DEVELOPING A NUTRIENT POLLUTION INDICATOR FOR THE
BARNEGAT BAY-LITTLE EGG HARBOR ESTUARY USING
EELGRASS, ZOSTERA MARINA
Michael J. Kennish and Scott M. Haag
Institute of Marine and Coastal Sciences,
Rutgers University
New Brunswick, New Jersey 08901
ABSTRACT
We conducted a study in the Barnegat Bay-Little Egg Harbor Estuary from JuneOctober in 2008 to determine the nitrogen concentrations in eelgrass (Zostera marina)
blades along a north-south estuarine gradient. These data were compiled to generate a
Nutrient Pollution Index (ratio of leaf nitrogen to leaf mass) for different areas of the
estuary in an effort to determine the efficacy of applying the method as a robust indicator
of early nutrient over-enrichment of the system. Results of this investigation indicate that
leaf nitrogen levels in Z. marina do not provide a sensitive early indicator of nitrogen
over-enrichment in the Barnegat Bay-Little Egg Harbor Estuary. Eelgrass leaf nitrogen
was not significantly different between up-estuary sampling stations and stations downestuary, which did not reflect environmental nitrogen and other gradients. However, leaf
nitrogen levels gradually increased throughout the seasonal sampling period (June to
October) estuary-wide, indicating that this method may provide an accurate integrative
measure of environmental nitrogen in the system.
INTRODUCTION
The Barnegat Bay-Little Egg Harbor Estuary, similar to other coastal lagoon
systems in the Mid-Atlantic region, is subject to an array of natural and anthropogenic
1
stressors that pose a potential threat to the structure of seagrass habitat and the function of
the ecosystem.
Included here are nutrient over-enrichment, phytoplankton and
macroalgal blooms, epiphytic overgrowth, high turbidity, prop scarring, and other factors.
With continued population growth and development in coastal watershed areas
surrounding this shallow waterbody, future impacts on seagrass and other vital habitats in
the estuary are likely to escalate.
Nutrient enrichment and excessive algal growth
resulting from anthropogenic activities are ongoing problems in this system, and they
must be effectively addressed to mitigate the ecosystem decline. Cultural eutrophication
poses the most serious threat to the long-term health and viability of the estuary (Kennish
et al., 2007a, b).
Investigations of seagrass beds in the Barnegat Bay-Little Egg Harbor Estuary
over the past five years have yielded a number of important findings. For example, the
analysis of seagrass biomass during the 2004-2006 study period revealed important
temporal and spatial patterns. Although the aboveground and belowground biomass of
seagrass varied considerably during the spring to fall period each year, they generally
declined from June to November. This temporal pattern is attributed to more favorable
light conditions during the late spring and summer and increasing eutrophic conditions
linked to nutrient loading. Aboveground and belowground biomass values also varied
spatially due to a wide range of physicochemical conditions over small spatial scales,
including marked differences in shading, light availability, macroalgae cover, and other
factors. In addition, seagrass density and areal cover in the estuary exhibited declining
patterns over the 2004 to 2006 period, reflecting unfavorable environmental conditions
over a protracted period of time.
2
Symptom expressions of eutrophication in the Barnegat Bay-Little Egg Harbor
Estuary include low dissolved oxygen in the northern segment, diminishing seagrass
habitat, epiphytic overgrowth on seagrass blades, nuisance/toxic algal blooms, and
marked reduction of fisheries (e.g., hard clams). Since 2004, the condition of submerged
aquatic vegetation (SAV) in the estuary has worsened, and extensive areas of the northern
estuary have experienced reduced dissolved oxygen levels. Hence, eutrophic conditions
appear to have increased during the past five years. The aboveground and belowground
biomass of seagrass in the estuary decreased by 50-87.7% over the 2004-2006 period,
and sampling conducted in summer 2008 revealed that the degraded conditions have
persisted. Seagrass biomass, density, blade length and areal cover in 2008 were similar
to those recorded during the 2004-2005 period (Kennish et al., 2008, 2009).
The
decrease in seagrass areal cover has eliminated habitat for bay scallops, hard clams
(Mercenaria mercenaria), as well as many other benthic and demersal organisms.
Blooms of the sea nettle (Chrysaora quinquecirrha), possibly coupled to increasing
eutrophic conditions, have likewise occurred at greater abundance in the estuary in recent
years. The aforementioned changes have been linked to changes in ecosystem structure
and function in the estuary.
The Barnegat Bay-Little Egg Harbor Estuary is classified as a highly eutrophic
system, being particularly susceptible to nutrient loading because it is shallow, poorly
flushed, and bordered by highly developed watershed areas. Most of the nitrogen load to
the estuary (~54%) is from surface water inflow, but substantial fractions also originate
from atmospheric deposition (~35%), and direct groundwater discharges (~11%). No
point source inputs of nutrients exist in the Barnegat Bay watershed. To effectively
3
address nutrient loading problems in the estuary, it is important to determine the
threshold loadings of nutrients that produce observable impacts in the estuary. It is also
vital to continually monitor and assess priority indicators of water quality change and
estuarine health.
The principal objective of this investigation is to determine the nitrogen
concentrations in seagrass blades along a north-south gradient in the estuary over a
growing season. These data are necessary for the development of a Nitrogen Pollution
Index (NPI) for different areas of the estuary. Although two species of seagrasses occur
in the Barnegat Bay-Little Egg Harbor system, eelgrass (Zostera marina) and widgeon
grass (Ruppia maritima), eelgrass is overwhelmingly more abundant and thus the target
of this investigation. Ground surveys yielded few widgeon grass samples.
STUDY AREA
Barnegat Bay-Little Egg Harbor is a lagoonal estuary located along the central
New Jersey coastline (Figure 1). It forms an irregular tidal basin ~70 km long, 2-6 km
wide, and 1.5 m deep. The surface area amounts to 280 km2, and the volume, 3.54 x 10
m8 (Kennish, 2001). The location of the barrier island complex (Island Beach and Long
Beach Island) restricts exchange of water with the coastal ocean; therefore, flushing times
of the estuary are protracted, ~74 days in summer. Exchange of bay and ocean water
occurs through Barnegat Inlet, Little Egg Inlet, and the Pt. Pleasant Canal.
The adjoining Barnegat Bay watershed covers an area of 1730 km2, and the
watershed:estuary areal ratio is 6.5:1. Nearly 565,000 people live in the surrounding
watershed year round, but the population exceeds 1,400,000 people during the summer
4
tourist season. A north-to-south gradient of decreasing population density occurs in the
watershed. As a result, nutrient loading is highest in the northern segment of the estuary
(Seitzinger et al. 2001).
PROJECT DESCRIPTION
Because progressive eutrophication is a debilitating process in aquatic systems,
the development and application of a nutrient pollution indicator would be extremely
valuable for delineating the onset of nutrient enrichment problems. By applying an
indicator of this type, remedial measures could be formulated in a more timely fashion to
address the sources and effects of nutrient enrichment in the estuary. Therefore, more
rapid management mediated intervention would play a significant role in mitigating
nutrient impacts on essential habitat and biotic communities. Such an indicator would
also be useful for determining when water quality conditions are degraded from year to
year.
Estuary-wide SAV surveys are time consuming, labor intensive, and costly. Most
of these surveys are conducted to track changes in presence/absence, abundance,
biomass, and areal distribution of seagrasses in these coastal systems to assess their
overall condition (Short et al., 2004; Larkum et al., 2006; Beem and Short, 2009).
However, they have been rarely used as tools to quantitatively measure nutrient
enrichment in estuaries. Zostera marina abundance is a potentially effective tool for
early assessment of nutrient over-enrichment (Lee et al., 2004).
It can serve as a
consistently simple and reliable indicator of nutrient over-enrichment in shallow estuarine
systems.
5
Nitrogen, the primary limiting nutrient in the estuary, is the principal driver of
eutrophication in the system. Therefore, development of a nutrient pollution indicator for
Barnegat Bay-Little Egg Harbor must target nitrogen. A nutrient indicator cannot be
developed directly from in situ nitrogen concentrations in the water column because of
rapid biotic uptake, dissipation via tidal exchange, and benthic fluxes. Although water
column nitrogen concentration is not a reliable indicator of eutrophic conditions in the
estuary, seagrasses are useful bioindicators because they provide an integrated measure of
environmental nitrogen experienced by the plants (Lee et al., 2004). The objective of the
proposed work is to apply and test a robust indicator of nutrient over-enrichment for the
Barnegat Bay-Little Egg Harbor Estuary that may yield rapid detection of early
eutrophication during the plant growing season. By using this approach, appropriate
remedial management actions could then be implemented. If successful, this indicator
could have great utility for future monitoring of estuarine condition at a significant
reduction of time and cost relative to traditional seagrass surveys. Since it is generally
too labor-intensive and costly to conduct estuary-wide seagrass surveys on an annual
basis, the tracking of eutrophic condition in the estuary must be based on statistically
sound sampling linked to an innovative approach.
Here we apply a practical tool to formulate a quantitative measure that will serve
as an indicator of nitrogen over-enrichment in the estuary. More specifically, we have
collected data on the ratio of leaf nitrogen concentration to leaf mass of Z. marina
samples from disjunct seagrass beds along the estuary gradient from Mantoloking to
southern Little Egg Harbor. Quantitative measures are then calculated to generate a
matrix of values across the plant growing season. Leaf nitrogen content has been shown
6
to provide an accurate integrated measure of environmental nitrogen experienced by
eelgrass in other estuarine systems (see Lee et al., 2004). This project is part of an
overall effort to define and remediate eutrophic condition of the Barnegat Bay-Little Egg
Harbor system.
PREVIOUS WORK
Lee et al. (2004) showed that the leaf N content of Z. marina provided an accurate
integrated measure of environmental nitrogen in estuarine systems. Working in Great
Bay Estuary (NH), Narragansett Bay (RI), and Waquoit Bay (MA), these investigators
demonstrated that by measuring the ratio of leaf nitrogen to leaf mass in Z. marina, a NPI
value could be calculated that provides a sensitive and consistent indicator of early
eutrophication. Changes in both plant nitrogen chemistry and plant morphology are
captured by the NPI value as follows:
NPI =
Leaf N
Normalized Leaf Mass (mg dry wt cm-1)
In eelgrass samples collected in Great Bay, Narragansett Bay, and Waquoit Bay, Lee et
al. (2004) reported that the area normalized leaf mass exhibited a consistently negative
relationship with leaf tissue nitrogen. In addition, the NPI values varied regularly along
the estuarine nutrient gradients, with higher NPI values observed upestuary.
concluded that the NPI is an effective pollution indicator in these estuarine systems.
7
They
MATERIALS AND METHODS
Water quality parameters (temperature, salinity, dissolved oxygen, pH, turbidity,
and nutrients) were measured along 12 transects in Barnegat Bay and Little Egg Harbor
during June, August, and October 2008 to characterize conditions in the general area as
part of a separate seagrass demographic survey (Kennish et al., 2009).
These
measurements were taken with a handheld YSI 600 XL datasonde coupled with a
handheld YSI 650 MDS display unit and an automated YSI 6600 unit (equipped with a
turbidity probe). The physicochemical measurements are listed in Tables 1-6.
We sampled seagrass beds at 10 locations along a north-south gradient from
Mantoloking to lower Little Egg Harbor as part of this NPI study (Figure 2). At these 10
locations, 3 Z. marina samples were collected on each sampling date from June to
October 2008. Although we attempted to collect 90 samples at the 10 sites over the
entire sampling period, only 77 seagrass samples were obtained over the course of the
study because some of the sampling sites were devoid of seagrass.
At the 10 NPI sampling sites, water quality parameters (temperature, salinity,
dissolved oxygen, pH, turbidity, and nutrients) were also measured using the
aforementioned handheld YSI 600 XL datasonde coupled with a handheld YSI 650 MDS
display unit and an automated YSI 6600 unit (equipped with a turbidity probe) (Table 7).
The water quality data were obtained at a uniform depth (~10 cm) above the sedimentwater interface prior to collecting seagrass samples at each sampling site.
Simple
statistics of key parameters in the NPI survey are compiled in Table 8.
After the water quality data were collected, a diver was deployed to obtain
seagrass samples using a PVC corer. Three cores of seagrass were collected at each site
8
on each sampling date. Coring methods followed those of Short et al. (2002), with a 10cm (.00785 m2) diameter PVC coring device used to collect the seagrass samples. The
diver-deployed corer extended deep enough in the sediments to extract all belowground
fractions (roots and rhizomes). Each core was placed in a 3 x 5 mm mesh bag and rinsed
to separate plant material from the sediment. The seagrass sample was then removed
from the mesh, placed in a labeled bag, and stored on ice in a closed container prior to
transport back to the Rutgers University Marine Field Station (RUMFS) in Tuckerton.
In the laboratory, the samples were carefully sorted and separated into
aboveground (shoots) and belowground (roots and rhizomes) components. The shortest
full blade from each core sample was subsequently selected and measured in length and
width to the nearest millimeter, cut into three segments, and then oven dried at 50-60 ºC
for 48 hours. The blade segments were run for C/N concentrations on a Carlo Erba NA
1500 series 2 Elemental Analyzer. From these measurements, the percent concentration
of nitrogen was calculated in each seagrass blade. The leaf mass (mg dry wt cm-2) of the
blade was also measured to the third decimal place.
QA/QC examination of the generated databases revealed several outliers for leaf
mass. We accepted only sample measurements within two standard deviations of the
median value for leaf mass. We also removed from the databases sample measurements
where the standard deviation of the nitrogen content was greater than 0.4. Removal of
these outliers resulted in the elimination of an additional 31 samples from statistical
analyses, leaving a total of 46 of 90 samples to be analyzed in the study.
The samples were tested for normality and homogeneity of variance to meet
parametric statistical criteria. Leaf nitrogen and leaf mass content among the sampling
9
stations were tested using standard ANOVA testing. The means were analyzed by the
Tukey’s multiple comparison test to determine where significant differences occur within
the system. A matrix of values was developed for the eelgrass leaf nitrogen and leaf
mass content and assessed for the environmental nitrogen exposure which the plants
experienced in different areas of the estuary.
RESULTS
Leaf Nitrogen Content
Leaf nitrogen content of Z. marina in the Barnegat Bay-Little Egg Harbor Estuary
ranged from 0.94 to 3.84% dry weight (Table 9). The highest median values were
recorded at sites 1, 5, and 10, and the lowest median values, at sites 4 and 6 (Figure 3).
However, an Analysis of Variance (ANOVA) test applied to the data revealed no
statistically significant differences (F = 1.91; P > 0.1742) between NPI values of samples
collected south of Barnegat Inlet (sites 1-4) compared to NPI values of samples collected
north of Barnegat Inlet (sites 5 to 10).
However, a distinct temporal pattern was evident
over the course of the study, with the leaf nitrogen content increasing markedly over the
three sampling periods from June to October (Figure 4). Median leaf nitrogen content
exceeded 3% only during sampling period 3.
Leaf Mass
The area normalized leaf mass values varied from 0.73 to 5.45 mg dry wt cm-2
(Table 9). The highest median values were registered at sites 5 and 7, and the lowest
median values, at sites 2 and 4 (Figure 5). An Analysis of Variance (ANOVA) test
10
applied to the data revealed statistically significant differences (F = 6.47; P > 0.0146)
between leaf mass values of samples collected south of Barnegat Inlet (sites 1-4) than for
leaf mass values of samples collected north of Barnegat Inlet (sites 5 to 10). Leaf mass
values were statistically greater at sampling sites in northern Barnegat Bay. In contrast to
the distinct increase in leaf nitrogen content (%) across the survey period, leaf mass
peaked in samples collected in June (sampling period 1), with lowest leaf mass observed
in samples collected in August (sampling period 2). Intermediate leaf mass values were
recorded in October (Figure 6).
Leaf Nitrogen to Leaf Mass Relationship
There was no consistent relationship between leaf nitrogen content and leaf mass
(Figure 7). A plot of leaf nitrogen content vs. leaf mass was highly scattered with no
clear pattern. Most of the samples had leaf nitrogen and leaf mass content values of less
than 1.5% and 3.5%, respectively.
Ratios of Leaf Nitrogen to Leaf Mass
NPI values ranged from 0.30 to 3.17 (Table 9).
An Analysis of Variance
(ANOVA) test applied to the data revealed statistically significant differences (F = 7.74;
P > 0.0079) between NPI values of samples collected south of Barnegat Inlet (sites 1-4)
and NPI values of samples collected north of Barnegat Inlet (sites 5 to 10). NPI values
were significantly higher at the southern sampling sites (Figure 8).
11
DISCUSSION
Seagrasses are important indicators of water and sediment quality in estuaries
(Bortone, 2000; Larkum et al., 2006). Other studies have shown that leaf nitrogen in Z.
marina provides an integrated measure of nitrogen experienced by the plants in the
estuarine environment (Fourqurean et al., 1990; Lee et al., 2004).
Leaf nitrogen
concentrations of Z. marina recorded in our study of the Barnegat Bay-Little Egg Harbor
Estuary corroborate these findings. They increased consistently and significantly across
the study period from June through October (Figure 4). The mean leaf nitrogen content
over this period increased from less than 1.5% to more than 3%. However, leaf nitrogen
concentrations were not consistent across sampling sites; the highest values were
recorded at sites south of Barnegat Inlet, with progressively higher values found at sites
farthest to the south (sites 1-3).
In a study of three New England Estuaries (Great Bay Estuary, NH; Narragansett
Bay, RI; and Waquoit Bay, MA), Lee et al. (2004) showed that the ratio of leaf nitrogen
to leaf mass was a more sensitive and consistent indicator of early eutrophication than
either of the plant characteristics alone (i.e., leaf nitrogen or leaf mass) when applied to
ecosystem assessment. The same methods of Lee et al., (2004) have been applied in this
study to provide a measure of early assessment of nutrient enrichment in the Barnegat
Bay-Little Egg Harbor Estuary.
Inorganic nitrogen concentrations in the water column are not steady state, but
can vary substantially both temporally and spatially due to fluxes in nutrient loading,
uptake by plants, removal to bottom sediments, ammonification, circulation patterns,
flushing to the nearshore ocean, and other factors. In addition, Z. marina assimilates
12
nitrogen from both the water column and bottom sediments, and thus the concentration of
nitrogen in eelgrass blades reflects its availability in both media. Inorganic nutrient
levels in the water column during the warmer months of the year are typically very low,
often less than 1 µM, largely due to biotic uptake. As a consequence, nutrient
measurements in the water column typically are not a good indicator of the eutrophic
condition of estuarine water bodies. Biotic responses to nutrient loading, therefore, may
provide a more realistic measure of nutrient over-enrichment of these systems (Bricker et
al., 2007; Kennish et al., 2007a).
The range of Z. marina leaf nitrogen concentrations in the Barnegat Bay-Little
Egg Harbor Estuary (0.9 to 3.8% dry weight) was greater than that recorded by Lee et al.
(2004) in the Great Bay Estuary, NH (2.1 to 3.5% dry weight), Narrangansett Bay, RI,
(2.0 to 2.3%), and Waquoit Bay, MA (1.6 to 2.4% dry weight). A distinct gradient of Z.
marina leaf nitrogen content was evident in the Great Bay Estuary, Narragansett Bay, and
Waquoit Bay, decreasing from up-estuary to down-estuary areas. In contrast, Z. marina
leaf nitrogen content did not show the same spatial gradient in the Barnegat Bay-Little
Egg Harbor Estuary (Figure 3).
The spatial distribution of leaf mass values in the Barnegat Bay-Little Egg Harbor
Estuary also differed from those in the Great Bay Estuary, Narragansett Bay, and
Waquoit Bay. While the leaf mass was significantly higher in a seaward direction in the
latter three estuaries, the leaf mass in the Barnegat Bay-Little Egg Harbor Estuary was
significantly greater at up-estuary (northern) locations. The range of leaf mass values in
the Barnegat Bay-Little Egg Harbor Estuary (0.73 to 5.45 mg dry wt cm-2) exceeded that
13
in the other three estuaries. However, the highest leaf mass values (>7 mg dry wt cm-2)
were registered in Narragansett Bay (Lee et al., 2004).
NPI values were statistically greater in Little Egg Harbor than Barnegat Bay.
These results differed from those of Lee et al. (2004) who reported that the area
normalized leaf mass exhibited a consistently negative relationship with leaf tissue
nitrogen in Great Bay Estuary, Narragansett Bay, and Waquoit Bay. In addition, while
Lee et al. (2004) showed that the NPI values varied regularly along estuarine nutrient
gradients, with higher NPI values observed up-estuary, the findings in our study show the
reverse, with higher NPI values recorded down-estuary. Marked changes in NPI values
in the estuary were observed in proximity to Barnegat Inlet where flushing is greatest,
with much lower values documented north of the inlet.
There is no clear relationship or trend between leaf nitrogen content and leaf mass
among the sampling sites as evidenced by a scatter plot for the samples collected during
this study (Figure 7). These results differ significantly from those reported for other
estuaries where leaf nitrogen content exhibited a negative relationship with leaf mass and
a significant positive response to estuarine nutrient gradients. In the Barnegat Bay-Little
Egg Harbor Estuary, higher nitrogen loading and water column nitrogen concentrations
have been reported up-estuary in the northern reaches of Barnegat Bay where highest
coastal watershed development occurs (Seitzinger et al., 2001; Kennish et al., 2009).
However, as shown in this study, NPI values are significantly higher down-estuary (Little
Egg Harbor) than up-estuary (Barnegat Bay), a pattern opposite to that reported for the
three New England estuaries (Lee et al., 2004). There may be several reasons for these
differences. First, the salinity gradients in Great Bay (NH), Waquoit Bay (MA), and
14
Narragansett Bay (RI) are stronger than the gradients in the Barnegat Bay-Little Egg
Harbor Estuary, where salinities are lowest in the area off Toms River in the northern
estuary and highest near Barnegat Inlet and in Little Egg Harbor. A salinity gradient is
best developed between Toms River and Barnegat Inlet, with a secondary increasing
salinity gradient from Toms River northward to the Pt. Pleasant Canal. Hence, there are
two gradients in the northern estuary.
Barnegat Inlet provides strong flushing of waters in the central bay, but at
increasing distances north and south of the inlet the water residence times in the estuary
increase appreciably such that in the summer months the flushing time in areas away
from the inlet amounts to ~75 days (Kennish et al., 2007b). High levels of total nitrogen
occur estuary-wide during the summer months, with peak levels found in both the upper
areas of Barnegat Bay and in Little Egg Harbor. Therefore, nitrogen compounds disperse
throughout the estuary and, because of the long water residence times and location of the
barrier islands, they tend to be retained in the system most of the summer months when
eutrophication problems escalate. Highest water residence times may be found in areas
of northern Little Egg Harbor and Manahawkin Bay far removed from Barnegat Inlet and
Little Egg Inlet. This could explain why the highest NPI values were recorded in this
area of the estuary and not in Barnegat Bay in the northern part of the system.
CONCLUSIONS
Results of this study indicate that the ratio of leaf nitrogen content to leaf mass
(NPI) in Z. marina does not provide a sensitive early indicator of nitrogen overenrichment in the Barnegat Bay-Little Egg Harbor Estuary. Eelgrass leaf nitrogen was
15
not significantly different in up-estuary sampling stations than stations down-estuary,
which did not reflect environmental nitrogen gradients. However, leaf nitrogen levels
progressively increased through the seasonal sampling period (June to October),
indicating that this method may provide an accurate integrative measure of environmental
nitrogen in the system.
Total nitrogen reaches peak levels in the upper reaches of Barnegat Bay and in
Little Egg Harbor. These areas are characterized by protracted water residence times,
being removed from the more rapid flushing effects at Barnegat Inlet.
Strong water
circulation at the inlet affects eelgrass plant morphology, leaf nitrogen concentrations,
and leaf mass. Thus, eelgrass tissue nutrient and mass values commonly differ in upestuary and down-estuary areas. For example, the leaf mass values in the Barnegat BayLittle Egg Harbor Estuary were significantly greater at up-estuary (northern) locations
than at down-estuary locations, whereas the NPI values were significantly greater at
down-estuary (southern) locations. Future studies of seagrass tissue nutrients must take
into consideration the important role of flushing at Barnegat Inlet and water residence
times in areas distant from the inlet.
REFERENCES
Beem, N. T. and F. T. Short. 2009. Subtidal eelgrass declines in the Great Bay Estuary,
New Hampshire and Maine, USA. Estuaries and Coasts, 32: 202-205.
Bricker, S. B., B. Longstaff, W. Dennison, A. Jones, K Boicourt, C. Wicks, and J.
Woerner. 2007. Effects of Nutrient Enrichment in the Nation’s Estuaries: A
16
Decade of Change. NOAA, National Ocean Service, Special Projects Office and
National Centers for Coastal Ocean Science, Silver Spring, Maryland, USA.
Bortone, S.A. (Ed.). 2000. Seagrasses:
Monitoring, Ecology, Physiology, and
Management. CRC Press, Boca Raton, Florida.
Fourqurean, J. W., T. O. Moore, B. Fry, and J. T. Hollibaugh. 1997. Spatial and temporal
variation in C:N:P ratios δ15N and δ13C of eelgrass Zostera marina as indicators
of ecosystem processes Tomales Bay, California, USA. Marine Ecology Progress
Series, 157: 147-157.
Kennish, M. J. (Ed.). 2001. Barnegat Bay-Little Egg Harbor, New Jersey: Estuary and
Watershed Assessment. Journal of Coastal Research, Special Issue 32, 280 pp.
Kennish, M. J., S. B. Bricker, W. C. Dennison, P. M. Glibert, R. J. Livingston, K. A.
Moore, R. T. Noble, H. W. Paerl, J. M. Ramstack, S. Seitzinger, D. A. Tomasko,
and I. Valiela. 2007a. Barnegat Bay-Little Egg Harbor Estuary: case study of a
highly eutrophic coastal bay system. Ecological Applications 17(5) Supplement:
S3-S16.
Kennish, M. J., S. M. Haag, and G. P. Sakowicz. 2007b. Demographic Investigation of
SAV in the Barnegat Bay-Little Egg Harbor Estuary with Assessment of Potential
Impacts of Benthic Macroalgae and Brown Tides. Technical Report 107-15,
Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick,
New Jersey. 366 pp.
Kennish, M. J., S. M. Haag, and G. P. Sakowicz. 2008. Seagrass demographic and spatial
habitat characterization in Little Egg Harbor, New Jersey, using fixed transects.
Journal of Coastal Research, SI 55: 148-170
17
Kennish, M. J., S. M. Haag, and G. P. Sakowicz. 2009. Assessment of Eutrophication in
the Barnegat Bay-Little Egg Harbor System: Use of SAV Biotic Indicators of
Estuarine Condition. Technical Report 2009-07, Institute of Marine and Coastal
Sciences, Rutgers University, New Brunswick, New Jersey. 70 pp.
Larkum, W. D., R. J. Orth, and C. M. Duarte (Eds.). 2006. Seagrasses: Biology, Ecology,
and Conservation. Springer, Dordrecht, The Netherlands.
Lee-D-S., F. T. Short, D. M. Burdick. 2004. Development of a nutrient pollution
indicator using the seagrass, Zostera marina, along nutrient gradients in three
New England estuaries. Aquatic Botany 78: 197-216.
Olsen, P. S. and J. B. Mahoney. 2001. Phytoplankton in the Barnegat Bay-Little Egg
Harbor estuarine system:
species composition and picoplankton bloom
development. In: M. J. Kennish, (ed.), Barnegat Bay-Little Egg Harbor, New
Jersey: Estuary and Watershed Assessment. Journal of Coastal Research, Special
Issue 32, pp. 115-143.
Seitzinger, S. P., R. M. Styles, and I. E. Pilling. 2001. Benthic microalgal and
phytoplankton production in Barnegat Bay, New Jersey (USA): microcosm
experiments and data synthesis. Journal of Coastal Research, Special Issue 32,
pp. 144-162.
Short, F. T., L. J. McKenzie, R. G. Coles, and K. P. Vidler. 2002. SeagrassNet Manual
for Scientific Monitoring of Seagrass Habitat. (QDPI, PFS, Cairns). 56 pp.
18
FIGURE CAPTIONS
Figure 1. Barnegat Bay-Little Egg Harbor Estuary. The inset shows the location of the
estuary with respect to the State of New Jersey.
Figure 2. Ten seagrass sampling sites used in this study.
Figure 3. Box plots showing leaf nitrogen content (%) in Z. marina samples collected at
10 sites in the Barnegat Bay-Little Egg Harbor Estuary during 2008. See Figure 2
for the sampling sites.
Figure 4. Box plots showing median leaf nitrogen content (%) of Z. marina collected in
the estuary over a six-month sampling period in 2008. Sampling period 1, JuneJuly; sampling period 2, August-September; and sampling period 3, OctoberNovember.
Figure 5. Box plots showing median leaf mass (mg dry wt cm-2) of Z. marina samples
collected at 10 sites in the estuary during 2008. See Figure 2 for the sampling
sites.
Figure 6. Box plots showing median leaf mass (mg dry wt cm-2) of Z. marina collected
in the estuary over a six-month sampling period in 2008. Sampling period 1,
June-July; sampling period 2, August-September; and sampling period 3,
October-November.
19
Figure 7. Plot of leaf nitrogen content (%) vs. leaf mass (mg dry wt cm-2) of Z. marina
collected at 10 sites in the estuary during 2008. See Figure 2 for the sampling
sites.
Figure 8. Box plots showing median NPI values recorded at 10 seagrass sampling sites in
the estuary during 2008. See Figure 2 for the sampling sites.
20
Figure 1
21
Figure 2
22
Figure 3
23
Figure 4
24
Figure 5
25
Figure 6
26
Figure 7
27
Figure 8
28
Table 1. Mean water temperature recorded at seagrass survey sites in the Barnegat BayLittle Egg Harbor Estuary during three sampling periods in 2008.
Sample Period
Mean Temperature (ºC)
Standard Deviation
1
23.37
3.63
2
23.99
1.06
3
19.08
2.21
Sample Period 1 = June-July
Sample Period 2 = August-September
Sample Period 3 = October-November
29
Table 2. Mean salinity values recorded at seagrass survey sites in the Barnegat BayLittle Egg Harbor Estuary during three sampling periods in 2008.
Sample Period
Mean Salinity (ppt)
Standard Deviation
1
26.39
3.38
2
28.22
2.74
3
26.17
5.56
Sample Period 1 = June-July
Sample Period 2 = August-September
Sample Period 3 = October-November
30
Table 3. Mean dissolved oxygen levels recorded at seagrass survey sites in the Barnegat
Bay-Little Egg Harbor Estuary during three sampling periods in 2008.
Sample Period
Mean Dissolved
Oxygen (mg Lˉ¹)
Standard Deviation
1
7.33
1.07
2
6.55
0.98
3
7.27
1.06
Sample Period 1 = June-July
Sample Period 2 = August-September
Sample Period 3 = October-November
31
Table 4. Mean pH values recorded at seagrass survey sites in the Barnegat Bay-Little
Egg Harbor Estuary during three sampling periods in 2008.
Sample Period
pH
Standard Deviation
1
8.09
0.20
2
7.95
0.27
3
8.00
0.15
Sample Period 1 = June-July
Sample Period 2 = August-September
Sample Period 3 = October-November
32
Table 5. Mean Secchi depth (m) recorded at seagrass survey sites in the Barnegat BayLittle Egg Harbor Estuary during three sampling periods in 2008 when the Secchi reading
was not unlimited.
Secchi
(Meters)
1.21
Number of Samples
Sample Period
1
20
Standard Deviation
0.26
2
1.09
29
0.21
3
1.28
41
0.41
Sample Period 1 = June-July
Sample Period 2 = August-September
Sample Period 3 = October-November
33
Table 6. Range of nutrient values recorded in the seagrass survey area of Barnegat Bay
during the June-September period.1
________________________________________________________________________
NO3- plus
NH4+
TDN
PO4
Si
NO2________________________________________________________________________
1.5 – 0
5.6 – 0.0
25.0 – 1.5
1.4 – 0.1
61.6 - 0.3
________________________________________________________________________
1
Values in µM
Sample Period 1 = June-July
3
Sample Period 2 = August-September
2
34
Table 7. Physicochemical data recorded at 10 NPI sampling sites in the Barnegat BayLittle Egg Harbor Estuary during 2008.
Station
npi-1
npi-2
npi-3
npi-4
npi-5
npi-6
npi-7
npi-8
npi-9
npi-10
npi-1
npi-2
npi-3
npi-4
npi-5
npi-6
npi-7
npi-8
npi-9
npi-10
npi-1
npi-2
npi-3
npi-4
npi-5
npi-6
npi-7
npi-8
npi-9
npi-10
Date
Sample
Period
Temperature
(Cº)
Salinity
(psu)
Dissolved
Oxygen (%)
6/12/08
6/12/08
6/12/08
6/12/08
6/12/08
6/12/08
6/12/08
6/12/08
6/12/08
6/12/08
8/29/08
8/29/08
8/29/08
8/29/08
8/29/08
8/29/08
8/29/08
8/29/08
8/29/08
8/29/08
10/15/08
10/15/08
10/15/08
10/15/08
10/15/08
10/15/08
10/15/08
10/15/08
10/15/08
10/15/08
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
23.70
26.12
27.11
25.84
26.15
27.17
27.41
27.81
29.03
27.94
23.92
23.72
24.73
23.94
23.96
23.62
23.45
23.94
23.70
22.51
20.21
19.60
19.41
19.37
19.49
18.90
18.72
18.57
18.48
18.78
29.79
29.30
28.06
27.48
27.60
26.82
24.43
18.26
18.08
20.44
30.14
30.41
30.09
29.40
29.48
27.88
27.37
24.37
22.74
27.65
29.42
28.98
27.62
16.71
27.97
26.10
24.82
21.00
19.90
25.29
83.5
95.2
101.0
96.5
110.3
101.6
14.4
95.5
105.1
128.8
116.5
93.8
101.8
99.0
87.9
94.5
94.2
94.9
79.2
83.4
113.8
96.4
91.9
99.0
122.3
87.9
94.9
102.2
95.1
95.8
35
Dissolved
Oxygen
(mg/l)
5.95
6.42
6.74
6.66
7.62
6.93
7.82
6.71
7.31
8.98
8.26
6.67
7.09
7.03
6.25
6.76
6.85
6.96
5.70
6.16
8.67
7.45
7.17
7.70
9.51
6.99
7.61
8.43
7.92
7.67
Depth
(m)
secchi
(m)
pH
130
80
50
85
45
110
135
115
115
115
145
*
50
110
75
130
170
140
140
110
115
120
105
115
80
150
170
145
85
130
u
u
u
u
u
u
u
u
u
u
120
*
u
u
u
u
u
90
60
80
u
u
u
u
u
u
u
90
75
u
7.98
8.26
8.26
8.17
8.23
8.46
8.46
8.06
8.20
8.21
7.95
7.63
7.99
7.88
8.23
8.11
8.05
8.18
7.88
7.88
8.12
8.16
8.16
8.15
8.28
8.19
8.11
8.22
8.12
8.16
Table 8. Parameters and simple statistics measured in the NPI survey.
Variable
Units
Biomass per leaf area
Percent Nitrogen
NPI index
Temp
Dissolved Oxygen
Dissolved Oxygen
pH
Depth
Secchi
Salinity
mg /cm
percent
(Lee et al.)
ºC
percent
mg/L
pH
cm
cm
PSU
-2
Min
Mean
Median
Max
Standard
Deviation
0.73
0.94
0.30
18.48
79.2
5.7
7.63
45
60*
16.71
2.64
2.43
1.10
23.24
98.88
7.27
8.12
113
86*
25.92
2.55
2.50
0.97
23.7
95.5
7.03
8.16
115
85*
27.48
5.45
3.84
3.17
29.03
128.8
9.51
8.46
170
120*
30.41
0.99
0.76
0.67
3.34
11.01
0.89
0.17
33.07
20*
4.01
36
Table 9. Leaf tissue biomass, nitrogen content, and NPI values of
Zostera marina blades collected at 10 sampling sites along a northsouth gradient in the Barnegat Bay-Little Egg Harbor Estuary.
Site
Sampling
Period
Replicate
Biomass
(mg/cm-2)
Percent
Nitrogen
NPI
1
1
1
1
1
1
2
2
2
3
3
3
3
3
4
4
4
4
4
4
5
5
5
5
6
6
6
6
6
6
7
7
7
7
7
8
8
8
8
8
8
10
10
1
2
3
2
3
3
1
2
3
2
3
1
2
3
3
1
2
3
2
3
3
1
3
2
1
3
1
3
1
2
1
3
1
2
3
2
3
3
1
2
3
1
3
1
1
1
2
2
3
2
2
3
1
1
2
3
3
1
2
2
2
3
3
1
2
2
3
1
1
2
2
3
3
2
2
3
3
3
1
1
2
3
3
3
1
1
2.50
1.00
2.84
2.30
2.37
2.29
0.73
2.11
1.25
1.17
2.41
3.57
2.24
2.40
2.22
1.19
1.66
3.09
3.11
1.04
5.45
3.73
2.29
2.48
2.91
3.23
3.31
3.15
2.59
2.75
4.01
2.97
4.84
2.96
3.75
2.87
3.26
2.88
2.51
3.00
4.56
2.75
2.46
2.75
2.96
3.14
2.92
2.77
2.97
1.05
2.69
3.72
1.65
3.84
1.43
2.66
3.15
2.93
1.85
1.67
2.38
1.43
3.31
3.33
1.36
3.31
2.47
1.21
2.45
0.99
2.51
0.94
1.81
2.49
2.76
1.86
2.42
2.35
2.32
3.09
2.37
1.91
2.51
2.33
1.28
3.07
1.10
2.96
1.10
1.27
1.17
1.29
1.45
1.28
2.98
1.41
1.59
0.40
1.19
1.31
1.32
1.56
1.00
0.77
0.46
3.17
0.61
0.37
1.45
0.99
0.41
0.76
0.30
0.80
0.36
0.66
0.62
0.93
0.38
0.82
0.63
0.81
0.95
0.82
0.76
0.84
0.51
0.47
1.25
37
10
10
10
2
3
3
2
2
3
1.71
2.22
1.50
38
2.52
3.35
3.36
1.48
1.51
2.25