure 2-1
National rainfall pH trends (Source: NADP 2008).
Figure 2-2
Average annual precipitation in Texas 1971 – 2000 (Source: TWDB 2007).
2-5
Texas pH Evaluation Project
Background
2-6
Texas pH Evaluation Project
Definition of Study Areas and Methods of Data Analysis
SECTION 3
DEFINITION OF STUDY AREAS AND METHODS OF DATA ANALYSIS
3.1 Definition of Study Areas
For the impaired water bodies included in this study, the following segment and
assessment unit (AU) descriptions are from TCEQ (2008b). Segments are designated in the
water quality standards and AUs are units created to facilitate sub-segment characterization.
Rita Blanca Lake (Segment 0105): From Rita Blanca dam up to normal pool level of 1176.5
m (impounds Rita Blanca creek). Segment 0105 contains only one AU.
Upper Prairie Dog Town Fork Red River (Segment 0229): From a point 100 meters
upstream of the confluence of Salt Fork Creek in Armstrong County to Lake
Tanglewood Dam in Randall County.
•
AU 02—Palo Duro Canyon State Park upstream boundary to upper end of
segment at Tanglewood Dam.
Caddo Lake (Segment 0401): From the Louisiana State Line in Harrison/Marion County to
a point 12.3 km downstream of SH 43 in Harrison/Marion County, up to pool elevation
of 51.4 m (impounds Big Cypress Creek).
•
AU 02—Harrison Bayou arm
•
AU 03—Goose Prairie arm
•
AU 05—Clinton Lake
Big Cypress Creek Below Lake O’ the Pines (Segment 0402): From a point 12.3 km
downstream of SH 43 in Harrison Marion County to Ferrell’s Bridge Dam in Marion
County.
•
AU 01—Lower 14.5 km
•
AU 02—17.7 km below Black Cypress Creek
Lake Tawakoni (Segment 0507): From Iron Bridge Dam in Rains County up to normal
pool elevation of 133.2 m (impounds Sabine River).
•
AU 04—Cowleech Fork of Sabine River arm
Lake Palestine (Segment 0605): From Blackburn Crossing Dam in Anderson/Cherokee
County to a point 6.7 km downstream of FM 279 in Henderson/Smith County, up to
normal pool elevation of 105.2 m (impounds Neches River).
•
AU 03—Mid-lake near Tyler PWS intake
•
AU 09—Flat Creek arm
•
AU 10—Upper Lake
Neches River above Lake Palestine (Segment 0606): From a point 6.7 km downstream of
FM 279 in Henderson/Smith County to Rhines Lake Dam in Van Zandt County.
•
AU 02—Prairie Creek to river km 11.3
3-1
Texas pH Evaluation Project
Definition of Study Areas and Methods of Data Analysis
•
AU 03—River km 11.3 to headwaters
Lake Livingston (Segment 0803): From Livingston Dam in Polk/San Jacinto County to a
point 1.8 km upstream of Boggy Creek in Houston/Leon County, up to normal pool
elevation of 39.9 m (impounds Trinity River).
•
AU 01—Lowermost portion of reservoir, adjacent to dam
•
AU 06—Middle portion of reservoir centering on US 190
Cedar Creek Reservoir (Segment 0818): From Joe B. Hoggsett Dam in Henderson County
up to normal pool elevation of 98.1 m (impounds Cedar Creek).
•
AU 01—From dam to just above Clear Creek cove entrance
•
AU 02—Caney Creek cove
•
AU 03—Clear Creek cove
•
AU 04—Lower portion of reservoir east of Key Ranch Estates
•
AU 05—Cove off lower portion of reservoir adjacent to Clearview Estates
•
AU 06—Middle portion of reservoir downstream of Twin Creeks cove
•
AU 07—Twin Creeks cove
•
AU 08—Prairie Creek cove
•
AU 09—Upper portion of reservoir adjacent to Lacy Fork cove
•
AU 11—Upper portion of reservoir east of Tolosa
•
AU 12—Uppermost portion of reservoir downstream of Kings Creek
Somerville Lake (Segment 1212): From Somerville Dam in Burleson/Washington County
up to normal pool elevation of 72.5 m (impounds Yegua Creek).
•
AU 01—Eastern end of reservoir near dam
•
AU 03—Middle of reservoir near Birch Creek State Park
See Figure 3-1 for a state map showing all segments not meeting the criteria for pH and
Table 3-1 for a summary of designated uses and pH criteria for each segment and its impaired
assessment units. These 10 segments are concentrated in the eastern quarter of the state, with the
exception of Segments 0105 and 0229 in the Panhandle. Altogether the segments span three
Level-III and five Level-IV ecoregions (Griffith et al. 2004). Table 3-2 briefly summarizes
ecoregion descriptions and the segments they contain.
Texas water bodies are listed for concern if any of their nutrient or chlorophyll-a (CHLA)
samples exceed screening levels more than 20 percent of the time. Screening levels have been
established as the 85th percentile values for each analyte in freshwater streams and reservoirs and
they are provided in Table 3-3. These screening levels were used to assess the potential impact
of cultural eutrophication through nutrient loading, a cause of pH exceedances in some segments.
3.2 Methods and Data Analysis
At the start of this investigation the TCEQ provided TIAER a nearly complete body of
surface water sample data for all of the 10 impaired segments in this study. These data were
taken from TCEQ’s SWQMIS database. This data set included many samples that did not meet
the requirements for inclusion in the 305(b) assessment, the section of the CWA that requires
biennial state water quality assessment reporting and from which the 303(d) list is developed. A
3-2
Texas pH Evaluation Project
Figure 3-1
Definition of Study Areas and Methods of Data Analysis
Map of Texas showing distribution of the eight reservoirs and two streams
considered in this study.
3-3
Texas pH Evaluation Project
Table 3-1
Definition of Study Areas and Methods of Data Analysis
Segment names, impaired assessment units (AU), pH criteria, year first listed
for pH, and designated uses. Uses are according to Texas Surface Water
Quality Standards (TNRCC 2000a).
Segment
AU
Rita Blanca Lake
0105_01
Upper Prairie Dog Town
Fork Red River
Caddo Lake
2004
NCR, L, WF
9.0
2006
CR, H
0401_02
0401_03
0401_05
6.0
6.0
6.0
8.5
8.5
8.5
1996
CR, H, PS
6.0
8.5
2000
CR, H, PS
6.0
9.0
2008
CR, H, PS
6.0
8.5
2002
2004
CR, I, PS
6.0
6.0
8.5
8.5
2006
CR, H, PS
6.0
8.5
6.0
8.5
2002
CR, I, PS
6.5
9.0
6.5
9.0
2008
CR, H, PS
0818_01
0818_02
0818_03
0818_04
0818_05
0818_06
0818_07
0818_08
0818_09
0818_11
0818_12
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
8.5
8.5
8.5
8.5
8.5
8.5
8.5
8.5
8.5
8.5
2002
CR, H, PS
6.0
8.5
1212_01
1212_03
6.0
6.0
8.5
8.5
2002
CR, H, PS
Neches River above Lake
Palestine
Lake Palestine
0606_02
0606_03
0605_03
0605_09
0605_10
Lake Somerville
Designated
Uses
6.5
0402_01
0402_02
0507_04
Cedar Creek Reservoir
First
Listed
0229_02
Big Cypress Creek below
Lake of the Pines
Lake Tawakoni
Neches River above Lake
Palestine
Lake Livingston
pH Criteria
Low High
6.5
9.0
0606_02
0606_03
0803_01
0803_06
CR = contact recreation; NCR = non-contact recreation; H = high aquatic life use; I = intermediate aquatic life use; L = limited aquatic life use;
WF = waterfowl habitat; PS = public water supply
3-4
Texas pH Evaluation Project
Table 3-2
Ecoregion descriptions for impaired segments derived from Griffith et al.
(2004).
Segment
0105
III
25
IV
25e
0229
26
26c
0507
0818
33
33
33a
33a
1212
33
33b
0401
0402
0605
0606
0803
35
35
35
35
35
35a
35a
35a
35a
35e
Table 3-3
Definition of Study Areas and Methods of Data Analysis
Ecoregion Level
Level IV Brief Description
High, dry, flat, large % is cropland, some grazeland, high oil/gas
production, Ustic soil
Badlands with little cropland, some grazeland, riparian vegetation
includes cottonwood, willow, hackberry, highly saline Ustic soil
Post-oak savanna though most land is now pasture and range, Udic
acid sandy to clayey loams in low-lying areas, many areas with dense
underlying clay pan
Hardwood forests with much pasture and range, irregular topography,
Ustic sandy to sandy-loam soil
Mostly well drained sandy-loamy Ultisols and Alfisols, mix of
hardwoods, loblolly pine, and grasses, gentle rolling slopes, some
grazing pasture, lumber, oil/gas production
Mostly longleaf pine forest on hilly, dissected topography, acidic
sandy-loamy soil
Screening levels for nutrients and CHLA in Texas freshwater streams and
reservoirs (TCEQ 2008a).
Freshwater
Stream
Reservoir
0.33
0.11
Ammonia
NH3 -N (mg/L)
Nitrate
Orthophosphate
Total Phosphorus
Chlorophyll-a
NO3 -N (mg/L)
OP (mg/L)
TP (mg/L)
CHLA (μg/L)
1.95
0.37
0.69
14.10
0.37
0.05
0.20
26.70
concerted effort was made to analyze the same body of data TCEQ used in its 305(b)
assessments. For segments first listed in 2008 (0507 and 0803) TIAER analyzed samples from
1999 – 2006 per TCEQ guidance (TCEQ 2008a). Because some segments were first listed in
1996, 2000, 2002, 2004, or 2006, TIAER used additional data collected prior to 1999 that TCEQ
used in their initial listings of these segments. A comparison of TIAER’s culled dataset to
TCEQ’s dataset revealed near perfect matches to the number of samples assessed and the rate of
exceedances.
A summary of pH, alkalinity, dissolved oxygen (DO), and specific conductance data by
segment and impaired assessment unit are provided in Table 3-4, which provides a general
characterization of several water quality constituents associated with pH.
3-5
Texas pH Evaluation Project
Table 3-4
Definition of Study Areas and Methods of Data Analysis
Summary of pH, alkalinity, DO, and specific conductance for each impaired
assessment unit. ND indicates no data.
Alkalinity
Sp. Cond.
DO
pH
(mg/L as CaCO3 )
(mg/L)
(μmhos/cm)
Median Range Mean Range Mean Range Mean Range
RitBla 0105_01 18
9.4 7.9-10.5 312 208-443 11.4 4.9-20.0 1266 946-2029
PraDog 0229_02 13
9.2 8.2-10.1 222 156-375 8.4 5.3-11.5 1769 1280-2350
Caddo 0401_02 88
6.4
5.3-7.9
23
7-47
4.1 0.3-12.1 162
70-347
0401_03 8
6.2
4.9-7.9
16
5-47
3.6 0.2-12.1 120
73-347
0401_05 86
6.3
5.5-7.3
13
6-26
4.4 0.1-11.0 115
68-160
BigCyp 0402_01 72
6.4
5.5-8.1
14
6-23
7.3 3.7-13.4 112
53-161
0402_02 76
6.5
5.4-7.6
15
7-29
7.3 1.8-12.7 121
64-325
Tawako 0507_04 144
8.4
7.1-9.3
68
36-94
9.3 5.3-12.7 170
80-225
Palest 0605_03 38
7.5
6.8-9.4
33
20-50
8.5 3.6-13.2 213 128-307
0605_09 19
8.3
7.3-9.2
41
27-52
8.5 5.3-13.7 249 203-301
0605_10 10
8.2
7.3-8.9
45
22-62
8.1 4.6-10.3 293 256-353
NecPal 0606_02 38
6.7
3.5-7.0
42
5-114
4.2 0.4-9.7 332 80-1840
0606_03 17
6.7
5.4-7.7
33
5-69
5.0 0.2-8.1 304 130-622
Living 0803_01 104
8.2
6.7-9.9
89 59-144
9.8 3.6-16.1 346 264-397
0803_06 43
8.6
7.2-9.6
95 43-116
9.6 1.9-23.0 432 368-539
CedCrk 0818_01 60
7.9
6.6-9.4
54
40-72
8.2 2.1-14.1 191 124-270
0818_02 17
8.3
7.4-9.1 ND
ND
8.5 4.1-16.1 166 128-190
0818_03 17
8.4
7.4-9.7 ND
ND
8.8 4.0-15.5 167 127-192
0818_04 49
8.0
7.3-9.4
55
44-73
8.1 4.1-11.8 191 125-273
0818_05 18
8.6
7.5-9.6 ND
ND
9.4 5.9-16.0 168 125-206
0818_06 157
8.0
6.5-9.4
56 42-101
8.1 1.9-15.2 197 123-354
0818_07 15
8.6
7.6-9.3 ND
ND
8.5 5.5-13.6 171 128-192
0818_08 46
8.6
7.2-9.3
50
36-59
8.4 4.9-11.1 187 130-245
0818_09 49
8.1
7.2-9.7
54
36-80
8.3 3.5-12.3 199
95-287
0818_11 43
8.3 7.3-11.6 56
41-77
8.2 5.0-12.5 212 129-327
0818_12 16
8.1
7.2-9.8 ND
ND
9.1 4.8-13.0 600 138-1322
Somerv 1212_01 81
8.2
5.4-9.3
62
41-72
8.4 2.8-13.6 398 232-571
1212_03 36
8.6
7.8-9.6
60
44-72
9.5 5.8-13.0 405 264-550
Segment
AU
n
Seasonality of median pH for each segment was calculated with ANOVA for segments
that qualified for parametric analysis, i.e., segments with normally distributed data. For
segments with data that was not normally distributed (Segments 0507, 0606, 0818, 1212), overall
seasonality was determined with a Kruskal-Wallis test, and Wilcoxon two-sample z-tests were
used for between-season comparisons. Pearson correlation coefficients were determined by
using the means of combined data for selected analytes from each segment. Correlation matrices
are presented in Appendix A. Dissolved oxygen percent saturation (DO%sat), an indicator of
primary productivity, was not available in the dataset acquired from TCEQ. To allow calculation
3-6
Texas pH Evaluation Project
Definition of Study Areas and Methods of Data Analysis
of DO%sat, an equation from the American Society of Civil Engineers (ASCE 1960) was used to
approximate DOsat using water temperature (T; °C):
DOsat =14.652 - 0.41022T + 0.007991T2 - 0.000077774T3
Eq. 5
Correlations between DO%sat and pH were determined with Pearson correlation coefficient
analysis.
As a matter of convention, all statements of statistical significance are based on α = 0.05.
The term “impaired” is used in the context of stations, assessment units, and segments, and in all
cases refers to failure to meet designated uses. Precipitation information was taken primarily
from NOAA (2002). In a few cases, precipitation means are provided instead of medians
indicating they originated from local weather stations closer to the segment under discussion.
Historical stream discharge and reservoir storage data was taken from USGS gage data.
Population numbers are based on the 2000 U.S. Census (U.S. Census Bureau 2008). There are
several references to TCEQ’s Trophic State Index (TSI) ranks of reservoirs (TCEQ 2008c). The
rankings were determined by Carlson’s Trophic State Index for chlorophyll-a (CHLA) and
reservoirs are ranked relative to one another out of a total of 102 for which data were available.
As examples, among the study reservoirs, Caddo Lake, ranked 53rd, is considered moderately
eutrophic for CHLA whereas Rita Blanca Lake, ranked 102nd, is the most hypereutrophic. For
reference, Lake Nacogdoches was ranked number one.
3-7
Texas pH Evaluation Project
Definition of Study Areas and Methods of Data Analysis
3-8
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
SECTION 4
HISTORICAL DATA REVIEW OF IMPAIRED SEGMENTS AND
POTENTIAL SOURCES OF pH IMPAIRMENT
4.1 Segment 0105—Rita Blanca Lake
Rita Blanca Lake (Figure 4-1) is located in the extreme Northwestern Panhandle of
Texas, south of Dalhart in Hartley County. Rita Blanca Creek was impounded in 1939, is owned
by the Texas Parks and Wildlife Department, and is managed as a sanctuary for migratory birds,
including 40,000-100,000 geese that visit the lake every year. A designated use of the lake is
that of high quality waterfowl habitat (TNRCC 2000a). The lake is relatively small with a
capacity of 12,100 acre-feet, a surface area of 212 ha and a maximum depth of 1.5 m. The Red
River Authority (RRA 2008) states that the City of Dalhart WWTF is “the only significant
inflow” (RRA 2008) and is supplemented by occasional rainfall (approx. 432-483 mm annually).
The Dalhart WWTF is permitted for 1.5 MGD.
The local geology is highly alkaline limestone with high salt content that is expressed in
the limnology of surface and groundwater in the region (see Table 3-4 for alkalinity and specific
conductance in Rita Blanca Lake). The climate is also arid and these regional geological and
climatic characteristics are consistent with systems dominated by evaporative processes (Gibbs
1970, Ground and Groeger 1994).
4.1.1 Historical Data Review
Segment 0105 is small and consists of one AU with one monitoring station (10060). Rita
Blanca Lake was first listed for pH exceedances in 2004 and currently ranks last among Texas
reservoirs in TCEQ’s TSI, making it the most eutrophic lake in Texas for chlorophyll-a (CHLA)
concentrations, secchi depth and total phosphorus concentrations. The CHLA mean from 14
samples was 349 μg/L. The mean Secchi depth was 0.08 m and an upward trend in algal content
was apparent between 2006 and 2008 (TCEQ 2008c). The mean total phosphorus concentration
was 3.36 mg/L and every sample assessed in the 303(d) list exceeded the total phosphorus and
orthophosphate phosphorus screening levels. Ammonia and nitrate samples also consistently
exceeded screening levels. Historical monitoring data for pH exists as early as 1972 and has
continued with only a few brief interruptions through the present. Frequent pH exceedances
above the current criteria of 9.0 occurred during the mid 1980s and again in recent years, 2002 –
2008. Since 2002, spring, summer, and fall had median pH values of 9.5, 9.7, and 9.8,
respectively. Winter had a significantly lower median pH of 8.6.
Local geology is high in calcium carbonate (CaCO3), and alkalinity levels in Rita Blanca
Lake reflected this fact with a range of 208-443 mg/L as CaCO3 from 2002 – 2007. The mean
instantaneous DO was 11.4 mg/L and specific conductance was high, relative to Central and East
Texas (Table 2-1), averaging 1267 μS cm-1. Interestingly, pH was not significantly correlated
with a positive increase in DO%sat, as would be expected if algae and phytoplankton activity
4-1
Texas pH Evaluation Project
Figure 4-1
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Map of Rita Blanca Lake (Segment 0105).
4-2
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
were causing spikes in pH. This disconnect may be attributable to other factors driving DO
levels such as microbial respiration processes and wind mixing—Dalhart wind averages
approximately 20 km/h and is located in one of the windiest regions in the state (Berner
International Corp 2008). Satellite images reveal several bright green drainage ditches leading
from Dalhart to the reservoir, presumably draining runoff from residences and businesses (Figure
4-2). Clearly visible in the image are also several green circles of crop production; presumably
from center-pivot irrigation.
Figure 4-2
Satellite image of Rita Blanca Lake, Hartley County, Texas
(www.maps.live.com, accessed 08 August 2008).
4.1.2 Potential Sources of pH Impairment and Recommendations
The City of Dalhart WWTF is the dominant source of inflow to the lake, 40,000-100,000
migratory geese visit the lake every year, numerous drainage ditches lead from Dalhart to the
lake, and crop circles from center pivot irrigation that dominate the landscape to the west and
east may produce nutrient-rich runoff during infrequent wet-weather runoff events. The lake is
also very shallow which allows for complete wind-mixing of nutrients, thus enhancing metabolic
processes that contribute to the productivity of the lake. Cultural eutrophication† and lake
management practices are clearly contributing to the hypereutrophy of the lake. Intense
photosynthetic removal of CO2 likely is to blame for high-pH values. Although alkalinity is high
in the region, it cannot buffer Rita Blanca Lake from pH spikes over 10 (Figure 4-3). This could
be explained by high sodium in the region’s geology and surface waters (Table 2-1). Sodium
bicarbonate is more soluble than CaCO3 and allows for larger accumulations of CO32- which
subsequently hydrolyzes in water (Eq. 2) to produce hydroxyl ions (Boyd 1990). Thus, pH
values above the criterion of 9.0 can be explained by primary production—enriched by cultural
eutrophication—and the geologic context in which the eutrophication is occurring.
Rita Blanca Lake is experiencing cultural eutrophication and may be characterized as
hypereutrophic. The lake periodically experiences pH exceedances more than 1 standard unit
†
The portion of eutrophication attributable to human development.
4-3
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Texas pH Evaluation Project
10.5
10
pH
9.5
9
8.5
8
Month
10060
Figure 4-3
Time history of pH for the impaired AU of Rita Blanca Lake, Segment 0105 (data for 1998 – 2006).
4-4
Mar-07
Dec-06
Sep-06
Jun-06
Mar-06
Dec-05
Aug-05
May-05
Feb-05
Nov-04
Aug-04
May-04
Feb-04
Nov-03
Aug-03
May-03
Feb-03
Nov-02
Aug-02
May-02
Feb-02
Nov-01
Aug-01
May-01
Jan-01
Oct-00
Jul-00
Apr-00
Jan-00
Oct-99
Jul-99
Apr-99
Jan-99
Oct-98
Jul-98
Apr-98
Jan-98
7.5
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
higher than the upper pH criterion of 9.0. Since cultural eutrophication is an explanatory
variable in the pH exceedances and the lake is part of the State of Texas park system, it would at
first seem that the TMDL process should be a high priority for restoration of Rita Blanca Lake.
However, the shallowness of the lake in addition to its climatic and geologic setting and the
seasonal abundance of migratory birds are all conditions that support eutrophication and elevated
pH readings and portend difficulties in implementing sufficient control measures to reduce pH
exceedances. Careful consideration should be given prior to embarking on the TMDL process
regarding the priority of this water body compared to others in the state and as to whether the
watershed protection planning process or consideration of standards revision might be viable
alternatives to a TMDL.
4.2 Segment 0229—Upper Prairie Dog Town Fork Red River
Assessment unit 2 of the Upper Prairie Dog Town Fork Red River begins at the upstream
boundary of Palo Duro Canyon State Park and ends at Tanglewood Dam. The lone sampling
station for this AU is 18317, approximately 100 m below the dam (Figure 4-4). TCEQ has
records from other stations further downstream in AU 2 but the data predates the period of record
for the 2006 303(d) list (data ranged from 1992 – 1998) and there were no exceedances at these
stations. The City of Amarillo WWTF has two outfalls with a combine permitted discharge of
12 MGD. Outfall 001 is approximately 1 km below sampling station 18317, and outfall 002 is in
the upper end of Lake Tanglewood. The segment is located in the middle of the Texas
Panhandle in the Southwestern Tablelands ecoregion (Table 3-2), the arid “badlands.”
Gustavson et al. (1982) described the geology as karst with an abundance of salts, gypsum, and
dolomite.
4.2.1 Historical Data Review
This segment was first listed for pH in 2006 and, as of 2008, 8 of 13 samples have
exceeded the 9.0 criteria (Figure 4-5). During the last 5 years of record, the pH has not dipped
below 8.2—not surprising considering the segment’s high alkalinity (156-375 mg/L as CaCO3).
High pH readings occurred most often during the spring and summer, which had median values
of 9.2 and 9.5, respectively. Dissolved oxygen hovered between 9 and 12 mg/L during the
winter months and 3-8 mg/L during the summer. A possible explanation for the seasonal
difference in DO is that flow over Tanglewood Dam (Figure 4-6) is greater during the winter and
lower during the summer when a local power plant recycles much of the discharge from the City
of Amarillo WWTF, outfall 002 (Pat Bohannan, personal communication, October, 2008). This
implies that during summer months, seeps, which are often DO-poor, are a more significant
source of flow in the channel. Further study is needed to confirm this speculation.
4.2.2 Potential Sources of pH Impairment and Recommendations
The Red River Authority considered nutrient-rich discharge from Lake
Tanglewood and the City of Amarillo WWTF possible sources of eutrophication in the AU
(RRA 2007). The TCEQ ranked Lake Tanglewood 91st in TSI and it has a CHLA TSI trophic
class of hypereutrophic. Nitrate, orthophosphate phosphorus, and total phosphorus (mean 1.18
4-5
Texas pH Evaluation Project
Figure 4-4
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Map of Upper Prairie Dog Town Fork Red River (Segment 0229).
4-6
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Texas pH Evaluation Project
10.5
10
pH
9.5
9
8.5
8
Dec-06
Sep-06
Jun-06
Mar-06
Dec-05
Aug-05
May-05
Feb-05
Nov-04
Aug-04
May-04
Feb-04
Nov-03
Aug-03
7.5
Month
18317
Figure 4-5
Time history of pH for the impaired AU (station 18317) of Upper Prairie Dog Town Fork Red River, Segment
0229 (data for 2003 – 2006).
4-7
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
mg/L) exceeded screening levels in all 16 lake samples as of 2006. The spillover dam exposes
nutrient-rich, shallow outflow to full sun before it enters the stream bed less than 100 m
upstream from station 18317 (Figure 4-6). As mentioned above, this might be a more significant
source of nutrients during winter months when City of Amarillo WWTF flows are not recycled
to the extent they are during the summer. Because the greatest number of exceedances occurred
during the spring and summer, further research is needed to determine the seasonal impact of
Lake Tanglewood overflow on the water quality at station 18317.
18317
Figure 4-6
Satellite image of Lake Tanglewood dam and station 18317 of Segment 0229,
Randall County, Texas (www.maps.live.com, accessed 08 August 2008).
Access may have restricted AU 2 sampling to station 18317, but it is questionable
whether this site is representative of the entire assessment unit. Because of its proximity to Lake
Tanglewood, station 18317 is strongly influenced by the eutrophication of the reservoir,
hydrologic modification to the stream from presence of the dam, and the exposure of the shallow
flow as it descends over the dam. The TCEQ should consider evaluating the availability of
additional or alternative sample sites that would be distributed more evenly throughout the
assessment unit. Data from additional sample sites should be added to the existing body of data
and the AU re-evaluated before a decision is made regarding TMDL actions.
Because the City of Amarillo WWTF outfall 002 is downstream of station 18317 and pH
is not a concern in downstream AU 1 of Upper Prairie Dog Town Fork, it cannot be determined
whether the WWTF discharge at outfall 002 is a source of pH impairment for the lower portion
of AU 2. However, AU 1 did have several samples exceeding screening levels for CHLA,
nitrate, orthophosphate phosphorus, and total phosphorus. It is within reason to presume that the
lower portion of AU 2 could experience pH exceedances associated with WWTF dischargesupported eutrophication but the evidence is circumstantial. Unless additional sampling sites are
monitored downstream, efforts to address this water quality concern should be directed at
upstream processes affecting eutrophication in Lake Tanglewood.
4-8
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
4.3 Segment 0401—Caddo Lake
Caddo Lake spans portions of Marion County, Texas, and Caddo County, Louisiana. It
has a surface area of approximately 12,140 ha, an average depth of one meter, and a maximum
depth of about three meters. Naturally impounded by a log jam that originated during the period
1799 – 1835, it has been permanently impounded since 1914 by earthen and concrete dams
operated by the U.S. Army Corps of Engineers for purposes of water supply and recreation
(USACE 2008). The lake is fed primarily by Big Cypress, Little Cypress, and Black Cypress
Creeks. Big Cypress Creek flows out of Lake of the Pines and through the City of Jefferson
before its confluence with the other tributaries to form the upstream marshy portion of the lake.
Nearly a third of Caddo Lake is a cypress swamp (Darville et al. 1998), situated in the
upper half of the lake. The watershed is heavily forested and is characterized by acid soils, low
alkalinity (mean of 18 mg CaCO3 L-1), and relatively high amounts of rainfall (average of 11681270 mm annually). Warm annual temperatures also support dense communities of macrophytes
and high rates of microbial decomposition in Caddo Lake’s shallow waters. These natural
conditions predispose the lake to low pH.
4.3.1 Historical Data Review
Caddo Lake is divided into six AUs numbered 1, 2, 3, 5, 7, and 8. Assessment units 2, 3,
and 5 are currently listed for low-pH and the segment has been listed since 1996. According to
recent data the majority of exceedances occurred in AU 2 at station 10286 and in AU 5, station
14236 (Figure 4-7) and from February 2003-July 2004 (Figure 4-8). The three impaired AUs for
pH exceedances are also included on the 303(d) list for depressed DO. According to findings by
Crowe et al. (2007), pH exceedances in the upper mid-lake during the same time period were
associated with high flows from tributaries, especially following dry spells. The upper mid-lake
is not included in impaired AUs 2, 3, and 5.
Darville et al. (1998) delineated three primary sub-habitats within the Caddo Lake
ecosystem using discriminant analysis with over 93% accuracy: riverine, wetland, and lake
(open water). Their analysis used 20 water quality parameters, including pH, alkalinity, and
assorted nutrients, and covered 79 sampling sites during the summer of 1997. Their pH data
ranged 5.7-8.4 with the lowest readings occurring in the wetland sites and the highest readings in
open lake water, presumably due to greater phytoplankton productivity and lower microbial
respiration in open water. Mean alkalinity of their combined sites was 16 mg/L as CaCO3. Total
phosphorus and nitrate concentrations were much lower in lake habitats, and Darville et al.
attributed this to assimilation by phytoplankton. Finally, it is anticipated that conditions will be
suitable in the wetland habitats for high microbial activity, which lowers the p:r ratio for the
system and, typically, the pH as well.
The City of Jefferson is about 18 river miles upstream of Caddo Lake and has a WWTF
outfall that discharges into an unnamed tributary of Black Cypress Creek about 10 km upstream
of the confluence with Big Cypress Creek (Figure 4-7). The facility is permitted for 0.55 MGD.
Big Cypress Creek below Lake of the Pines (Segment 402) is listed for low pH in the lower and
4-9
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Texas pH Evaluation Project
Figure 4-7
Map of Caddo Lake and Big Cypress Creek below Lake of the Pines (Segments 0401 and 0402).
4-10
Mar-94
Jun-94
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pH
Texas pH Evaluation Project
7.5
Figure 4-8
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
8
AU 2
AU 3
AU 5
10286
14946
15275
14236
7
6.5
6
5.5
5
4.5
Month
10286
14946
4-11
15275
14236
Time history of pH for impaired AUs of Caddo Lake, Segment 0401 (data for 1994 – 2006).
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
middle assessment units of the river immediately upstream of Caddo Lake, and it is the next
segment discussed. Black Cypress Creek is listed for depressed DO concentrations and bacteria
concerns.
4.3.2 Potential Sources of pH Impairment and Recommendations
Point source contributions are scarce around Caddo Lake. The City of Jefferson WWTF
has a relatively small permitted discharge, which flows a long distance to Caddo Lake through a
productive stream system—capable of rapid nutrient assimilation. The WWTF effluent is
unlikely to have direct significant effects on the lake’s limnology. Nonpoint nutrient sources are
also relatively scarce since only 10% of the watershed is dedicated to agriculture (NETMWD
2005). The NETMWD also reported that despite “substantial” retirement and recreational
development around the lake, 88% of the land use was still forest and wetlands. The degree to
which on-site sewage facilities (OSSFs) might contribute to nutrient enrichment could not be
ascertained in this “desktop” study and remains largely an unknown.
It is fully anticipated that observed pH values and exceedances below the lower criterion
for Caddo Lake are dominantly the result of natural conditions in the lake’s assessment units that
are impaired. Respiration processes in swamps result in acid waters as CO2 is produced in large
amounts, especially in a setting with naturally acidic soils and low alkalinity in surface waters.
Thus, buffering capacity is naturally low on account of the geological and climatic context of
Caddo Lake and its contributing watershed. Generally, swamps—some of which can be
extremely acidic—are documented to support thriving communities of plants, animals, and
microorganisms (Cain 1928, Benke et al 1984). More specifically, the Louisiana Department of
Wildlife and Fisheries (Lester et al 2005) listed 18 animal species of concern found in cypresstupelo-blackgum swamp habitats, and the Texas Parks and Wildlife Department (TPWD 2008)
describes a rich fish diversity (71 species) and many kinds of waterfowl, mammals, and
vegetation that are flourishing under the acidic conditions of Caddo Lake.
Caddo Lake is a unique and important natural resource of the state that warrants
protection of its water quality. At the same time, the previously discussed findings of Darville et
al. emphasized the role sample location has in the assessment process. The impaired AUs in
Caddo Lake are all in wetland and riverine habitats where the p:r ratio is lower than in open
water habitats and where lower pH values would be anticipated than in the main body of the
lake. The majority of pH exceedances in the impaired AUs occurred during the 18-month period
of February 2003 through July 2004 and for the subsequent three years of monitoring only one
excursion has been observed (Figure 4-8). The pH exceedances during this period have been
associated with high flows that followed dry periods (Crowe et al. 2007) and a similar pattern of
pH exceedances was also noted during the same period in the major tributary to Caddo Lake ─
Big Cypress Creek (which is the next segment discussed).
It is suggested that the pH
exceedances in Caddo Lake may be related to characteristics of both the wetland and riverine
habitat included in the impaired AUs and hydrologic patterns that were reported to have
perpetrated the rash of exceedances in 2003 and 2004.
Continuation of the monitoring of Caddo Lake is recommended as well as investigation
of the implications of station location on monitored pH. Additionally a re-evaluation of the low
4-12
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
pH criterion should be considered, since the excursions seem to be attributable to natural
conditions present in the lake.
4.4 Segment 0402—Big Cypress Creek below Lake O’ the Pines
Big Cypress Creek flows from below Lake of the Pines to the marshy headwaters of
Caddo Lake (Figure 4-7). The City of Jefferson (Marion County) is the only major municipality
discharging directly into the segment’s watershed and its WWTF discharges into a tributary of
Black Cypress Creek approximately 10-km upstream of Big Cypress Creek.
The watershed is well-forested (81%) with pine, cypress, and a mix of hardwoods
including sweetgum (NETMWD 2005), especially in the eastern half. Soils are acidic, welldrained sandy-loams and the region receives approximately 1168-1270 mm annually of
precipitation.
4.4.1 Historical Data Review
The two downstream AUs (AU 1 and AU 2) of Segment 0402, representing the 32 km
between Black Cypress Creek and Caddo Lake, were first listed for low pH in 2000. Low pH
exceedances were recorded in 17% and 13% of samples in AU 1 (stations 10295, 15022) and AU
2 (stations 14471 and 16254), respectively, and most of the exceedances occurred from February
2003 – July 2004 (Figure 4-9), as was experienced in Caddo Lake. Winter months (December –
February) contained particularly low readings (range 5.4-5.9) and account for 41% of the
exceedances. This seasonality is particularly stark considering only 26 samples were taken
during the winter compared to 37, 57, and 28 samples for spring, summer, and fall, respectively.
Calcium carbonate is nearly absent from the soil in the region (Griffith et al. 2004) and thus
alkalinity in the impaired stations is extremely low (6-29 mg/L as CaCO3). Precipitation pH
averages around 4.8 (Figure 2-1).
Assessment units 1 and 2 are also listed for low DO. The impaired stations are located
near the marshy headwaters of Caddo Lake where respiration is expected to meet or exceed
production (Darville et al. 1998). Relative to West Texas, the riparian zone is more densely
vegetated and contributes a larger amount of leaf litter and large woody debris to the river
channel, food resources for microbes and macroinvertebrates (TNRCC 2000b). Warm humid
conditions support a high metabolism in East Texas waterways that at times becomes anoxic
(Darville et al. 1998; NETMWD 2005).
4.4.2 Potential Sources of pH Impairment and Recommendations
The natural environment predisposes Big Cypress Creek to relatively low pH throughout
the year but winter exceedances predominate in measured values. This winter predominance is
likely tied to sap-drop, increased groundwater contribution to surface water, and microbial
decomposition of leaf litter. Significant effects on pH by sap-drop were discovered in the same
ecoregion 120 km to the southwest (see Neches River above Lake Palestine, Section 4.7).
4-13
Historical Data Review of Impaired Segments and
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Texas pH Evaluation Project
8.5
AU 1
AU 2
8
10295
15022
14471
16254
7.5
pH
7
6.5
6
5.5
Half of all exceedances:
February 2003 – July 2004
Jun-93
Sep-93
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Feb-04
May-04
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Nov-04
Feb-05
May-05
Aug-05
Dec-05
Mar-06
Jun-06
Sep-06
Dec-06
Mar-07
Jun-07
Sep-07
5
Month
10295
Figure 4-9
15022
14471
16254
Time history of pH for impaired AUs of Big Cypress Creek below Lake O’ the Pines, Segment 0402 (data for
1994 – 2006).
4-14
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
There are few cultural eutrophication agents in the watershed: the three municipalities,
Jefferson, Karnack, and Uncertain, all have populations under 3,000 and the only major
discharger, the City of Jefferson WWTF outfall (0.55 MGD permitted flow), discharges into
Black Cypress Bayou more than 10 kilometers upstream of Big Cypress Creek. Lake O’ the
Pines marks the upstream boundary of Segment 0402. Lake O’ the Pines is considered
moderately eutrophic with occasional exceedances above nutrient screening levels. Considering
the productivity of this system, the assimilative capacity of Black Cypress Bayou and Big
Cypress Creek should be sufficient to attenuate most of the nutrient impact from Lake O’ the
Pines and the City of Jefferson WWTF before streamflows reach the downstream AUs of Big
Cypress Creek, though further research is needed to confirm this supposition.
As with Caddo Lake, many natural factors drive acidic processes in Big Cypress Creek
and cultural eutrophication does not appear to be a significant contributor to the pH exceedances.
For these reasons, re-evaluation of the pH standard should be considered in this segment. The
majority of exceedances occurred in sluggish wetland areas and during the winter season, which
also suggests a need for an expanded sampling effort that extends the spatial and temporal scope
of the dataset.
4.5 Segment 0507—Lake Tawakoni
Lake Tawakoni is the most upstream reservoir of the Sabine River and it is situated about
48 km east of Dallas. It was dammed in 1960 for water supply and has evolved into a source for
recreation. The north arm of the reservoir is fed by Cowleech Fork Sabine River and it is the
only portion of Lake Tawakoni listed for any impairment (pH or otherwise) on the 2008 303(d)
list (Figure 4-10). The depth of the Cowleech Fork arm ranges from 0 to 4.8 m. (TWDB 2003).
The Cowleech Fork arm drains 458 km2 and much of the watershed has agricultural land uses
such as grazed land, hay production, and crop production such as wheat, cotton, and sorghum.
Cowleech Fork is intermittent until its confluence with Long Branch Creek which receives
effluent from the City of Greenville WWTF (4.23 MGD permitted) about 17 km upstream of
Lake Tawakoni. According to a special study by the Sabine River Authority (SRA 1999), the
river becomes perennial at this juncture. Based on this circumstantial evidence, a considerable
portion of flow into the Cowleech Fork of Lake Tawakoni would be WWTF effluent during dry
periods. More study is needed to confirm this speculation.
Ground and Groeger (1994) classified Lake Tawakoni as an East Texas reservoir where
pH, specific conductance, alkalinity, and other measures of ionic composition were low (see
Table 2-1). Indeed, alkalinity in the current dataset only ranged from 36-94 mg/L as CaCO3, and
specific conductivity was 80-225 μS cm-1. Instream pH readings in the Neches River, just one
county to the south, were heavily influenced by groundwater and regularly dropped below a pH
of 5.0 (Crowe 2008).
4.5.1 Historical Data Review
pH is the only analyte for which the Cowleech Fork arm of Lake Tawakoni is listed,
although some exceedances were noted for screening levels of CHLA, nitrate, and
orthophosphate phosphorus. Data from stations 17836 and 10440 were used to determine
4-15
Texas pH Evaluation Project
Figure 4-10
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Map of Lake Tawakoni (Segment 0507).
4-16
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
attainment based on the pH criteria for this area. Seasonality of pH was significant in a KruskalWallis test (X = 65.08, p < .0001) and is graphically apparent in the recent pH data for Cowleech
Fork arm (Figure 4-11). Most pH exceedances occurred during the summer (56%) when the
median pH was 8.9 (range 7.8-9.3). Summer-winter (z = -6.78, p < .0001) and summer-spring (z
= -6.29, p < .0001) differences were the most distinct in Wilcoxon two-sample z-tests with
summer having the higher pH.
Photosynthetic assimilation of NO3- can cause alkalinity to increase with an
accompanying rise in pH (Stumm and Morgan 1996), in addition to pH increases from CO2
uptake during photosynthesis. In Lake Tawakoni, there was a significant negative correlation
between pH and NO3- (r = -0.74, p < .0001) suggesting uptake of NO3- by primary producers
caused elevations in alkalinity and pH. CHLA was positively correlated with pH (r = 0.69, p <
0.0001), further supporting the role of a high p:r ratio and photosynthesis in increasing pH.
4.5.2 Potential Sources of pH Impairment and Recommendations
Evidence that cultural eutrophication is the most likely cause for high pH in Lake
Tawakoni is observed in a) the fact that natural environmental factors work to bring the pH
down, b) summer peaks in pH, and c) significant correlations between pH and NO3- (negative)
and pH and CHLA (positive). Summer pH spikes coincide with the peak season for algae
growth (indicated by CHLA) when temperatures are warm and sunlight is more abundant.
However, algae is only an indicator of nutrient enrichment; the evidence for cultural nutrient
enrichment is found in an examination of the potential point and nonpoint sources in the
watershed. MB Wastewater Services L.L.C. is a permitted discharge immediately near station
17836 (Figure 4-10), but the permit was not issued until January 2006 and no discharge seems to
have occurred before the end of the assessment period-of-record in November 2006. The City of
Greenville WWTF could be a significant source of nutrient-enriched flows during dry weather
for the Cowleech Fork arm. Exceedances of pH occurred most often during July – September
when precipitation and lake levels were generally low. Because of proximity to the Cowleech
Fork arm and size of discharge (permit limit of 4.23 MGD), the City of Greenville WWTF is a
potential contributor of the nutrient enrichment causing cultural eutrophication and summer pH
exceedances in this portion of Lake Tawakoni. However, nutrient loadings to the lake from
nonpoint sources during the typical highest rainfall months of spring and early summer could
also contribute to the conditions resulting in pH exceedances during mid and late summer.
Regarding nonpoint source loading contributions, McFarland et al. (2001) made similar
conclusions in the North Bosque River which is periodically intermittent and fed by a WWTF in
the upper reaches before entering Lake Waco, a reservoir with nutrient enrichment concerns.
Significant exceedances in pH appear limited to the Cowleech Fork arm of the lake and
are likely the result of cultural eutrophication processes beginning to be manifest in this upper
arm of Lake Tawakoni that functions as a transition from riverine to lacustrine environments.
Spikes occur shortly after high-rainfall months of the year, suggesting nonpoint source pulses of
nutrients, along with WWTF flows, could be responsible for a large portion of the enrichment
that spurs algal blooms in the Cowleech Fork arm and the corresponding exceedances in pH.
Since the pH exceedances are associated with the typical summer season of maximum primary
productivity, the impairment appears to be associated with nutrient enrichment. Hence, the pH
4-17
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Texas pH Evaluation Project
9.5
9
pH
8.5
8
7.5
Month
10440
Figure 4-11
17836
Time history of pH for the impaired AU of Lake Tawakoni, Segment 0507 (data for 1999 – 2006).
4-18
Jun-07
Mar-07
Dec-06
Sep-06
Jun-06
Mar-06
Dec-05
Aug-05
May-05
Feb-05
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Aug-04
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Jul-00
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Jul-99
7
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
exceedances in a reservoir with limited buffering capacity (i.e., relatively low alkalinity) are
likely a harbinger of cultural eutrophication, an issue that can be addressed through the TMDL
process.
4.6 Segment 0605—Lake Palestine
Lake Palestine in northeast Texas was dammed in 1962 for municipal and industrial
water use. There are numerous communities surrounding the lake that utilize this resource and
the lake experiences heavy recreation use. The lake has a conservation pool capacity of 370,908
acre-feet but during a period of dry weather from spring 2005 – fall 2006 the storage was
considerably lower than normal and dropped as low as 297,000 acre-feet in October 2006. The
region receives on average about 864-990 mm of precipitation a year with peak median rainfall
in May (114 mm) and June (86 mm) and low median rainfall in December – February (39-49
mm). Despite low pH in regional soils (Griffith et al. 2004), shallow groundwater (Crowe 2008),
and some surface streams [e.g. Neches River above Lake Palestine (Segment 0606), Table 3-4],
several stations in upper and mid Lake Palestine are listed for high pH exceedances (Figure 412).
The City of Tyler (Westside) WWTF discharges into Black Fork Creek, a tributary of the
Neches River above Lake Palestine, approximately 10 km upstream of Lake Palestine. This
WWTF has a permitted discharge of 13 MGD; fully 10 times the discharge of the other six
permitted facilities in the watershed combined (Crowe 2007). The City of Chandler WWTF (0.5
MGD permitted) discharges into a drainage ditch almost adjacent to the west shore in the upper
arm of the lake just below the Neches River.
Assessment unit 3 was first listed in 2006, followed by the addition of assessment units 9,
and 10 in Lake Palestine in 2008. Assessment unit 3 has one sampling station, 16346, located on
the east shore of the middle portion of the lake where the City of Tyler operates a raw-water
intake. Crowe (2007) reported higher phytoplankton abundance here than in the upstream AUs
where macrophytes were more abundant. Assessment unit 9 (stations 18371 & 18557) is located
just inside the Flat Creek arm near the town of Moore Station. Assessment unit 10 (station
18643) is on the east shore immediately below the confluence of Kickapoo Creek and the Neches
River; a transition zone with large amounts of submerged and floating macrophytes.
4.6.1 Historical Data Review
Lake Palestine is classified hypereutrophic and has a TSI ranking of 88 (TCEQ 2008c).
A large number of CHLA exceedances were noted in all three AUs resulting in a status of
Concern for Screening Level in the 2008 303(d) list. In a t-test of seasonality for pH, all seasons
differed significantly except for winter-spring (graphically depicted on Figure 4-13). Seventeen
of the 20 exceedances in Segment 0605 occurred from August – October (Figure 4-14). The
other three occurred in May, June, and November. The exceedances are not extreme ─ most
were under 9.0 and the highest, 9.4, occurred only one time (Sept. 2002, station 16346). During
the dry weather and low-storage period of 2005 – 2006, pH at all stations was below 8.0.
Pearson correlation analysis indicated a significant relationship between pH and CHLA (r = 0.61,
p < 0.0001) and pH and DO%sat (r = 0.60 p < 0.0001).
4-19
Texas pH Evaluation Project
Figure 4-12
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Map of Lake Palestine (Segment 0605) and Neches River above Lake
Palestine (Segment 0606).
4-20
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
pH
Season
Figure 4-13
Seasonality of pH in Lake Palestine, assessment units 3, 9, and 10 combined.
Center bars are medians, plus signs are means and boxes without
overlapping notches are significantly different (p < 0.05). Width of boxes
denotes relative n (winter = 14, summer = 18).
4.6.2 Potential Sources of pH Impairment and Recommendations
Seasonality, CHLA, and DO%sat were all significantly correlated with pH and the lake
has been listed as hypereutrophic by the TCEQ (2008c), which all strongly suggest that
exceedances are a response to photosynthetic activity by primary producers. Where macrophytes
and attached algae are dominant, light penetration is reduced and this lowers phytoplankton
abundance. This is the case in the shallow, turbid, upstream reaches where macrophyte
productivity is high yet DO and pH are not concerns. Phytoplankton is the dominant primary
producer where the sampling stations are located in the impaired AUs, including station 18643
(AU 10), which is located in the upper lake east shore but was noted by Crowe (2007) for high
CHLA.
There are only two likely point sources of nutrient enrichment, based on their size and
location, affecting the listed assessment units: City of Tyler (Westside) WWTF and The City of
Chandler WWTF. Art Crowe (TCEQ Region 5, Tyler Office, personal communication, July
2008) also confirmed the likely impact of the Tyler facility which discharges into Black Fork
Creek, a tributary of the Neches River above Lake Palestine. Interestingly, several other
sampling stations exist along the Neches River and Lake Palestine in closer proximity to the
Tyler outfall and they are not listed for any impairment. The maintenance of pH below 8.5 at
these stations, in spite of nutrients from WWTF effluent, is likely attributable to three things, 1)
the influence of acidic groundwater into the narrow riverine channel of the Neches, 2) canopy
cover that discourages algal growth, and 3) the upstream influx of acidic flows from the Neches
4-21
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Texas pH Evaluation Project
9.5
AU 3
AU 9
16346
18371
18557
AU 10 18643
9
pH
8.5
8
7.5
Month
16346
Figure 4-14
18371
18557
18643
Time history of pH for impaired AUs of Lake Palestine, Segment 0605 (data for 1999 – 2006).
4-22
Mar-07
Dec-06
Sep-06
Jun-06
Mar-06
Dec-05
Aug-05
May-05
Feb-05
Nov-04
Aug-04
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Jul-99
7
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
River above the Black Fork Creek confluence. These natural environmental sources of low-pH
waters and barriers to eutrophication are removed once the Neches River opens into the
lacustrine zone of Lake Palestine.
Urban nonpoint sources abound in the watershed with lake-front homes, recreation
facilities, marinas, etc. Besides Tyler, with a population of 83,650 and Chandler (pop. 2,099),
there are four towns with populations under 800 situated within 10 km of the reservoir.
A TMDL seems reasonable in this segment where cultural eutrophication appears very
likely to be at the root of high pH exceedances with the sources potentially being both point and
nonpoint sources. Natural processes explaining high-pH exceedances are simply lacking for
Lake Palestine. In addition, because problems are restricted to a season (late summer-early fall)
and a particular group of primary producers (phytoplankton) and are within close range of the 8.5
pH criteria, it is recommended that a study of inter-annual phytoplankton structure and function
be conducted (sensu Roelke et al. 2004) to determine whether a focused control mechanism
could be put in place to limit blooms of phytoplankton during certain times of the year.
4.7 Segment 0606—Neches River above Lake Palestine
The Neches River above Lake Palestine begins in Henderson/Smith Counties, 6.7 km
downstream of FM 279, and ends at Rhines Lake Dam in Van Zandt County (Figure 4-12). The
segment is in the same ecoregion as Lake Palestine (35a) and is subjected to approximately the
same climate. The immediate watershed is less populated than Lake Palestine and land use is
more agricultural based on a qualitative assessment of maps and satellite images. The City of
Van (pop. 2,362) is the only local municipality that drains into the segment directly (or nearly so)
upstream of the impaired assessment units. It has a WWTF (0.6 MGD permitted) with an outfall
in Big Sandy Creek about 4 river kilometers upstream of its confluence with the Neches River.
It is worth repeating that low pH and alkalinity are characteristic of the regional soils and
waterways (Griffith et al. 2004, Crowe 2008, TNRCC 2000b). Due to extremely low alkalinity
(Ground and Groeger 1994), pH fluctuations of higher magnitude and a generally lower mean
than West Texas streams are to be expected.
4.7.1 Historical Data Review
Only the upper two AUs (2 & 3) are listed for low pH exceedances. Station 10597 was
used to assess AU 2, and station 10598 was used to assess AU 3. They were first listed for pH in
2002 but have been listed for low DO since 1996. The lowermost assessment unit (AU 1) is
listed for bacteria and was first listed for bacteria in 2008. Seasonality was not significant for
pH, but exceedances only occurred between August and March with 7 of the 11 exceedances
occurring between October and January. Excursions of pH were almost an annual event from
1998-2006 and ranged between 4.9 and 5.8 except for an event in late 2006 that dropped the pH
in the lower station (10597) to 3.5 (Figure 4-15). This event was tied to moderate rain events
(approximately 25-40 mm) in mid-October that ended a prolonged period of dry weather in the
basin (Crowe 2008). The rain was not sufficient to cause runoff but filtered into the soil, reemerging several weeks later as isolated pools in the river channel that had been dry at the start
4-23
Jun-95
Figure 4-15
Jul-96
10597
4-24
Jun-07
Mar-07
Dec-06
Sep-06
Jun-06
Mar-06
Dec-05
Aug-05
May-05
Feb-05
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Feb-03
Nov-02
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Jul-00
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AU 3
Mar-96
Dec-95
8
Sep-95
pH
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
10597
10598
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
Month
10598
Time history of pH for impaired AUs of Neches River above Lake Palestine, Segment 0606 (data for 1995 –
2006).
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
of the month. Crowe (2008) postulated that seasonal sap-drop and leaf-fall coupled with the
timing and intensity of rainfall contributed to the low pH. Citing the high abundance of
hardwoods in the watershed, Crowe suggested that when the trees go dormant it provides
shallow groundwater a longer period of saturation time in the sulfuric soils characteristic of the
area. A mild sulfuric acid is the product that enters the streambed through seeps following lowrunoff rains. Because rainfall is typically stronger and more regular than it was in 2006, such
extreme drops in pH are not common. Nevertheless, the 2006 event appears to have been a
natural process driven by hydrogeology, climate, and vegetation.
The median pH across all assessed samples was 6.7 and DO averaged 4.4 mg/L. These
values are indicators of low p:r ratios, and it is reasonable to assume that microbial breakdown of
leaf litter is a major driver of biochemical processes in this reach of the Neches River. The dense
canopy likely drops large amounts of organic matter into the stream and shades the channel with
strong effect (based on satellite imagery), precluding significant algal growth and the
commensurate photosynthetic assimilation of CO2.
4.7.2 Potential Sources of pH Impairment and Recommendations
Low-pH exceedances do not appear to be unnatural in this stream based on the evidence
presented above. There is little readily identifiable as significant point or nonpoint sources in the
watershed of the impaired AUs, since the major discharger and urban area (i.e., the City of Tyler)
would impact the Neches River below the impaired AUs. The regional alkalinity is naturally so
low that pH “perfect storms” will occur periodically with little remedy. There is simply little in
the hydrogeology to buffer against dramatic swings in hydrogen ion concentration.
Under the ambient conditions identified in this study, it would be reasonable to reevaluate the lower pH criterion for Segment 0606, since the pH exceedances appear to be
associated with natural conditions rather than cultural eutrophication as the term is broadly
defined in this study.
4.8 Segment 0803—Lake Livingston
Lake Livingston, an impoundment of the Trinity River in Southeast Texas, was dammed
in 1969. It is the largest dam built for water supply in the state of Texas, the lake covers 33,590
ha and has 1,750,000 acre-feet of water at normal pool elevation (40 m). It has an average depth
of 7 m, a maximum depth of 27.4 m, and more than 724 km of shoreline. There are numerous
recreational facilities on the lake shore which is heavily developed with residential
neighborhoods, particularly along the east shore in Onalaska (pop. 1,174) and West Livingston
(pop. 6,612). Huntsville (pop. 35,078) is the only major city in the watershed and has a WWTF
(1.6 MGD permitted) that discharges into a tributary about 20-km upstream of the west fork of
Lake Livingston. The Trinity River is the major tributary contributing flow into the
impoundment.
The lake is located in the Southern Tertiary Uplands ecoregion (35f) where longleaf pine
abounds along with some open beech forests (Table 3-2). Soils are sandy-loamy and generally
acid (pH ranges about 4.5 – 7.5) with very low alkalinity. Rainfall totals about 1090-1245 mm
4-25
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
per year; May is the wettest month (median 107 mm) and July is the driest (53 mm). However,
precipitation is appreciable throughout the year with 76-102 mm falling each month from
September through January.
4.8.1 Historical Data Review
Assessment units 1 (stations 10899, 14003, and 14004) and 6 (stations 10911 and 14010)
were listed for the first time in 2008 for high pH concerns (Figure 4-16). Assessment unit 1 is
located near the dam and 14 of 104 samples were above the 9.0 criteria. The median pH at AU 1
was 8.2. All pH exceedances in the segment were recorded during summer months (June –
August) except one in May 2005, a year that accounted for 6 of the 14 exceedances (Figure 417). Assessment unit 6 is located in the mid-lake region between Onalaska and West Livingston,
centered on US Highway 190. Seven of the eight exceedances in AU 6 occurred in the summer
and only two of the exceedances were recorded at station 14010. Six of the eight exceedances
were from 2003, the other two were in the summers of 2000 and 2001, leaving no exceedances
from 2003 – 2006 in AU 6. Across both AUs all but two samples in exceedance were taken after
13:00 hours and most were taken after 14:00 hours, which are sample collection times favoring
high pH values from photosynthesis and CO2 uptake processes. An anonymous source at the
Trinity River Authority (TRA) cited high turbidity in AUs 7-11 (upper reservoirs and coves) to
explain the lack of phytoplankton-induced pH exceedances in those portions of Lake Livingston
(personal communication 28 July 2008). For the combined dataset of impaired AUs 1 and 6,
summer pH values are statistically higher (p < 0.05, pH meansummer = 8.8) than those of the other
three seasons (Figure 4-18).
Lake Livingston is classified as hypereutrophic and ranked 73rd among Texas reservoirs
(TCEQ 2008c) based on the Carlson TSI index. Throughout the reservoir (including the AUs
listed for pH) nitrate, total phosphorus, and orthophosphate phosphorus are a concern based on
exceedances of screening levels. The upper arms of the reservoir appear very eutrophic in
satellite images based on their green and olive-green color; however, the upper portion of the
reservoir has not experienced excessive pH values.
In late September 2005, Hurricane Rita created large waves (up to 1 m) and surges that
damaged the upstream side of Livingston Dam. This event occurred within the period of record
assessed by the 2008 303(d) report (TCEQ 2008a); however, no exceedances were recorded after
August 2005, and no atypical pH patterns were noted in the months following Rita. It is
concluded that Hurricane Rita, as a large episodic event for the lake, did not in its aftermath
exacerbate pH excursions.
4.8.2 Potential Sources of pH Impairment and Recommendations
The seasonality of the exceedances, the time of day they were recorded, the high nutrient
loads, and the hypereutrophy of the lake point to algal blooms as the driver of pH exceedances in
Lake Livingston. Because the natural ecology of the region should predispose the lake to low
pH, it is likely that cultural eutrophication is to blame for the nutrient enrichment.
4-26
Texas pH Evaluation Project
Figure 4-16
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Map of Lake Livingston (Segment 0803).
4-27
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Texas pH Evaluation Project
10
AU 1
AU 6
9.5
10899
14003
14004
10911
14010
9
pH
8.5
8
7.5
7
Month
10899
Figure 4-17
10911
14003
14004
14010
Time history of pH for impaired AUs of Lake Livingston, Segment 0803 (data for 1999 – 2006).
4-28
Mar-07
Dec-06
Sep-06
Jun-06
Mar-06
Dec-05
Aug-05
May-05
Feb-05
Nov-04
Aug-04
May-04
Feb-04
Nov-03
Aug-03
May-03
Feb-03
Nov-02
Aug-02
May-02
Feb-02
Nov-01
Aug-01
May-01
Jan-01
Oct-00
Jul-00
Apr-00
Jan-00
Oct-99
Jul-99
6.5
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
pH
Season
Figure 4-18
Seasonality of pH in Lake Livingston, assessment units 1 and 6 combined.
Center bars are medians, plus signs are means, and boxes without
overlapping notches are significantly different (p < 0.05). Width of boxes
denotes relative n (fall = 21, summer = 57).
There are over a dozen minor permitted discharges (< 0.3 MGD each) in the lower half of
the lake alone and nearly a dozen more occupy space very close to the lake in the upper half.
Waterwood MUD No. 1 (0.1 MGD) empties into a tributary of a cove about 1 km upstream of
14010 in AU 6 and this could be a point source of steady nutrient enrichment locally affecting
the mid-lake region where the sampling station is located. The largest outfall near the lake is the
City of Trinity (0.6 MGD; pop. 2,721) between the two northwest arms. Because these
permitted facilities are small and the lake volume is so large, point sources surrounding the lake
probably do not pose more than localized nutrient concerns.
The lake is a major center for recreation and is surrounded by residential neighborhoods,
marinas, golf courses, and businesses. Urban runoff must be a significant source of nutrient
loading throughout much of the year based on monthly precipitation records. It would be useful
to study the relative nutrient contributions of urban and agricultural runoff and their effects on
primary productivity in the lake.
Finally and likely most importantly, Lake Livingston is in the Trinity River Basin which
is heavily impacted by the urban runoff and WWTF effluents of the Dallas-Fort Worth
Metroplex. The enormous volume of water flowing into the Trinity River from point and
nonpoint discharges in Dallas-Fort Worth begs attention, in spite of the distance of Lake
Livingston from the cities. Unfortunately, such a thorough investigation of Trinity River inflows
4-29
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
and Dallas-Fort Worth area contributions to the pH excursion issue in Lake Livingston was
beyond the scope of this study. It is noted, however, that all AUs in the Trinity River above
Lake Livingston (Segment 0804) for which there were sufficient data to allow assessment are
indicated to have a concern for screening level exceedances for CHLA, nitrate, orthophosphate
phosphorus, and total phosphorus (TCEQ 2008d) and that the most downstream U.S. Geological
Survey gauge before Lake Livingston had an annual average flow of 216 cms (7,627 cfs) for the
period of 1988-2007. This information on nutrient screening level exceedances and large annual
flows in the Trinity River immediately above Lake Livingston bespeaks very large nutrient
contributions to the lake from its major tributary, the Trinity River.
The symptoms of the high pH exceedances in some AUs of Lake Livingston are most
likely associated with seasonal algal blooms and generally high phytoplankton concentrations in
the reservoir as a response to cultural eutrophication. The watershed of Lake Livingston is large
(multiple thousands of square miles) and the watershed includes the Dallas-Fort Worth
Metroplex, all of which indicate a myriad of nutrient sources contributing to the lake. Despite
the enormity of the undertaking, the source of the impairment appears to be cultural
eutrophication which is amenable to being addressed by the TMDL process.
4.9 Segment 0818—Cedar Creek Reservoir
Cedar Creek, a tributary of the Trinity River, was dammed in 1965 to provide water for
Forth Worth and Tarrant County, Texas. The conservation storage is 644,785 acre-feet and the
surface area is 133 km2 (TRWD 2008) with a maximum depth of 18.9 m. Three islands in the
reservoir totaling 64.7 ha are protected by the TPWD as a bird sanctuary and Wildlife
Management Area (WMA).
According to the TRA (2008), the watershed is not heavily populated but it is being
rapidly developed. The City of Terrell, roughly 38 km to the north, operates the largest WWTF
(3 MGD permitted) in the watershed. The City of Kaufman is about 19 km to the north and has a
WWTF permitted at 1.2 MGD. In addition, there are several smaller dischargers (0.125 - 0.626
MGD permitted) distributed along the length of the reservoir (Figure 4-19; note that the Cities of
Terrell and Kaufman are not in the area shown on this map). West Cedar Creek MUD near the
west side of the reservoir discharges into a spillway supplying the Trinity River to the southwest
and does not affect the reservoir.
Pasture (64%) and row-crop (6%) agriculture dominate the landscape around the
reservoir and increased ranching has been cited as a cause of worsening soil erosion and
sedimentation in the reservoir (CCWP 2008). The northern post-oak savanna (ecoregion 33a) is
characterized by a gently rolling morphology with scattered hardwood forests and finelytextured, loamy soils. Rainfall averages 990 mm annually and May is the wettest month (median
114 mm). August is the driest month (median 38 mm) and winters are only slightly dryer than
other seasons.
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Texas pH Evaluation Project
Figure 4-19
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Map of Cedar Creek Reservoir (Segment 0818).
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Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
4.9.1 Historical Data Review
There are 14 AUs in Cedar Creek Reservoir and beginning in 2002 all except AUs 10, 13,
and 14 have been listed for high pH exceedances. There are no other chemical or bacterial
constituents causing impairment to the reservoir, but ammonia, total phosphorus, and
orthophosphate phosphorus have been sufficiently elevated to cause concern for screening level
exceedances. Chlorophyll-a concentrations have also been rising since 1992 (Figure 4-20) and
since 1999 have exceeded screening levels numerous times in most of the AUs. The DO%sat, an
indicator of primary productivity, was somewhat correlated with pH (Pearson coefficient = 0.62,
p < 0.0001) using data from all impaired AUs.
Nearly 90% of the exceedances in the reservoir were recorded during the summer (Figure
4-21). All seasons were significantly different (p < 0.02) from one another in Wilcoxon twosample tests, with the greatest differences between summer-winter (z = -10.6, p < 0.0001) and
summer-spring (z = -8.7, p < 0.0001) comparisons. Most non-summer exceedances occurred
during fall and winter of 1999 – 2000; since then, exceedances have been strictly a summer
phenomenon. There was a regional drought in 2005 – 2006 and by December 2006 the reservoir
reached a record low of 95.69 m, 2.45 m below normal. Significant rains during the next several
months quickly brought lake levels back to normal. There were no major changes in magnitude
or frequency of pH exceedances during this time.
CHLA
(μg/L)
Season
Figure 4-20
Cedar Creek Reservoir chlorophyll-a 17-yr trend (CCWP 2008). Annual
percentage rate (APR) indicates the percentage increase in CHLA per year.
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Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Texas pH Evaluation Project
10
AU 1
13845
16745
16748
AU 2 16744
AU 3 16743
AU 4 13848
16749
AU 5 16746
AU 6 15812
16741
16747
16750
17090
AU 7 16739
AU 8 16751
16752
AU 9 13854
16753
AU 11 16772
AU 12 16774
9.5
9
pH
8.5
8
7.5
7
Jun-07
Mar-07
Dec-06
Jun-06
Sep-06
Mar-06
Dec-05
Aug-05
May-05
Feb-05
Nov-04
Aug-04
May-04
Feb-04
Nov-03
Aug-03
May-03
Feb-03
Nov-02
Aug-02
May-02
Feb-02
Nov-01
Aug-01
May-01
Oct-00
Jan-01
Jul-00
Apr-00
Jan-00
Jul-99
Oct-99
Apr-99
Jan-99
Jul-98
Oct-98
Apr-98
Jan-98
Jul-97
Oct-97
Apr-97
6.5
Month
Figure 4-21
13845
13848
13854
15812
16739
16741
16743
16744
16745
16746
16747
16748
16749
16750
16751
16752
16753
16772
16774
17090
Time history of pH for Cedar Creek Reservoir, Segment 0803 (data for 1997 – 2006). An outlier (11.6) from
station 16772 on 6 October 2004 was removed for graphical considerations.
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Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Texas pH Evaluation Project
During the last decade, Cedar Creek Reservoir has trended towards higher median pH
and the magnitude of exceedances has also increased. Figure 4-22 displays all of the pH samples
from the impaired AUs, except for AUs 2, 3, 5, and 7 because these AUs were only sampled
between 1999 and 2000 (representing a period outside of the 2008 assessment period) and should
thus be excluded from long-term trend analyses. An outlier from AU 11 in 2004 was also
excluded for graphical considerations. The paucity of exceedances during 2001 – 2002 may be
attributable to a lack of sample data from AU 12 from 2001 – 2004; an assessment unit with a
high rate of exceedances that is located in the uppermost portion of the reservoir (station 16774).
Assessment units 2, 3, 5, and 7 accounted for nearly half of the abundant exceedances in 1999 –
2000, and when they are removed the frequency of summer exceedances during those two years
is comparable to that of other years. Assessment units 2 (station 16744), 3 (station 16743), 5
(station 16746), and 7 (station 16739) represent the four major coves on the middle and lower
east-side of the reservoir.
10
9.5
9
y = 0.00009x + 5.61468
pH
8.5
8
y = 0.00018x + 1.30918
7.5
Apr-07
Feb-07
Oct-06
Dec-06
Aug-06
Apr-06
Jun-06
Feb-06
Dec-05
Jul-05
Oct-05
May-05
Jan-05
Mar-05
Nov-04
Jul-04
Sep-04
May-04
Jan-04
Mar-04
Nov-03
Jul-03
Sep-03
Jan-03
Mar-03
May-03
Nov-02
Jul-02
Sep-02
Jan-02
Mar-02
May-02
Nov-01
Jul-01
Sep-01
May-01
Oct-00
Mar-01
Dec-00
Aug-00
Apr-00
Jun-00
Feb-00
Oct-99
Dec-99
Aug-99
Apr-99
Jun-99
Feb-99
Oct-98
Dec-98
Aug-98
Apr-98
Jun-98
Feb-98
Oct-97
Dec-97
Apr-97
Jun-97
6.5
Aug-97
7
Month
Figure 4-22
Cedar Creek Reservoir pH and trend lines for exceedances (red) and entire
dataset (black). An outlier was removed (pH = 11.6; 06 September 2004, AU
11) for graphical considerations.
Among mainstem AUs, the lower half of the reservoir comprising AUs 1, 4, and 6, had
the lowest rate of pH sample exceedances and nine of the ten lowest pH values (6.5-7.2) were
sampled in AUs 1 and 6. Seven of the ten highest values (9.4-11.6) were sampled in AUs 9, 11,
and 12, which are located in the upper portion of the reservoir. The very highest values, 9.74,
9.76, and 11.6, were taken from AUs 12, 12, and 11, respectively. All of the coves except Lacy
Fork (AU 10) and Cedar Creek (AU 13) were pH-impaired based on samples from 1999 – 2000.
The pattern is not stark, but it does suggest greater pH problems in the upstream reaches and
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Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
coves of the reservoir, all of which are relatively shallow, presumably well-mixed, and receive
waters from permitted dischargers and nonpoint sources.
In the lower middle reservoir, AU 6 (stations 15812, 16741, 16747, 16750, and 17090)
contained the most sampling stations (5) and contributed the most pH samples (156) and
exceedances (38 of 123 mainstem exceedances), but the excursion rate was the second lowest in
the reservoir. It is bounded on the north by Twin Creeks Cove. To the east is Enchanted Oaks, a
residential community with a shoreline dominated by boat docks. The Cherokee Shores WWTF
discharges into AU 6.
Assessment unit 8 (stations 16751 and 16752) is in Prairie Creek Cove, a relatively
narrow waterway surrounded on all sides by residential property and docks. It receives effluent
from East Cedar Creek FWSD (0.626 MGD). Assessment unit 12 in the upper western arm and
AU 11 in the upper mainstem surround the largest of the three islands protected by the TPWD
for birds.
4.9.2 Potential Sources of pH Impairment and Recommendations
The summer-seasonality of exceedances coupled with near-parallel perennial increases in
both CHLA and pH promote an eutrophication explanation for pH impairment. Attempts to
moderate pH should focus on reducing the nutrient loadings that enhance algae and
phytoplankton abundance in the lake. As stated in Section 2 of this report, runoff is typically the
largest contributor of nutrient pollution in Texas reservoirs. In 2007, the CCWP analyzed
modeling data from Texas A&M University (TAMU) to determine the relative load contributions
of sediment, phosphorus, and nitrogen, arising from urban land, WWTFs, pasture, and row-crops
(Table 4-1; CCWP 2008). According to their analysis, agriculture is the largest contributor of
loadings; row-crops, in particular, contribute a disproportionate amount of sediment and
phosphorus to the reservoir. However, urban land use is expected to rise dramatically in the
north watershed in coming decades (NCTCOG 2003) and this increase will likely diminish the
extent of crop land and pasture. Yet urban runoff itself contributes more phosphorus per acre
than pasture land, though less than crop land (see Table 4-1). Permitted discharges will also
increase in size and number as the population in the watershed grows.
Table 4-1
Watershed pollutant loadings (% contribution) per land use, adapted from
CCWP (2008).
Source (% of total watershed) Sediment Phosphorus Nitrogen
Urban land (6.39%)
7.37
13.29
7.37
WWTFs
0.10
12.11
7.21
Pasture (63.52%)
15.73
22.57
44.06
Crop land (6.17%)
41.79
42.52
23.51
Cultural eutrophication in the middle portion of the reservoir is more likely to be
influenced by urban runoff and point source nutrient enrichment than the upper third based on
the density of development in the middle reaches. The townships of Seven Points (pop. 1,145)
and Tool (2,275) on the west side, and Mabank (2,151), Gun Barrel City (5,145), Payne Springs
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Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
(683), and Eustace (798) on the east side all lie adjacent to the lake or within 5 km of its coves.
Prairie Creek Cove (AU 8) is a very narrow waterway (50-150 m wide) and is surrounded by the
community of Gun Barrel City. East Cedar Creek FWSD (0.626 MGD permitted) discharges
directly into the cove and as of 2003 delivered 23.38 mg/L of total nitrogen on average (CCWP
2008). The City of Mabank WWTF (0.4 MGD permitted) also discharges into a tributary of
Prairie Creek roughly 5 km upstream of the cove.
Caney Creek Cove (AU 2) and Clear Creek Cove (AU 3) were only sampled for pH from
February 1999 – October 2000, but around 30% of the samples were above the 8.5 criteria.
Furthermore, the coves connect to AU 1 and the station nearest to the coves in AU 1 (16748)
recorded 12 of the 15 exceedances in the assessment unit. With only a few exceptions,
exceedances in the coves coincided with exceedances at station 16748 while the near-dam
stations in AU 1 (16745 and 13845) recorded pH levels within the upper criterion of 8.5. This
pattern suggests problems in AU 1 are attributable to the location of a station in close proximity
to the coves. The boundaries of the cove assessment units should be considered for extension
towards the mainstem to include station 16748, leaving the other two near-dam stations to
represent AU 1 since their data appears less-influenced by the cove limnology.
The upstream end of the reservoir receives the inflow of King’s Creek from the northwest
and Cedar Creek from the northeast. As noted earlier, the Cedar Creek arm is not listed for pH.
King’s Creek carries the discharge of WWTFs in Terrell and Kauffman. These facilities, though
relatively large, are a lengthy distance from the reservoir and their influence is probably
attenuated by King’s Creek to a significant degree. A more likely source of enrichment is
derived from the crops and pasture that dominate the northern half of the watershed. The upper
reaches of the reservoir itself are a protected bird sanctuary and migratory bird populations could
provide seasonal, localized pulses of phosphorus and nitrogen.
The pH exceedances appear to be a response to seasonally high primary productivity in
Cedar Creek reservoir, which in turn appears most likely caused by cultural eutrophication. The
TMDL process is an appropriate means to address the high pH exceedances that are a secondary
response to cultural eutrophication.
4.10 Segment 1212—Lake Somerville
Lake Somerville, an impoundment of the Yegua Creek watershed in the Brazos River
basin, was dammed in 1967 for flood control, conservation, and other uses. It covers 4,638 ha
and depths range from 2 m (shallow upstream reaches) to 9 m (near the dam). Oil and gas
operations are active in the watershed and numerous trails, parks, campgrounds, and marinas are
established around the immediate vicinity of the lake. The City of Somerville sits on the
northeast corner of the lake with a WWTF outfall in a tributary downstream of the dam.
Vegetation in the region is primarily hardwood (post-oak) forests, rangeland and pasture. Soils
are somewhat less leached than those of far-east Texas, but have a similar sandy-loam texture
and are slightly to moderately acidic with low alkalinity (TAMU-SCL 2006). The region
receives approximately 914 mm – 1041 mm of precipitation per year, with typically highest
rainfall in May and Oct. The driest months are July and August.
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Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
4.10.1 Historical Data Review
TCEQ’s assessment data of Lake Somerville pH included 24-hr maximum and minimum
values, an approach that diverges from the protocols used in the other nine segments in this study
where it does not appear that 24-hr pH data were included in the assessment process. All of the
exceedances were from high pH values and occurred in summer months, June – August, when
primary productivity is at its peak (Figure 4-23). Only two of the three stations in the listed AUs
actually recorded pH exceedances: station 11881 in AU 1 (near-dam) and station 16879 in AU 3
(mid-lake), (Figure 4-24). Station 11885 is in a cove on the north shore, east of station 16879,
and was sampled monthly from April 1999 – March 2000 with no exceedances. Across all sites
and dates, only one of the samples in exceedance of the pH criteria was taken in the morning.
Fourteen of 15 exceedances occurred in the afternoon.
TCEQ classified Lake Somerville as hypereutrophic (TCEQ 2008c). TCEQ ranked Lake
Somerville 98th in the TSI and noted that CHLA values are still trending upward. Based on
phytoplankton data from Roelke et al. (2004), spikes in pH above criteria (9.0) as well as pH dips
below 8.5 corresponded with algal biomass spikes and dips (see July 1999, July-August 2000,
and February – August 2001 for examples; Figure 4-24). pH was also strongly correlated with
DO%sat (r = 0.76, p <0.0001) and never exceeded 9.0 except during summer afternoons when
primary production usually peaks. This analysis indicates that pH exceedances are primarily a
response to algal blooms that occur on a nearly annual basis.
4.10.2 Potential Sources of pH Impairment and Recommendations
High primary productivity in the lake is very likely the cause of the pH exceedances, but
the cause of the lake’s hypereutrophy is unknown. Surprisingly, none of the four AUs on the
lake were identified as having concerns for nutrients, though there were a handful of phosphate
phosphorus samples that exceeded screening levels. Although the phytoplankton and algae in
Lake Somerville are apparently maximizing available nutrients, the sources of nutrients to the
lake cannot be determined at this time. There are no permitted dischargers in the immediate
vicinity of the lake, except the City of Somerville WWTF, which discharges well below the dam.
The ALCOA plant in Rockdale is situated about 50 km upstream of Lake Somerville and
discharges into East and Middle Yegua Creeks. From 2002 – 2004 ALCOA outfalls combined
for an average daily discharge of over 72 MGD. According to the BRA (personal
communication, October, 2008) many years of testing upstream and downstream of ALCOA in
East and Middle Yegua Creeks indicates that ALCOA discharges actually improved water
quality in those tributaries. Therefore it is unlikely that ALCOA operations are exacerbating pH
exceedances in Lake Somerville.
The high pH exceedances in Lake Somerville are most likely linked to the hypereutrophy
of the reservoir. The sources of nutrients for this eutrophication are not clearly apparent from the
data readily available for this study. The TMDL process is designed to address the nutrient input
issues that appear to be driving pH exceedances, even if this “desktop” study could not determine
conclusively point or nonpoint sources contributing to the hypereutrophic status of Lake
Somerville.
4-37
Historical Data Review of Impaired Segments and
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Texas pH Evaluation Project
10
AU 1
AU 3
9.5
11881
11885
16879
9
8.5
pH
8
7.5
7
6.5
6
5.5
Month
11881
Figure 4-23
11885
16879
Time history for pH of impaired AUs of Lake Somerville, Segment 1212 (data for 1997 – 2006).
4-38
Jun-07
Mar-07
Dec-06
Jun-06
Sep-06
Mar-06
Dec-05
Aug-05
May-05
Feb-05
Nov-04
Aug-04
Feb-04
May-04
Nov-03
Aug-03
Feb-03
May-03
Nov-02
Aug-02
Feb-02
May-02
Nov-01
Aug-01
May-01
Oct-00
Jan-01
Jul-00
Apr-00
Oct-99
Jan-00
Jul-99
Apr-99
Jan-99
Jul-98
Oct-98
Apr-98
Jan-98
Jul-97
Oct-97
Apr-97
Jan-97
Oct-96
5
Texas pH Evaluation Project
Figure 4-24
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
Map of Lake Somerville (Segment 1212).
4-39
Texas pH Evaluation Project
Historical Data Review of Impaired Segments and
Potential Sources pH Impairment
4-40
Texas pH Evaluation Project
Summary of Factors Contributing to pH Excursions in
Listed Texas Water Bodies and Recommended Actions
SECTION 5
SUMMARY OF FACTORS CONTRIBUTING TO pH EXCURSIONS IN
LISTED TEXAS WATER BODIES AND RECOMMENDED ACTIONS
Fluctuations in pH are ultimately an intrinsic quality of most reservoirs and streams,
including those in this study. If primary production outpaces respiration, there is a net loss of
CO2 through photosynthetic assimilation and pH increases. If respiration processes dominate,
CO2 is replaced faster than primary producers can assimilate it and pH drops. Problems arise
when pH peaks and valleys become exaggerated during times of high abundance of producers
and microbes and by naturally low alkalinity concentrations that limit the buffering capacity of
the water body. Natural upsets in the production-respiration balance do occur, but cultural
eutrophication increases the frequency and magnitude of the upsets. Annual summer algal
blooms resulting in pH exceedances and poor water quality caused primarily by cultural
eutrophication occur in many reservoirs throughout the State.
Through the analysis of data and information from this “desktop” study, it appeared that
the pH exceedances resulting in the 303(d) listing of the ten study segments fell into two broad
categories. Category one were those water bodies in a climatic and geologic setting predisposed
to naturally have pH exceedances, and category two were those water bodies where nutrient
enrichment from anthropogenic point and nonpoint sources resulted in seasonally high primary
productivity that in turn resulted in elevated pH values due to uptake of CO2. The recommended
actions for the ten segments are provided in Table 5-1 and additional elaboration is provided
immediately below.
In the Texas Panhandle alkalinity is very high and primary producers are subjected to
high levels of sun exposure. Thus pH levels are maintained over 8.0 throughout the year. In
addition, high sodium content in the geology enables high accumulation of carbonate during
seasons of peak productivity which leads to pH spikes well above the 9.0 criteria. Cultural
eutrophication exacerbates the alkaline and saline condition of Texas Panhandle surface waters
by nurturing high amounts of primary producers through nutrient enrichment. The morphology
and management of Rita Blanca Lake would cause rapid eutrophication in any watershed, but in
Northwest Texas there is little in the natural environment to curb the high pH spikes. The lone
station used for assessment in Upper Prairie Dog Town Fork Red River is situated immediately
below a reservoir where cultural eutrophication causes phytoplankton blooms and the underlying
geology of the station and low canopy cover lend additional support for high pH exceedances as
the data show.
In East Texas alkalinity is very low, precipitation is acidic, soils are acidic, and stream
canopy cover is usually dense. These factors contribute greatly to the low-pH of the upper
portion of Caddo Lake, Big Cypress Creek below Lake of the Pines, and the Neches River above
Lake Palestine. Low-end exceedances are not infrequent in this region, and are even to be
expected. In these cases, the current minimum criterion of 6.0 may be high if maintenance of
natural conditions is the end point. Alternatively, since exceedances are associated with winter
months when groundwater flows more freely and instream leaf litter decomposition is
5-1
Texas pH Evaluation Project
Summary of Factors Contributing to pH Excursions in
Listed Texas Water Bodies and Recommended Actions
maximized, seasonal relaxation of criteria may be an option. All three of these classified
segments that periodically experience low pH and for which re-evaluation of the minimum pH
criterion is recommended could be amenable to further investigation through strategic location of
continuous monitoring stations.
The segments of greatest concern are those listed for high pH despite their location in
ecoregions with naturally low soil pH and surface water alkalinity. This group of segments
includes Lake Tawakoni, Lake Livingston, Cedar Creek Reservoir, and Lake Somerville.
Phytoplankton production is causing pH exceedances in this group as evidenced by the summer
seasonality of the exceedances, the significant correlation between pH and DO%sat, and other
factors unique to each reservoir. Nonpoint sources are the most likely contributors of nutrient
enrichment in these reservoirs. Point source influence varied among the reservoirs but generally
impacted phytoplankton growth in localized patches (e.g. impairment in coves of Cedar Creek
Reservoir).
Table 5-1
Summary of Recommendations for pH Impaired Segments Included in the
Study.
Name
Segment/
Assessment
units
Suspect cause of Recommended Actions
pH exceedances
Rita Blanca Lake
0105_01
TMDL process or other watershed-based
approach (watershed protection plan) §
Upper Prairie Dog
Town Fork Red
River
Caddo Lake
0229_02
Cultural
eutrophication &
natural conditions
Unrepresentative
station location
0401_02, 03, 05
Natural conditions
Big Cypress Creek
below Lake O’ the
Pines
Lake Tawakoni
0402_02, 03, 05
Natural conditions
Review of standards (low pH criterion
re-evaluation)
Review of standards (low pH criterion
re-evaluation)
0507_04
Lake Palestine
0605_03, 09, 10
Neches River above
Lake Palestine
Lake Livingston
0606_02, 03
Cultural
eutrophication
Cultural
eutrophication
Natural conditions
Cedar Creek
Reservoir
Lake Somerville
0803_01, 06
0818_01, 02, 03, 04,
05, 06, 07, 08, 09,
11, 12
121_01, 03
Cultural
eutrophication
Cultural
eutrophication
Consider additional monitoring station
locations and more data collection
TMDL process or other watershed-based
approach (watershed protection plan)
TMDL process or other watershed-based
approach (watershed protection plan)
Review of standards (low pH criterion
re-evaluation)
TMDL process or other watershed-based
approach (watershed protection plan)
TMDL process or other watershed-based
approach (watershed protection plan)
Cultural
TMDL process or other watershed-based
eutrophication
approach (watershed protection plan)
§
While Rita Blanca Lake is experiencing hypereutrophication as a result of cultural eutrophication processes, the
geology, morphology, climate, and the use of the lake as migratory waterfowl habitat predisposes the lake to
conditions that naturally favor high pH exceedances. Hence, the recommendation for a TMDL must be tempered by
these confounding factors.
5-2
Texas pH Evaluation Project
References
SECTION 6
REFERENCES
ASCE (American Society of Civil Engineers). 1960. Solubility of atmospheric oxygen in water.
ASCE Journal of the sanitary engineering division, SE7 (86):41.
Benke, A. C., T.C. Van Arsdall, Jr., and D.M. Gillespie. 1984. Invertebrate productivity in a
subtropical blackwater river: the importance of habitat and life history. Ecological
Monographs 54: 25-63.
Berner International Corporation. 2008. <http://www.berner.com/sales/energy_windspeed.html>.
Accessed 20 August 2008.
Boyd, C. E. 1990. Water quality in ponds for aquaculture. Alabama Agricultural Experiment
Station, Auburn University. Birmingham Publishing Company, Birmingham, Alabama.
Cain, Stanley A. 1928. Plant succession and ecological history of a central Indiana swamp.
Botanical Gazette 86: 384-401.
CCWP (Cedar Creek Watershed Partnership). 2008. Cedar Creek watershed protection plan.
<http://nctx-water.tamu.edu/docs/2008-06-19/CedarCreekWPP.pdf>. Accessed 04
August 2008.
Cole, G. A. 1994. Textbook of limnology. 4th ed. Waveland Press, Inc., Prospect Heights, Ill.
Crowe, A. L. 2008. An east Texas riddle--or what the old folks have always known. The water
monitor 1:1. Texas Commission on Environmental Quality.
Crowe, A. L. 2007. Lake Palestine diurnal survey, October 2005 – 2006. Field Operations
Division—Region 5 Tyler, Texas Commission on Environmental Quality. Tyler, Texas.
Crowe, A. L., M. Prater, and R. E. Cook. 2007. Acid rain potential in east Texas reservoirs. AS198. Field Operations Division—Region 5 Tyler, Texas Commission on Environmental
Quality. Tyler, Texas.
Darville, R., D.K. Shellman, Jr., and R. Darville. 1998. Intensive water quality monitoring at
Caddo Lake, a ramsar wetland in Texas and Louisiana, USA. Caddo Lake Institute,
Aspen, Colorado and Austin, Texas. Conference Paper Team Wetlands, Arlington,
Virginia. 15-17 April 1998.
Dodds, W. K. 2002. Freshwater ecology: concepts and environmental applications. Academic
Press, San Diego.
Dodds, W. K. 2006. Eutrophication and trophic state in rivers and streams. Limnology and
Oceanography 51: 671-680.
6-1
Texas pH Evaluation Project
References
Gibbs, R. J. 1970. Mechanisms controlling world water chemistry. Science 170: 1088-1090.
Griffith, G. E., S. A. Bryce, J. M. Omernik, J. A. Comstock, A. C. Rogers, B. Harrison, S. L.
Hatch, and D. Bezanson. 2004. Ecoregions of Texas (color poster with map, descriptive
text, and photography). USGS (map scale 1:2,500,000), Reston, VA.
Ground, T. A., and A. W. Groeger. 1994. Chemical classification and trophic characteristics of
Texas reservoirs. Lake and Reservoir Management 10: 189-201.
Gustavson, T. C., W. W. Simpkins, A. Alhades, and A. Hoadley. 1982. Evaporite dissolution and
development of karst features on the rolling plains of the Texas Panhandle. Earth Surface
Processes and Landforms 7: 545-563.
Lester, G. D., S.G. Sorensen, P.L. Faulkner, C.S. Reid, and I.E., Maxit. 2005. Louisiana
comprehensive wildlife conservation strategy. Louisiana Department of Wildlife and
Fisheries. Baton Rouge, LA.
McFarland, A., and L. Hauck. 1999. Existing nutrient sources and contributions to the Bosque
River Watershed. PR9911. Texas Institute for Applied Environmental Research.
Stephenville, TX.
McFarland, A., R. Kiesling, C. Pearson. 2001. Characterization of a Central Texas reservoir with
emphasis on factors influencing algal growth. TR0104. Texas Institute for Applied
Environmental Research. Stephenville, TX.
NADP (National Atmospheric Deposition Program/National Trends Network). 2008.
<http://nadp.sws.uiuc.edu.>. Accessed 11 August 2008.
NCTCOG (North Central Texas Council of Governments). 2003. North central Texas 2030
demographic forecast. North Central Texas Council of Governments Research and
Information Services. Arlington, TX.
NOAA (National Oceanic and Atmospheric Administration). 2002. Climatography of the United
States No. 81 Supplement No. 1: monthly precipitation probabilities and quintiles 1971 –
2000. NOAA, National Environmental Satellite, Data, and Information Service, National
Climatic Data Center. Asheville, NC.
NETMWD (Northeast Texas Municipal Water District). 2005. Basin highlights report 2005.
Hughes Springs, TX.
Roelke, D., Y. Buyukates, M. Williams, and J. Jean. 2004. Interannual variability in the seasonal
plankton succession of a shallow, warm-water lake. Hydrobiologia 513: 205-218.
RRA (Red River Authority of Texas). 2008. Canadian River Basin highlights report: 2008. Red
River Authority of Texas. Wichita Falls, TX.
6-2
Texas pH Evaluation Project
References
RRA. 2007. Red River Basin highlights report: 2007. Red River Authority of Texas. Wichita
Falls, TX.
Skousen, J. G., C. A. Call, and R. W. Knight. 1990. Natural revegetation of an unreclaimed
lignite surface mine in east-central Texas. The Southwestern Naturalist 35: 434-440.
Smith, V. H., S. B. Joye, and R. W. Howarth. 2006. Eutrophication of freshwater and marine
ecosystems. Limnology and Oceanography 51: 351-355.
SRA (Sabine River Authority of Texas). 1999. Cowleech Fork special study—subwatershed
7.07. <http://www.sratx.org/srwmp/tcrp/state_of_the_basin/special_studies_on_priority_
watersheds/1999/Subwatershed7_07/default.asp>. Accessed 05 August 2008.
Stumm, W., and Morgan, J.J. 1996. Aquatic Chemistry. 3rd ed. John Wiley and Sons, Inc. New
York.
TAMU-SCL (Texas A&M University-Soil Characterization Laboratory). 2006.
http://soildata.tamu.edu/. Accessed 29 July 2008.
TCEQ (Texas Commission on Environmental Quality). 2008a. Draft 2008 Guidance for
Assessing and Reporting Surface Water Quality in Texas (March 19, 2008). TCEQ,
Austin, TX.
TCEQ. 2008b. Draft 2008 Texas 303(d) list (March 19, 2008). TCEQ, Austin, TX.
TCEQ. 2008c. Trophic Classification of Texas Reservoirs: 2008 Texas water quality inventory
and 303(d) list. TCEQ, Austin, TX.
TCEQ. 2008d. Draft 2008 Texas Water Quality Inventory Water Bodies Evaluated (March, 19,
2008). TCEQ, Austin, TX.
TNRCC (Texas Natural Resource Conservation Commission). 2000a. Texas Surface Water
Quality Standards. §307.1-307.10. Adopted by the Commission: July 26, 2000; Effective
August 17, 2000 as the state rule. Austin, Texas.
TNRCC. 2000b. Texas water quality inventory 2000: Volume 2: Basins 1-11: narrative basin
summaries, basin maps, graphical basin summaries, and water body fact sheets. SFR050/00. TCEQ, Austin, TX.
TPWD (Texas Parks and Wildlife Service). 2008. <http://www.tpwd.state.tx.us/spdest/findadest/
parks/caddo_lake>. accessed 22 July 2008.
TRA (Trinity River Authority). 2008. Trinity River Authority 2008 basin highlights report.
Trinity River Authority. Arlington, TX.
TRWD (Tarrant Regional Water District). 2008.
<http://www.twrd.com/prod/Lakes_CedarCreek.asp>. Accessed 02 August 2008.
6-3
Texas pH Evaluation Project
References
TWDB (Texas Water Development Board). 2007. Water for Texas. Texas Water Development
Board, Austin, Texas.
TWDB. 2003. Volumetric survey of Lake Tawakoni. Texas Water Development Board,
Hydrographic Survey Group. Austin, TX.
USACE (U.S. Army Corps of Engineers). <http://www.mvk.usace.army.mil/lakes/caddolake/
main.php?page=mainContent>. Accessed 21 July 2008.
U.S. Census Bureau. 2000. <http://www.census.gov/>. Accessed 05 August 2008.
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Wetzel, R. G. 2001. Limnology: lake and river ecosystems. 3rd ed. Academic Press, San Diego.
6-4
Texas pH Evaluation Project
Appendix A
APPENDIX A
CORRELATIONS OF SELECTED ANALYTES FROM IMPAIRED
SEGMENTS
A-1
Texas pH Evaluation Project
Appendix A
A-2
Texas pH Evaluation Project
Appendix A
Pearson correlation coefficients (r) were calculated by combining data from impaired
stations in each segment and taking the means of the selected analytes including pH (median),
alkalinity (Alk, mg/L as CaCO3), DO (mg/L), specific conductance (SpCond, μmhos/cm), total
nitrate nitrogen (NO3, mg/L), secchi depth (Secchi, m), CHLA (μg/L), and the sample end time
(EndTime). One asterisk indicates p < 0.05; two asterisks indicate p < 0.01. A “--” indicates
insufficient data.
Table A-1. Rita Blanca Lake (Segment 0105).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
-0.40
-0.05
0.21
-0.48
-0.01
0.44
-0.37
-0.10
0.44
-0.23
0.25
-0.34
0.43
-0.04
0.64
0.18
-0.05
0.08
-0.48
-0.10
-0.21
0.10
0.56
-0.37
0.32
-0.16
0.23
-0.69**
Table A-2. Upper Prairie Dog Town Fork Red River (Segment 0229).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
-0.52
-0.46
0.36
0.14
-0.54
-0.54
0.19
-0.27
-0.11
0.19
-0.003
0.17
0.34
-0.32
0.51
0.45
0.78*
-0.46
0.21
-0.28
-0.39
0.34
-0.59
0.55
0.02
0.36
-0.26
-0.34
Table A-3. Caddo Lake (Segment 0401).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
0.58**
0.07
0.13**
--0.02
0.29
0.06
-0.27
0.52*
--0.02
0.14
-0.09
-0.25**
-0.40**
-0.27
0.22**
--0.34**
-0.10
0.03
----
-0.38
0.05
-0.13
A-3
Texas pH Evaluation Project
Appendix A
Table A-4. Big Cypress Creek (Segment 0402).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
0.58**
-0.05
0.34**
-0.27
0.16
0.02
0.004**
-0.19
0.46**
-0.20
0.02
0.53**
0.20
-0.07
-0.34
0.26**
-0.53**
-0.14
-0.16
0.30*
0.16
0.002
0.05*
-0.30
0.24
-0.14
-0.19*
0.01
Table A-5. Lake Tawakoni (Segment 0507).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
0.38**
-0.29**
0.2*
-0.74**
0.23*
0.69**
0.24**
-0.30*
0.70**
-0.44**
-0.11
0.35*
0.23
-0.08
0.61**
-0.01
0.02
0.05
-0.11
0.04
0.13
0.38**
-0.17
-0.45*
-0.32*
-0.08
-0.004
0.31*
Table A-6. Lake Palestine (Segment 0605).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
0.71**
0.24
0.38**
--0.02
0.61**
0.35**
-0.08
0.68**
--0.18
0.69**
0.16
-0.11
-0.10
-0.01
0.25
--0.31*
0.41**
0.08
----
-0.10
-0.04
0.26
A-4
Texas pH Evaluation Project
Appendix A
Table A-7. Neches River above Lake Palestine (Segment 0606).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
0.54**
-0.01
-0.68**
0.31
-0.26
0.07
0.43**
-0.78**
0.05
-0.30
-0.54**
0.38**
0.49**
-0.08
-0.07
0.59**
-0.46**
-0.25
-0.75
0.21
0.18
-0.15
0.59**
-0.46**
-0.25
0.27
-0.22
0.33*
Table A-8. Lake Livingston (Segment 0803).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
0.39*
0.14
0.21
-0.58**
0.26**
0.54**
0.39**
-0.03
0.75
-0.38*
0.22
0.44**
0.001
-0.01
-0.02
0.003
0.06
0.19*
-0.16
-0.70**
-0.02
-0.53
-0.59**
-0.30
0.14
-0.11
0.11
Table A-9. Cedar Creek Reservoir (Segment 0818).
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
0.41**
0.02
0.14**
-0.25
0.09
0.40**
0.002
-0.19**
0.70**
-0.07
0.15
0.55**
-0.001
0.03
-0.01
-0.19**
-0.13*
0.16**
0.06
-0.08
0.22**
0.08
-0.18
-0.05
-0.11
-0.15**
-0.06
-0.12*
Table A-10. Lake Somerville (Segment 1212)
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
EndTime
pH
Alk
DO
SpCond
NO3
Secchi
CHLA
0.03
0.48**
0.31**
-0.22
-0.37**
0.07
0.40**
-0.18
0.86**
0.57
-0.61*
0.48*
0.46*
0.18
-0.20
-0.12
-0.09
0.03
-0.21
-0.30**
0.45*
0.15
0.17
0.68
0.15
-0.34
-0.19
0.32
A-5
Texas pH Evaluation Project
Appendix A
A-6