Download Density Paul Radomski DNR Research Scientist

Density
Paul Radomski
DNR Research Scientist
Welcome. This is a short presentation that was given to advisory committees of the Shoreland
Rules Update Project in the fall of 2008.
1
Objectives
• Consequences of
human density on
water quality
• Introduction to
potential standards
The objectives of this short presentation was to outline the consequences of density on water quality and
then introduce various options for consideration.
2
Data from the PCA on impervious surface coverage for Detroit Lakes, MN.
3
Lu et al. 2006, Elvidge et al. 2007, Chabeave et al. 2004
As density increases, the amount and percent of impervious surface increases. Much of the increase in
impervious surface is attributable to the increase in roads as density increases.
4
Schueler 2003
An increase density has implications on the quality of the aquatic biota.
5
Cumulative Impacts of
Impervious Cover
Protected
0
20
Impacted
40
Degraded
60
80
100
Watershed Impervious Cover
Schueler 2003, Wang et al. 2001, adapted from NEMO
The amount of impervious cover is a key indicator of the quality of the water flowing into our lakes.
Research consistently shows that as the amount of impervious surface increases in the watershed, the
health of the lake inlets decreases. Streams draining watersheds with more than 12% imperviousness
have shown to be consistently in poor condition, indexed by poor fish communities (Wang et al. 2001).
Average % of Impervious Cover by Land Use:
2-acre Residence: 12
1-acre Residence: 20
0.5-acre Residence: 25
0.33-acre Residence: 30
0.25-acre Residence: 38
0.125-acre Residence: 65
Industrial: 75
Commercial: 85
Shopping Center: 95
Studies have shown that 55-75% of impervious surfaces are for vehicles, 35% for human habitat. As
impervious cover increases, runoff increases linearly.
6
As watersheds become developed, management of stormwater becomes critical. Runoff from homes,
lots, driveways, and roads picks up pollutants and moves downhill and downstream.
7
Courtesy UW – Green Bay
Failure to address added runoff results in poor water quality, increases in algal bloom, and greater
frequency of poor water conditions.
8
Phosphorus Pollution increases
with % Impervious Cover
Scheuler and Caraco 2001
The predicted benefits in this example watershed show that stormwater treatment practices (STP) with
better site design (BSD; or low-impact development) can reduce phosphorus loading and running off
into lakes.
The practices include infiltration basins, bioretention systems, and low impact designs such as rain
gardens.
9
Typical residential development changes the hydrology of streams. The loss of rainwater infiltration
with development leads to less groundwater recharge, which means lower base river flows. Higher
runoff with development leads to high peak flows, which blows out stream channels (next slide).
10
Stream Channel Blowout
CWP
As impervious surface coverage increase, the probability of destroying the stream channel increases.
11
Impact of Conventional
Development on Habitat
Excellent Stream Habitat
Original Bank
Some Urbanization
A comparison of two streams, one in a watershed with little runoff (left) and one in a watershed with
poor stormwater management.
12
Fish Species Richness in
Streams
Wang et al. 2001
Impacts of Urbanization on Stream Habitat and Fish Across Multiple Spatial Scales
LIZHU WANG, JOHN LYONS, PAUL KANEHL, ROGER BANNERMAN
ABSTRACT / We analyzed the relation of the amount and spatial pattern of land cover with
stream fish communities, in-stream habitat, and baseflow in 47 small southeastern Wisconsin,
USA, watersheds encompassing a gradient of predominantly agricultural to predominantly
urban land uses. The amount of connected impervious surface in the watershed was the best
measure of urbanization for predicting fish density, species richness, diversity, and index of
biotic integrity (IBI) score; bank erosion; and base flow. However, connected imperviousness
was not significantly correlated with overall habitat quality for fish. Nonlinear models were
developed using quantile regression to predict the maximum possible number of fish species,
IBI score, and base flow for a given level of imperviousness. At watershed connected
imperviousness levels less than about 8%, all three variables could have high values, whereas
at connected imperviousness levels greater than 12% their values were inevitably low.
Connected imperviousness levels between 8 and 12% represented a threshold region where
minor changes in urbanization could result in major changes in stream condition. In a spatial
analysis, connected imperviousness within a 50-m buffer along the stream or within a 1.6-km
radius upstream of the sampling site had more influence on stream fish and base flow than did
comparable amounts of imperviousness further away. Our results suggest that urban
development that minimizes amount of connected impervious surface and establishes
undeveloped buffer areas along streams should have less impact than conventional types of
development.
13
Mallin et al. 2000
Ecological Applications, 10(4), 2000, pp. 1047–1056
EFFECT OF HUMAN DEVELOPMENT ON BACTERIOLOGICAL WATER QUALITY IN
COASTAL WATERSHEDS
MICHAEL A. MALLIN, KATHLEEN E. WILLIAMS, E. CARTIER ESHAM, AND R. PATRICK
LOWE
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Pollution from Septic Systems
• Excess
nutrients
– nitrogen and
phosphorus
p t ic
d se re
r
a
a
nd
S ta ste m s e m o v e
r
sy
o
t
T
ed ns N O
n
g
i
d e s th o g e n ts
p a u t r ie
n
Septic systems, while generally good a slowing down the migration of phosphorus to the lake, do create
environmental problems.
15
Cabana and Rasmussen 1996
At low population densities, nitrogen enrichment has been observed in aquatic systems.
Proc. Natl . Acad. Sci . USA
Vol. 93, pp. 10844 –10847, October 1996
Ecology
Comparison of aquatic food chains using nitrogen isotopes
GILBERT CABANA AND JOSEPH B. RASMUSSEN
16
Mean % Emergent and Floating-leaf
Vegetation Coverage
14.0
12.47
Undeveloped Shore
Developed Shore
12.0
10.0
8.55
8.30
8.0
6.0
4.61
4.0
2.82
2.50
2.0
0.0
lightly developed lake
moderately developed
lake
highly developed lake
Relative Total Lake Development
Radomski and Goeman 2001
Vegetative coverage was estimated in 12 randomly selected 935-m 2 digitized photograph plots for both
developed and undeveloped shorelines of 44 lakes representing a gradient of development. Vegetative
cover in littoral areas adjacent to developed shores was less abundant than along undeveloped
shorelines. On average, there was a 66% reduction in vegetation coverage with development. The above
graph shows the vegetative coverage by relative total lake development.
17
25
20
Natural
Environment
Plant cover lost (%)
15
10
5
0
25
20
Recreational
Development
15
10
5
0
25
20
General
Development
15
10
5
0
1939 1955 1960 1969 1978 1989 1996 2003
Time period
Radomski 2006
Mixed-effects models indicated floating-leaf and emergent vegetative cover (% of lake surface,
transformed) was significantly affected (P < 0.1) by development (docks variable). Increases in
shoreline development, indexed by dock sites per km, reduced plant cover. The preferred model,
judged by the lowest Akaike’s information criteria (AIC) score, to estimate vegetative cover loss was a
linear mixed-effects model with time, shoreland development class, timing of photograph within the
year, and the between time and shoreland development class interaction as fixed effects and dock sites
per kilometer (transformed) as a linear effect. Since two-way interactions between shoreland
development class and time were observed, mean comparisons were conducted according to the twoway interaction. This linear mixed-effects model estimated the mean floating-leaf and emergent
vegetation cover loss in 2003 from development was 6% for natural environment class lakes, 14% for
recreational development, and 17% for general development class lakes. The weighted average
vegetation cover loss in 2003, weighted by surface area in each shoreland development class, was 15%
for the five county northcentral Minnesota area.
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Radomski and Goeman 2001
Even though fish surveys have considerable measurement uncertainty and the correlations were low, this
comparative analysis suggests that declines in emergent and floating-leaf vegetation due to development
may result in lower fish production. (And analysis by other investigators support this).
North American Journal of Fisheries Management 21:46–61, 2001Consequences Of Human Lakeshore
Development on Emergent and Floating-Leaf Vegetation Abundance
PAUL RADOMSKI AND TIMOTHY J. GOEMAN Minnesota Department of Natural Resources,
Division of Fisheries, 1601 Minnesota Drive, Brainerd, Minnesota 56401, USA
Abstract
Vegetation abundance along undeveloped and developed shorelines of Minnesota lakes was compared to
test the hypothesis that development has not altered the abundance of emergent and floating-leaf
vegetation. Aerial photographs of clear-water lakes dominated by centrarchids and walleyes Stizostedion
vitreum were analyzed for vegetation. Vegetative coverage was estimated in 12 randomly selected 935-m
2 digitized photograph plots for both developed and undeveloped shorelines of 44 lakes representing a
gradient of development. Vegetative cover in littoral areas adjacent to developed shores was less
abundant than along undeveloped shorelines. On average, there was a 66% reduction in vegetation
coverage with development. The estimated loss of emergent and floating-leaf coverage from human
development for all Minnesota’s clearwater centrarchid–walleye lakes was 20–28%. Significant
correlations were detected between occurrence of emergent and floating-leaf plant species and relative
biomass and mean size of northern pike Esox lucius, bluegill Lepomis macrochirus, and pumpkinseed
Lepomis gibbosus (Spearman’s rank correlation, P < 0.05). Current shoreline regulatory policies and
landowner education programs may need to be changed to address the cumulative impacts to North
American lakes.
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Build-out Predictions
Itasca County Lake Sensitivity Project, Rian Reed, Minnesota DNR
Scientific models used to estimate water clarity and phosphorus levels for our lakes can be used to
predict the consequences of development build-out with our existing shoreland rules. This prediction
for a lake in Itasca County shows that as more development occurs around the lake, water clarity
declines.
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21
22
Asplund 1996
Average change from weekday to weekend for shallow and deep lakes studied in Wisconsin by Tim
Asplund. Boat density increased on weekends, and water clarity decreased by about 16 inches in the
shallow lakes and about 8 inches in the near-shore areas of all lakes.
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Watercraft and Waterfowl
• Loss of feeding time
• Energy loss
• Reduced breeding
success
• Reduced survival of
chicks
Korschgen and Dahlgren 1992, Cywinski 2004
1.
Kahl (1991) found that disturbance in a Wisconsin lake resulted in about a 50% reduction in
feeding time for canvasbacks.
2.
Knapton (2000) found that disturbance lead canvasbacks, redheads, and scaup to feed in less
productive areas.
3.
Belanger and Bedard (1990) found for snow geese that disturbance caused a 5.3% increase in
hourly energy expenditure.
4.
Disturbance can cause female nesting ducks to take flight, leaving eggs exposed. And chicks are
more prone to predation after disturbance.
5.
Korschgen and Dahlgren (1992) reviewed over 200 investigations, and this review revealed that
disturbance from development displaced waterfowl from feeding grounds, increased energetic costs
associated with flight, and likely lowered productivity of nesting or brooding waterfowl.
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