Download atmospheric nitrogen deposition to the new jersey coastal waters

Ecological Applications, 17(5) Supplement, 2007, pp. S31–S41
Ó 2007 by the Ecological Society of America
ATMOSPHERIC NITROGEN DEPOSITION TO THE NEW JERSEY COASTAL
WATERS AND ITS IMPLICATIONS
YUAN GAO,1,3 MICHAEL J. KENNISH,2
1
AND
AMANDA MCGUIRK FLYNN2,4
Department of Earth and Environmental Sciences, Rutgers University, Newark, New Jersey 07102 USA
Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey 08901 USA
2
Abstract. In situ measurements of atmospheric NO3 and NH4þ at Sandy Hook on the
northern New Jersey (USA) coast and at Tuckerton on the southern New Jersey coast reveal
significant temporal and spatial variations of these inorganic N constituents. The mean
concentration of NO3 in precipitation was higher at Sandy Hook (44.6 lmol/L) than at
Tuckerton (29.1 lmol/L). The mean concentration of NH4þ in precipitation exhibited a similar
pattern, being higher at Sandy Hook (26.3 lmol/L) than at Tuckerton (18.3 lmol/L). Aerosol
NO3 and NH4þ concentrations at Sandy Hook were also higher than those at Tuckerton. On
an annual basis, the total atmospheric deposition of NO3 was estimated to be 51.1
mmolm2yr1 at Sandy Hook and 32.9 mmolm2yr1 at Tuckerton. For NH4þ, the total
atmospheric deposition was 32.8 mmolm2yr1 at Sandy Hook and 20.3 mmolm2yr1 at
Tuckerton. Wet deposition accounted for up to 89% of the total NO3 deposition and 76–91%
of the total NH4þ deposition on the New Jersey coast.
By comparison, NO3 and NH4þ concentrations are relatively low in estuarine waters of
New Jersey. The annual mean NO3 concentrations recorded in surface waters of the Mullica
River–Great Bay Estuary near the Tuckerton atmospheric site during the 2002–2004 period
were as follows: 12.1 lmol/L for the upper estuary, 4.5 lmol/L for the mid-estuary, 2.5 lmol/L
for the lower estuary, and 1.2 lmol/L for the bay inlet area. The annual mean NH4þ
concentrations in these waters were as follows: 1.5 lmol/L for the upper estuary, 3.8 lmol/L
for the mid-estuary, 3.8 lmol/L for the lower estuary, and 2.4 lmol/L for the bay inlet area. In
the Barnegat Bay–Little Egg Harbor Estuary, the mean concentrations of NO3 plus NO2
were ,4 lmol/L. In this system, atmospheric deposition accounts for ;39% of the total N
load. These results suggest that atmospheric deposition appears to be an important pathway of
new N inputs to New Jersey coastal waters and a potentially significant N enrichment source
for biotic production.
Key words: ammonium; New Jersey coast; nitrate; nitrogen loading; wet and dry atmospheric
deposition.
INTRODUCTION
Excessive N loading has been linked to eutrophication
problems in many estuarine and coastal marine waters
of the world, manifested by deleterious algal blooms,
hypoxic and anoxic events, reduced biodiversity, and
altered ecosystem structure and function (Cosper et al.
1989, Smetacek et al. 1991, Nixon 1995, Paerl et al.
2002, Rabalais 2002, Livingston 2003). Anthropogenic
N inputs from point and nonpoint sources in coastal
watersheds and airsheds can have devastating consequences for the long-term health and viability of coastal
systems. Municipal and industrial discharges, storm
water runoff, agricultural and urban inputs, and
anthropogenically mediated atmospheric N emissions
Manuscript received 27 July 2005; revised 23 February 2006;
accepted 6 March 2006; final version received 29 March 2006.
Corresponding Editor: A. Townsend. For reprints of this
Special Issue, see footnote 1, p. S1.
3 E-mail: [email protected]
4 Present address: Limno-Tech, Inc., 501 Avis Drive, Ann
Arbor, Michigan 48108.
all contribute to the total N load of these systems (Nixon
1986, Galloway et al. 1995, Paerl et al. 2000).
Atmospheric N deposition is becoming more significant,
concomitant with increasing urbanization (NOx, peroxyacetyl nitrate) and agricultural expansion (NH4þ).
According to Valigura et al. (2000) and Paerl et al.
(2002), for example, 10% to more than 40% of the new N
entering estuarine and coastal marine waters derives
from atmospheric sources and may be a major factor
driving primary production. This is particularly true for
coastal waters, such as those adjacent to or downwind of
large urban and industrial centers along the eastern
seaboard of the United States, which are heavily
impacted by pollution emissions, as high concentrations
of pollutants in coastal air can substantially raise air-tocoastal sea deposition fluxes. An array of studies along
the U.S. East Coast indicates that atmospheric deposition is an important source of NO3 and NH4þ, and
these constituents constitute a substantial fraction of the
total atmospheric input of inorganic N to coastal water
bodies (Paerl 1985, Fisher et al. 1988, Fisher and
S31
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YUAN GAO ET AL.
Oppenheimer 1991, Scudlark and Church 1993, Janicki
and Wade 1996, Valiela et al. 1997, Valigura et al. 2000).
Atmospheric NO3 is an end product of a series of
gas-phase photochemical and heterogeneous reactions
involving N oxides (NO þ NO2), which are primarily
derived from the combustion of fossil fuels and certain
natural N fixation processes (Seinfeld and Pandis 1998).
Atmospheric NH4þ originates from heterogeneous
reactions involving ammonia (NH3), the major sources
of which are animal waste, fertilizer application, soil
emissions, and industrial emissions (Dentener and
Crutzen 1994). Both NO3 and NH4þ can be readily
utilized by a variety of marine microorganisms and
plants (Glibert et al. 1991). Characterizing the atmospheric deposition of NO3 and NH4þ has become a
critical element in assessing the N loads to U.S. estuaries
and their ecological implications (Dennis 1997, Valigura
et al. 2000).
In general, there are two major processes that deliver
atmospheric substances to an aquatic system: wet
deposition through precipitation scavenging and dry
deposition by aerosol particle settlement and gas
impaction on the surface. Wet deposition refers to the
removal processes that occur within clouds (in-cloud
scavenging) through gas–liquid phase transformation
and below the cloud base (below-cloud scavenging) by
precipitation. Dry deposition of aerosol particles is
controlled by diffusion, impaction, and gravitational
settling, largely a function of particle size and wind
speed. Dry deposition can also be carried out by nitric
acid vapor, a surface-active N species. The magnitude of
this dry deposition flux in certain densely covered fields
of vegetation and forested land can be substantially
higher than the dry deposition flux by aerosol NO3
(Sievering et al. 2000). However, in most estuaries with
simple and flat surface topography, nitric acid dry
deposition is often not considered, as it may not
contribute significantly to the total atmospheric N
deposition fluxes. Although the subject of atmospheric
N deposition to coastal waters has been explored
intensively in recent years, the estimates of N deposition
to certain receiving estuaries and coastal marine waters
have been based either on data collected outside of the
immediate study areas or derived from models due to
the lack of onsite measurements. Therefore, atmospheric
N deposition to the coastal areas may need to be
reassessed, incorporating more accurate data from
onsite measurements.
The New Jersey, USA, coast, with ;200 km of ocean
shoreline, is characterized by extensive barrier islands,
sandy beaches, coastal dunes, productive back-bays, and
broad expanses of tidal wetlands. These vital habitats
make the coastal ecosystems in the region extremely
sensitive to nutrient inputs from coastal watersheds and
airsheds. Phytoplankton blooms have frequently occurred in estuarine and nearshore ocean waters,
periodically impacting water quality. They have adversely affected commercially and recreationally impor-
Ecological Applications
Special Issue
tant fish and shellfish populations. For example, in the
Barnegat Bay–Little Egg Harbor system alone, brown
tide blooms have been observed in 1995, 1997, 1999,
2000, 2002, and 2003. These blooms have affected
habitats that are important as nursery and spawning
grounds for a variety finfish, shellfish, and benthic
infauna. At times, they have also impacted human use of
coastal resources for recreational and commercial
purposes. With relatively low concentrations of N
entering these shallow bays from many of the tributary
systems, development of the blooms could be caused by
atmospheric N deposition directly on the water surface
of the bays. Recent model calculations of the N budget
in Barnegat Bay suggest that atmospheric deposition is a
major source of N entering the bay, accounting for
nearly 40% of the total N load (Moser 1997, Seitzinger
and Sanders 1999, Seitzinger et al. 2001).
The aim of this work is to contribute to the existing
database on atmospheric N inputs to the U.S. eastern
seaboard by focusing on in situ N measurements along
the New Jersey coast. We first examine atmospheric
deposition of inorganic N (i.e., NO3 and NH4þ) based
on a time series of atmospheric measurements, one
conducted at Sandy Hook in northern New Jersey and
the other at Tuckerton in southern New Jersey (Fig. 1,
inset). These measurements provide a comparison of the
differences in atmospheric deposition rates between the
more urban and industrialized northern coastal region
and the more rural southern coastal region of the state.
The atmospheric deposition data are then discussed with
respect to the measurements of NO3 and NH4þ in the
water column of nearby estuaries, notably Great Bay
and the Barnegat Bay–Little Egg Harbor Estuary (Fig.
1a).
METHODS
Atmospheric sample collection and measurements
To investigate the temporal and spatial variability of
atmospheric N deposition to New Jersey, USA, coastal
waters, specifically atmospheric NO3 and NH4þ, two
data sets were generated from in situ measurements at
sampling sites in the northern and southern regions of
the state. The first sampling site was at Sandy Hook
(40830 0 N, 74800 0 W), a coastal location on a peninsula
between Raritan Bay and waters of the New York Bight
in northern New Jersey (Fig. 1b). This site, representative of the New York–New Jersey Harbor, is heavily
influenced by industrial sectors in northern New Jersey
and the metropolitan complexes of Newark and New
York City, as well as many highways across the region,
which serve as sources of large amounts of pollutants to
the ambient air. Therefore, high concentrations and
deposition fluxes of N from the atmosphere may be
expected at this location, although air circulation along
the coastline, in particular the land–sea breezes during
the summer months, may dilute pollutant loading in the
ambient air. The second sampling site was at the Rutgers
University Marine Field Station (RUMFS) at Tuck-
July 2007
COASTAL ATMOSPHERIC NITROGEN DEPOSITION
S33
FIG. 1. Map (inset) showing the location of water column nutrient sampling sites in (a) the Mullica River–Great Bay Estuary,
(b) the Sandy Hook atmospheric sampling site, and (c) the Rutgers University Marine Field Station (RUMFS) atmospheric
sampling site. Data sources: New Jersey Department of Environmental Protection, New Jersey Department of Transportation, and
Center for Remote Sensing and Spatial Analysis.
erton (39818 0 N, 74812 0 W; Fig. 1c), located on the
southern tip of a salt marsh peninsula on the southern
New Jersey coast. This site is remote from major
industrial centers, in contrast to the surroundings of
the Sandy Hook site; hence, it is less influenced by air
pollution. Both Sandy Hook and Tuckerton belong to
the coastal zone, one of the five climate regions within
New Jersey; therefore they share similar climatic
conditions, although the exact values of certain meteorological parameters at the two sites may differ on daily
basis.
Samples were collected from February 1998 to March
1999 at Sandy Hook and from February 1999 to
February 2001 at Tuckerton. Biweekly integrated
precipitation samples were collected at both sites using
a MIC wet-only automatic precipitation sampler con-
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Ecological Applications
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YUAN GAO ET AL.
TABLE 1. Concentrations of nitrate and ammonium in precipitation at the Sandy Hook and Tuckerton sampling sites, New Jersey,
USA.
Nitrate (lmol/L)
Ammonium (lmol/L)
Location (year)
N
Mean
Range
SD
Mean
Range
SD
Sandy Hook (1998–1999)
Tuckerton (1999–2001)
31
65
44.6
29.1
1.20–153
2.26–84.6
41.3
20.4
26.3
18.3
0.275–93.6
0.625–107
24.5
19.4
trolled by an onsite rain sensor (MIC Company,
Richmond, Ontario, Canada). After sampling, plastic
bottles containing the samples were immediately sealed
in plastic bags and frozen unfiltered until analysis. For
aerosol sample collection at the Sandy Hook site, a
modified Cal Tech type PM2.5 low-volume aerosol
sampler was used with a flow rate of ;9 L/min. The
sampling media were Millipore HA mixed cellulose
filters (47 mm diameter, 0.45 lm pore size) (Millipore,
Bedford, Massachusetts, USA). Details of the aerosol
sampling methodology are given in Gao et al. (2002).
At the Tuckerton site, bulk aerosol samples were
collected using a high-volume aerosol sampler (flow rate
of ;1 m3/min) (Andersen Instrument, Smyrna, Georgia,
USA), with a sampling interval of ;24 h. Sampling
media for aerosols were Whatman 41 cellulose filters.
The sampling procedures followed were those of Gao et
al. (1996). All samples were kept refrigerated until
analyzed, except for the period of shipment between
sampling sites and the laboratory at Rutgers University.
Briefly, frozen precipitation samples were thawed at
room temperature prior to analysis. For aerosol
samples, a portion of each sample filter was extracted
with deionized water, and all extracted filters were
ultrasonicated for 1 hour before analysis. Determinations of NO3 and NH4þ in precipitation and in aerosol
particles were made using a Dionex DX-100 Ion
chromatograph (IC) (Dionex Corporation, Marlton,
New Jersey, USA). The IC detection limits were 0.05
mg/L for both NO3 and NH4þ. Details of the analytical
procedures are given in Church et al. (1991) and Gao
(2002).
Water column sample collection and measurements
To effectively address nitrogen loading of estuarine
and coastal marine waters, it was also necessary to
examine the concentrations of inorganic N constituents
in the water column itself, the seasonal N fluxes, and the
principal delivery systems. We examined water column
inorganic nitrogen concentrations by taking monthly
surface grab samples from February 2002 to March
2004 at seven sites along a well-defined salinity gradient,
beginning at the freshwater entrance in the Mullica
River (0 mg/kg) and ending at the mouth of Great Bay
(0.031 mg/kg) (Fig. 1a). All samples were collected in
amber, high-density polyethylene sample bottles that
were previously acid washed (15% H2SO4). The samples
were placed on ice and processed immediately after
sample collection was completed. They were then stored
at 208C until laboratory analyses were performed. All
samples were collected as part of the monitoring
requirements of the Jacques Cousteau National Estuarine Research Reserve, a 45 000-ha protected area along
the south-central New Jersey coastline (Kennish 2004).
The water samples were filtered through precombusted (5008C for 4 hr) Whatman GF/F filters (0.7
lmol) for the analysis of NO3 plus NO2 (Lachat
QuikChem Method 30-107-04-1-A) and NH4þ (Lachat
QuikChem Method 31-107-06-1-A). The detection limit
for NO3 was 0.7 lmol, and that for NH4þ was 0.08
lmol. For statistical analysis of the data, seasons were
defined as follows: spring (March, April, and May),
summer (June, July, and August), fall (September,
October, and November), and winter (December,
January, and February).
RESULTS
Variation of nitrate and ammonium in precipitation
and in aerosols
The data in Table 1 show that the concentrations of
both NO3 and NH4þ in precipitation varied dramatically at both locations during the sampling period. The
NO3 concentrations ranged 1.20–153 lmol/L at Sandy
Hook and 2.26–84.6 lmol/L at Tuckerton, and the
NH4þ concentrations ranged 0.275–93.6 lmol/L at
Sandy Hook and 0.625–107 lmol/L at Tuckerton. In
addition, the mean concentration of NO3 in precipitation at Sandy Hook was 44.6 lmol/L, nearly 1.5 times
that measured at Tuckerton (29.1 lmol/L). The higher
levels of NO3 in precipitation at Sandy Hook certainly
suggest a greater impact of air pollution emissions on
this site. The concentrations of NO3 and NH4þ at the
Sandy Hook and Tuckerton sites are comparable to the
range of concentrations typically observed at several
locations along the Mid-Atlantic coast. At a National
Atmospheric Deposition Program (NADP) New Jersey
site located in the Edwin B. Forsythe National Wildlife
Refuge, the reported annual range of concentrations was
4.52–126 lmol/L for NO3 and 1.11–36.7 lmol/L for
NH4þ (NADP 2002). At Lewes, Delaware, USA, Russell
et al. (1998) found mean concentrations of 21.5 lmol/L
for NO3 and 13.6 lmol/L for NH4þ in precipitation.
Fig. 2a, b illustrates the concentrations of NO3 and
NH4þ, respectively, at the Sandy Hook and Tuckerton
sites on a seasonal basis. The concentration of NO3 in
precipitation during summer (June, July, August) was
highest at the Sandy Hook site, indicating not only
higher air pollution emissions at the site, but also high
July 2007
COASTAL ATMOSPHERIC NITROGEN DEPOSITION
S35
However, the upper range of the concentrations for both
NO3 and NH4þ at Sandy Hook was higher than those
observed at Tuckerton, a consistent feature with
precipitation. High aerosol NO3 concentrations were
with particles of 9.3 lm in diameter at Tuckerton (Gao
2002). The formation of NO3 in supermicrometer
aerosol particles could be due to the dissolution of
NO2 and HNO3 in the alkaline sea-salt droplets
(Parungo and Pueschel 1980). Over the southern North
Sea, Ottley and Harrison (1992) indicated that NO3
primarily concentrates on particles of 8–20 lm in
diameter, and the peak and shape of NO3 size
distributions paralleled those of sodium (a representative element for sea-salt aerosol). The high concentrations of aerosol NH 4þ were associated with
submicrometer particles of ;0.5 lm in diameter (Gao
2002). Submicrometer aerosol NH4þ is formed through
gas phase reactions involving NH3 vapor from pollution
or agricultural activities (Warneck 1999, Schlesinger and
Hartley 1992). The particle sizes of NO3 and NH4þ
could affect their dry deposition fluxes.
FIG. 2. Concentrations of (a) nitrate and (b) ammonium in
precipitation measured in situ in the northern (Sandy Hook)
and southern (Tuckerton) coastal regions of New Jersey, USA.
photochemical reactions involving N oxides that favor
the production of NO3.
Table 2 provides a summary of NO3 and NH4þ
concentrations associated with aerosol particles at the
two sampling sites. The original results for the Sandy
Hook site were obtained from aerosol particles of ,2.5
lm in diameter, known as PM2.5. Recent aerosol particle
size measurements at Tuckerton indicate that ;75% of
the total aerosol NO3 and ;87% of the total aerosol
NH4þ are associated with particles ,3.0 lm in diameter
(Gao 2002). Assuming that the same partitioning applies
to aerosol NO3 and NH4þ at Sandy Hook, the
concentrations of total aerosol NO3 and NH4þ at
Sandy Hook were calculated based on these partitioning
factors and reported as ‘‘adjusted TP’’ in Table 2.
The concentrations of NO3 and NH4þ in the
particulate phase varied dramatically at both locations.
Atmospheric wet and dry deposition
The atmospheric flux via wet deposition (F w )
(mmolm2mo1) is calculated using the following
equation:
Fw ¼ 10ðCr PÞ
ð1Þ
where Cr is the concentration of a substance in
precipitation (mmol/L), and P is the precipitation rate
(cm/mo) along with a unit conversion factor (10). Some
degree of uncertainty is associated with the calculation
of wet deposition, primarily due to errors in rainfall
measurements. The dry deposition flux (F d )
(mmolm2mo1) is obtained through the following
equation:
Fd ¼ 2:592 3 104 ðCair Vd Þ
ð2Þ
where Cair is the atmospheric concentration of that
substance (mmol/m), Vd is the dry deposition velocity
(cm/s), and 2.592 3 104 is a unit conversion factor. It is
important to note that few reliable methods are
available to directly measure dry deposition of aerosol
TABLE 2. Concentrations of aerosol nitrate and ammonium in the ambient air at the Sandy Hook and Tuckerton sampling sites,
New Jersey, USA.
Nitrate (lg/m3)
Ammonium (lg/m3)
Treatment
N
Mean
Range
SD
Mean
Range
SD
Sandy Hook (1998–1999)
PM2.5
Adjusted TPà
48 2.44
3.18
0.658–6.29
0.878–8.39
1.30
2.07
2.32
0.636–4.93
0.731–5.66
1.17
14
2.04
0.531–3.54
0.887
0.497
0.152–1.17
0.280
Tuckerton (1999–2001)
TP
Note: Key to abbreviations: TP, total particulate nitrate and ammonium; PM2.5, aerosol particles of ,2.5 lm in diameter.
This applies to aerosol nitrate only. The number of samples analyzed for ammonium is 38.
à Adjusted values for total particulate nitrate and ammonium, assuming that PM2.5 nitrate accounts for 75% of the total aerosol
nitrate and that PM2.5 ammonium accounts for 87% of the total aerosol ammonium at this location.
S36
YUAN GAO ET AL.
Ecological Applications
Special Issue
FIG. 3. Wet and dry deposition fluxes (mmol/m2) of nitrate and ammonium on a seasonal basis at Sandy Hook and Tuckerton
coastal regions of New Jersey, USA.
N-containing species, and all estimates indirectly obtained through the use of the above dry deposition
model have a large degree of uncertainty, mainly
attributable to the uncertainties associated with dry
deposition velocities. More details of the calculation are
given in Gao (2002).
Recent particle size measurements of aerosol NO3
and NH4þ at Tuckerton suggest that an appropriate dry
deposition velocity is 0.34 cm/s for aerosol NO3 and
0.19 cm/s for aerosol NH4þ (Gao 2002). These values
will be used in this study for calculating dry deposition
fluxes at Sandy Hook as well as at Tuckerton, assuming
that aerosol NO3 and NH4þ at Sandy Hook follow the
same particle size distributions as those observed at
Tuckerton. More comprehensive reviews and discussions of these models and their applications are given
elsewhere (Duce et al. 1991, Jickells 1995).
Using the atmospheric wet and dry deposition models
described above, wet and dry deposition fluxes of NO3
and NH4þ were calculated for the two sites on a seasonal
basis (Fig. 3). Here the seasons are defined as spring
(March, April, May), summer (June, July, August), fall
(September, October, November), and winter (December, January, February). Wet deposition of both NO3
(Fig. 3a) and NH4þ (Fig. 3b) varied seasonally. High wet
deposition rates for both NO3 and NH4þ occurred
during the summer season at both locations. The summer
wet deposition rate for NO3 was 16.1 mmol/m2 at Sandy
Hook and 12.4 mmol/m2 at Tuckerton. The summer wet
deposition rate for NH4þ was 12.4 mmol/m2 at Sandy
Hook and 10.7 mmol/m2 at Tuckerton. The increased
summer flux reflects seasonal variability in both source
strength, related to NOx and NH3 peak production
during the warmer seasons, and removal processes, such
as precipitation scavenging, which could be amplified in
summer. The wet deposition fluxes of both NO3 and
NH4þ at Tuckerton were about 30–40% lower than those
at Sandy Hook, largely attributable to differences in the
magnitude of air pollution emissions affecting the
northern and southern regions of the state. This seasonal
pattern observed over the New Jersey coast is consistent
with the results from Delaware Bay and Chesapeake Bay
(Scudlark and Church 1993, Russell et al. 1998).
The dry deposition fluxes of NO3 in Fig. 3c exhibit a
different seasonal pattern than its wet deposition fluxes,
with the highest values occurring in the winter (1.91
mmol/m2); however, there are no dramatic changes in dry
deposition fluxes through seasons. The monthly mean dry
deposition fluxes of NO3 were 0.447 mmolm2mo1 at
Sandy Hook and 0.308 mmolm2mo1 at Tuckerton.
Therefore, the flux at Tuckerton was ;27% lower than
that at Sandy Hook. The NH4þ fluxes at Tuckerton were
significantly lower (Fig. 3d), being only ;20% of the
fluxes at Sandy Hook. Because dry deposition velocities
may vary under different meteorological conditions from
one location to another, these dry deposition estimates
involve a certain degree of uncertainty.
Annual atmospheric deposition
Table 3 lists the total annual deposition fluxes of
NO3 and NH4þ at Sandy Hook and Tuckerton. On an
annual basis, the total atmospheric deposition flux of
July 2007
COASTAL ATMOSPHERIC NITROGEN DEPOSITION
S37
TABLE 3. Total atmospheric deposition rates of nitrate and ammonium over the New Jersey coast as measured at Sandy Hook and
Tuckerton.
Nitrate (mmolm2yr1)
Ammonium (mmolm2yr1)
Location
Wet
Dry
Total
% wet
Wet
Dry
Total
% wet
Sandy Hook
Tuckerton
Percentage lower at Tuckerton
45.7
29.2
36
5.37
3.74
30
51.1
32.9
36
89
89
25.0
18.6
26
7.84
1.74
78
32.8
20.3
38
76
91
NO3 is 51.1 mmolm2yr1 at Sandy Hook. This value
is considered to be typical of the northern New Jersey
coast. The total deposition flux of NO3 at Tuckerton
amounted to 32.8 mmolm2yr1, which was ;36%
lower than that measured at Sandy Hook. A similar
pattern was evident for atmospheric NH4þ, with a total
deposition flux of 32.8 mmolm2yr1 at Sandy Hook
and 20.3 mmolm2yr1 at Tuckerton. Wet deposition is
the dominant removal process, accounting for 89% of
the total NO3 deposition and 76–91% of the total NH4þ
deposition along the New Jersey coast. The magnitudes
of these deposition fluxes to the New Jersey coast are
comparable to those of nearby coastal regions, such as
Chesapeake Bay, where atmospheric deposition rates are
18 mmolm2yr1 for NO3 and 35 mmolm2yr1 for
NH4þ (Correll and Weller 1997).
Water column nitrogen measurements
To effectively address nitrogen loading of estuarine
and coastal marine waters, it is also necessary to
examine the concentrations of inorganic N constituents
in the water column itself, the seasonal N fluxes, and the
principal delivery systems. Most of the inorganic N
entering estuarine waters of New Jersey derive from
tributary inflow and groundwater discharges (HunchakKariouk and Nicholson 2001). However, while the
majority of atmospheric N exists as inorganic N, the
bulk of N in waters of the coastal bays occurs in organic
form, with highest concentrations (;40 lmol/L) observed in summer. Organic N levels are about 10 times
greater than inorganic N in these waters (Seitzinger et al.
2001). Thus, in Barnegat Bay, a system previously
classified as highly eutrophic (S. Bricker, personal
communication), NO3 and NH4þ concentrations are
generally ,4 lmol/L. According to Seitzinger et al.
(2001), the concentration of NO3 plus NO2 in the bay
is highest in winter, when the mean value is ,4 lmol/L.
In contrast, the highest levels of NH4þ occur in summer,
when the mean concentration amounts to ,2.5 lmol/L.
The rate of inorganic N input to the bay from both point
and nonpoint sources is estimated to be 4 mmolm2d1
(Seitzinger et al. 2001). The total atmospheric deposition
of NO3 and NH4þ to the Barnegat Bay–Little Egg
Harbor estuarine ecosystem amounts to 9.2 3 106 and
5.7 3 106 mol/yr, respectively. The total annual
atmospheric deposition of these constituents to the
Barnegat Bay watershed, in turn, amounts to 4.6 3 107
mol/yr (NO3) and 2.9 3 107 mol/yr (NH4þ) (Gao 2002).
Thus, large concentrations of these inorganic N forms
enter waters of this important coastal bay system either
directly from atmospheric deposition on the water
surface or secondarily from export off the watershed.
An extensive database has been generated on NO3
and NH4þ concentrations in the Mullica River–Great
Bay Estuary from the upper to the lower reaches,
including the waters adjacent to the atmospheric
deposition sampling site at Tuckerton (Rutgers University Marine Field Station; RUMFS) (Fig. 1c). The
temporal and spatial distributions, fluxes, and fate of
these inorganic N constituents have been targeted along
the estuarine salinity gradient. Mullica River–Great
Bay, a shallow, well-mixed coastal plain estuary, differs
significantly from the bar-built, lagoon-type estuaries
found north and south along the New Jersey coastline
from Sandy Hook to Cape May (Kennish 2001a).
During a two-year (2002–2004) sampling period, the
levels of NO3 decreased along the salinity gradient
from the head to the mouth of the estuary. For example,
the annual mean concentration of NO3 during this
period declined from 12.1 lmol/L in the upper estuary
to 4.5 lmol/L in the mid-estuary, 2.5 lmol/L in the
lower estuary, and 1.2 lmol/L at the bay inlet area near
RUMFS (Table 4). Maximum concentrations in the
upper estuary occurred in late winter, and minimum
TABLE 4. Annual concentrations of nitrate and ammonium in the Mullica River–Great Bay
Estuary, New Jersey, USA.
Nitrate (lmol/L)
Ammonium (lmol/L)
Location
N
Mean
Range
N
Mean
Range
Upper estuary
Mid-estuary
Lower estuary
Bay inlet
70
70
92
46
12.1
4.5
2.5
1.2
0.09–33.9
1.0–10.2
bd–9.8
bd–4.2
70
70
92
42
1.5
3.8
3.8
2.4
0.3–5.9
1.2–7.0
bd–15.6
bd–7.5
Note: In the ‘‘Range’’ columns, ‘‘bd’’ indicates that lower values were below the detection limit.
S38
YUAN GAO ET AL.
concentrations, in the summer and fall. From the midestuary to the bay inlet area, maximum concentrations
were observed in fall and winter, and minimum
concentrations, in spring and summer, indicative of
biotic uptake during the warmer months of the year.
Durand (1988) reported a similar trend of NO3 in the
estuary during the 1971–1979 period, with the mean
concentration being 6.8 lmol/L (range, 0.5–17.9
lmol/L) in the upper estuary, 4.3 lmol/L (range, 0.5–
13.2 lmol/L) in the mid-estuary, and 2.3 lmol/L (range,
0.1–10.5 lmol/L) in the lower estuary. MacDonald
(1983) recorded an annual mean concentration of NO3
in the lower estuary during the 1974–1977 period
amounting to 2.6 lmol/L.
Upland areas of the Mullica River watershed appear
to be the major sources of NO3 for the estuary. The
marked increase in NO3 levels in the upper estuary
since 1979 may reflect changes in land use. For example,
during the 1979–1991 period, 5.3% of the land in the
Mullica River Basin was converted from undeveloped
forest to developed and agricultural land (Zampella et
al. 2001), which has likely contributed to increased N
input to the upper estuary in recent years.
In the case of NH4þ, the annual mean concentration
during the 2002–2004 period was lower for the upper
estuary (1.5 lmol/L) than for the mid-estuary (3.8
lmol/L), lower estuary (3.8 lmol/L), and bay inlet area
(2.4 lmol/L) (Table 4). The concentrations of NH4þ
increased from early spring and summer to the fall and
then decreased through the winter. These values
compare favorably with those of Durand (1988), who
calculated mean annual NH4þ concentrations of 2.2
lmol/L for the upper estuary, 3.3 lmol/L for the midestuary, and 3.7 lmol/L for the lower estuary during the
1971–1979 period. The seasonal variations of NH4þ
concentrations were usually lower in Great Bay than in
the Mullica River, while NH4þ concentrations were
typically greater in the bay than in the river. The
temporal and spatial distributions were more variable
for NH4þ than for NO3 in the estuary.
DISCUSSION
The coastal waters of New Jersey are downwind of
substantial anthropogenic N emissions from multiple
sources, both within the state and beyond its borders.
Urbanization, industrial operations, and agricultural
activity in the Ohio Valley, adjoining states, and within
New Jersey municipalities have substantially increased
the loading of NO3 and NH4þ in coastal airsheds.
Delivery of these inorganic N constituents to coastal
waters via atmospheric wet and dry deposition can
significantly increase the inputs of new N, thereby
enhancing primary production and leading to potentially greater incidence of eutrophication. In the Barnegat
Bay–Little Egg Harbor estuarine system, wet deposition
through precipitation scavenging accounts for 90% of
the total deposition of both NO3 and NH4þ on the
water body surface. With phytoplankton production
Ecological Applications
Special Issue
values approaching 500 g Cm2yrl in Barnegat Bay
(Seitzinger et al. 2001), increasing N inputs may be
contributing to overenrichment problems. The downgrade in classification of the bay from moderately
eutrophic in the early 1990s to highly eutrophic in
1999 provides evidence of escalating nutrient enrichment
problems in this system (Kennish 2001a). Since nearly
40% of the total N load to the bay derives from
atmospheric deposition (Moser 1997, Seitzinger and
Sanders 1999, Seitzinger et al. 2001), management
efforts must be made to limit anthropogenically
mediated atmospheric N emissions to the airshed in
the region.
Results of this investigation clearly show that coastal
waters nearby large urban and industrial centers are
more strongly impacted by the atmospheric deposition
of nutrient elements than are coastal waters in rural
areas. While measurements of NO3 and NH4þ in
precipitation and in aerosol particulate matter indicate
considerable temporal variations in ambient air at both
the northern and southern sampling sites in New Jersey,
spatial differences in the data are distinct, with
consistently higher values recorded at the Sandy Hook
site downwind of urban and industrialized regions of the
state. The concentrations of NO3 in precipitation for
both the northern and southern regions of the state
ranged 1.20–153 lmol/L, while NH4þ concentrations
ranged 0.275–107 lmol/L. Most precipitation along the
coastal zone is acidic in nature, with pH values generally
,4.5 (Gao 2002). Acidic precipitation appears to
stimulate primary production in coastal waters more
significantly than does neutral precipitation (Paerl 1985,
Willey and Cahoon 1991). Acidic precipitation, therefore, can contribute to or exacerbate eutrophic conditions in estuarine and coastal marine waters.
Biologically available inorganic constituents, such as
NO3 and NH4þ, are readily assimilated by phytoplankton and benthic flora in the estuary, stimulating their
growth and production. In a system already receiving
substantial NO3 and NH4þ inputs from the adjoining
watershed, new N inputs via atmospheric deposition can
exacerbate enrichment problems. Such is the case for the
Barnegat Bay–Little Egg Harbor Estuary.
The greater frequency of brown tide (Aureococcus
anophagefferens) and benthic macroalgal blooms, accelerated seagrass epiphytic overgrowth, and declining
shellfish resources in the Barnegat Bay–Little Egg
Harbor Estuary since 1995 suggest that escalating N
loading is having detrimental biotic consequences (Olsen
1989, Olsen and Mahoney 2001). Accelerated growth of
drifting macroalgae (e.g., Ulva lactuca) has produced
extensive mats that pose a potential threat to seagrass
beds in some areas of the estuary. The rapid growth of
other macroalgal species in the estuary, such as the
Rhodophytes Agardhiella subulate, Ceramium spp., and
Gracilaria tikvahiae, can also impact benthic habitat and
resident infauna (Kennish 2001b). In addition, the
spread of a thick blanket of macroalgae on seagrass
July 2007
COASTAL ATMOSPHERIC NITROGEN DEPOSITION
beds (e.g, Zostera marina) in the estuary and its
subsequent decomposition may promote hypoxic/anoxic
conditions and alter the biogeochemistry of the affected
habitat. Studies indicate that seagrass beds in the estuary
may have decreased by 25% since the mid-1970s
(Lathrop et al. 1999).
Progressive eutrophication, such as that in the
Barnegat Bay–Little Egg Harbor Estuary, has been
linked to a series of biotic changes in other impacted
systems (Kennish 2002, 2005, Rabalais 2002). For
example, diatom species are commonly replaced by
dinoflagellates, and shifts often occur in the benthos
from filter feeders to deposit feeders and from larger,
long-lived benthic species to smaller rapidly growing,
but shorter lived forms. Ultimately, benthic macrophytes may become locally extinct, and phytoplankton
can overwhelmingly dominate the autotrophic communities (Schramm 1999, Rabalais 2002). Altered food web
interactions will also impact secondary production
(Livingston 2003). Continued nutrient enrichment will
pose an even greater threat to the structure and function
of the ecosystem, manifested by the permanent alteration of biotic communities (Rabalais 2002).
With limited tributaries and a long residence time, the
Barnegat Bay–Little Egg Harbor Estuary is readily
affected by atmospheric deposition through both
precipitation and aerosol particle dry deposition. The
Mullica River–Great Bay Estuary to the south is a
coastal plain estuary having greater circulation and
exchange of water with the coastal ocean than does the
Barnegat Bay–Little Egg Harbor Estuary. However, it is
also very shallow (,2 m at mean low water) in most
areas, and thus susceptible to atmospheric deposition of
NO3 and NH4þ, which augments inputs of these
constituents in freshwater inflow from the Mullica River
watershed. The mean concentrations of NO3 and NH4þ
in the Mullica River–Great Bay Estuary are 1.2–12.1
lmol/L and 1.5–3.8 lmol/L, respectively. Concentrations of NO3 decrease with increasing salinity downestuary, whereas NH4þ concentrations vary along the
salinity gradient. Since the mid-1970s, the annual mean
NO3 concentration increased in the upper estuary
region due to accelerated land development and
associated wastewater impacts in this area. Zampella et
al. (2001) found the highest NO3 concentrations in
tributaries of the Mullica River with a large proportion
of upland agriculture (49–62%) and developed land (13–
42%).
The potential biotic changes mediated by the input of
new N via atmospheric deposition must be monitored
for effective resource management of this biologically
productive system. The results of this study illustrate the
magnitude and variation of atmospherically deposited
NO3 and NH4þ inputs to shallow estuarine and coastal
marine waters of New Jersey at locations downwind of
heavy anthropogenic emissions. Estuarine waters of
New Jersey are subject to considerable nonpoint source
nutrient enrichment from coastal watersheds and air-
S39
sheds. Consequently, eutrophication has emerged as one
of the most serious environmental problems in New
Jersey’s coastal bays.
CONCLUSIONS
Results of this work indicate that the concentrations
of NO3 and NH4þ in the ambient air over the New
Jersey, USA, coast exhibit strong temporal and spatial
variations that can significantly affect N enrichment of
coastal waters. The mean concentration of NO3 in
precipitation in the northern New Jersey coastal region
(44.6 lmol/L) as measured at Sandy Hook was higher
than that in the southern New Jersey coastal region (29.1
lmol/L) as measured at Tuckerton. The mean concentration of NH4þ in precipitation was similar, being
higher in the northern (26.3 lmol/L) than in the
southern (18.3 lmol/L) region. The mean concentrations
for aerosol NO3 were 3.18 lm/m3 at Sandy Hook and
2.04 lm/m3 at Tuckerton. The mean concentrations for
aerosol NH4þ varied from 2.32 lm/m3 at Sandy Hook to
only 0.497 lm/m3 at Tuckerton. High wet deposition
rates of NO3 and NH4þ were observed during the
summer at both northern and southern New Jersey
sampling sites. On an annual basis, the total atmospheric deposition of NO3 was estimated to be 51.1
mmolm2yr1 on the northern New Jersey coast and
32.9 mmolm2yr1 on the southern New Jersey coast.
The total deposition of NH4þ was 32.8 mmolm2yr1
on the northern coastal area and 20.3 mmolm2yr1 on
the southern coastal area. Wet deposition accounted for
;89% of the total deposition for NO3 and 76–91% of
the total deposition for NH4þ on the New Jersey coast.
In the coastal bays of New Jersey, the concentrations
and distributions of NO3 and NH4þ have distinct
patterns. The concentrations of NO3 decrease consistently from the head to the mouth of the Mullica River–
Great Bay Estuary. During the 2002–2004 period, for
example, the annual mean concentration of NO3
declined from 12.1 lmol/L in the upper estuary to 1.2
lmol/L at the bay inlet area. Nutrient studies conducted
in the estuary during the 1971–1979 period revealed
similar concentrations and distributions, with the annual
mean concentration of NO3 decreasing from 6.8
lmol/L in the upper estuary to 2.3 lmol/L in the lower
estuary. The higher concentrations of NO3 in the upper
estuary during recent years are attributed to changes in
land use, most notably the loss of forest to developed
and agricultural land in the upper watershed.
The concentrations of NH4þ are typically lower than
those of NO3 in the estuary. During the 2002–2004
period, the annual mean concentration of NH4þ ranged
1.5–3.8 lmol/L; the highest concentrations occurred in
the mid- and lower estuary. During the 1971–1979
period, the annual mean concentration of NH4þ ranged
2.2–3.7 lmol/L; the highest concentrations were also
found in the lower estuary at this time.
The lowest concentrations of NO3 in the Mullica
River–Great Bay Estuary occur during the summer
S40
YUAN GAO ET AL.
when biotic uptake is greatest. The concentrations of
NH4þ, however, peak during the summer and fall. In
contrast to NO3 concentrations, which are usually
lower in the bay than in the river, NH4þ concentrations
are typically higher in the bay than in the river.
Atmospheric deposition of N to the coastal bays is
significant, accounting for nearly 40% of the total N
load to the Barnegat Bay–Little Egg Harbor Estuary. In
this system, NO3 and NH4þ concentrations in the water
column are generally ,4 lmol/L. Thus, atmospheric
deposition appears to be an important pathway of new
N inputs to the coastal bays and a potentially significant
N enrichment source for biotic production. The estuary
is classified as a highly eutrophic system, with increasing
occurrence of brown tide (Aureococcus anophagefferens)
and benthic macroalgae blooms, decreasing shellfish
resources, and potentially significant losses of seagrass
habitat. These biotic changes suggest that the structure
and function of the estuarine ecosystem have been
impacted by bottom-up effects associated with N
enrichment.
ACKNOWLEDGMENTS
Y. Gao thanks Kenneth Able and John Dighton for the use
of the research facilities at Rutgers University Marine Field
Station and Pinelands Field Station and Roger Hoden and
Dennis Gray for technical assistance. Funding for atmospheric
field sampling was provided to Yuan Gao by the New Jersey
Sea Grant College Program (R/E-9801, NJSG-002-485 and
R/E-9704, NJSG-002-485) and the New Jersey Department of
Environmental Protection (SG-99-032 and SG-99-031).
Water column nutrient work reported herein for the Mullica
River–Great Bay Estuary was supported by a graduate research
fellowship grant (#NA03NO54200052) to A. M. Flynn from the
Estuarine Reserves Division, Office of Ocean and Coastal
Resource Management, National Ocean Service, National
Oceanic and Atmospheric Administration (NOAA). The
collection and analysis of nutrient monitoring data by M.
Kennish and his colleagues in this estuarine system and
contiguous waters were also supported by operation grants
(NA170R2488 and NA03NOS4200143) from the Estuarine
Reserves Division of NOAA to the Jacques Cousteau National
Estuarine Research Reserve.
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