CBP/TRS 138/95
EPA903-R-95-011
June 1995
Chesapeake Bay
Nutrients, Light and SAV:
Relationships Between
Water Quality and SAV Growth
in Field and Mesocosm Studies
Year 1 - Final Report
1995
Chesapeake Bay Program
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Chesapeake Bay Nutrients, Light and SAV:
Relationships Between Water Quality and SAV Growth
in Field and Mesocosm Studies
Kenneth A. Moore and Jill L. Goodman
School Of Marine Science
Virginia Institute Of Marine Science
College Of William And Mary
Gloucester Point, Virginia 23062
and
J. Court Stevenson, Laura Murray and Karen Sundberg
Horn Point Environmental Laboratories
Center For Environmental And Estuarine Studies
University Of Maryland System
Cambridge, Maryland 21613
Year 1- Final Report
Under Cooperative Agreement
CB003909-02 between
US Environmental Protection Agency and
Virginia Institute of Marine Science
Chesapeake Bay Program
Environmental Protection Agency
Annapolis, Md 21401
1995
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Table of Contents
Section (Principal Authors) Page
Executive Summary (Moore) 1
Introduction (Moore) , 3
I. Field Study Goodwin Island (Moore and Goodman) .. . 7
II. Field Study Havre de Grace (Stevenson and Sundberg) 26
III. Mesocosm Study (Murray) 44
Report Summary (Moore) 50
Literature Cited 57
Appendix A: Goodwin Island A1-A69
Appendix B: Havre de Grace B1-B35
Appendix C: Mesocosm C1-C5
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EXECUTIVE SUMMARY
Short term variability in water quality constituents was measured over 10-
day, seasonal studies at two sites in the Chesapeake Bay (June, August, October,
1993; and April, 1994 at the lower bay site only). The first site, Goodwin Island,
located near the mouth of the bay in the highest salinity region (12-24 psu), was
vegetated primarily with the strap-leaved species Zostera marina (eelgrass), with
lesser amounts of Ruppia maritima (widgeon grass). The second site was located
at Havre de Grace in the Susquehanna Flats, a low salinity (<1 psu; practical
salinity units) region at the head of the bay. It was characterized by a canopy-
dominated meadow vegetated with mixed species of primarily Vallisneria
americana (wild celery), Myriophyllum spicatum (eurasian watermilfoil), and
Hydrilla verticillata and minor amounts of Heteranthera dubia (water stargrass)
and Ceratophyllum demerswn (coontail) . The Goodwin Island site was
dominated by the adjacent lower bay waters while the Havre de Grace site was
dominated by the riverine influence of the Susquehanna River. Both sites were
sampled at intervals of 15 minutes to 3 hours, at 3 or 4 stations, using fixed arrays
of remote water quality sampling equipment. Other samples for plant biomass
were obtained monthly, and additional water quality samples obtained at
biweekly intervals. Our objectives were to investigate the spatial and temporal
variability in water quality relative to these SAV communities and to compare
these results to biweekly monitoring data currently used to evaluate water quality
trends in the Chesapeake Bay system. In addition, a mesocosm study using
Potamogeton perfoliatus (redhead grass) as a test species investigated SAV
community response to variable water quality regimes using pulsed versus
continuous dosing of SAV by nitrogen and phosphorus. The objective was to
determine which was more deleterious to SAV, equal inputs of inorganic nutrients
in lower level continuous doses, and higher level pulsed doses? And, how do
these compare to equal loadings of nitrogen and phosphorus in particulate
organic form?
The SAV beds at both field sites attained comparable maximum biomass
(160-250 gdm m-2), and vegetated the littoral zone to similar depths (0.8-1.0 m
MLW), suggesting comparable limits to growth in spite of differences in growth
forms. The upper bay bed attained maximum biomass in late summer, while in the
lower bay maximum growth and biomass occurred in the spring, followed by
dieback in mid-summer, and partial regrowth in the fall.
The two SAV beds demonstrated different capacities to attenuate
inorganic nutrients and suspended particles from adjacent channel waters. At
Goodwin Island the meadow canopy effectively trapped suspended particles
including phytoplankton during April and June when bed development was high,
thereby reducing concentrations in the water column within the bed compared to
the channel. At Havre de Grace, fine particles carried in by the Susquehanna
River were deposited throughout the shallow vegetated flats where they were
continually resuspended by wind and currents. This resulted in higher suspended
loads and light attenuation within in the bed compared to the channel area. In
1
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the lower bay site this same phenomenon was observed in August when an
abundance of fine organic and inorganic material was present within the bed.
Inorganic nitrogen was much higher at Havre de Grace than Goodwin
Island and consisted of principally nitrate compared to ammonium in the lower
bay study area. Orthophosphate concentrations were, in contrast/much lower at
Havre de Grace and may be considered limiting to algal growth there compared to
Goodwin where nitrogen was limiting. We did not observe nutrient levels within
the bed at Havre de Grace to be significantly lower than the adjacent channel
site. In contrast, nitrogen levels were greatly reduced during April and June at
Goodwin Island within the bed compared to the adjacent channel. This may have
been simply an artifact of lower current velocities and therefore longer residence
time of water at the lower bay site rather than faster uptake at Goodwin, although
further research would be needed to confirm this. During August, increased
standing stocks of remineralized ammonium and orthophosphate were observed
at night at Goodwin Island. This was observed to a lesser extent at Havre de
Grace in August.
Diurnal patterns of dissolved oxygen (D.O.) demonstrated greater range
within the beds compared to outside, illustrating higher metabolic activity per
volume of water in the shallows than in the channel. Daily mean and maximum
D.O. levels were higher in the beds than in adjacent channel areas during periods
of maximum S AV growth and biomass (spring in lower bay and summer in upper
bay), and lower during periods of SAV decline (summer in lower bay and fall in
upper bay). D.O. minima were generally less in the lower bay site than the upper
bay study area. In August, D.O. minima each night were accompanied by
increased water column levels of orthophosphate, presumably due to release of
orthophosphate from the sediment. These increases were reduced to background
levels during the day.
Results of the fall mesocosms experiments demonstrated that when equal
loadings of inorganic nitrogen and phosphorus were applied to SAV in pulsed
dissolved, continuous dissolved and pulsed particulate forms, continuous
loadings elicited the greatest biomass increase by algal components of the
systems. Concurrently, decreases in macrophyte growth were greatest in these
treatments. In spite of the high loading rates in the pulsed inorganic treatments,
water column nutrient concentrations remained, or returned quickly to near
background levels. Much of the uptake occurred in the algal components of the
system which increased in dominance throughout the experiment. Thus
concentrations of nutrients in the water column over a SAV bed are the net of the
uptake and release of the system and at times may not necessarily reflect the
degree of total nutrient stress, especially in pulsed inputs. On a per unit mass
basis, continuous inputs appear more deleterious to SAV than pulsed inputs.
In spite of the fact that daily variability may exceed seasonal ranges in
most parameters measured, biweekly monitoring measurements provided a good
seasonal measure of median water quality in these two sites. Both sites, which
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contained persistent SAV, met the habitat requirements set for their respective
areas as determined from the biweekly data.
Further research is needed on the effect of pulsed inputs of nutrients to
SAV beds. This is especially important in areas where long-term levels of water
quality are near the Habitat Requirements levels. Areas which just meet long-
term, median water quality levels but have no SAV may be limited by irregularly
high levels of TSS, nutrients, or chlorophyll which are not effectively measured by
biweekly sampling. For example, a month-long decrease in turbidity may be
measured by only one or two biweekly samplings.
In addition, we understand little of the processes which are affecting the
large daily changes which we observed in levels of the water quality constituents
within the SAV beds, especially in the lower Bay. The seasonal linking of these
processes, i.e. uptake and deposition during the spring and re-release during the
summer, needs further investigation. The impacts of these processes are important
not only for the SAV beds, but the bay system as a whole.
INTRODUCTION
The decline of submersed aquatic vegetation (SAV) in the Chesapeake
Bay has been associated with light limitation resulting from changes in water
quality (Kemp et al. 1984, Orth and Moore 1983). Eutrophication severely limits
the potential for the growth of submersed aquatic macrophytes, not only by
promoting planktonic algal blooms (Swingle 1947), but also by promoting
excessive epiphytic algal overgrowth (Phillips et al. 1978). Evidence for the
negative impacts of eutrophication on submersed macrophytes spans northern
and southern hemispheres in marine as well as freshwater environments
(Stevenson 1988). For example, nutrient loading of coastal salt ponds in New
England has been shown to enhance marine macroalgae at the expense of
seagrass species (Lee and Olsen 1985, Valiela and Costa 1988), and appears to be
associated with a significant decline of seagrasses in Cockburn Sound, Australia
(Shepherd et al. 1989).
Because of these and other relationships observed between water quality
and declines in living resources in the Bay, the 1987 Chesapeake Bay Agreement
called for the development and adoption of guidelines for the protection of
habitat conditions necessary to support Bay living resources (Chesapeake
Executive Council 1987). In response to this request, habitat requirements for
Chesapeake Bay SAV were developed using empirical models of seasonal
medians in water quality, and corresponding growth and survival of natural and
transplanted SAV at various regions throughout the bay (Orth and Moore 1988,
Funderburk et al. 1992, Batiuk et al. 1992, Dennison et al. 1993, Stevenson et al.
1993).
The major sources of nutrient inputs to Chesapeake Bay, in general, are
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from agricultural drainage, atmospheric loading, point source outfalls, and oceanic
sources; however specific sites can also receive nutrient inputs from adjacent
deeper waters via tidal exchange, or wind-forced bottom water intrusion (Sanford
and Boicourt 1990). Although the original sources of these nutrient inputs to
SAV beds are the same as those to the Bay in general (agriculture, point source,
atmosphere), there can be considerable time delays and modulating processes
between original input to the estuary and eventual input to the SAV bed.
Whereas, nutrient inputs from ground water and point source outfalls are
relatively continuous, inputs from rainfall/runoff and tidal exchange are
intermittent at various frequencies. The timing, frequency and form (dissolved vs.
particulate; organic vs. inorganic) of these nutrient inputs are likely to
substantially alter the responses and competitive interactions of SAV,
phytoplankton, and epiphytes. However, the response of any one type of SAV
system to these different loading scenarios is only now beginning to be
determined.
Although general relationships between water quality and SAV response
have been defined, a number of questions still remain. Of particular importance in
Bay management is the need for a better understanding of the temporal variability
of water quality relative to SAV habitat requirements. SAV habitat requirements
have been defined based upon seasonal medians using biweekly or monthly
sampling of the water column. Only a few studies have investigated short-term
variability of certain water quality parameters in shallow SAV sites (Ward et al.
1984). The critical question is whether short-term variability in measured
parameters at shallow water vegetated, or potentially vegetated, sites are
important considerations for both monitoring programs and/or ecosystem model
simulations. Currently, the water quality monitoring program stations that are
monitored are sampled at biweekly to monthly intervals, and most sampling is
conducted in mid-channel areas. Although this may provide a relative measure of
comparison among areas sampled at similar time scales, the variable exposure
levels which are likely influencing plant response in the littoral zone may not be
adequately measured. Episodic events such as storms of moderate, regular nature
are important forcing functions of the system, however their influence on shallow
water conditions have not been well documented. Effects of other regular,
physical forcing factors such as tidal influences are not easily interpreted by such
data (Hutchinson and Sklar 1993). High frequency field sampling is necessary
not only to define these conditions, but to validate current ecosystem processes
models that simulate certain parameters using stochastic or other functions.
Spatial variability in water quality relative to SAV habitats is another factor
that is an important consideration in the continued refinement of SAV habitat
requirements and restoration targets. Small scale differences in certain parameters
have been documented, such as decreases in the concentration of suspended
solids (Ward et al. 1984), that are associated with the baffling effect of the SAV
community (Kemp et al. 1984). However, variability of many other factors such
as nutrients or light availability are not as well known. SAV beds have the ability
to modify their environment, and this may provide one key to their survival.
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Because of this capacity it is possible that conditions which permit the continued
existence of S AV beds may not be suitable for recovery of denuded sites; or, that
conditions which originally caused the declines of SAV beds in the Bay are not
the same as those inhibiting recovery. What effects do the SAV beds have on
modifying the levels of the individual factors used to define water quality suitable
for SAV? How do levels obtained from within a vegetated area compare to those
obtained in adjacent, deeper areas? Can any differences be related to some
measure of SAV abundance? Are there differences in these relationships that are
associated with different community types? How do these relationships change in
the short-term (days) and long-term (seasonal)?
Various regional differences in the relationships between SAV communities
and habitat conditions throughout the Bay have been identified (Batiuk et al.
1992). In the upper Bay in the Havre de Grace area, for example, dissolved
inorganic phosphorus (DIP) may be limiting to algal growth as nitrate levels
remain relatively high (>0.70 mg H; >50|iM) in the vicinity of SAV beds during
summer months (Staver 1986, Posey et al. 1993). In the lower bay regions
(Choptank and York Rivers) dissolved inorganic nitrogen (DIN) of greater than
0.14 mg 1-1 (10 (iM) is correlated with no SAV growth and N is likely the limiting
nutrient to algae. The differences in nitrogen habitat requirements of the SAV
beds in different salinity regimes have yet to be satisfactorily explained.
Experimental studies using both micro- and mesocosms have also been
used to determine cause-effect responses between nutrient loadings, light
availability and SAV growth and survival. Twilley et al. (1985) demonstrated that
low levels of nutrient additions (0.42 g N m-2 d-i and 0.09 g P m-2 d-i) to ponds
receiving ambient water from the lower Choptank River caused a 50 percent
reduction in SAV biomass, due primarily to epiphyte growth on leaf surfaces,
while higher levels resulted in loss of one species (Ruppia maritima). Other
studies have similarly demonstrated negative response to nutrient enrichment as
well as light reductions for bay SAV species (Staver 1986, Goldsborough and
Kemp 1988, Neckles 1990, Burkholder et al. 1992, Neundorfer and Kemp 1993).
Some of these studies simulated nutrient loadings as pulsed additions, while
others have elevated nutrient concentrations through continuous dosing to
simulate system eutrophication. In the pulsed nutrient loading studies, in
particular, the relationships between loading rates and resultant concentrations in
the experimental systems were not well defined. In addition, the question of
whether macrophyte community response is different under one or the other
loading regime has not been investigated. Therefore, given similar loading rates,
are there differences in the resultant autotrophic community (SAV,
phytoplankton, algae) response that can be related to the pattern of nutrient
availability?
In this project we investigated the patterns of variability in water quality,
and resultant effects on SAV using both field and laboratory mesocosm
approaches. Our goals are two-fold: to study the spatial and temporal variability
in water quality relative to the SAV community, and, investigate SAV response to
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variable water quality regimes.
Two sites, which represent endpoints in the distribution of SAV in the
Chesapeake Bay, have been chosen for intensive study of temporal and spatial
variability associated with habitat requirements. The first site, Goodwin Island, is
located near the mouth of the York River in the high salinity region of the bay
(37°12' N 76°23' W). It is vegetated with higher salinity SAV species (e.g., Z.
marina and R. maritima), that declined to low levels in the 1970's (Orth and
Moore 1983), but have been increasing in abundance in recent years (Orth et al.
1992). It is an National Estuarine Research Reserve System (NERRS) site and the
location of other ongoing field studies (Seufzer 1994; Buzzelli et al., unpublished
data). The second site, Havre de Grace, is located at the head of the Bay in the
Susquehanna Flats Region (39° 32' N 76° 05' W), and is the site of previous
investigations (Serafy et al. 1988, Posey et al. 1993). The area is vegetated with
intermittent beds of freshwater and low salinity SAV species (e.g., V. americana,
M. spicatum, and H. verticillatd) and their abundance is significantly reduced
compared to historic levels (Bayley et al. 1978).
The seasonal timing of perturbations may have differing effects on
ecosystems. Nutrient inputs to SAV communities in the upper bay during their
initial growth phase in the spring, may have a greater detrimental effect on
survival than inputs in the fall when plants are senescent. SAV mesocosm
experiments were therefore conducted during the summer-fall of 1993 and spring-
summer of 1994 to encompass the entire growing season of P. perfoliatus, a
dominant upper bay species. In addition, the form of nutrient input (dissolved vs.
particulate), as well as the mode of delivery (pulsed vs. continuous) was tested.
Nutrients entering a system on a pulsed basis may result in a short-lived algal
bloom, however a continual input may sustain an ongoing bloom condition that
may result in greater impacts to the macrophyte community. The results of the
summer-fall 1993 mesocosm experiment are included in this annual report.
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I. FIELD STUDY GOODWIN ISLAND
Methods
At the Goodwin Island site (37<> 12'N 76o 23'W), four stations were
established along a transect running approximately NW/SE, beginning in the
shallow subtidal flat adjacent to the east shoreline of Goodwin Island, and
extending 1.25 km channelward (Figure 1). Stations 1 and 2 were located in the
SAV bed and were 130 m and 400 m respectively from the island shoreline.
Station 1 (0.4 m MLW) had a mixture of Ruppia maritima (widgeon grass) and
Zostera marina (eelgrass). Z. marina was the predominant species at Station 2
(0.6 m MLW). Station 3 (0.8 m) was located at the outer edge of the grass bed,
925 m from the island shoreline, in an area sparsely vegetated with Z. marina.
Station 4 (1.5 m MLW) was located outside the bed in an area of bare sand
bottom, 1250 m from the island with a depth of 1.5 m MLW. At each station a
permanent pole, which supported a box that housed the remote sampling
equipment, was placed in the bottom (Figure 2).
Water Quality
Water quality at the site was sampled using both intensive (every three
hours) and periodic (biweekly) sampling schedules. Intensive sampling was
undertaken during four, 10-day periods in June, August, October, 1993, and April,
1994. During each intensive sampling period, water samples were obtained at 3
hr. intervals at each station using automated samplers (ISCO, Inc.) (Table 1).
Biweekly sampling was conducted as part of the regularly scheduled Virginia
Nearshore Submerged Aquatic Vegetation Habitat Monitoring Program (Heasly et
al. 1989).
Water samples from the intensive sampling were obtained at fixed depths
of 0.3 m above the bottom, stored on ice for no more than 24 hours, filtered
through .45 fi filters, then analyzed in duplicate for dissolved inorganic nutrients
and suspended particles. Ammonium was determined spectrophotometrically
after Parsons et al. (1984). Nitrite, nitrate and orthophosphate were measured
using an Alpkem autoanalyzer, equipped with a model 510 spectrophotometer.
Total suspended solids (TSS) were determined by filtration, rinsed with
freshwater, and dried at 60°C. Filterable inorganic matter (FIM) and filterable
organic matter (FOM) were obtained by ashing the material at 550°C.
Chlorophyll a was extracted using DMSO/acetone (after Shoaf and Lium 1976)
and analyzed by fluorometry. Dissolved oxygen (D.O.), pH, salinity, temperature
and water depth were measured at 15-minute intervals using Hydrolab Datasonde
instrument systems placed adjacent to the ISCO sampler intakes, and individually
calibrated before each field deployment. In situ photosynthetically active
radiation (PAR) light attenuation was measured continuously and integrated
over 15 minute periods using fixed arrays of underwater, scalar (4 7t), quantum
sensors (LI-193SA, LI-COR, Inc.). The sensors were calibrated by the
manufacturer prior to use, and when deployed in the field were cleaned daily to
remove any accumulated epiphytes. Atmospheric, downwelling irradiance (2n
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Goodwin
Island
37°
12'
76° 24'
Figure 1: Goodwin Island Site
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Fig. 2: Diagram depicting individual station instrument arrays.
Isco Automated Sampler
LI-1000
Datalogger
Hydrolab
Datasonde
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Table 1: Summary of parameters and sampling intervals for SAV and water quality
measurements at Goodwin Island, VA study area.
Parameter
Interval
SAV
Community Transect (% Cover)
Periodic
(June, August, October, April)
Biomass
Above/Belowground, Density ,
Canopy Height, Attached Epiphytes
Monthly
Water Quality
Routine Sampling
(TSS, Kd, Chla, Nitrite, Nitrate,
Ammonium, Dissolved Inorganic
Nitrogen, Orthophosphate,
Temperature, Salinity)
Biweekly
Intensive Sampling
TSS (FBVI, FOM)
Chla
Nitrite (NO2)
Nitrate (NO3)
Ammonium (NH4)
Dissolved Inorganic Nitrogen (DIN)
Orthophosphate (PO4)
Periodic
Every 3 hours for 10 days
Temperature
Salinity
Dissolved Oxygen (D.O.)
pH
Tidal Depth
Wind Direction/Speed
Every 15 min for 10 days
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quantum, LI-190S A, LI-COR, Inc), and six minute, vector-averaged wind speed
and direction were recorded continuously at Gloucester Point, Va., meteorological
station (height +45 m Mean Sea Level).
Bi-weekly water samples were obtained in triplicate, at a depth of 0.25 m
at Station 2, and placed on ice until returned to the laboratory for analysis of
dissolved nitrite, nitrate, ammonium, orthophosphate, Chi a, TSS, FEVI, and FOM.
Triplicate analyses were made in situ for D.O., pH, water temperature, salinity, and
integrated water column Kd (2rc quantum, LI- 192SA, LI-COR, Inc.).
Macrophyte Sampling
Monthly, from May, 1993, through April, 1994, measurements of
macrophyte biomass were determined at each of the vegetated stations. Five,
replicate 0.1 m2 rings were irregularly placed on the bottom at Stations 1 and 2.
All vegetation, including roots and rhizomes to a depth of approximately 0.2 m
was removed, gently shaken to remove sediments, placed in plastic bags on ice,
and returned to the lab for morphometric and mass determinations. Each sample
was separated by species, the shoots were rinsed, counted, measured for length,
cleaned of epiphytes and separated into shoots and roots/rhizomes (standardized
to the first 5 internodes). Shoot leaf area (LAI; m2/m2) was determined using a
meter (Li-Cor, Inc., Model 3100 area meter). Dry mass of the shoot and
root/rhizome samples were determined by drying at 60 °C.
Separate samples were obtained for epiphyte mass determinations in June,
August, October, 1993, and April, 1994. Individual shoots were carefully placed
in plastic bags in the field, returned immediately to the lab where they were gently
scraped to remove attached epiphytes. The epiphytic material was collected on
glass fiber filters, rinsed with freshwater, dried and ashed. Leaf areas of shoots
used to obtain each subsample of epiphytes were determined.
Macrophyte Relative Abundance
A transect, adjacent and parallel to the four stations, was sampled for
macrophyte abundance during each of the seasonal, 10-day sampling periods in
June, August, October, 1993, and April, 1994. At 10-meter intervals, beginning at
the shoreward marsh edge and continuing past the channelward edge of the bed,
macrophyte standing crop was estimated by point intercept method (Orth and
Moore 1988). At each 10-meter point, percent cover of macrophytes, by species,
was estimated by a diver who randomly placed a 0.1 m2 ring on the bottom. At
each measurement, water depth, distance along the transect, and time were
recorded. A fixed, tidal reference staff was used to measure water height change.
These relative depth data were then normalized to mean low water (MLW) using
referenced tidal measurements at the National Ocean Survey Gloucester Point
tidal gauging station located approximately 10 km west in the York River.
1 1
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Statistical Analyses
Friedman's ANOVA (Zar 1984), a non-parametric procedure for testing
repeated measures, was used to compare dissolved nutrients, TSS, Chla, and
physical parameters for significance differences among stations within each
sampling period. Analyses were accomplished using Statistica/Mac, StatSoft Inc.,
Tulsa, OK. If differences among stations were determined significant (P< .05),
multiple, pairwise comparison analysis (Zar 1984) was used to test individual
means.
Results
SAV Community Structure and Biomass
SAV Relative Abundance and Biomass
A integrated view of seasonal changes in the Goodwin Island SAV bed are
illustrated in Appendices A1-A4. The four stations were located approximately
130 m, 400 m, 925 m, and 1250 m from the island shoreline. Only two species
were reported within the bed, Z. marina and R. maritima. At the location of the
transect the bed was approximately 550 m wide and the vegetation extended to a
depth of 0.8 m MLW. This depth limit is similar to that reported for other beds in
the region (Orth and Moore 1988). Greatest bed structure occurred in June 1993
when nearly the entire bed exceeded 60 percent in cover by vegetation. Z.
marina dominated at all seasons, while R. maritima was found in the shallowest
areas near shore. The topography of the meadow area was quite flat with only up
to 0.1 m relief over the first 350m of width. After this point the bottom gradually
deepened in the offshore direction. Bed width varied with season. During June,
1993, the bed extended nearly 550 m from shore. Dieback throughout the
summer resulted in retreat of the apparent, channelward edge to about 350 m by
October 1993. This appears to be a seasonal phenomenon, however, as regrowth
of this deeper, outer bed area was evident in April, 1994.
. Z. marina was most abundant in June throughout the bed with R.
maritima occurring largely as an understory in inshore areas during this period
(Appendix Al). By August, a large die-back in Z. marina, particularly in the
shallow inshore areas, was evident (Appendix A2). R. maritima, however,
reached its greatest abundance during this period. Large masses of decaying
macrophyte shoot material was present throughout the bed at this time. By
October the R. maritima standing crop had decreased and although the Z.
marina standing crop was still low, new growth was evident (Appendix A3). It is
during this period that germination of Z. marina seeds released in May and June
is most pronounced (Moore et al. 1993). Large, unvegetated areas, however,
were still observed throughout the bed. By April, 1994, significant regrowth of
the bed had occurred, with Z. marina predominating (Appendix A4).
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The monthly, biomass measurements confirmed the seasonal trends
observed in the transect measurements. Both aboveground (Appendix A5) and
belowground (Appendix A6) biomass were greatest in May with a rapid decline
observed throughout the summer, to a minimum during the winter. Z. marina
demonstrated a maximum during the spring, a decrease in the summer, and a small
regrowth during September and October. R. maritima achieved maximum
biomass during July and August. Shoot density (Appendix A7) paralleled
biomass. R. maritima exceeded 500 shoots m-2 from July to September, while Z.
marina reached greatest densities (>150 m-2) in April. Average bed canopy
height (Appendix A8) followed a bimodal seasonal pattern, as Z. marina
dominated the bed structure, with maximum height (>0.3 m) observed in June,
minimum in late summer (=0.1 m) and some regrowth in the fall (=0.15 m).
Epiphytes
Epiphytes (reported as grams dry mass) were measured during each
intensive sampling only. Specific abundances were consistently greater on R.
maritima than Z marina throughout the year (Appendix A9). Epiphyte loads
were lowest in April and June, and greatest in August and November.
Physical Factors
Wind
Wind velocities recorded at the Gloucester Point meteorological station for
each of the sampling periods are reported in Appendix A10. Daily, vector
averaged wind speeds and directions over the ten-day study periods are
presented in Appendices Al 1-A14. Distinct differences in the seasonal patterns
of winds are evident for each of the study periods. During June 1993, winds
were light (
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samples from the ISCO samplers during several occasions.
Tides
Tidal heights normalized to mean tidal depth over each ten-day, seasonal
study period are presented in Appendix A15. Spring and neap periods were
sampled during each of the studies. Tides ranged from approximately 0.5m to
nearly one meter with the greatest difference in range occurring during the
August study period. During October 1993 the water depth increased nearly 0.5
m over the latter half of the study, while during June 1993 an increase in mean
tidal level was observed during mid-study. Tidal levels varied less during the
April 1994 study than during the other study periods. Spring to neap ranges
were similar and generally low compared to the other seasonal studies.
Water Temperature
Water temperatures demonstrated periodicity on hourly, daily, and
seasonal time scales (Appendices A16-A19) with distinct differences among
stations. During June, water temperatures exhibited greater range both within a
day (6° C), and between days (10° C) at Station 1 compared to channel ward
Stations 3 and 4. Conversely, the daily temperature ranges at Stations 3 and 4
were just l°-2° C. Station 2 Hydrolab failed to record during this period. Mean
temperatures were also higher at Station 1 (25.3 °C) compared to Stations 3 and 4
(23.8 and 24.0 °C respectively; Table 2a). Daily temperatures exhibited a 5 °C
sinusoidal fluctuation throughout the study period with a periodicity of
approximately a week. This pattern dampened with distance offshore.
During August 1993, the inshore vegetated stations (1 and 2) again
exhibited greater daily temperature variances when compared to Stations 3 and 4
(Appendix A17). Mean temperatures at the stations over the 10-day field study
were within 0.4 °C (26.9-27.3 °C; Table 2a), although they were greater in the
shallower sites. Daily and weekly fluctuations in temperature were reduced
compared to June.
October temperature patterns demonstrated an irregular pattern
throughout the study period with day-to-day variability generally exceeding diel
ranges. Water temperatures decreased 3-4 °C beginning on Oct. 11. This
coincided with increased water levels and a period of strong easterly winds. In
contrast to June and August, water temperatures were lower in the inshore,
shallow areas compared to offshore as these sites experienced a more rapid fall
cooling.
During April, 1994, water temperatures were quite similar at stations 2, 3,
and 4 (Appendix A19; Table 2b). Mean temperature was significantly higher at
Station 1. This appears principally due to warming of the shallows at Station 1
during the afternoons of April 13-16.
14
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Table 2a: Medians of physical parameters by station from intensive sampling for June
and August, 1993 at Goodwin Island, VA. Identical superscripts denote no
significant differences (ft>0.05) among stations within each study period.
June 1993
PH
D.O.(mgl-l)
Salinity (psu)
Temp (°C)
Kd
Station 1
8.70*
9.293
15.84a
25.35a
0.98a
Station 2
N/A
N/A
N/A
N/A
1.13b
Station 3
7.85C
9.80b
14.8QC
23.89b
1.05a>b
Station 4
8.08b
10.54C
IS.OOb
23.76c
1.55C
August 1993
pH
D.O.(mgl-l)
Salinity (psu)
Temp (°C)
Kd
Station 1
7.98a
5.02a
17.90a
27.203
1.19a
Station 2
8.13b
6.46b
19.70d
27.00b
0.80b
Station 3
7.66C
7.82C
18.30b
26.79°
0.90b»c
Station 4
8.17b
6.78b
18.70C
26.83d
0.94C
-------
Table 2b: Medians of physical parameters by station from intensive sampling for
October 1993 and April 1994 at Goodwin Island, VA. Identical superscripts
denote no significant differences (P>0.05) among stations within each study
period.
October 1993
pH
D.O. (mg I'1)
Salinity (psu)
Temp (°C)
Kd
Station 1
N/A
N/A
N/A
N/A
1.37a
Station 2
8.03a
7.12a
23.903
19.06**
1.47a
Station 3
8.12C
7.94C
24.10b
19.62b
1.33b
Station 4
8.10b
7.77b
24.20°
19.74C
1.23b
April 1994
PH
D.O. (mg 1-1)
Salinity (psu)
Temp (°C)
Kd
Station 1
8.73a
N/A
N/A
17.263
0.95a
Station 2
8.63a
11.02a
12.50s
I5.92b
0.92a
Station 3
8.32b
8.25C
12.62b
15.75b
N/A
Station 4
8.33b
9.52b
13.10°
15.70b
0.79b
-------
Salinity
\
Salinities varied with season and ranged from 15 psu in June, 18-20 psu in
August, 24 psu in October, and 13 psu in April (Appendices A20-A23; Table 2a
and 2b). Seasonal increases in salinity in the fall reflect typical regional patterns
related to river flows to the bay. There were few differences among the stations,
as expected, since there is no freshwater input other than rain to the site. Some
differences among the stations did occur, however. During June, salinities were
highest at Station 1. While, overall, during all the other study periods salinities
were greater at the deeper, channelward stations, especially Station 4. This
reflected the higher salinity bottom water present at these deeper areas.
Water Quality Constituents
Chlorophyll a and Total Suspended Solids
Suspended particles in the water column, reflected in measurements of
both TSS and Chi a , demonstrated differences among stations and study periods
(Table 3a and 3b; Appendices A24-A31). In June 1993, when SAV biomass was
greatest (Appendices A24 and A28), levels of TSS and Chi a were consistently
lower in the bed (study period means 4.2-4.6 mg-i and 8.7-14.9 |ig H,
respectively) than out (7.7-8.5 mg-i and 23.8-24.5 (ig H). Additionally, pulses of
markedly higher suspended loads were much more evident in the two
channelward stations compared to the vegetated stations. In August 1993 when
bed development was greatly reduced, levels of suspended particles in and out of
the bed were quite similar over the study period (Table 3a). Periods with
increased concentrations of TSS and Chi a, lasting from 3 to 15 hours, were more
evident at Stations 1 and 2 compared to 3 and 4. Wave action in the shallows
may have been resuspending bottom sediments. The pulses of suspended
particles reached higher concentrations in mid-bed Station 2. At the shallowest
site reduced wave action may have limited resuspension, while greater depths and
less fine material available for resuspension, limited resuspension at stations 3 and
4. Due, in part, to these pulsing events in August, mean TSS and.Chi a levels
were highest at Station 2.
By October 1993, fall regrowth of the SAV was occurring, the detrital
material was largely gone, and mean concentrations of TSS and Chi a were again
lower at the two inshore, vegetated stations compared to channelward stations 3
and 4 (Table 3b). A strong northeast wind and storm event precluded sampling
during the period of October 11-13. Although suspended particle and nutrient
samples were not available for this time period, elevated light attenuation
measurements indicate that resuspension was very high within the bed.
Bed canopy structure, i.e.. shoot length, density and biomass, was again
high in April, 1994, when Chi a and TSS concentrations were consistently lower
in station 1 (in bed) compared to station 4 (outside bed). This pattern supports
17
-------
Table 3a:
NO2
N03
NH4
• *
DIN
PO4
TSS
Chlfl
Medians of inorganic nutrients and suspended particles by station from
intensive sampling for June and August, 1993 study periods at Goodwin Island,
VA. Identical superscripts denote no significant differences (R>0.05) among
stations within each study period.
June 1993
Station 1
0.0006 a
(0.044)
0.0034 a
(0.242)
0.0147 a
(1.05)
0.0195 a
(1.40)
0.013 a
(0.41)
3.58 a
8.48 a
Station 2
0.0005 a
(0.038)
0.0024 a
(0.181)
0.0161 a
(1.15)
0.02 14 a
(1.53)
0.015 a
(0.48)
3.90 a
14.40 b
Station 3
0.0009 a
(0.069)
0.0034 a
(0.244)
0.0167 a
(1.19)
0.0216 a,b
(1.54)
0.015 a
(0.48)
7.35 b
24.80 c
Station 4
0.0003 a
(0.024)
0.0043 a
(0.310)
0.0281 a
(2.01)
0.0322 b
(2.30)
0.015 a
(0.48)
7.50 b
24.80 c
August 1993
NO2
NO3
NH4
DIN
PO4
TSS
Chla
Station 1
0.0013 a
(0.100)
0.0039 a
(0.280)
0.025 a
(1.77)
0.032 a
(2.30)
0.01 la
(0.335)
4.05 a
9. 12 a
Station 2
0.0004 b
(0.030)
0.0029 a
(0.210)
0.016 b
(1.17)
0.021 b
(1-51)
0.0096 a
(0.300)
6.1 lb
10.96 b
Station 3
0.0003 b
(0.020)
0.0042 a
(0.300)
0.012 b
(0.87)
0.017 b
(1.22)
0.010 a
(0.325)
3.91 a
9.44 a
Station 4
0.0004 b
(0.030)
0.0041 a
(0.290)
0.014 b
(0.98)
0.019 b
(1.33)
0.010 a
(0.290)
4.58 a
10.48 b
AH parameters in mg r*», () in /iM; Chla in jig H
-------
Table 3b: Medians of inorganic nutrients and suspended particles by station from intensive
sampling for October 1993 and April 1994 study periods at Goodwin Island, VA.
Identical superscripts denote no significant differences (R>0.05) among stations
within each study period.
NO2
N03
NH4
DIN
PO4
TSS
Chla
NO2
N03
NH4
DIN
PO4
TSS
Chla
October 1993
Station 1
0.0012 a
(0.085)
0.0049 a
(0.348)
0.025 a
(1.78)
0.034 a
(2.40)
0.008 a
(0.265)
3.95 a
5.96 a
Station 2
0.0015 a
(0.109)
0.0056 a
(0.403)
0.025 a
(1.77)
0.033 a
(2.35)
0.010 a
(0.325)
4.84 a,b
8.32 b
Station 3
0.0003 b
(0.019)
0.0080 b
(0.570)
0.025 a
(1.80)
0.037 a
(2.67)
0.010 a
(0.325)
5.73 a,b
14.24 c
Station 4
0.0002 b
(0.015)
0.0074 b
(0.530)
0.024 a
(1.70)
0.046 a
(3.29)
0.009 a
(0.290)
6.51 b
13.92 c
April 1994
Station 1
0.003 a
(0.193)
0.009 a
(0.64)
0.019 a
(1.36)
0.043 a
(3.07)
0.0099 a
(0.310)
2.40 a
15.65 a
Station 2
0.006 b
(0.430)
0.077b
(5.50)
0.012 a
(0.85)
0.096 b
(6.84)
- 0.0106 a
(0.330)
2.46 a
23.20 b
Station 3
0.007 c
(0.525)
0.133 b
(9.53)
0.016 a
(1.11)
0.160C
(11.41)
0.0104 a
(0.325)
2.68 a
25.20 b
Station 4
0.007 b
(0.510)
0.136b
(9.74)
0.015 a
(1.08)
0.158C
(11.27)
0.0091 a
(0.285)
4.92 b
24.24 b
All parameters in mg I'l, () in /*M; Chla in ftg I'
-------
similar observations in June and October.
Light Attenuation
Light attenuation (reported as Kd) demonstrated considerable variation
throughout each day with greatest apparent attenuation during the morning and
afternoon, and least at mid-day. This pattern has been observed elsewhere
(Moore and Goodman 1993) when continuous measurements of shallow water
light attenuation have been recorded. It is possibly a function of the longer path
length of light in shallow water during low sun angles and not related to
increased turbidity of the water. To compensate for this apparent diel variability
only mid-day (1000-1400) attenuation values were used here (Appendices A32-
A35).
Except for the June, 1993, field study, all other study periods (August
1993, October 1993, April 1994) demonstrated higher mean attenuation values at
stations 1 or 2 or both, compared to stations 3 and 4 (Table 2a and 2b). This does
not agree with the patterns evident for suspended particle concentrations (Chi a
and TSS), which demonstrated consistently lower levels for stations in the bed
compared to out, during all study periods except August. There may have been
differential fouling between the sensors at each site with greater fouling on the
bottom sensor compared to the top. This appears unlikely since the sensors were
cleaned each morning, however, resuspension of bottom sediments with relatively
greater deposition on the bottom sensor remains a possibility. Conversely,
attenuation by dissolved substances, which were not measured here, may be
important.
Dissolved Oxygen and pH
Dissolved oxygen levels demonstrated markedly greater diurnal range in
concentrations inside the SAV bed compared to outside during all study periods
(Appendices A36-A39). In June 1993, for example, diurnal D.O. levels varied up
to 10 ppm within the bed at station 1, compared to approximately 3 ppm at station
4. Overall, mean levels were higher at station 1 than stations 3 and 4 during this
period. Maximum daily levels occurred in the afternoon at 1700 hrs. EST, while
minimum levels were observed at 0600-0700 hrs. In August D.O. was lower, on
average, at station 1 than stations 2, 3, and 4. This higher relative respiration is
evidenced by the very low nighttime oxygen concentrations at this time. During
October a coastal storm with sustained strong winds occurred during the 10th to
12th. During this period, diel variability in D.O. was dampened considerably.
Overall mean D.O. levels among all stations in each study period were lowest at
stations 1 and 2 compared to stations 3 and 4 during June, August, and October
(Table 2a and 2b). In April, D.O. was higher inside the bed than outside, however,
malfunctioning of the Hydrolab at station 1 limited the data available for this
comparison. Rapid Z. marina growth, characteristic during this spring period,
20
-------
supports these observations. Seasonally, D.O. concentrations reached highest
levels in June and April during periods of greatest SAV biomass and productivity,
and lowest levels in August when decaying organic material was observed
throughout the bed.
As pH levels in marine waters generally reflect the inverse of total carbon
dioxide (bicarbonate) concentrations, pH varied in a pattern similar to D.O
(Appendices A40-A43). High levels of photosynthesis within the SAV bed
resulted in lower total carbon dioxide and therefore higher pH levels in the late
afternoon. Nighttime respiration increased carbon dioxide in the water and
therefore pH was lower. As with D.O., pH levels had greater daily range within
the SAV bed compared to without. Overall, mean levels were lower in the bed
that out during each season except April. Seasonally, pH levels were highest in
April and June and lowest in August (Table 2a and 2b).
Dissolved Inorganic Nitrogen
Ammonium comprised the overwhelmingly largest fraction of the dissolved
inorganic nitrogen (DIN) species measured at Goodwin Island during the June,
August, and October 1993 study periods (Table 3a and 3b). Only during April,
1994, was nitrate the most abundant nitrogen species.
During June, DIN consisted of approximately 80% ammonium. Levels
were highest at station 4 and decreased within the bed. Intermittent periods of
elevated ammonium lasting from 3 to 12 hours were apparent at station 4,
especially during June, 12-14 (Appendix A48). These increases were not evident
at the shallower stations. Both salinity and water temperatures decreased during
this period, possibly due to a change in water mass enriched with ammonium in
the offshore area. Lower ammonium levels within the bed suggest that uptake
was occurring in the vegetated area. Chi a levels (Appendix A28) were lower in
the bed compared to out. Epiphytes were also low, while macrophyte biomass
was at seasonal maximum. Thus, most uptake was likely accomplished by the
SAV. Nitrite and nitrate demonstrated little difference among the stations over
this June study period (Table 3a). Small pulses of nitrite and nitrate lasting 12 to
18 hours were evident, especially at the channel stations 3 and 4 (Appendices
A52 and A56). These pulses were dampened or were absent at stations 1 and 2.
In August DIN was, on average, higher at station 1 than at the other three
stations in contrast to June (Table 3a). The increase was due principally to
diurnal pulses of ammonium that were observed within the bed each night. This
diurnal increase was not observed during the other seasonal study periods.
When ammonium concentrations are aggregated over a diel cycle the nightly
increase in water column levels is evident. Potentially, these increased
concentrations could be due to release of remineralized ammonium from the
sediments. When dissolved oxygen concentrations are similarly aggregated a
relationship between D.O. and ammonium is evident. At stations 3 and 4 average
diurnal variability in water column D.O. was approximately 3 mg H (Appendix
21
-------
A64) and, on average, D.O. minima are 6 mg H at the sensor height of 20 cm.
Mean ammonium concentrations are relatively consistent at 0.014 mg I-1 (1 |iM).
At station 2, however, increased biological activity decreases average D.O. levels
during the evening to 5 mg H and ammonium concentrations increase to 0.025
mg l-i (1.75 |J,M) (Appendix 64). Finally, at station 1 mean D.O. concentrations at
the 20 cm sensor height fall to below 3 mg H with a corresponding increase in
ammonium to 0.042 mg I-1 (3 |iM) (Appendix 64). Nitrate and nitrite
concentrations were low with little difference among the stations in August
(Table 3a). Nitrite was near undetectable levels throughout the study period
except for several periods when levels reached 0.007 mg H (0.5 |iM) (Appendix
A53). There was both spatial and temporal discontinuity in these small pulsing
events. Nitrate demonstrated more regular increases (Appendix A57).
In October DIN consisted principally of ammonium with no differences
detected among station means (Table 3b). Levels were higher overall compared
to June and August. Concentrations were elevated at all stations beginning
October 9th, immediately preceding a period of increasing wind velocities
(Appendix A46). Nitrate demonstrated higher levels offshore, especially after the
wind event (Appendix A58). Nitrite concentrations were consistently low, but
increased markedly during the period October 12th to 14th after the storm
(Appendix A54).
Higher DIN levels were recorded in April compared to the other three
sampling periods. During this spring study period nitrate was the most abundant
inorganic nitrogen species. Nitrate levels were highest overall in the channel
station and decreased to very low levels inshore at station 1 (Table 3b).
Ammonium demonstrated few consistent differences among the stations (Table
3b; Appendix A51). Nitrite concentrations were consistent and highest overall at
the channel stations 3 and 4 (Table 3b; Appendix A55). At stations 1 and 2,
levels were lower and demonstrated periodicity in the standing stocks. Nitrate
concentrations also demonstrated considerable periodicity that appeared to be
tidally influenced. When time-series plots of nitrate and tidal height are compared
(Appendices A65-A68) the correspondence of increased nitrate concentrations
and tide height are evident. Thus the shallows were receiving flooding water
high in nitrate, and these concentrations decreased markedly during ebb. Salinity
changes during the tidal cycles were minimal (less than 5 to 10% change from
high to low tide) while nitrate varied from 2 to 5 times or more. It would appear
that rapid uptake of nitrate was occurring both within the water .column and the
macrophyte community. Overall deceased levels within the SAV bed suggest that
uptake from the water column was occurring. Chi a levels were observed to be
lower in the bed compared to out (Table 3b) while epiphytes were lowest of all
seasons sampled (Appendix A9). This suggests that the macrophyte may be
largely responsible for this decrease.
Dissolved Inorganic Phosphorus
22
-------
Orthophosphate concentrations maintained consistent levels of 0.0064 to
0.016 mg l-i (0.2 to 0.5 |iM) among all four stations and all four sampling periods
(Table 3a and 3b; Appendices A60-A63). This suggests rapid buffering of
orthophosphate, most likely through sorption-desorption processes involving
suspended clay and organic detrital particles. During August, however, there was
evidence of significant increase in orthophosphate concentrations in the SAV
bed during the early morning when water column D.O. concentrations were at
daily minima. This was not observed during other study periods. Appendix A69
present mean D.O. and orthophosphate concentrations aggregated over a diel
cycle for stations 1 through 4 respectively. At stations 3 and 4 mean
orthophosphate concentrations consistently average 0.0096 mg H (0.3 pM)
throughout the day while diurnal D.O. variability is moderate. At station 2,
however, a sharp rise in orthophosphate concentrations was observed at about
0400 hrs. EST which corresponded to average water column D.O. minima of
approximately 5.0 mg H (Appendix A69). At the most inshore, vegetated station
as D.O. decreased to average minima of 2.5 mg l-i, water column orthophosphate
correspondingly increased to over 0.019 mg H (0.6 (iM) before returning to
average levels of 0.0096 mg H (0.3 fiM) by mid-day (Appendix A69). This
relationship between D.O. and orthophosphate is consistent with the hypothesis
that dissolution of insoluble phosphorus precipitates from the sediments or water
column particles is occurring under conditions of low redox.
Water Quality Comparisons
Table 4 presents a summary comparison of median levels of five key water
quality parameters that have been used to define habitat requirements for SAV
growing in polyhaline regions of the Chesapeake Bay (Batiuk et al. 1992).
Polyhaline SAV habitat requirements have been defined as median levels of these
particular water quality constituents measured at regular intervals during the
growing season, that correspond to areas where SAV beds have remained
persistent in the highest salinity regions of the bay (Moore 1992). Results of
biweekly monitoring of water quality at station 2 in Goodwin Island in 1993
demonstrate that this SAV bed would have met all criteria except that for Chi a
during this year. These results support the habitat requirement concept, where
similar comparisons have demonstrated that all or all but one of the habitat
requirements will be met in areas where SAV are persistent.
Medians of each intensive monitoring study at station 2 are presented for
comparative purposes. For the five parameters, the habitat requirement criteria
were exceeded only twice: during October, 1993, for K^, and during April, 1994,
for Chi a. K^ medians in October are influenced by high K^ values during the
morning and afternoon. During the April study period high levels of DIN (mostly
nitrate) are supportive of the highest levels of phytoplankton observed.
Quantitative comparison with the biweekly sampling results is difficult, since both
sets of medians reflect different intensities and duration of sampling. Obviously,
the biweekly sampled growing season medians do not reflect the short term or
seasonal variability associated with this site. In areas of marginal water quality
23
-------
X
Table 4: Summary comparison of Polyhaline SA V Habitat Requirements for five key water quality parameters with median
levels calculated using: 1) 1993 growing season biweekly monitoring at Station 2; 2) Station 2 seasonal, intensive
study data; 3) 1993 growing season, biweekly monitoring data at two nearest bay mainstem monitoring stations
(WE4.2/4.3); 4) Station 4 seasonal, intensive study data. Underlined values exceed habitat requirements.
Key Water
Quality
Parameters
Polyhaline
SAV
*Habitat
Requirements
Kd (m-1)
TSS (mg I'1)
Chiang 1-1)
DIN (mgl'1)
0
-------
this variability could be important in determining long term success of the S AV
The biweekly growing season medians do, however, appear to accurately
characterize the water quality classification of this area in regard to S AV
requirements. They provide an overall measure of water quality that is similar to
that presented by the short term, hourly sampling.
Growing season medians were also determined using surface data from
adjacent, mainstem monitoring stations. These medians when compared to similar,
biweekly data for station 2, inside the bed, are: identical for Kd, higher for TSS
and DIN, and lower for Chi a and DIP (Table 4). Habitat requirement levels were
not exceeded for any of the parameters. Of the five parameters investigated, only
TSS and DIP seem to be somewhat out of line with values from the shallow water
site. These differences may also reflect differences in methodologies. At a deeper
water, mid-channel station, TSS might be expected to consist in large part of Chi
a. However, Chi a levels are lower here than at station 2. DIP, which were
generally consistent across the Goodwin Island transect stations, were much
lower at the mid-channel station 2. When the mainstem data are compared to
seasonal medians from station 4, the site of intensive monitoring closet to the mid-
channel, similar results are obtained. Although there are some differences with
data from the intensive studies, overall, the mid-channel monitoring data do
support the conclusion that water quality in this area meets the SAV habitat
requirements, and therefore SAV should survive and grow in this region.
Study period medians from both inside the SAV bed, at station 2 and
outside SAV bed at station 4 are very similar (Table 4). During June, 1993, median
levels of Chi a exceeded the habitat requirement limits at station 4 and not at
station 2, while during April, 1994, DIN was also exceeded at station 4 and not at
station 2. These differences, potentially, reflect the ability of SAV beds to baffle
out suspended particles and take up nutrients; especially during periods when
SAV growth and bed development is high. These results suggest that during
certain seasons, established SAV can improve water quality sufficiently within the
bed to achieve the habitat requirements when the adjacent water mass is above
these habitat requirements. These results suggest that during seasonal pulses in
reduced water quality, the existence of beds provides a positive feedback which
may enhance their continued growth and survival.
25
-------
H. FIELD STUDY HAVRE DE GRACE
Methods
Havre de Grace is located at the head of Chesapeake Bay, near the mouth
of the Susquehanna River, 20 km downriver of the Conowingo Dam (Figure 3).
The submersed aquatic vegetation (SAV) in this area has been studied previously
(Staver 1986, Serafy et al. 1988, Posey et al. 1993, Wigand and Stevenson 1994).
The site is strongly influenced by two physical factors: unprotected exposure to
southerly winds across a large fetch (approx. 10 km), and river flow from the
Susquehanna. The shallows adjacent to the shore line were vegetated with
mixed beds composed primarily of Vallisneria americana, Myriophyllum spicata,
and Hydrilla verticillata and minor amounts of Heteranthera dubia and
Ceratophyllum demersum during the 1993 study period.
Three stations, approximately 100 m from each other (Figure 3), were
chosen for intensive sampling. Two stations were located within an SAV bed in
an area that had been sampled over the last eight years (Staver 1986, Serafy et al.
1988, Posey et al. 1993, Wigand and Stevenson 1994). The shallowest, Station 1
(39« 32.20' N x 76o 05.11' W; 0.5 m mean water depth), was consistently
dominated by H.verticillata, and the other, Station 2 (39<> 32.17' N x 76o 05.13'
W; 0.75 m mean water depth), was consistently dominated by V. americana. An
unvegetated station, Station 3 (39o 32.17' N x 76oQ5.06'W; 0.5m mean water
depth), was located outside of the grassbed on a slope of rapidly deepening water
20 m from a channel with MLW=2.1 m. The channel led into an active marina
that accommodates primarily recreational boaters. The mean water depths at
Stations 1, 2, and 3 were 0.5, 0.75, and 1.5 m, respectively. In order to facilitate
sampling, 4"x 6" posts (12' to 16' long) with plywood boxes housing ISCO water
samplers, LI-COR data loggers and Hydrolab Sonde Units were jetted into the
sediments at each station (Figure 4).
Water Quality
In order to compare water quality sampling strategies, two separate regimes
(Table 5) were used for this study. Twice monthly sampling of physical
parameters and nutrient conditions was undertaken at one vegetated station
(Station 2) from May through October 1993. Temperature, D.O., pH and
conductivity were measured with a Hydrolab Surveyor II, light attenuation was
determined with LI-COR spherical sensors and a data logger (see below), and
water samples for nutrient, chlorophyll a and total suspended solids were
collected in an acid washed nalgene bottle and kept on ice or in a refrigerator
until processing (see below).
26
-------
Figure 3. Study site at Susquehanna Rats.
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Rgure 4. Schematic drawing of equipment deployed at
Havre de Q-ace. (A) LI-OOR data logger (B) SCO
water sampler (C) Hydrolab (D) water sampler intake
(E) light attenuation array .
-------
Table 5. Summary of parameters and sampling intervals for SAV and water quality
measurements at Havre de Grace, MD study area.
Parameter
Interval
SAV
(Above and Belowground biomass)
Periodic (June, August, October)
WATER QUALITY
ROUTINE SAMPLING
(TSS, Kd, Chi, NO2, NO3, NH4,
DIN, PO4, Temperature, Conductivity)
Monthly (May-October)
INTENSIVE SAMPLING
(TSS, Chi, NO2, NO3, NH4, DIN, PO4)
(Kd, Temp, Conductivity, pH, D.O., Depth)
Periodic (June, August, October)
(every 3 hours for 10 days)
(every 30 min for 10 days)
-------
Intensive water quality monitoring was conducted at all three stations during
three ten day periods (June 15-25, 1993; August 1- 12, 1993; and October 3-13,
1993). Water samples for nutrient analysis were collected at approximately 30 cm
from the bottom at 3-hour intervals using automated ISCO samplers. The raw
water samples were kept on ice in the ISCO canister, retrieved from the field once
daily, and brought to the GEES Northern Bay Facility at Havre de Grace for
immediate processing. Hydrolab Sonde II units were deployed such that the
sensors were 30 cm above the bottom; conductivity, pH, D.O., temperature and
water depth were measured and recorded at 30-minute intervals. Light extinction
coefficients (Kj) were determined at two stations during each sampling period by
measuring photosynthetically active radiation (PAR) at 30-minute intervals at
two depths (35 cm (Station 1) or 50 cm (Stations 2 and 3) apart with a LI-COR
(model 1000) datalogger equipped with underwater spherical (4 pi) quantum
sensors which were cleaned daily of fouling organisms throughout the study
period. An average daily K
-------
Results
Plant Community
The three most abundant species of SAV at Havre de Grace during 1993
were V. americana, M. spicata, and H. verticillata. V.americana is indigenous to
Chesapeake Bay (Stevenson and Confer 1978) whereas the latter two species are
introduced. V americana is a meadow forming grass that emerges from tubers in
early spring. M.spicata is a canopy forming macrophyte that often overwinters
along the bottom and sprouts from the previous year's roots and quickly reaches
the water's surface to form a dense canopy (Staver 1986). H.verticillata is also a
canopy forming macrophyte, but differs from the other species at Havre de Grace
because it has a very small amount of root biomass (Stevenson 1988). It requires
warmer water temperatures than the other two species to germinate, and grows
more slowly than M. spicata does in spring (Carter et al. 1994). Therefore, the H.
verticillata canopy typically forms later in the growing season (Staver and
Stevenson 1994) which accounts for the lack of this species in the shallows on
our first sampling in June.
Biomass
In June, aboveground biomass at Station 2 was estimated to be 25 g m-2.
The bed consisted of V. americana, with a small amount of M. spicata and no H.
verticillata present. Vegetation was absent at Station 1 during the June study
period..
By August, the two introduced species dominated the SAV bed. Total
aboveground biomass was much greater at Station 2 (183 g m-2) than at Station 1
(60 g m-2) (Appendix Bl). At Station 1, the greatest percentage of biomass
consisted of H. verticillata, whereas at Station 2, H. verticillata and M. spicata
each comprised about half of the biomass.
Production in the SAV bed increased dramatically after June and
continued throughout August and September with peak biomass in October.
Aboveground biomass at Station 2 (161 g m-2) was slightly less than at Station 1
(182 g m-2) (Appendix Bl). During the October study period, M. spicata and H.
verticillata each contributed to roughly half of the biomass at both stations, with
V. americana making up 9 percent of the biomass at Station 1, and 4 percent at
Station 2.
No vegetation was present at Station 3 during the June, August or October
study periods.
Physical Factors
Depth, Temperature and Conductivity
31
-------
Hydrolabs were deployed at all three stations for each time period, but
because of malfunctions data was only logged at Stations 1 and 2 in June and at
Stations 2 and 3 in August. A complete record of all three stations was obtained
in October.
The tidal range at all three stations during each sampling period was about
1 m (Appendix B2). Mean depth varied between the three stations from 0.5 m at
Station 1 to 0.75 m at Station 2 to 1.5 m at Station 3. Water depth at the Havre de
Grace site is strongly influenced by wind and discharge of the Susquehanna
River as well as by gravitational forces. The tidal cycle was most consistent in
August, when the river discharge was low, and most erratic in October.
Generally water temperatures showed strong diel patterns at all three
stations (Appendices B3-B9). The range of temperatures within a day were
consistently greater at the shallower vegetated stations, and the range between
days was greater in October than in June. In August the water temperature
ranges were notably smaller than during the other two sampling periods. Water
temperatures were highest in August and lowest in October (Table 6).
In June, water temperatures at Stations 1 and 2 were similar (Table 6).
Hydrolabs at both stations were collecting data simultaneously from June 18-22.
During this time, water temperatures at Station 1 exhibited a greater daily range of
values (Appendix B3) than at Station 2 which was deeper (Appendix B4). The
dampening of the daily water temperature cycle seen at both stations beginning
June 21 corresponds to a rain event (Appendix BIO).
In August, the mean water temperatures at Stations 2 and 3 were similar
(Table 6), but the two stations displayed distinct differences. The shallower
station showed more variability, 23.5-30.0 °C at Station 2 compared to 24.2-29.4
oC at Station 3, and was more strongly influence by the rain of August 6
(Appendices B5, B6 and Bl 1).
In October, the water temperatures at all three stations had cooled almost
10 degrees and Stations 2 and 3 were similar, while Station 1 was about 0.5 «C
cooler (Table 6). Maximum temperatures ranged from 19.5 »C (Station 3) to 20.6
oC (Station 2), while minimum temperatures ranged from 11.4 «C at Station 2 to
13.9 °C at Station 3 (Appendices B7-B9). Once again, the deeper station showed
less variability and was less dramatically influenced by meteorological events
such as the rapid decrease in air temperatures from October 9-11 and the rain of
October 12.
Salinity at the Havre de Grace site is <1 psu; therefore conductivity was
recorded as a more reliable measure of total dissolved solids. Although sinusoidal
curves of conductivity suggested tidal influences, there were several records
where conductivity is comparatively flat over several days, indicating the
importance of both riverine and atmospheric inputs (Appendices B3-B9). The
differences between stations were in the range of 25 ^.S cm-i in June with the
shallower Station 1 being lowest, varying from 280 to 300 p,S cm-i. There was a
slight increase in conductivity throughout the June sampling period at both
stations, with no major precipitation events. In August conductivity at both
32
-------
Table 6. Physical parameter medians by station for each sampling period
at Havre de Grace, MD.
June 1993
pH
DO (mg/L)
Conductivity (nS/cm)
Temperature (°C)
Kd
Station 1
7.53
6.08
293
26.23
Station 2
7.80
10.86
334
26.31
1.59
Station 3
* *
* *
* *
* *
1.56 ns
PH
DO (mg/L)
Conductivity (nS/cm)
Temperature (°C)
Kd
August 1993
Station 1
1.15
Station 2
8.20
8.58
322
27.22
1.98
Station 3
8.49
5.82
356
27.07
* *
* *
* *
*
* *
October 1993
pH
DO (mg/L)
Conductivity (nS/cm)
Temperature (°C)
Kd
Station 1
8.35
17.07
1.73
Station 2
8.38
10.00
342
17.59
Station 3
7.82
9.69
320
17.56
1.29
* *
nc
nc
* *
* *
*-- statistically significant at p<0.05
**- statistically significant at p<0.01
ns-- not statistically significant
nc-- no statistical analyses performed
-------
Stations 2 and 3 increased after the August 6 rain, and then oscillated with the
deeper station (Station 3) having a higher range of 345-385 |LiS cm-i compared
with Station 2 (305-345 |J,S cm-1). In October Station 2 conductivity is much
more erratic (320-350 (iS cm-i) than Station 3 (320-325 |iS cm-i) despite two
precipitation events.
Dissolved Oxygen and pH
During all months at all stations, dissolved oxygen concentrations
exhibited diel patterns (Appendices B3-B9) which were correlated with
macrophyte and phytoplankton production of oxygen by day and respiration at
night. Greater daily D.O. variances occurred at the vegetated stations. For
example, in August the daily change in D.O. at Station 2 was approximately 10
mg l-i, while at Station 3 it was only 5 mg H, and in October the daily change in
D.O. at Station 2 was approximately 7 mg I-1, while it was only 2 mg H at Station
3. D.O. concentrations were lowest during the August sampling period (Table 6).
Oxygen production by macrophytes contributed to higher D.O. levels at the
vegetated stations during all three sampling periods.
All stations exhibited diel pH patterns similar to the D.O. patterns with
greater daily variability again observed at the vegetated stations (Appendices
B3-B9). In addition to enhancing daily pH ranges, macrophyte consumption of
CO2 for photosynthesis increased pH values (Table 6) throughout the growing
season in the vegetated stations (Station 1 pH was 7.53 in June and 8.35 in
October, Station 2 mean pH was 7.80 in June, 8.20 in August, and 8.38 in
October). In comparison, pH decreased from August (8.49) to October (7.82) at
Station 3 (Table 6). This decrease is associated with markedly lower temperatures
in October as compared with August.
Response to precipitation and higher runoff is especially evident in the
August data. The pH maximum was dampened at both Stations 2 and 3 on
August 6, after a substantial rain (Appendices B5 and B6), but are much more
evident at Station 2 where macrophyte photosynthesis controls pH fluctuations.
In October there was a pH peak and dampening of the daily range at Station 3
towards the end of the sampling period. This corresponded to a chl a pulse
which was observed at all three stations (see below). The increase in pH at
Station 3 is most likely due to phytoplankton photosynthesis. The effects of
additional algal production in the grassbed was insignificant when compared to
macrophyte production.
Weather
Weather conditions in June remained relatively stable, with light rain
showers on June 19, 20 and 21 (Appendix BIO). A front moved through the area
on August 6 (Appendix Bl 1). It was accompanied by decreasing barometric
pressure and air temperatures, and a light to moderate rain event from 0700h to
34
-------
2000h. This coincided with an immediate drop and subsequent increase in
conductivity, a depression in the D.O. and pH peaks, and a steady decrease in
water temperature (Appendices B5 and B6). Weather conditions were least
stable in October. Barometric pressure exhibited more fluctuations than during
the June and August sampling periods. Air temperatures dropped from a high of
26.7 oC for October 9 to a high of only 13.3 <>C for October 10 (Appendix B12).
Similarly, the low air temperatures for October 9,10, and 11 were 12.2, 6.7, and 2.8
oC, respectively. A corresponding decline in water temperature was observed at
all three stations (Appendices B7-B9).
Water Quality Constituents
Light Attenuation
Light attenuation was successfully recorded at Stations 2 and 3 in June,
Stations 1 and 2 in August, and Stations 1 and 3 in October. In June, light
attenuation was fairly consistent from day to day (Appendix B13), and there were
no significant differences (Table 6) between the two stations (K
-------
less than 1 % of total plant biomass and do not hold the fine grained sediments
which can become easily resuspended.
This easily resuspended flocculent layer is the most likely scenario for why
the shallow water TSS concentrations were so variable at Stations 1 and 2,
compared with the deeper sandier Station 3 during all sampling periods
(Appendices B14-B16). In general, TSS concentrations consistently increased
from June, which had no frontal passages, to August and into October when
weather conditions were much harsher (Table 7).
In order to portray temporal variability over the ten-day study periods, it is
important to consider average (± standard error) concentrations in addition to
median values. In June, TSS concentrations were 12.26 (±1.64) and 9.68 (±1.62)
mg l-i at Stations 1 and 2, respectively, and only 4.86 (±0.31) mg H at Station 3.
Concentration peaks of 30 to 60 mg H were observed at the vegetated stations,
whereas the maximum TSS concentration at Station 3 was only 11.43 mg H
(Appendix B14). The vegetated sites were shallower and the sediments sillier,
both of which facilitate resuspension. This explains the higher TSS variability
inside the grassbed.
In August, TSS concentrations at the three stations were all significantly
different from each other (Table 7). Seston concentrations at Stations 1 and 2
were 35.42 (±7.02) and 21.68 (±3.88) mg H, respectively (Table 7). At Station 3,
TSS concentrations were lower than both vegetated stations, with a mean of
10.26 (±0.54) mg l-i. In addition to variability, the range at the unvegetated
station (Station 3) was also much smaller (3.29-23.46 mg H) than the range for
the shallower vegetated stations (3.52-261.13 mg H) (Appendix B15). The peaks
in TSS seen at all three stations on August 6 occurred after a substantial rain. The
peaks seen at all three stations on August 9, 10, 11 and 12 correspond to
increasing wind speed and alternating high tides (Appendices Bll and B2), and
are dampened with increasing depth.
TSS concentrations were less variable at all stations in October (Appendix
B16), although the trend of significantly higher TSS concentrations (Table 7) and
greater variability at the vegetated stations continued. The October TSS means at
Stations 1, 2 and 3 were 36.75 (±0.83), 26.76 (±3.94) and 10.44 (±0.50) mg 1-1,
respectively. All three stations showed sharp increases in TSS concentrations on
October 12. This corresponded to a light rain event locally (Appendix B12), but
is more likely due to increased runoff and riverine flow down the Susquehanna
(see discussion of chl a below).
TSS comparisons within and outside of the SAV bed show that TSS was
always significantly higher inside the bed throughout the growing season (Table
7). This does not support the hypothesis that TSS concentrations are lower inside
than outside of a grassbed (e.g. Kemp et al. 1984). Generally, dense vegetation
increases fine particle deposition and decreases resuspension by baffling water
movement (Ward et al. 1984). However, the Havre de Grace grassbed is
dominated by H. verticillata and M. spicata, two canopy forming species with
whorled leaves (that are highly branched in M. spicata) and a high surface area.
The increased surface area enhances fine particle deposition on the leaves
36
-------
Table 7. Nutrient medians by station for each sampling period at
Havre de Grace, MD.
June 1993
N02 (mg/L)
(liM)
NO3 (mg/L)
NH4 (mg/L)
(HM)
DIN (mg/L)
PO4 (mg/L)
(HM)
TSS (mg/L)
CHL A (ng/L)
Station 1
0.029 a
2.06
1.045 a
74.66
0.045 a
3.25
1.144 a
81.71
0.0006 a
0.02
8.81 a
5.07 ab
Station 2
0.035 b
2.49
1.255 a
89.65
0.045 a
3.24
1.358 a
97.02
0.0006 a
0.02
7.06b
4.80 a
Station 3
X
2.45
1.312 a
93.68
0.052 a
3.71
1.427 a
101.90
0.0006 a
0.02
8.63 b
5.19 b
August 1993
NO2 (mg/L)
(HM)
N03 (mg/L)
(HM)
NH4 (mg/L)
(HM)
DIN (mg/L)
(nM)
P04 (mg/L)
TSS (mg/L)
CHL A (ng/L)
Station 1
0.031 ab
2.22
0.568 ab
40.58
0.034 a
2.40
0.634 ab
45.30
0.0001 a
0.03
13.33 a
5.63 nc
Station 2
0.026 a
1.88
0.490 a
34.97
0.027 a
1.91
0.538 a
38.42
0.0003 b
0.01
11.45 b
6.65 nc
Station 3
0.041 b
2.95
0.700 b
49.97
0.019 b
1.37
0.767 b
54.78
0.0006 c
0.02
8.55 c
7.44 nc
October 1993
NO2 (mg/L)
(HM)
N03 (mg/L)
NH4 (mg/L)
(HM)
DIN (mg/L)
PO4 (mg/L)
TSS (mg/L)
CHL A (ng/L)
Stationl
0.009 a
0.62
941 a
67.21
0.011 a
0.80
0.964 a
68.83
0.0019 A
0.06
16.34 a
5.27 nc
Station 2
0.008 a
0.555
0.773 a
55.24
0.010 a
0.68
0.788 a
56.30
0.0016 B
0.05
12.67 a
5.69 nc
Station 3
0.016 b
1.12
0.915 a
65.33
0.010 a
0.72
0.940 a
67.14
1622 AB
0.05
9.43 b
5.53 nc
values followed by identical letters (A,B or a,b) are not significantly different
from each other at p<0.05 or p<0.01, respectively
nc=no statistical analysis performed
-------
themselves. Also carbonate forms on the leaves as a product of the high pH in
the bed. When the vegetation is disturbed, the particulates on the leaves can be
easily resuspended and thus the bed is particularly susceptible to waves and
currents resulting from frontal passages and even wind events from the exposed
southeast.
All the evidence suggests that this Havre de Grace site is very physically
influenced by river flow from the Susquehanna. The Susquehanna River is the
largest source of freshwater to Chesapeake Bay. Current speeds outside the SAV
bed near Concord Point at Havre de Grace have been measured as high as 60 cm
s-i (Wigarid, pers. comm.). During high flow we would expect currents to exceed
1 m s-i when Conowingo Dam has all the sluice gates open, as happened in
March and April of 1993. Stations 1 and 2 are more protected from strong
currents by Concord Point which allows the deposition of silty substrate. Station
3 is less protected from the flow, as evidenced by a sandier substrate.
The Havre de Grace site is also physically influenced by unprotected
exposure to southeasterly winds across a fairly large fetch (approx. 10 km).
August data illustrates the effects of strong winds on suspended solid
concentrations. The effects are more obvious at the shallower vegetated stations
than at Station 3 where the deeper waters and sandier sediments minimize the
effects of wind driven resuspension. Similarly, rain showers and thunderstorms
during all three sampling periods illustrate the effects of rain driven resuspension
of sediments.
It has been suggested that disturbances during sampling may have caused
the elevated TSS levels in the grassbed. Although this seems to be the case at
Stations 1 and 2 in August when TSS peaked at over 100 mg H three times, the
exclusion of samples taken during these potential disturbances revealed no
change in the overall means. This analysis suggests that although there may be
problems during actual visits, our long term data collection was unaffected. Thus,
in these environments, automatic sampling is very important in reducing artifacts.
It appears that physical factors such as water depth, substrate type, wind
and rain have the most long lasting impacts on suspended solids at the Havre de
Grace site. The impact of general boating activities, aside from our sampling, on
TSS is still an open question.
Chlorophyll a
Due to observations in a previous Chesapeake Bay study (Kemp et al.
1984), we expected significantly less chl a in the SAV bed compared to Station 3.
However, few consistent differences were observed. All stations exhibited
considerable variability, and although variability at Station 3 was always lower
than at the vegetated stations, the discrepancy was not as great as that seen in
the TSS data. During June, mean chl a concentrations at Stations 1 and 2 were
5.64 (±0.42) and 5.04 (±0.30) jig H, respectively. At Station 3, however, chl a
concentrations were noticeably lower, at 3.96 (±0.22) jig H (Appendix B17).
38
-------
In August, mean chl a concentrations at Stations 2 and 3 were similar (8.30
(±0.65) [O.g l-i and 7.99 (±0.41) fig l-i), while chl a concentrations at Station 1
were lower (6.40 (±0.39) (ig H, Appendix B18). Chl a concentrations increased
slightly towards the end of the August sampling period at the two vegetated sites
after a substantial rain (Appendix B18).
Chl a concentrations were similar at all stations in October. The means at
Stations 1, 2 and 3 were 6.68 (±0.55), 7.31 (±0.63), and 6.37 (±0.46) |ig l-i,
respectively. Chl a concentrations at all stations ranged from 0.80 to 28.90 |ig H,
and variability was lowest outside of the SAV bed (Appendix B19). Chlorophyll
a increased on October 11 and 12 after a three day weekend, when flow from
Conowingo Dam increased again (Appendix B32). Most likely this chlorophyll
rich water came from the lake. Regulation of flow from the dam in combination
with high flow rates allows for parcels of water, in this case a chlorophyll rich
parcel, to pass through the Havre de Grace study site quickly.
Both inside and outside the grassbed chl a concentrations increased from
June to August, then decreased from August to October (Table 7). In June, chl a
concentrations were significantly lower at Station 2. In August and October
there was no difference between the vegetated and unvegetated areas. Station 2
was the only station with vegetation in June (Appendix Bl) that was capable of
shading the water column.
An important consideration for the August data is the peak chl a
concentrations (>15 jig H) at all three sites (Appendix B18). If one considers the
median values, which are more applicable in determining habitat requirements (see
discussion below), chl a concentrations are highest at Station 3 (7.44 (j,g H), and
lowest at Station 1 (5.63 |o.g H). This suggests that the Kemp et al. (1984)
hypothesis may be viable. Although their data is limited to one day, it was at the
same time of the year. Inside the grassbed, phytoplankton may be filtered
somewhat and production may be limited by low light from high TSS and by the
macrophyte canopy and relatively low water column phosphorus (see below).
At the beginning of our sampling in October, when water temperatures
were lower, phytoplankton biomass had decreased considerably outside of the
grassbed. Inside the grassbed, macrophyte uptake of nutrients was past the peak
growth period and senescence had begun, presumably rendering nutrients more
available to phytoplankton. However, other factors, such as decreased
temperature, lower ambient light with shorter days as well as generally increased
turbulence due to storm events, may all have limited in situ planktonic
productivity in the shallows. Our hypothesis that the sudden rise in chl a (to 25
jig l-i) at 1800 hours on Oct. 11 at Station 3 is due to runoff from Lake
Conowingo, needs to be checked further. However, the fact that the peak at
Station 1 is three hours later than at Station 3 strongly suggests that the origin of
the chl a is from outside the bed.
39
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Dissolved Inorganic Nitrogen: Nitrite, Nitrate, Ammonium
Dissolved inorganic nitrogen (DIN) concentrations were very high (0.538
to 1.427 mg I-1 (38.42 to 101.90 [iM)) and extremely variable at all three stations
throughout the growing season (Appendices B20-B22, DIN; Appendices
B23-B25, ammonium; Appendices B26-B28, nitrate; Appendices B29-B31,
nitrite), with >90% of DIN being attributed to nitrate. The variability cannot be
easily attributed to tides, storms, or boating activities. There was a decrease in
DIN concentrations at all stations from June to August, and an increase from
August to October, although DIN concentrations were not restored to the June
levels (Table 7). The nitrate fraction at all three stations followed the same
seasonal pattern that DIN did (Table 7). This may be related to discharge at
Conowingo Dam, which was about 13,500 cfs during the June and October
sampling periods, but less than half that during August (Appendix B32) and to
uptake by macrophytes and phytoplankton. Ammonium, on the other hand,
snowed a steady decline from June to August to October (Table 7). This can
probably be attributed to nitrification as well as uptake by macrophytes and
phytoplankton.
In June there were no significant differences in DIN or the component DIN
species (ammonium, nitrate, nitrite) between sites (Table 7). Macrophyte growth,
and therefore nutrient uptake, had not yet peaked. Ammonium levels exhibited a
slightly diel pattern, with concentrations increasing during the night as D.O.
decreased. This diel pattern was more evident at Stations 1 and 2 than at Station
3 (Appendix B23).
In August, DIN and nitrate concentrations were lower inside the grassbed
than at Station 3, due to macrophytic uptake, while ammonium concentrations
were higher inside the grassbed than at Station 3 (Table 7). Ammonium
concentrations again exhibited a diel pattern which was dampened at Station 3
(Appendix B24). Higher ammonium concentrations and the enhanced diel curve
inside the grassbed may be attributed to regeneration of nutrients in the surficial
sediment layer.
In October, as in June, there were no differences between DIN
concentrations between the three sites (Table 7). Even though macrophyte
biomass was at its peak in October, growth of both macrophytes and
phytoplankton was past peak, and there were no differences in nutrient uptake
between the vegetated and unvegetated stations. Ammonium concentrations
(Appendix B25) exhibited the same diurnal pattern, dampened at the deeper
station, as was noted previously. At all three stations, nitrite concentrations were
highly variable during the first half of the sampling period, then decreased in both
concentration and variability from October 7 to 12, then increased again, perhaps
a result of incomplete nitrification (Appendix B31).
40
-------
Dissolved Inorganic Phosphorus
Phosphate concentrations were very low at all three stations throughout
the growing season, although the data reveal several pulses (Appendices
B33-35). These pulses may be parcels of water originating from Conowingo
Lake that had very brief residence times at the study site. Phosphate
concentrations decreased from June to August at Stations 1 and 2, while at
Station 3, they remained the same (Table 7). The decrease inside of the SAV bed
can be attributed to nutrient uptake by macrophytes.
From August to October, phosphate concentrations increased at both
stations inside of the grassbed. Macrophyte and phytoplankton growth, and
therefore nutrient uptake, was past its peak, explaining the increasing water
column concentrations. Plants were also beginning to senesce and may have
been leaking phosphate from the leaves. There was a trend in October of
decreasing phosphate concentrations outside the grassbed during the ten day
sampling period (Appendices B35 and B31). Concentrations of these nutrients
were generally higher October 3- 8 than October 8-14. This could be related to
increases in chl a concentrations during this time (Appendix B19).
Water Quality Comparisons
A summary of median values of five water quality parameters we have
used previously to define the health of SAV in Chesapeake is presented in Table
8. Results of biweekly monitoring and intensive monitoring inside and outside of
the grassbed are compared to each other and to the tidal freshwater SAV habitat
requirements (Batiuk et al. 1992). Both inside and outside of the grassbed, the
biweekly sampling regime produced median levels comparable to those
determined during the intensive sampling periods. However, the biweekly
median does not adequately represent either the seasonal variations or the daily
variations that the intensive monitoring characterizes.
Light availability is the single most important single factor influencing SAV
distribution and growth (Kemp et al. 1983, Wetzel and Neckles 1986, Dennison
et al. 1993). Light availability for SAV is dependent on at least four additional
factors in estuaries such as Chesapeake Bay: TSS, chl a, DIN, and DIP (Batiuk et
al. 1992). Table 8 compares the tidal freshwater SAV habitat requirements to
median levels of these environmental factors determined in the grassbed at Havre
de Grace in 1993. There are no habitat requirements for DIN in areas with less
than 5 psu salinity because phosphorus limitation usually acts to inhibit algal
growth which competes with SAV.
41
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Table 8. Comparison of median water quality parameters during the 1993 growing
season at Havre de Grace, MD with tidal freshwater SAV habitat requirements.
Parameter
Kd (/m)
TSS (mg/L)
CHLa (ng/L)
DIP (mg/L)
DIN (mg/L)
Tidal Freshwater
SAV
Habitat
Requirements*
<2
<15
<15
<0.02
—
Havre de Grace
Grassbed
Biweekly
Monitoring
May-October
1.42
8.00
5.76
0.00093
0.90
Havre de Grace
Grassbed
Intensive
Monitoring
Jun 15-25 Aug 1-12 Oct 3-13
1.59 1.15 1.73
8.81 13.33 16.34**
5.07 5.63 5.27
0.0006 0.0001 0.0019
1.144 0.634 0.964
MDE
monitoring
station
CB1.1
May-October
1.55
4.95
7.2
0.0025
1.13
Havre de Grace
Channel Site
Intensive
Monitoring
Jun 15-25 Aug 1-12 Oct 3-13
1.56 — 1.29
8.63 8.55 9.43
5.19 7.44 5.53
0.0006 0.0006 0.0016
1.427 0.767 0.940
* from Batiuk et al. 1992
** exceeds habitat requirements
-------
The Havre de Grace SAV bed met all of the habitat criteria during the 1993
growing season as determined by biweekly monitoring. In fact, the habitat
requirements were only exceeded in October when median TSS concentrations
were 16.34 mg H. These data support the habitat criteria established by Batiuk et
al. (1992). As the intensive monitoring medians were within the range of the
bimonthly medians, it appears that the latter sampling strategy is an appropriate
measure for water quality, even in an area where temporal variability is high.
One of the problems that Batiuk et al. (1992) encountered was the lack of
sufficient nitrogen data to establish a water quality parameter for DIN in the tidal
freshwater regions of the Bay. Although our research was not specifically
designed to obtain a DIN threshold, it is clear that SAV survives at a median DIN
concentration of 0.9 mg I-1 at Havre de Grace, which is six times higher than the
habitat requirements in higher salinity zones (Batiuk et al. 1992). Interestingly,
this concentration is more than double the maximum that Burkholder et al. (1992)
found to deregulate growth of Z. marina in mesocosms in North Carolina.
Although their work is somewhat controversial due to other possible factors, i.e.
high temperatures which interfere with Z. marina growth, the possibility that
nitrate inhibits SAV directly needs to be better understood. Previous studies in
Chesapeake Bay have only explored the indirect problems of high DIN in the
water column, for example epiphytic overgrowth and planktonic competition for
light. It is not clear to what extent similar physiological processes might exist in
freshwater and low salinity species such as V. americana. Nitrogen inhibition
might be one of the reasons that V. americana growth was so low during 1993 at
Havre de Grace, after the large freshet brought in high nitrogen. Although it is
perhaps still premature to offer a DIN habitat requirement for SAV, it might be in
the range of 1.4 mg H (100 |iM). This may not apply for species such as H.
verticillata and M. spicata and may therefore account for species shifts in the
Upper Bay towards introduced species.
43
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HI. FALL 1993 MESOCOSMS STUDY
Methods
The first phase of the S AV mesocosm experiments was conducted in the
fall of 1993 to test the temporal scaling on nutrient inputs to SAV ecosystems. A
series of small mesocosms, under natural light with continuous flushing were
established to examine the seasonal (fall) response of a native Chesapeake Bay
SAV species (Potamogeton perfoliatm L.) and its associated phytoplankton and
epiphytic algal assemblages to nutrient enrichment in varying forms and
frequencies. In these experiments, the same moderate level of nutrient loading
(38 \imol l-i d-i) was delivered to replicate mesocosms in three ways: 1) as
continuous dissolved inorganic N and P; 2) as weekly pulses of dissolved
inorganic N and P; and 3) as weekly pulses of particulate organic N and P (Table
9). These three treatments are compared to continuous inputs of low nutrient
waters. Dissolved inorganic nutrient concentrations in the mesocosm water
columns were measured routinely and community responses were measured as
SAV growth, biomass, morphology and tissue nutrients, biomass of algal and other
epiphytic materials and biomass of phytoplankton. Similar experiments were
conducted in the spring and summer of 1994 to complete the temporal cycle, with
the results to be reported separately.
Experimental Design
Experiments were conducted in the greenhouse located at Horn Point
Environmental Laboratory; Cambridge, Md. Plants were collected from
experimental ponds located on the property, planted in a PVC pot containing 1.5
L of sediments collected from the Choptank River. The pots were then placed in
clear acrylic microcosms (15.2 cm x 15.2 cm base x 61 cm height) containing a
volume of 10L. The microcosms were placed in large cooling tanks to maintain
ambient river water temperature. Each pot contained ten P. perfoliatus plants,
which were allowed to acclimate for a period of two weeks with Choptank River
water cycling through the chambers at a turnover rate of once per week. Each
microcosm was bubbled with air to facilitate mixing and to minimize oxygen
inhibition and carbon dioxide limitation.
Nutrients in the pulse treatments were added by hand to each of four
replicate chambers on a weekly basis, while continuous inputs were administered
with a peristaltic pump. All nutrient additions were made at a loading rate of
38(iM N -1 -i-d -i, with phosphorus added to result in a 10:1 atomic NP ratio.
Dissolved nutrient additions were made using ammonium nitrate and sodium
phosphate. Particulate nutrient additions were made using heat killed algal
slurries ( Kana, pers. comm.).
44
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Table 9. Nutrient loading rate, input concentrations and input rate
for experimental chambers.
TREATMENT N-LOADING INPUT CONC INPUT RATE
(M mol -L^-D-1) (p M)
CONTROL
DISSOLVED
CONTINUOUS
DISSOLVED
PULSE
0.2
38.2
38.2
1.3
364 input
532 xlO3
1cm3-
1cm3-
5 cm3-
mur1
miir1
wk-1
PARTICULATE 38.2
PULSE
984 x103
2.7
-------
Results
Physical Parameters
As expected with season temperatures in the chambers declined over the
experimental period from a high in August of 28.6 °C to a low of 22.1 °C in late
October. Salinities ranged from 14.3 to 15.4 psu. Generally, light conditions also
declined throughout the period. However, in the two dissolved (pulse and
continuous) nutrient treatments, light conditions were considerably lower than
the control and particulate treatments.
Nutrient Concentrations
Nutrient concentrations exhibited different patterns with each mode of
delivery. Continuous input concentrations were relatively constant throughout
the experimental period (Appendices Cla-c), while dissolved pulse
concentrations exhibited peaks immediately following nutrient additions, but
returned to low levels fairly rapidly (Appendices C2a-c).
Despite relatively high levels of nutrient inputs, concentrations in the
continuous treatments were comparable to concentrations in the control
chambers (Appendices Cla-c). Ammonia levels were very similar in both
treatments throughout the experiment, but were somewhat elevated in the
continuous addition toward the end of the experiment, suggesting nutrient
regeneration (Appendix Cla). Nitrite-nitrate concentrations were only slightly
higher in the nutrient addition chamber, but concentrations remained low (around
1 juM) throughout the experiment (Appendix Clb). Phosphate concentrations,
although relatively high (0.2-1.0 fiM), were very similar in both chambers for the
first 3-4 weeks of the experiment, then became slightly elevated in the nutrient
enriched chambers (Appendix Clc), suggesting phosphate saturation and
possible nitrogen limitation.
Time series of the nutrient concentrations in the dissolved pulse treatments
indicate that ammonia and phosphate are greatly reduced after three hours and
are comparable to control levels by twelve hours (Appendices C2a and C2c).
Nitrate and nitrite levels remain elevated for approximately 48 hours following
addition (Appendix C2b). There were no differences in these patterns
throughout the experimental period. Nutrient concentrations in the particulate
treatments were not different from controls.
Plant Response
Plant growth rate generally exhibited a similar growth pattern in all
treatments for the duration of the experiment (Appendix C3). During the first 4
weeks plant growth rates increased slightly, but declined steadily for the
remainder of the experiment. However, during the last five weeks of the
46
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experiment, plant growth rate in the dissolved treatments declined more rapidly
than in the particulate and the control treatments, with negative values beginning
after week eight (Appendix C3).
Other indicators of plant response further suggest stress in the plants
within the dissolved treatments. Above and below ground plant biomass and
root to shoot ratio were reduced in both dissolved treatments (Table 10), but
slightly enhanced in the particulate treatment. Plants in all nutrient treatments
were longer, but had less leaves per stem, perhaps indicating etiolation and light
stress (Table 10).
Algal Concentrations
As expected, algal concentrations increased with nutrient additions.
Chlorophyll levels in all treatments, except the dissolved continuous, remained
relatively low and ranged from 0.5 to 14.3 |ig-H (Appendix C4). For the first 4
weeks, levels in the continuous chambers also were relatively low, but then
showed a steady weekly increase to very high concentrations of 150 fig.I-1.
Macroalgae increased, in comparison to controls, in all chambers with nutrient
additions, but exhibited variability within treatments (Appendix C4). Epiphyte
biomass was higher in all nutrient enriched treatments at the end of the
experiment (October), but followed different patterns with mode of nutrient
addition. Epiphytic mass actually decreased in the particulate pulse treatment,
but increased in both dissolved treatments. Epiphytic mass in the control
changed little during the experimental period. Estimates of benthic deposition
and algal concentrations can be derived from the percent organic matter in the
top five centimeters of sediment. This value was higher in all treatments, but
highest concentrations were found in the continuous treatment (Appendix C4).
Discussion
The water column nutrient concentrations remained low (around 1.0 fimol,
Appendix Cl) in spite of the relatively high loading rates (38 [imol -H • d-i),
suggesting a lack of correspondence between loading rates and water column
concentrations. Obviously, the nutrients were utilized rather rapidly upon
addition to the chambers (Appendices C2a, b, c) and resulted in an increase in
algal components (phytoplankton, macroalgae, epiphytic algae and benthic algae)
(Appendix C4). A nitrogen budget (Appendix C5) was calculated from direct
measurements (plant CHN analysis, sediment CHN analysis) and from literature
values for nitrogen concentrations in phytoplankton, epiphyte and macroalgae
(Twilley et al 1986). This budget supports the redirection of nutrients from plant
biomass (control) to algal biomass (dissolved nutrient treatments).
Nutrients added continuously in the dissolved form elicited the greatest
response by the algal communities, while those added on a pulse bases in both
47
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Table 10: Morphological parameters. Summary of mean (+SE) values for Potamogeton
perfoliatus biomass, root to shoot ratio, shot length, and leaf number in control and nutrient
enriched treatments (n=4).
Biomass (adw) RootrShoot Shoot # Leaves per
Treatment
Control
Paniculate
Pulse
Dissolved
Pulse
Dissolved
Continuous
Above
.32322
(+-106)
.51477
(+106)
.32250
(+.082)
.10327
(+.176)
Below
.91856
(+.304)
1.23791
(+.142)
.52267
(+.129)
.19965
(+414)
Ratio
2.8377
(+.176)
2.9574
(+.422)
1.6531
(+.641)
1.8552
(+1.720)
Length (cm)
52.9
(*20.4)
152.4
(+57.4)
134.4*
(+32.4)
123.6
(*10.4)
Shoot Length
1.05
r.o3)
1.07
r.14)
.79*
(+.06)
.84*
(+.06)
* Indicates significance at p<0.05 from Control, student's t-test.
-------
the dissolved and particulate form had less of an effect. These findings suggest
that nutrients entering aquatic systems from any continuous input (i.e. waste
water treatment plants) may result in higher algal concentrations than those
entering on a pulse basis (i.e. storm runoff).
Plant response, to these nutrient additions were not as evident as in past
experiments (Twilley et al. 1985; Neundorfer and Kemp 1993). This may be, in
part, because of the seasonal timing of the experiment. All plants exhibited a
general senescence (die back) due to the natural growth cycle of these plants.
However, there was evidence of plant stress in the dissolved nutrient treatments
in plant growth rates (Appendix C3) and end of experiment plant biomass and
morphological features (Table 10). The low root:shoot ratio in the dissolved pulse
and dissolved continuous additions suggests that these plants have less storage
for spring regrowth. In nature this lack of reserves could lead to the demise of the
plants.
These results suggest that dissolved nutrients have a greater immediate
effect on SAV communities than particulate nutrient additions. Increased algal
growth and declines in plant growth rates and storage capabilities support this
hypothesis. Furthermore, seasonal timing of nutrient additions may play an
important role in SAV survival.
49
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REPORT SUMMARY
SAV Community Structure and Biomass
The SAV beds studied in the two field sites contained five species, three in
the upper bay at Havre de Grace and two in the lower bay at Goodwin Island.
Maximum biomass was comparable at each site, 200-250 gdm m-2 at Goodwin
and 160-180 gdm m-2 at Havre de Grace. Depths were also similar, approximately
0.25m and 0.5m at MLW at the vegetated stations in the upper bay study area
and 0.4m and 0.6m in the lower bay site. Offshore stations were also similar in
depth at approximately 1.3 to 1.5m MLW. These results suggest that during this
study period the two SAV communities occupied comparable zones in the
subtidal and were similarly successful in vegetating these zones. However,
because both SAV communities can attain higher peak standing crops than are
reported here, it may be alternatively suggested that they were responding to
conditions that limited growth to similar degrees.
There were distinct differences in the seasonality of the development of
the macrophyte communities. The upper bay SAV community grew throughout
the summer and attained maximum standing crop at the end' of the growing
season in October. V. americana (wild celery) was initially dominant in the early
summer, while H. verticillata and M. spicatum (Eurasian watermilfoil) developed
later and eventually became the dominants in the community. At Goodwin Island
in the lower bay, vegetation was persistent throughout the entire year. Maximum
standing crop in the spring consisted principally of eelgrass (Z. marina) with R.
maritima (widgeon grass) dominating the inshore shallow areas in the mid-
summer as Z. marina died back. In the fall as temperatures dropped below 25 °C
a second growth period of Z. marina occurred, with new growth consisting of
vegetated shoots and newly germinated seedlings. In the winter the standing
crop consisted of Z marina only.
P.perfoliatus (redhead grass), which was used as the test species in the
mesocosm study, did not occur at either of the two field study sites. It is,
however, common throughout the mid bay region where salinities are
intermediate between these study areas, and can co-occur with SAV species
found at the Havre de Grace site. It develops a canopy more similar to H.
verticillata and M. spicatum than the filiform plant structure of V. americana or
Z marina, and is characterized by a unimodal annual growth cycle with maximum
biomass in late summer and early fall.
Physical Parameters
Although there were differences in physical regimes at the two sites, in
general, wind speeds and tidal ranges were similar. Afternoon sea breezes were
more prevalent at the lower bay site, but peak wind velocities were comparable.
50
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There were no extreme wind events at either of the sites, however during October
consistently high east and northeast winds were prevalent in the lower bay study
area. Tidal ranges were slightly higher at Goodwin Island than Havre de Grace
(0.5-0.6 vs 0.7-0.8 m; upper bay and lower bay neap-spring tides respectively).
Localized conditions such as wind effects and dam discharge rates seemed to be
related to the more dramatic day-to-day variability in tidal heights observed at the
upper bay site than the lower bay site, where the spring-neap tidal variability was
more evident.
Water velocities in and out of the beds were not measured, however,
general observations and other available data suggest that they were quite
different. This, in turn, has important implications for the measured standing
stocks of many water quality constituents such as inorganic nutrients, where
differences inside and outside of the beds are directly related to the residence time
of water within and over the canopy. Seufzer (1994) reported water velocities
within the Goodwin Island bed as generally not exceeding 10 cm sec-i.
Stevenson (unpublished data) observed velocities at the edge of the Havre de
Grace bed to reach 60 cm sec-i. Therefore, some observed differences between
the sites may not be related so much to differing bed processes, but to our ability
to detect the net result of these processes. In many cases, high water velocities
combined with high constituent levels can obscure the effect of an SAV bed on
water quality. Conversely, this highlights the fact that a SAV bed's ability to
modify the local environment can be limited by high water velocities.
Water temperatures varied seasonally between the areas, reflecting, in part,
the dominance of the oceanic environment at Goodwin Island and terrestrial
environment at Havre de Grace. Temperatures in the upper bay site were warmer
by June and cooler by October than the lower bay. August temperatures were
comparable. A greater diel temperature range was observed in both beds
compared to out, especially during August and October. This was due largely to
the shallower depths of the vegetated stations. Both areas demonstrated
dramatic day-to-day changes (up to 2 °C) in water temperatures that were driven
by changes in regional weather. The mesocosms were cooled with ambient
Choptank River, water during the experimental period of August, 1993 to
October, 1993. In August water temperatures were comparable to the field sites
at about 28°C, while by the end of the experiment in October water temperatures
were slightly higher than either field site at 22°C.
Salinities in the field sites reflected the two end points of the bay system.
Salinities in the upper bay (measured as conductivity) were less than 1 psu
(practical salinity units). In the lower bay they ranged from 12 to 24 psu.
Seasonally, salinities were highest in October and lowest in the spring (April-
June). There was little tidal variability in salinity in the lower bay, although there
were periods when salinities dropped up to 1 psu over the course of one day as
the water mass in the region changed due to wind and tides. In the upper bay
site tides were observed to have some effect on conductivity, however, absolute
51
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changes were slight. In general, salinities inside the beds were very similar to
outside. Salinities in the mesocosm experiment were intermediate between the
two field sites at 14 to 15 psu.
Water Quality Constituents
Chlorophyll a, Total Suspended Solids, and Light Attenuation
Previous research suggests that suspended particles should be, for the most
part, baffled out by the SAV canopy structure as water velocities are reduced.
Similarly, with fewer particles in the water column, light attenuation should
decrease. However, this was not always the case at both of the study sites, and it
suggests that particle concentrations and light attenuation levels result from a
complex interaction of dissolved and particulate levels in adjacent waters, and
settlement and resuspension of material within the bed. In comparing the two
field sites the general conclusions were that suspended particles were higher in
the bed than out at Havre de Grace and lower in than out at Goodwin Island.
This difference can be explained in large part as a difference in the dynamic
balance between source, deposition and resuspension of particles in the
vegetated shallows.
In the Susquehanna region large quantities of suspended sediments and
other seston are carried into the region by the river flow. This material is
deposited in the shallows, including the vegetated areas, where currents are
reduced and is therefore available for resuspension throughout much of the
growing season. Additionally, much of this fine particle load is deposited on the
canopy-forming leaves of H. verticillata and M. spicatum where, along with
carbonates it is easily resuspended. The channel areas are deeper and more
sandy, and therefore resuspension is less.
In contrast, at Goodwin Island in the lower bay, suspended particle loads
were lower in the bed than out during June, October and April. Sediments here
are sandy in comparison to the Susquehanna Flats area, and there is no large
source of suspended material. Carbonate formation on strap-like leaves was also
low. Therefore resuspension of deposits of fine material was less. During August,
however, when the bed contained an abundance of detrital material, apparent
resuspension of benthic and epiphytic material resulted in generally higher levels
of suspended particles in the bed than out.
From the standpoint of water quality monitoring we can conclude that
measures of suspended particles obtained from channel areas do not reflect the
actual particle loads, and potentially light attenuation within the SAV community.
In some areas or at certain times of the year, particle concentrations may be
higher, at other times or in other areas they may be lower. Therefore SAV models
which rely on empirical measurements of light attenuation from channel areas
need to be modified to account for these potential differences.
52
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In contrast to the field studies, resuspension in the mesocosm experiment
was negligible. However the study did demonstrate that under high levels of
dissolved nutrient enrichment, phytoplankton blooms can markedly decrease
light available to the macrophytes. In natural settings the SAV beds may either
decrease these concentrations (Goodwin Island) or trap and resuspend these
particles (Havre de Grace).
Dissolved oxygen and pH
Dissolved oxygen and pH measurements demonstrated greater diel ranges
in the SAV beds compared to out, reflecting the greater metabolic activity per
volume in the shallows compared to the channel. These greater ranges can have
potentially important implications for the SAV communities themselves. For
example, lower pH in the beds, as observed in the upper bay, can result in greater
carbonate deposition on leaves which, in turn, can reduce light availability.
Varying D.O. levels can affect sediment geochemistry with resultant effect on
nutrients, sulfides and other sediment constituents. Low D.O. levels can affect
the macrophytes themselves by increasing sediment oxygen demand, as well as
affect benthic and epibenthic organisms which play an integral role in system
stability. Seasonally, D.O. levels reached highest levels in the spring when
macrophyte photosynthesis rrespiration ratios are greatest, and lowest in the late
summer when temperatures are high and microbial activity is greatest.
Among the two sites, D.O. levels reached lower concentrations in the
lower bay site than in the upper bay study area, suggesting that heterotrophic
activity was greater there. Short term changes in pH were more buffered in the
lower bay than upper bay and less evident in the bed than out. Rain events
markedly decreased pH for short periods of time in the upper bay channel water,
however these spikes were rapidly attenuated within the bed.
Nutrients
Inorganic nitrogen demonstrated distinct differences in both
concentrations and dominant nitrogen species at the two field sites. Results from
the mesocosm study suggest that in the fall, at least, the mode of nitrogen delivery
can have important implications on macrophyte community response.
In the lower bay Goodwin Island area, the principal nitrogen species
during all study periods, except for April, was ammonium. This is sometimes
referred to as "old" or regenerated nitrogen as compared to nitrate or "new"
nitrogen whose primary source is the watershed. Considering that this site is near
the mouth of the bay, and farthest removed from river inputs the dominance of
ammonium observed is not surprising and has been well documented. Only
during April when riverine inputs were highest of all the study periods was nitrate
the dominant species. At the upper bay site 90% of the nitrogen was in the form
53
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of nitrate. Again, located close to the principal freshwater source of the bay one
would expect most nitrogen to be as "new" nitrate.
Uptake of dissolved inorganic nitrogen (DIN) was observed at both sites
during periods when macrophyte abundance was high. In the upper bay this was
in August, while in the lower bay in was in April and June. During periods of
highest water temperatures and therefore increased microbial activity,
regeneration of ammonium was observed in both S AV beds. Net uptake of nitrate
in the spring was replaced by net regeneration of ammonium in the summer at
Goodwin, while both uptake of nitrate and regeneration of ammonium were
observed at Havre de Grace at this time. Rapid uptake of DIN by the macrophyte
community reduces the pool of nutrients available for phytoplankton growth.
This may be especially important in the lower bay where nitrogen levels are
lower. In areas of transitional water quality, the existence of large established
beds of S AV may improve local conditions for their continued survival during
years of high runoff. Small isolated patches may be overwhelmed. In the upper
bay site DIN is in excess abundance and is apparently not limiting to epiphyte,
phytoplankton or macrophyte growth.
The ability of SAV community to reduce nutrient concentrations was very
evident in the mesocosm study where pulses of nutrients were rapidly removed,
and despite relatively high levels of nutrient inputs, concentrations in the
continuous dosing treatments were comparable to the controls. Much of the
nitrogen was taken up by the algal components of the system, with a resultant
negative effect on the macrophytes. At some point the macrophytes will become
overwhelmed and the system will shift to an algal community. Dissolved nitrogen
administered in a continuous mode had the most negative effect on the
macrophytes. This reinforces the importance of reducing the overall standing
stocks of DIN in bay waters for SAV, and especially in controlling long term
continuous sources such at waste water treatment plants.
Orthophosphate levels were well buffered and apparently not limiting in
the lower bay, but were very low in the upper bay site. Thus the ability of SAV in
the Susquehanna Flats region to sustain themselves despite very high DIN is
likely due to the low orthophosphate levels. Maintenance of existing SAV and
recovery to other areas in this region is related, in part, to controls of
anthropogenic sources of orthophosphate. Given the high ambient levels of DIN
in this region, the results of the mesocosm experiment suggest that any increase in
orthophosphate should have a deleterious effect on SAV.
Water Quality Monitoring
Given the negative effects of continuous dosing of inorganic nutrients on
SAV we observed in the mesocosm experiment, the importance of monitoring
inorganic nutrient concentrations over the long term as a measure of stress to
SAV is underscored. Organic, particulate nitrogen and phosphorus were not
54
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directly linked to SAV decline during the fall study period, however the
remineralization of this material and its impact on SAV, especially during the
summer are likely to be important. SAV beds similar to Goodwin Island are
effective traps for phytoplankton and other particulate material during the spring,
and secondary effects of microbial decomposition during high water temperatures
can contribute to SAV declines, or shorter growing seasons. When combined
with other stresses, such as reduced light availability, these annual diebacks may
become permanent.
Although biweekly to monthly sampling does not capture the diel, tidal
and other pulses or variability in water column constituents which we observed
in these studies, they do provide a reasonable characterization of water quality
levels in these areas. If elevated short-term pulses are important in reducing long-
term SAV survival they will not be effectively measured by this sampling
schedule. Daily variability may exceed seasonal variability for most parameters
measured, however the median levels of these constituents are near the lower
levels observed, and the high pulses are short lived. Thus only infrequently will
the pulses be measured in the biweekly sampling. Many times these pulses will
occur at night or during storm events and they will not be sampled with
infrequent, point sampling. However, the monitoring will likely capture the'
median conditions. In both areas studied here growing season medians were
below the SAV habitat requirement set for each area. Thus, they correctly
predicted that these areas should be suitable for SAV growth.
Records of seasonal, short term, site-specific variability such as those
investigated here are also important. Not only do they provide a more integrative
view of SAV-water quality relationships, and processes relating the two, but they
provide a test of the effectiveness of the more spatially distributed, infrequent
data.
Except in areas where groundwater or local upland runoff is high, mid-
channel nutrient concentrations are useful to characterize the long term inputs or
stresses to the macrophyte, or potential macrophyte areas. Where SAV occur,
concentrations inside the beds can be quite different than outside. These
differences reflect the net effect of the SAV bed community on the particular
water quality constituent. As the mesocosm and field studies demonstrate, rapid
uptake and release of inorganic nutrients can occur by the SAV, algal, ,
heterotrophic and microbial components of the system. Therefore, nutrient
concentrations outside the bed better reflect long term system impacts to SAV
areas than concentrations measured within large SAV meadows, especially where
water residence time is high. In areas where SAV beds are small and scattered, or
where water velocities are high and residence time is short, concentrations of
nutrients within the beds will more reflect channel concentrations.
Other important variables including suspended particle load and light
attenuation can also be quite different in and out of existing beds. However,
55
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since the macrophyte communities are integrating the light available to them, not
the light available outside of the bed, measurements should be made over the
vegetated areas. In shallow water areas this water column attenuation may be
more or less than attenuation in the channel. In sparsely vegetated areas
differences between channel and shallows may be less than in areas with
extensive vegetation. Estimates of these differences are needed if models relating
water quality to SAV are to be accurate. In certain areas, such as regions of
marginal water quality in the lower bay, persistence of vegetation is likely related
to the capacity of the vegetation to improve water clarity. The timing, duration
and intensity of seasonal pulses of higher turbidity water are also important for
long term SAV survival. In canopy forming species such as found at Havre de
Grace, survival may be linked to spring shoot elongation up to the water surface
where water column turbidity is less of a factor. This capacity is not only affected
by conditions during the spring, but to reserves stored from the previous year's
growth. Thus, there may be a time lag between limiting conditions and SAV
survival. In the lower bay limiting conditions earlier in the year may be reducing
survival during the summer. Natural year-to-year variability in SAV may also be
not only related to annual differences in water quality, but to the normal
interrelationships between SAV and bay waters.
56
-------
LITERATURE CITED
Batiuk, R.A., RJ. Orth, K.A. Moore, W.C. Dennison, J.C. Stevenson, L.
Staver, V. Carter, N. Rybicki, R.E. Hickman, S. Kollar, S. Bieber, P. Heasley,
and P. Bergstrom. 1992. Chesapeake Bay Submerged Aquatic Vegetation
Habitat Requirements and Restoration Goals: A Technical Synthesis. US
EPA, Chesapeake Bay Program, Annapolis, MD. 186 p.
Bayley, S., V.D. Stotts, P.P. Springer, and J. Steenis. 1978. Changes in submerged
aquatic macrophyte populations at the head of the Chesapeake Bay, 1958-
1974. Estuaries 1:171-182.
Burkholder, J.M., K.M. Mason, and H.B. Glasgow, Jr. 1992.
Water-column nitrate enrichment promotes decline of eelgrass Zostera
marina: evidence from seasonal mesocosm experiments. Marine Ecology
Progress Series 81:163-178.
Carter, V., N.B. Rybicki, J.M. Landwehr, and M. Turtora. 1994.
Role of weather and water quality in population dynamics of submersed
macrophytes in the tidal Potomac River. Estuaries 17:417-426.
Dennison, W.C., RJ. Orth, K.A. Moore, J.C. Stevenson, V. Carter, S. Kollar, P.
Bergstrom, and R. Batiuk. 1993. Assessing water quality with submersed
aquatic vegetation-habitat requirements as barometers of Chesapeake
Bay health. Bioscience 43:86-94.
Funderburk, S.L., S.J. Jordan, J.A. Mihursky, and D. Riley. 1992.
Habitat Requirements for Chesapeake Bay Living Resources; Second
Edition. Living Resources Subcommittee, Chesapeake Bay Program,
Annapolis, MD.
Goldsborough, W.J. and W.M. Kemp. 1988. Light responses of a submersed
macrophyte: implications for survival in turbid tidal waters. Ecology
69(6): 1775-1786.
Heasly, P., S. Pultz, and R. Batiuk. 1989. Cheasapeake Bay Basin Monitoring
Program Atlas. UBP/TRS 35/89. U.S. Environmental
Protection Agency, Annapolis, MD.
Hutchinson, S.E. and F.H. Sklar. 1993. Lunar periods as grouping variables for
temporally fixed sampling regimes in a tidally dominated estuary. Estuaries
16(4): 789-798.
57
-------
Kemp, W.M., W.R. Boynton, R.R. Twilley, J.C. Stevenson, and L.G. Ward. 1984.
Influences of submersed vascular plants on ecological processes in upper
Chesapeake Bay, pp. 367-394. In V.S. Kennedy (ed.) The Estuary As A
Filter. Academic Press, N.Y.
Kemp, W.M., W.R. Boynton, J.C. Stevenson, R.W. Twilley, and J.C. Means. 1983.
The decline of submerged vascular plants in upper Chesapeake Bay:
summary of results concerning possible causes. Marine Technology
Society Journal 17:78-89. (UMCEES Contrib. No. 1406).
Lee, V. and S. Olsen. 1985. Eutrophication and management initiatives for the
control of nutrient inputs to Rhode Island coastal lagoons. Estuaries
8(2B): 191-202.
Moore, K.A. 1992. Regional SAV Study Area Findings, Chapter 5. In Batiuk et
al. Chesapeake Bay Submerged Aquatic Vegetation Habitat Requirements
and Restoration Targets: A Technical Synthesis. US EPA, Chesapeake
Bay Program, Annapolis, MD.
Moore, K.A. and J.L. Goodman. 1993. Daily variability in the measurement of
light attenuation using scalar (spherical) and downwelling quantum
sensors. In L.J. Morris and D.A. Tomasko (eds) Proceedings and
Conclusions of Workshops on Submersed Aquatic Vegetation Initiative
and Photosynthetically Active Radiation.
Moore, K.A., R.J. Orth, and J.F. Nowak. 1993. Environmental regulation of seed
germination in Zostera marina L. (eelgrass) in Chesapeake Bay: effects of
light, oxygen and sediment burial. Aquatic Botany 45:79-91.
Neckles, H.A. 1990. Relative effects of nutrient enrichment and grazing on
epiphyton-macrophyte (Zostera marina L.) dynamics. 1990. PhD
Dissertation, College of William and Mary, Va Institute of Marine Science.
Neundorfer, J.A. and W.M. Kemp. 1993. Nitrogen versus phosphorus
enrichment of brackish waters: Responses of the submersed plant
Potamogeton perfoliatus and its associated algal community. Marine
Ecology Progress Series 94(1): 71-82.
Orth, R.J. and K.A. Moore. 1983. Chesapeake Bay: An unprecedented decline
in submerged aquatic vegetation. Science 222:51-53.
Orth, R.J. and K.A. Moore. 1988. Distribution of Zostera marina L. andRuppia
maritima L. sensu lato along depth gradients in the lower Chesapeake
Bay, USA. Aquatic Botany 32:291-305.
58
-------
Orth, R.J., J.F. Nowak, G.F. Anderson, and J.R. Whiting. 1992. Distribution of
submersed aquatic vegetation in the Chesapeake Bay and tributaries and
Chincoteague Bay. Final Report submitted to EPA, Chesapeake Bay
Program Office.
Parsons, T.R., Y. Maita, and C.M. Lalli. 1984. A Manual of Chemical and
Biological Methods for Seawater Analysis. Pergamon Press, Oxford, UK.
173 p.
Phillips, G.L., D. Eminson, B. Moss. 1978. A mechanism to account for
macrophyte decline in progressively eutrophicated freshwaters. Aquatic
Botany. 4:103-126.
Posey, M.H., C. Wigand, and J.C. Stevenson. 1993. Effects of an introduced
plant, Hydrilla verticillata on benthic communities in Upper Chesapeake
Bay. Estuarine. Coastal and Shelf Science 37:539-555.
Sanford, L.P. and W.C. Boicourt. 1990. Wind forced salt intrusion into a
tributary estuary. Journal of Geophysical Research 95: 13357-13371.
Serafy, I.E., Harrell, R.M., and Stevenson, J.C. 1988. Quantitative sampling of
small fishes in dense vegetation: Design and field testing of portable
"pop-nets". Journal of Applied Ichthyology 4:149-157.
Seufzer, WJ. 1994. Measurement of in situ eelgrass community metabolism in
standing and flowing waters; methods and models. M.A. Thesis, The
College of William and Mary, Gloucester Point, Virginia. 100 pp.
Shepherd, S.A., AJ. McComb, D.A. Bulthuis, V. Neverauskas, AJ. Steffensen, and
R. West. 1989. Decline of seagrasses, pp. 346-393. In A.W.D. Larkum,
AJ. McComb, and S.A. Shepherd (eds.) Biology of Seagrasses. Elsevier,
Amsterdam.
Shoaf, W.T. and B.W. Lium. 1976. Improved extraction of chlorophyll a and b
from algae using dimethyl sulfoxide. Limnology and Oceanography
21:926-928.
Staver, L.W. 1986. Competitive interactions of submersed aquatic vegetation
under varying nutrient and salinity conditions. M.S. Thesis, University of
Maryland, College Park, MD. 58p.
Staver, L.W. and J.C. Stevenson, 1994. The impacts of the exotic species Hydrilla
verticillata on the shallows in Chesapeake Bay. Chesapeake Research
Consortium, Solomons, MD.
59
-------
Stevenson, J.C. and N. Confer. 1978. Summary of Available Information on
Chesapeake Bay Submerged Vegetation. U.S. Dept. Interior, Fish and
Wildlife Service, Biological Services Program (FWS/OBS-78/66) 335p.
Stevenson, J.C. 1988. Comparative ecology of submersed grass beds in
freshwater, estuarine, and marine environments. Limnology and
Oceanography 33: 867-887.
Stevenson, J.C., L.W. Staver, and K.W. Staver. 1993. Water quality associated
with survival of submersed aquatic vegetation along an estuarine gradient.
Estuaries 16(2):346-361.
Swingle, H.S. 1947. Experiments on pond fertilization. Alabama Experiment
Station Bulletin 264:34.
Twilley, R.R., W.M. Kemp, K.W. Staver, J.C. Stevenson, W.R. Boynton. 1985.
Nutrient enrichment of estuarine submersed vascular plant communities.
Algal growth and effects on production of plants and associated
communities. Marine Ecology Progress Series 23:179-191.
Valiela, I., and J.E. Costa. 1988. Eutrophication of Buttermilk Bay, a Cape Cod
coastal embayment: concentration of nutrients and watershed budgets.
Environmental Management 12: 539-553.
Ward, L.G., W.M. Kemp, and W.R. Boynton. 1984. The influence of waves and
seagrass communities on suspended particulates in an estuarine
environment. Marine Geology 59:85-103.
Wetzel, R.L., and H.A. Neckles. 1986. A model ofZostera marina L.
photosynthesis and growth: Simulated effects of selected
physical-chemical variables and biological interactions. Aquatic Botany
26:307-323.
Wigand, C and J.C. Stevenson. 1994. The presence and possible ecological
significance of mycorrhizae of the submersed macrophyte, Vallisneria
americana. Estuaries 17:206-215.
Zar, J.H. 1984. Biostatistical Analysis (second edition). Prentice-Hall, Inc.
60
-------
Appendix A
-------
A1: Percent cover by species and depth profile along sampling station transect.
June 16,1993.
1
O
0)
o
CD
CL
100 -
80 -
60 -
40 -
20 -
0
0
-20-
-30 -
-40-
-50 -
-60-
-70 -
S -80H
-90
o
0
I I R maritime
Z. marina
100
STA1
200
300
STA2
400
500 600
STA3
100 200 300 400
Distance (m)
500
600
-------
A2: Percent cover by species and depth profile along sampling station transect.
August 10,1993.
100 -i
CD
_Q
If
Q
tL
CD
Q
0
-20 -,
-30 -
-40 -
-50 -
-60 -
-70 -
-80 -
-90
R. maritime
Z marina
STA1
STA2
100 200 300 400
Distance (m)
500
600
-------
A3: Percent cover by species and depth profile along sampling station transect.
Octobers, 1993.
100 -,
-20 -
-30-
^ -40 -
JD
CD -50 -
.Q
o
-60 -
-70 -
•.
-------
CD
O
O
*-*
CD
O
CD
Q_
A4: Percent cover by species and depth profile along sampling station transect.
April 18,1994.
R. maritime
Z. marina
0
500 600
$
:j
"5
«_.
£
O
0
CD
F
^
^•4
ti
CD
Q
-20 -i STA 1 STA 2 STA 3
-30 -
-40 -
-50 -
-60 -
-70 -
-80 -
.on -
;**\ A . '•••\
/ ;•• A •/••.• * \.
1 • *• / * •• •
VV.A ,
1A .
• • /
• ••
\ ••*
v/*
•
0 100 200 300 400 500 600
Distance (m)
-------
A5: Aboveground SAV biomass by species at Goodwin Island, VA study site. Values
are means of 10 replicates sampled in vicinity of stations 1 and 2.
300 -,
250 -
CM
200
CO
o
in
c
3
p
100 -
50-
0
K%g| Z. marina
ES3 f?. maritima
May Jun Jul Aug Sep Oct Nov Feb Apr
-------
A6: Belowground SAV biomass by species at Goodwin Island, VA study site. Values
are means of 10 replicates sampled in vicinity of stations 1 and 2.
200 -,
C\J
'e 150 -
I
CO
CO
CO
110°
1
!
1 50 -
0
Z. marina
R. maritima
May Jun Jul Aug Sep Oct Nov Feb Apr
-------
A7: SAV density by species at Goodwin Island, VA study site. Values are means
of 10 replicates sampled in vicinity of stations 1 and 2.
800 -!
600 -
I
QC
CM
E 400 -
o
o
.c
CO
200 -
0
\
I
I
I
i
i
Ruppia maritima
Zostera marina
T
I
I
- 250
- 200
- 150
CM
o
100 1
CO
- 50
May Jun Jul Aug Sep Oct Nov Feb Apr
0
-------
A8: Canopy height at Goodwin Island, VA study site. Values are means (+se)
of 10 replicates sampled in vicinity of stations 1 and 2.
40 -,
g>
'CD
I
o
c
CO
O
c
co
May Jun
Sep Oct
1993-94
-------
A9: Leaf Tissue specific mass of attached epiphytes at Goodwin Island, VA study site.
Values are means (+se) of 10 replicates sampled in vicinity of stations 1 and 2.
(gdm=grams dry mass)
HH Z marina
ESE3 R. maritima
June
August November
1993-94
April
-------
A10: Six minute, vector averaged wind speed at Gloucester
Point meteorological station.
15 -i
10 -
0
15 -i
10 -
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
June
'en 5 -
TT °
-------
A11: Integrated six-minute, vector-averaged (a.) wind direction and (b.)velocity
at Gloucester Point meteorological station, June 7-17,1993.
a.
WSW-i
0 24 6 8 10 12 14 16 18 20 22 24
b.
5.0 -n
4.5-
V 4.0-1
o
-------
A12: Integrated six-minute, vector-averaged (a.) wind direction and (b.) velocity
at Gloucester Point, Va. meteorological station, August 9-19,1993.
NW
W-
co sw-
(II
w
cc
a.
a SEJ
o SE-
HE I
r i ^ i ^ i T r • i T 1 • \ ^ 1
0 2 4 6 8 10 12 14 16 18 20 22 24
5 -
4 -
b.
O
CD
(0
1 -
0 2 4 6 8 10 12 14 16 18 20 22 24
HOUR (EST)
-------
A13: Integrated six-minute, vector-averaged (a.) wind direction and (b.) velocity
at Gloucester Point, Va. meteorological station, October 4-14,1993.
a.
CO
HI
LLJ
DC
O
LU
Q
E -
NE -
N -
NW-
W-
SW-
S-
SE
6 8 10 12 14 16 18 20 22 24
3.0n
8 10 12 14 16 18 20 22 24
HOUR (EST)
-------
A14: Integrated six-minute, vector-averaged (a.) wind direction and (b.) velocity
at Gloucester Point, Va. meteorological station, April 11-21,1994.
a.
NW
co
LLJ
LU
CC
S
Q
0 2 4 68 10 12 14 16 18 20 22 24
UULM
8 10 12 14 16 18 20 22 24
HOUR (EST)
-------
A15 : 15-minute relative tidal depths at Goodwin Island, VA.
1
.c
*J
Q.
DC
1.0-
0.5-
On
.u
-0.5-
-1 O
1.0 -i
0.5 .-
00 -
\J • V/
-0.5 -
-1 0
$
1.0 -,
0.5 -
0 0
-0.5 -
-1 0
4
1.0 -i
0.5 -
0 0
-0.5 -
-1 O
1
•
• **•£•£«•••« f* fl
:::„•::::•.:;::.••.: •..- r • •
tr»«trT»Tv-
i i i i i i
7 8 9 10 11 i2 13
June
v\AAAAAAA*ft*
• •»••••
i i i i i i
) 10 11 12 13 14 15
August
£ £ . .
**••**•*•* •»
• ••••* M <»•••••*•»•••••
• ••• •<• •» • ^ •••• ••••••
- T • • T -
i i i i i i
t 5 6 7 8 9 10
October
A A
» A A A A A A A A A A A
if \l\»\J\i \l\j \l\j \j\J V
™ Vy^'V ""V VV
i i i i i i
1 12 13 14 15 16 17
f\ n, A & . a
^ ••••• •• •• •• • •
• • • " ** ** *r t
i i i i
14 15 16 17
= ?. & s A A ?
•• •• •• •• •• *• ••
i i i i
16 17 18 19
£ n £ A£.
A? if \:\ H H A
/ tf tf 9 U W V I
•
i i i i
11 12 13 14
. ^ A
A A A AAAA
'VVVV V v\
^^ ^^ ^ ^ w
1 1 1 1
18 19 20 21
April
-------
A16 : 15-minute water temperatures at Goodwin Island, VA. June 1993.
35 n
30
25
20
o
V
o
35
30
£ 20
£
(0
35 -i
30-
25 -
20
Station 1
Station 3
I I I I I I I 1
Station 4
6 7 8 9 10 11 12 13 14 15 16 17 18
June 1993
-------
A17: 15-minute water temperatures at Goodwin Island, VA. August 1993.
0)
a
35 -
30 -
25 -
20
35 -,
O 30 -
o
25 -
20
35 n
-------
A18 : 15-minute water temperatures at Goodwin Island, VA. October 1993.
25 -i
20 -
15
Station 2
i r
i r
8
3
•»-•
CO
8. 20
I
I 15
25 n
20 -
Station 3
15
Station 4
4 5 6 7 8 9 10 11 12 13 14 15
October 1993
-------
A19: 15-minute water temperatures at Goodwin Island, VA. April 1994.
25 H
20 -
15 -
10 -
0
Station 1
O
2
3
0>
a
a>
a>
IS
25
20
15
10
5
0
25
20
15
10
5
0
Station 2
Station 3
i r
25 H
20
15 -
10 -
5 -
0
Station 4
11 12 13 14 15 16 17 18 19 20 21
April 1994
-------
A20 : 15-minute salinities at Goodwin Island, VA. June 1993.
18 -i
16 -
14 -
12
Station 1
F I I
I I I
18 -
16 -
.5 14-1
ca
CO
12
Station 3
T r i i i
18 -i
16 -
14 -
12
Station 4
i r
6 7 8 9 10 11 12 13 14 15 16 17 18
June 1993
-------
A21 : 15-minute salinities at Goodwin Island, VA. August 1993.
22 -,
20 -
18 -
16
Station 1
22 -,
20 -
, _
18 -
Station 2
i r
20 -
18 -
16
Station 3
22 H
20 -
18 -
16
Station 4
i i i i i i i i i i i
9 10 11 12 13 14 15 16 17 18 19 20
August 1993
-------
A22 : 15-minute salinities at Goodwin Island, VA. October 1993.
25 -i
24 -
23 -
22
Station 2
25 -
CO
24 H
.E 23 -
(0
(0
22
i r
Station 3
25 n
24 -
23 -
22
Station 4
4 5 6 7 8 9 10 11 12 13 14 15
October 1993
-------
A23 : 15-minute salinities at Goodwin Island, VA. April 1994.
16 -i
14 -
12 -
10
Station 2
T T
i r
^ 16 n
3
12 -I
(0
CO
10
Station 3
16 -i
14 -
12 -
10
Station 4
11 12 13 14 15 16 17 18 19 20 21
April 1994
-------
A24 : 3-hour total suspended solid (TSS) concentrations at
Goodwin Island, VA. June 1993.
r-
II
0)
to
0)
20 -
15 :
10 :
5 :
0 -
20 -
15 -
_
10 -
-
5 -
0 :
Station i
• ••
v. /^ y^^/^'UxV^^^Nu
*r •*• Hi
Station 2
J
? I
A /%0. • ]
•M» \ AjL- m t* V* **»f*£\l •ttuiv.
** * ^s%*^^*^»** •
1111111111
20-i
15 :
10 :
5 :
o :
20 -j
15 :
10 -
5 :
n -
I . Station 3 . •
.k -h. ru\.
•v% v*./w.«^» W V**- yV*
•
i i i i i i i i i i
Station 4
• • •
• « %f As A\/M /\^
*%/*"• V'W'vV^AJ \/>« * *"H •""
8 9 10 11 12 13 14 15 16 17
June 1993
-------
A25 : 3-hour total suspended solid (TSS) concentrations
at Goodwin Island, VA. August 1993
r—
O)
0)
H
30 -
20 -
10-
0_
30 -
20 -
10 -
0_
n
30 -i
20 -
10 -
n
30 -,
20 -
10 -
n -
Station 1
fl
--. Ar vn A 'I
1 1 II 1 1 1 1 1 1
Station 2 i
• ^^w w~
Station 3
^^vA*^ . -V ^ AV
i i n i r i i i i i
Station 4
^--H^V^^^V^-X^
9 10 11 12 13 14 15 16 17 18 19
August 1993
-------
A26 : 3-hour total suspended solid (TSS) concentrations
at Goodwin Island, VA. October 1993.
.^
1
mmm
O)
£,
0)
l~
25 -
20 =
15 -
10 =
5 :
n
bianon i
jiflMjhrf •/-
v i i i i i i
25 -, Station 2
20 =
15 -
—
10 -
5 -
0 H
A
• \
A J % . R
*V'W^^» *!%HMI> "XJ «y
1 1 1 1 1 1
25 -j Station 3
20 :
15 :
10 -
5 :
0 -
< «w^ r\ r* y\
/ %v*/%**«* •• \ ** \
•^T^MB ^MW^
I I I i I I
25 n Station 4
20 -
15 =
10 '-
-
n I
, A«Av «A^
* *V* • * **^» « ^» V.,,
till
•
A«
f ' -infjn^
^^^^r~
III!
|^»
III!
f, Vv^ ;
•**P
7 8 9 10 11 12 13 14
October 1993
-------
A27 : 3-hour total suspended solid (TSS) concentrations
at Goodwin Island, VA. April 1994.
^
1
C5)
,§
C/>
(0
1-
"•
10 -
8 :
6 :
4 :
2 =
0 =
btanon i
• tl \ K
••* 1/V /V n-i %A/\^
* 0»
10 n Station 2
8 -
6 -
4 :
2 -
0 -
T «T
V\ -u A /
/\ • • r» II / I
V\. V»"*^ .; llfl L
i i i i i i i i i i
10D Stations
8 -
6 -
4 :
2 -
n I
• •
• f. • A A
*** \f\ /*• \« / •* .* •* r\ ••*/«/\/
• •* * *• *•* w*W •***•* * * *
u i i i i i i i i i i i
Station 4
8 :
6 -
4 :
2 -
n ~
• 7 **
• A A 1 \
*«f*V>/» ,/V |1J\ / *\« • **\ Art
• * • v\J •• *\ SAIL/ vV %
• •/ V * * * • • •
• • • M
11 12 13 14 15 16 17 18 19 20 21
April 1994
-------
A28 : 3-hour chlorophyll a at Goodwin Island, VA. June 1993.
^^
p~
O)
3
0
50 -
40 -
30 -
20-
10 -
0 -
Station 1
• •.
•* •*«"^»V/i** ****** -j^V*-*'-**"/""""^
^^ ^i*"*
i i i i i i i i i i
50 n Station 2
40 -
30 -
20 :
10 -
0 -
50 n
40 :
30 :
20 :
10 :
0 :
«• n
*/* *• /* • *tl •*"**SS • •
*• *w\»*^" «**•/••••. /•• ^*V *•*•*•%
^
i i i i i i i i i i
Station 3
• * /***\/* > • * • -• *^ A
***• % »•• *•* *v v 'VMM *d>x*^fixit
(^l»
1 1 1 II 1 1 1 1 1
50 l Station 4
40 -
_
30 -
_
20 -
10 :
n I
fl
• • .*. 7^/1
^ 0V \ ^^* ^i*\i i A ^^^^^Mii^^^ W^ fl^te
^* ^ ^^^_^ ^w^~^ ^^* * A ^ i ^^^
~* ^^ *^ ^m^^^^^ ^^ ^^ ^^ ^*_
• «%
8
10 11 12 13 14 15 16 17
June 1993
-------
A29 : 3-hour chlorophyll a concentrations at Goodwin Island, VA. August 1993.
O)
3
o
50 -
40 :
30 :
20 =
10 -
0 -
50 H
40 -
30 "
20 =
10 -
0 -
50 -,
40 -
30 -
20 -
10 :
0 -
50 n
40 :
30 -
20 -
10 -
n I
station 1 •
I
.A .A 1 .
V-^X'V.' %.*^A^sV.i •*••*/••
Station 2
*
1 5
"VA.A /x....* AW^-
i i i i i i i i i i
Station 3
-.•X^^x^,X^^.^^
Station 4
• . ,
^^^^«^^^
10 11 12 13 14 15 16 17 18 19
August 1993
-------
A30 : 3-hour chlorophyll a concentrations at Goodwin Island, VA. October 1993.
^
r"
ro
3
(K
M»
o
40 H
30 -
20 -
10 -
40 -
30 -
20 -
•1 O
lU -
40 n
30 -
20 -
10 -
n
40 •-.
30 "
20 -
10 -
n .
bianon i
A
A •*• -%. ^
i i i i i i i i * i
Station 2
•
Station 3
•V *
/ * \
•f\f \/ • x;w Wip
Station 4
•»/*•
V^/* \ ••*/!..
V^* % v^- -X-K.
7 8 9 10 11 12 13 14
October 1993
-------
A31 : 3-hour chlorophyll a concentrations at Goodwin Island, VA. April 1994.
r-
i
O>
7T
o
80 -
60 -
40 -
20 -
0 :
80 n
60 -
40 -
20 -
0 -
80 n
60 -
40 -
20 -
0 -
station i
wA ... ju^jij\.
• «• • •• 0
Station 2
vrt* \ A •)!•••
xV^-jv/^7VV*v Wxr
i i i i it i ii i
Station 3
•£/*\j\ • ^ •> • A/W
V'^XA' ii*V7 """^V** •»
i i i i i i i i i i
Station 4
60 -
_
40 -
20 -
n
•
A •
•• A* /I •
v^» >V* •*• >* s> V/% V
11 12 13 14 15 16 17 18 19 20 21
April 1994
-------
A32: 15-minute integrated light attenuation (-K,,) at Goodwin Island, VA. June 1993.
2.0 -,
1.5 -
1.0 -
0.5 -
n n
WLUIIWI 1 1
.**«•••'**'
O
2.0 -i
1.5 -
1.0 -
0.5 -
no -
Station 2
O ft O
° 9 Jl t * *
« " / 4 « % »
2.0 H
1.5 -
1.0 -
0.5 -
0.0
Stations
8
2.0 n
1.5 -
1.0 -
0.5 -
0.0
i i i
Station 4
*
789
i i i i i i i i i
10 11 12 13 14 15 16 17
June 1993
-------
A33 : 15-minute integrated light attenuation (-Kd) at Goodwin Island, VA. August 1993.
3 -i
2 _
1 -
n _
oicuiuii i
% i * l *
If* * I • *
3 -i
2 -
1 -
0
t
Station 2
8
*
3 n
2 -
1 -
0
Station 3
3 -,
2 -
1 -
0
Station 4
i i i i i i i i i i
9 10 11 12 13 14 15 16 17 18 19
August 1993
-------
A34 : 15-minute integrated light attenuation (-Kd) at Goodwin Island, VA. October 1993.
6 -,
4 -
2 -
0
Station 1
*'
/•
6 n
4 -
2 -
n
Station
i
^ V /
* * *
2
\
9
\
+ 4 «
6 -i
4 _
2 -
n
Station 3
4 %
6 -,
4 -
2 -
0
Station 4
I I I I I I I I I I I
4 5 6 7 8 9 10 11 12 13 14 15
October 1993
-------
A35 : 15-minute integrated light attenuation (-Kd) at Goodwin Island, VA. April 1994.
4 -, Station 1
3 -
2 -
1 -
0
'***«.•»
4 -i
3 -
2 -
1 -
0
o
e
Station 2
O O o
> I ;
i r
i i i i r i i
4 -,
3 -
2 -
1 -
0
Station 4
i r
April 1994
-------
A36 : 15-minute dissolved oxygen (D.O.) at Goodwin Island, VA. June 1993.
15 n
12 "
9 -
6 -
3 -
0
Station 1
O)
15
12
9
6
0
Stations
\ I I I f I I T I I
15 n
12 -
9 -
6 -
3 -
0
Station 4
6 7 8 9 10 11 12 13 14 15 16 17 18
June 1993
-------
A37 : 15-minute dissolved oxygen (D.O.) at Goodwin Island, VA. August 1993.
16 -i
12 -
8 -
4 -
0
Station 1
\ i \ \ i i i r
16 n
12 -
8 -
*•-. 4 -
I °
O
Q 16 n
12 -
8 -
4 -
0
Station 2
Station 3
16 -,
12 -
8 :
4 -
0
Station 4
I I I T
I I
I 1
10 11 12 13 14 15 16 17 18 19 20
August 1993
-------
A38 : 15-minute dissolved oxygen (D.O.) at Goodwin Island, VA. October 1993.
12 -,
9 -
6-
3 -
0
Station 2
q
ci
12 -,
3 -|
0
Station 3
12 -i
9 -
6 -
3 -
0
Station 4
T I
4 5 6 7 8 9 10 11 12 13 14 15
October 1993
-------
A39: 15-minute dissolved oxygen (D.O.) at Goodwin Island, VA. April 1994.
18 H
15 -
12 -
9 -
6 -
3 -
0
Station 2
18 n
T 15 -
O) 12 -
Q
0
Station 3
I I I I
I 1
18 n
15 :
12 -
9 -
6 -
3 -
0
Station 4
I I
I I
11 12 13 14 15 16 17 18 19 20 21
April 1994
-------
A40 : 15-minute pH measurements at Goodwin Island, VA. June 1993.
10 -,
9 -
8 -
7
Station 1
10 -
9 -
8 -
7
Station 3
10 n
9 -
8 -
I I
I I I I I T
Station 4
6 7 8 9 10 11 12 13 14 15 16 17 18
June 1993
-------
A41 : 15-minute pH measurements at Goodwin Island, VA. August 1993.
9 _,
Station 1
9 -,
8 -
Station 2
9 -i
8 -
Station 3
9 -|
8 -
i r
Station 4
9 10 11 12 13 14 15 16 17 18 19 20
August 1993
-------
A42 : 15-minute pH measurements at Goodwin Island, VA. October 1993.
9 -i
8 -
Station 2
i i i r
i i i i
9
8 -
Station 3
II I II II III
9 -,
8 -
Station 4
i r
4 5 6 7 8 9 10 11 12 13 14 15
October 1993
-------
A43 : 15-minute pH measurements at Goodwin Island, VA. April 1994.
I
Q.
10 -
9 -
8 -
7
10 -,
9 -
8 -
10 -,
9 -
8 -
7
Station 1
Station 2
Stations
10 -
9 -
8 -
Station 4
I T I I I I I I I I
11 12 13 14 15 16 17 18 19 20 21
April 1994
-------
A44 : 3-hour dissolved inorganic nitrogen (DIN) at Goodwin Island, VA. June 1993.
12 -
8 -
4 -
0 -
12 -
9 -
6 -
s 31
3 On
5 12
9 -
6 -
3 -
0 :
12 -j
9 -
6 -
3 -
n _
Station!
.. .•
••*--.*.• • M*-~*-- «..- - »•• •*•.••»• W>
^r ^» ^^r^> •* •••• • ^ ^v
i i i i i i i i i
Station 2
vJv^A^VA^v> v- *-v
1 ^n i i i i i i i i
Station 3
Ww A *V^^Avx\.i ^
Station 4j
• n .
>wx^MifV^AA^
r 0.18
- 0.12
- 0.06
- 0.00
r- 0.18
- 0.12
- 0.06
- 0.00 V^
O)
c
r\ ^ Q ^™
- 0.12
- 0.06
- 0.00
- 0.18
- 0.12
r- 0.06
- nnn
8 9 10 11 12 13 14 15 16 17
June 1993
-------
A45: 3-hour dissolved inorganic nitrogen (DIN) at Goodwin Island, VA. August 1993.
12 -
8 -
4 -
0 -
12 -,
8 -
4 -
!•}
Z
Q 12 -,
8 -
4 -
0 -
12 -,
8 -
4 -
n -
Station 1
•
*^^+^.\^'*\^\J \J* V vj *
i i i i i i i i i
Station 2
•
.•%'v^^%^^%^^\/^^A*w* -*V Vv
Station 3
*>* ww»v* * • •-• /!*• V**.
Station 4
*A"~-^JUA.-rf^^ *
r 0.18
- 0.12
- 0.06
- 0.00
r 0.18
- 0.12
- 0.06
— ^"^
- o.oo 1-
O)
r 0.18 *^'
- 0.12
- 0.06
- 0.00
r 0.18
- 0.12
- 0.06
n nn
9 10 11 12 13 14 15 16 17 18 19
August 1993
-------
A46 : 3-hour dissolved inorganic nitrogen (DIN) at Goodwin Island, VA. October 1993.
8 -
6 -
2 -
0-
8 n
6 -
4 -
£ 2 "
3 o =
z
Q 8i
6 -
4 -
2 -
0 -
8 -,
6 -
4 -
2 -
0 -
4
Station 1
. ^ Ify ^ %-Av-
*/ *^/\^^*u*/ \w\«/ •* • *•
• •• \l • 0»/ *
Station 2
T j.
Mj^JiJ^Xv **•'
Station 3
n
]^\h
- 0.08
- 0.04
- 0.00
- 0.12
- 0.08
- 0.04
- 0.00
4
October 1993
-------
A47 : 3-hour dissolved inorganic nitrogen (DIN) at Goodwin Island, VA. April 1994.
20 -
15 -
10 -
5 -
0 -
20 n
15 -
10 -
5 -
0 -
20 -,
15 -
10 -
5 -
0 -
20 -,
15 -
10 -
5 -
n _
Station 1
• *%•• \«v . * r
i i i i i i ii i
Station 2
vv ^WWivA"
1 1 1 1 1 1 1 1 1
Station 3
A • /*V «.• v. n
Vl^ • •'*•' ' • * v v
1 1 1 1 1 1 1 1 1
Station 4
/[Vv^.. v\ *••*
^^ / l 1 ^
• I
r 0.3
- 0.2
- 0.1
- 0.0
r 0.3
- 0.2
-0.1
- 0.0
r 0.3
- 0.2
- 0.1
- 0.0
r 0.3
- 0.2
- 0.1
n n
11 12 13 14
15 16 17 18 19 20 21
April 1994
0)
-------
A48 : 3-hour ammonium (NH4) at Goodwin Island, VA. June 1993.
12 -
8 -
4 -
0 -
12 -
9 -
6 -
-
5 3"
1 °3
Station 1
' "T"^ ......
Station 2
• • «u
A %, • «A •v'***\ ^ \ •*•*
^-a •.«•** ••.* *** «•*• + «••** •(•"M^X^bV^V* *
I ^n i i i i . i i i
r 0.18
- 0.12
- 0.06
- 0.00
r 0.18
- 0.12
-
- 0.06
- 0.00 T"*
<± O)
i
"Z* 12 n
9 -
6 -
-
3 -
0 :
12 H
9 -
6 -
-
3 -
n -
Stations
• A • A
•VuU .A.. A •A»«
*%l>>i"*J|^ll)i*^ * <^»*%«* •*•• i.*«^»y '
Station 4,
••!•
n A 1? ?!•
• • wv/ **• i| V *\r* >•*• A r*-
/W*"^*^V» *«O*b' • • • • \sv V«-
r 0.18 £
- 0.12
-
- 0.06
- 0.00
r 0.18
- 0.12
-
- 0.06
- nnn
8 9 10 11 12 13 14 15 16 17
June 1993
-------
A49 : 3-hour ammonium (NH4) at Goodwin Island, VA. August 1993.
12 -
8 -
4 -
0 -
12 -
8 -
4 -
12 -n
8 -
4 -
0 -
12 -|
8 -
4 -
n _
Station 1
/
•^^.^•V\AJX^V'
Station 2
f\h + • - /*. • - ***• •
Station 3
W • ^
r 0.18
-0.12
- 0.06
- 0.00
r 0.18
- 0.12
- 0.06
- 0.00 I-
O)
r 0.18 ^
- 0.12
- 0.06
- 0.00
r 0.18
- 0.12
- 0.06
nnn
10 11 12 13 14 15 16 17 18 19
August 1993
-------
A50 : 3-hour ammonium (NH4) at Goodwin Island, VA. October 1993.
8 n
6:
4 -
2 _
0 :
8 r.
6 :
4 -
£ 21
3 o =
i 8q
6 :
4 -
2 -
0 :
8 n
6 :
4 -
2 -
n -
Station 1
.
Station 2
.
. ft >*"\.v '^X.,
Station 3
* • .•
i i i i t i i i i
• Station 4
•y«
. /MI . r"' w* ' A...
• •"X / • • u./*** •
.. ",r «^ ... ,.-? . .
w. 1 C.
- 0.08
- 0.04
- 0.00
r 0.12
- 0.08
- 0.04
- 0.00 '*-
D>
r 0.12 ^
- 0.08
- 0.04
- 0.00
p 0.12
- 0.08
- 0.04
- nnn
7 8 9 10 11
October 1993
12 13 14
-------
A51 : 3-hour ammonium (NHJ at Goodwin Island, VA. April 1994.
5 -
4 -
3 :
2 ~-
0 :
5 q
4 -
3 -
2 ^
Q -
4 =
3 -
2 -
1 -
—
n
VJ
Station 1
r . /IK A r
•/*• Wl* * A /%••*"*/"*""
• • ,/ « •
111111111
Station 2
•• «•
•*\ .
^ • • \ r f& *
• * ** V* «*v"%**
i i i i i i i i i
Station 3
/\
A •**\/M^*A n *^*\ • • • 1 .*
r/"Vy * *xAv^*\; \\^J$\*lY
* " * •/ *
• •«
i i i i i i i i i
r 0.06
- 0.04
- 0.02
- 0.00
r 0.06
- 0.04
- 0.02
- 0.00
r 0.06
- 0.04
- 0.02
L 0.00
Station 4
5 q
4 -
3 -
2 -
1 -
n I
«
* *• «• * *
•' *^» *«L* \9 • *H^t
•••*^*
- 0.06
- 0.04
- 0.02
-non
11 12 13 14
15 16 17 18 19 20
April 1994
21
0)
-------
A52 : 3-hour nitrite (NO2) at Goodwin Island, VA. June 1993.
S^
CM
O
z
0
0
0
0
n
u
0
0
0
n
\j.
0.
0.
0.
0.
n
u.
0.
0.
0.
0.
.
4 -
3 :
2 -
1 -
n
u
4 n
3 -
2 -
n
4 -j
3 :
2 -
-
1 -
n
4 -j
3 -
—
2 -
1 -
-
/
Station 1
•^•4*
• w **N**\^
*•%*•"** **«*w*»V*«*v •
i i i i i i
Station 2
i\
/ • *\ ?\ *«i*^* • 1 \ • «
^i • •flwr * • •%••• &nr .
I I I I I I
Station 3
• -
•1 •*• A •* •*s*«
•* • •*T*y»«^'/ •• S» «
Station 4
• •
n »
fr. . H
/ •• \ /v • \ .
' •• / •' » A "0
1 1 1 1 1 1
r 8 9 10 11 12 13
L
•S*.
1
1
I ••
M
u
•
1
V
4
V%M
A r
••••
i 1
n
/*• •
••
* *
0
k '<
M^ %•
1 1
•
/*•
•* •
«
1
•
• •
1
5 16 1
r °
- 0
-
- 0
n
r °
- 0.
-
- 0.
- 0
r 0.
h 0.
- 0.
.
- 0.
- 0.
-
- 0.
.
7
006
004
002
000
V/v/w
006
004
002
000'
\JU\J
006
004
002
nnn
uuu
006
004
002
nnn
uuu
i— '
i
O)
June 1993
-------
A53 : 3-hour nitrite (NO2) at Goodwin Island, VA. August 1993.
0.6-
0.4 -
0.2 -
0.0 -
0.6 -,
0.4 -
-
^0.2 -
3.0.0 -
Station 1
jfyr
Station 2
V^**« f **•"*• /W^w •
• «• n_J^*_rriiri*r *V"
i i i ™r * i r
N>"*'
d*
Z 0.6 -i
0.4 -
-
0.2 -
0.0 -
0.6 -,
0.4 -
-
0.2-
00 -
Station 3
•
™r»'^ p^^«** ft*^^*if^'
Station 4
«•**- .
W «!dA*»(y»rf^V»V* L-j^V-.-.
•
j4 Vk
1 1 1
r 0.008
: 0.006
- 0.004
- 0.002
: 0.000
r 0.008
*A*/i
• * •! •
I 1 -*'l
§ AjV^^M ^^a
^* f ^ i ^"P" •
: 0.006
- 0.004
- 0-002^
- o.oool-
O)
E,
i- 0.008^
. J M
m^ &^T '
"^ r F" ^-g*tpgi
: 0.006
: 0.004
- 0.002
: 0.000
,- 0.008
J
I
..AJ/'L
- 0.006
: 0.004
- 0.002
- 0.000
10 11 12 13 14 15 16 17 18 19
August 1993
-------
A54 : 3-hour nitrite (NO2) at Goodwin Island, VA. October 1993.
1.5 -
1.0 -
-
0.5 -
0.0 -
Station 1
A/U
*t**^ li^Tiin anna i o if*^^ • ""xy^*
i i 1 ""i i*l i i i
t
1.5 -
1.0 -
£gp 0.5 -
S o.o -
Station 2
n
1. .. W
•K • •A^feftA^.^M* • •***^»
^n — i • i i i i i
r 0.025
- 0.020
- 0.015
: 0.010
- 0.005
- 0.000
r 0.025
- 0.020
- 0.015
- 0.010
- 0.005 ~
- 0.000 ra
£W ......... ^^,
OE
z
1.5 -,
1.0 -
-
05 -
V/ . W
0.0 -
Station 3
«n ..y^^j^ VaSyrrt _»«_,
| Illl/IIIIII^L ••-^••ll ,• ,— --,- , , |
1.5 -,
1.0 -
0.5 -
w
n n -
Station 4
J
^ /^^ Li
A™
*^*»*-?~
4 5 6 78 9 10 11 12 13 1
r 0.025 ^
- 0.020
-0.015
- 0.010
_
- 0.005
- 0.000
- 0.025
- 0.020
: 0.015
: 0.010
- 0.005
~ 0000
V/*x/\/V/
4
October 1993
-------
A55 : 3-hour nitrite (NO2) at Goodwin Island, VA. April 1994.
1.0 -
0.8 =
0.6 ~
0.4 -
0.2 -
0.0 i
1.0 n
0.8 -
0.6 :
0.4 -
^ 0.2 -
a. °'° '
Station 1
% .. .*• /\
++*••*?+! './U • *•*"•**' ***
•
i i i i i i i i i
Station 2
••% '•-•f**A/*» /V^^V^/** V*./**
• '^ • *•* • * *
i i i i i i i i i
r 0.015
- 0.010
- 0.005
- 0.000
r 0.015
- 0.010
- 0.005
_
- o.ooo *r*
CM O)
§ LO n
0.8 -
0.6 :
0.4 -
0.2 -
0.0 -
1.0 n
0.8 -
0.6 :
0.4 -
0.2 ~
n n I
Station 3
vw •
v/\ % . ^. 0 •*,IM»**% •*«••• •• r^*
• *
i i i ii i i i i
Station 4
_ ^ •••JMU V,**"^1**
^ «%<^VV"V •
^v*»
r 0.015 S
- 0.010
- 0.005
_
- 0.000
r 0.015
- 0.010
- 0.005
_
r- n nnn
11 12 13 14 15 16 17 18 19 20 21
April 1994
-------
A56 : 3-hour nitrate (NO3) at Goodwin Island, VA. June 1993.
1
CO
o
3 -
2 -
-
1 -
0 -
3 -i
2 -
-
1 -
0 -
.A .
«•%** *•»>>•
i -f
•
n^ f
3 -,
2 -
-
1 -
0 -
3 -,
2 -
1 -
0 -
^ •
\_^la l_1*
1 '
station i 0.04
h 0 — .—
• —— ^^^bjfiW A -••
- 0.03
- 0.02
- 0.01
: 0.00
Station 2 r 0.04
'^•^^V.d*** *• L*B^**^« d^*HI»«* «M**
- 0.03
- 0.02
- 0.01
- 0.00
Station 3
s
.'\ .
• i. .'.A* I
! l»l,wl *| •* <^ *^ .•» 1 * •
i i T T ' i • 1
Station 4
1* •
*
*• *i^
i T
\.
kr\ _^^. yv^.
*t^^^^ja(Miff^^* lM8^ A___|^^^^^^^^
"1 T "" i 1 "T" 1 I r
r 0.04
-0.03
- 0.02
- 0.01
- 0.00
- 0.04
- 0.03
- 0.02
- 0.01
- 0.00
^r-
o>
£
7 8 9 10 11 12 13 14 15 16 17
June 1993
-------
A57 : 3-hour nitrate (NO3) at Goodwin Island, VA. August 1993.
2.0 -
1.5 -
1.0 :
0.5 -
0.0 -
2.0 H
1.5 -
1.0 -
-
^0.5 -
S
3.0.0 -
Station 1
A . K
MJB M •*> _ ^****» - \*U W\ 1 m m
•^•^ \ di * ***W ^ J> ay* j* ••* • • • ' jit
1 "^ 1 1 • i * 1 1 i II
Station 2
r ^**\ *
. % • *•' * •• »*\ /x *•*
/\ • / V* * ^**««^ -* ^ «*•• «/«.••• \ • **
• «.'•• ny jjijT ^^ • «/ «•» ^b • '
^ ^^ ^^ ~^ ^F~^ n^^*^. ^.»— i— .^^j-. ^ ^KK^
i I 1 IT* •••" • 1 1 ~ 1
r 0.03
- 0.02
-
- 0.01
- 0.00
r 0.03
- 0.02
-
- 0.01
^*
- 0.00 i-
^ o>
o
2 2.0 -,
1.5 :
1.0 :
-
0.5 -
_
0.0 -
2.0 -,
1.5 -
1.0 -
0.5 -
nn "
Station 3
• ***+ _• .'••
n •*• ^ • -..•!•»
/\*» \ /^.M • ^H*M* *-/ \ •» •
' l/ 1 A *|M" A. * w*^* 0* AV • A I / i
• Q^B \™ ^^ ^ •• * ' 49 ^ ^^pi^^F X / 0
'
Station 4
•
A
• V i[
• /•*x«^ / v •X^X^V%-%AJ *\*»x *"*
^Kad1^ ••• S»-, -. . . . •
r 0.03 ^
- 0.02
-
- 0.01
- 0.00
r 0.03
- 0.02
-
- 0.01
u nnn
10 11 12 13 14 15 16 17 18
August 1993
19
-------
A58 : 3-hour nitrate (NO3) at Goodwin Island, VA. October .1993
2?
3
cT
z
4 -
Q _
O
2 -
1 -
o :
station i
\V\ .. *V.
i ^^^^^^^Jb Q ^^k & £Q ^^J^
^^J^^^^fM^^ ^^^^^^^^ A^^^^^^ft^A ^A_^^^A ^^^
i i i i ' T i i i i
r 0.06
-
- 0.04
-
- 0.02
- 0.00
4 -i Station 2 r 0.06
Q _
O
2 -
1 -
0 -
•
^
** \ «\ *\ •''•*
1 • • ,—gj *•* ••*• •
i i r i i i i i i
-
- 0.04
- 0.02
- 0.00
4 n Station 3 r 0.06
Q _
o
2 -
1 -
0 :
4 -n
q _
o
2 -
1 -
n I
• 7*» +
v«- v* \ ..J^ jf
(^Mt^^k • • ^ i^'TB • T>
1 1 II 1 1 1 1 1
Station 4
0
v-M Jl
" \ r*
"
- 0.04
-
- 0.02
- 0.00
r 0.06
~
- 0.04
- 0.02
- nnn
^
O)
e,
8 9 10 11
October 1993
12 13 14
-------
A59: 3-hour nitrate (NO^ at Goodwin Island, VA. April 1994.
^^
s
^
CO
o
z
15 -
12 -
9 :
-
3 =
n
15 H
12 -
9 -
-
3 -
n
15 -j
12 -
9 :
6 -
3 -
n
15 -,
12 -
9 :
6 -
3 -
n _
station i
•
* • 1/X >. >
J f t\ ^^ ^^_ ^ * * A
' "^ '
Station 2
•0
• ?\ M r d* M /\
l\ n A / *r\ l\ I \f\ I w
vV.* v *• ' *
i i i i i i i i i
Station 3
• . • ,**• • •«.• f\. .
• ?• /*• nfvv •• V • "\ A^"
'Wy • ; ' '
*
1 1 1 1 1 1 1 1 1
Station 4
•
4* *• 0 1 1 \/«\/ \/« / \A l***0i
• •vAi *** " *
^^^ ^fc
r °-20
- 0.15
_
- 0.10
: 0.05
- 0 00
\J»\J\J
r 0.20
- 0.15
: 0.10
_
- 0.05
o on
r 0.20
- 0.15
: 0.10
- 0.05
Onn
.uu
- 0.20
- 0.15
_
- 0.10
- 0.05
^ nnn
T^**
L.
O)
£
11 12 13 14
15 16 17 18
April 1994
19 20 21
-------
A60 : 3-hour orthophosphate (PO4) at Goodwin Island, VA. June 1993.
2.0 -
1.5 -
1.0 -
-
0.5 -
0.0 -
2.0 -i
1.5 -
1.0 -
-
0.5 -
0.0 -
Station 1
* * •
/•^M\ * /\ 4* • •» */\ *x/ \*\ ^* *^ *•
• %% • + jf*
111111111
Station 2
0»^nf»?« «fc * • • A A • /
V*** *'•• •»*'L«»-v * /W* •'•**%• •"'•••V "
• * * • ** * * • ^%** *•
1 1 1 1 1 1 1 1 1
p 0.075
- 0.050
-
- 0.025
_
- 0.000
r 0.075
- 0.050
-
- 0.025
- 0.000
-------
A61 : 3-hour orthophosphate (PO4) at Goodwin Island, VA. August 1993.
1
0*
a.
3 -
2 -
1 -
0 -
3 n
2 -
0 -
3 n
2 -
1 -
0 -
3 -,
2 -
1 -
n -
Station 1
v-A • A. A • *
Station 2
• • *\ * «•
Station 3
• > \ .-,•••.•
\ ii ii i T i i
Station 4
r 0.10
- 0.05
-0.00
r 0.10
- 0.05
- o.oo 'L
D>
r 0.10 ^
- 0.05
- 0.00
>- 0.10
- 0.05
_ nnn
9 10 11 12 13 14 15 16 17 18 19
August 1993
-------
A62 : 3-hour orthophosphate (PO4) at Goodwin Island, VA. October 1993.
_.
I
0*
0-
2 -, Station 1
-
1 -
o -
2 -i
-
1 -
0 -
2 -i
-
1 -
0 -
2 -,
1 -
0 -
A
\r. ;W*AM \ . A-V.V . fa
Station 2
•i i i i 1*1
Station 3
.
A^ >V**vww V»VV»
Station 4
n • * A
/ \ A A^ A^^ • \/ \ OT 1 ^^^^(0
A ^^ ^^ ^^ f ^^ v ^0 ^^IK j ^ £• / ^^^ i wv^ '
• * •* a — *(•* S • ^
i i T T • i I I i i
I 5 6 7 8 9 10 11 12 13 1
•- 0.075
- 0.050
- 0.025
- 0.000
r 0.075
- 0.050
- 0.025
- 0.000
r 0.075
- 0.050
- 0.025
- 0.000
r 0.075
- 0.050
- 0.025
- 0.000
4
October 1993
-------
A63 : 3-hour orthophosphate (PO4) at Goodwin Island, VA. April 1994.
1.0 -
Oo
.8 -
0.6 -
0.4 :
0.2 -
0.0 -
1.0 q
0.8 -
0.6 -
0.4 -
^ 0.2 -
^ 0.0 -
Station 1
A • •
1\ • A* V
MA 1 "* • • * • • «
•j i • *• •*• •'•* »\ A 1^9
• •_* • • • • '
i i i i ii i i r^ * **^
Station 2
• A . A .. ••»..•..
•* •
1 1 1 1 1 1 III
r 0.035
- 0.028
- 0.021
- 0.014
- 0.007
- 0.000
- 0.028
- 0.021
- 0.014
- 0.007
- 0.000 f^
X o>
o ,n
OL 1-° n
0.8 -
0.6 -
0.4 -
0.2 -
0.0 -
1.0 -i
0.8 -
0.6-
0.4 -
0.2 -
no I
• Station 3
V\ A
* \ • •» •
• »• * • •• **• \/ * » /*'*\r\ f
Station 4
.
*• .Vu A»V. A//\ /% . •
If \J8^ Al/ ^ 1^^1/\|9 /I tt
0 4^ \ 4te \ i % • A A i CL. /\ ^A
r 0.035 £
V . V H ^^^^
- 0.028
- 0.021
- 0.014
- 0.007
= 0.000
- 0.035
: 0.028
- 0.021
- 0.014
- 0.007
" n nnn
11 12 13 14
15 16 17
April 1994
18 19 20 21
-------
A64: Mean dissolved oxygen and ammonium (NH4) concentrations aggregated
over a diel cycle for stations 1 through 4 in August 1993.
August 1993
^
X*
STATION 4
STATION 3
r10
-9
8
7
- 6
- 5
- 4
- 3
2
D
O
I
STATION 2
STATION 1
0.0
i • i • i • i • i • i • i
02468 1012141618202224
O
O
CO
i • i • i • i • i • i • i T r
02468 1012141618202224
HOUR
HOUR
-------
A65 : 3-hour nitrate (NOg) and 15-minute relative tidal depth. Station 1. Goodwin Island, VA. April 1994.
0.5 i
Q.
cc
-0.5
11
Relative Depth
N03
12 13
14
15 16
17
18 19 20 21
22
eo
o
April 1994
-------
A66 : 3-hour nitrate (NO3) and 15-minute relative tidal depth. Station 2. Goodwin Island, VA. April 1994.
0.5 -,
Q.
-------
A67 : 3-hour nitrate (NO3) and 15-minute relative tidal depth. Station 3. Goodwin Island, VA. April 1994.
-Relative Depth
0.5 n
a
0)
a
a>
DC
0.0 -
-0.5
• N03
- 14
- 12
- 10
- s a
cT
-6 Z
- 4
- 2
0
11
12 13 14 15 16 17 18 19 20 21
22
April 1994
-------
A68: 3-hour nitrate(NO3) and 15-minute relative tidal depth. Station 4. Goodwin Island, VA. April 1994.
0.5 -i
a
a>
a
§ 0.0
a>
cc
-0.5
-Relative Depth
N03
- 16
- 14
- 12
- 10 £
^
Q CO
" 8 O
Z
- 6
- 4
i- 2
0
11 12 13 14 15 16 17 18 19 20 21 22
April 1994
-------
A69: Mean dissolved oxygen (DO) and orthophosphate (PO4) concentrations aggregated
over a diel cycle for stations 1 through 4 in August 1993.
August 1993
STATION 4
STATION 3
STATION 2
STATION 1
02468 1012141618202224
HOUR
02468 1012141618202224
HOUR
-------
Appendix B
-------
Appendix B1. Biomass at Havre de Grace monitoring
stations, 1993.
TJ
O)
CO
CO
O
CO
200 -q
180H
160^
140-;
120-
100^
80^
60-j
40-I
20-^
0
Hydrilla verticillata
Myriophyllum spicata
Vallisneria americana
A. aboveground biomass
Station 1 Station 2
JUNE*
Station 1 Station 2
AUGUST
Station 1 Station 2
OCTOBER
CM
TJ
O)
CO
CO
O
CO
10
9-
8-
7-
6-
5-
4-
3-
2-
1-
0
B. belowground biomass
Station 1 Station 2
JUNE*
V////////A
Station 1 Station 2
AUGUST
Station 1 Station 2
OCTOBER
*=estimates only
-------
Appendix B2. Tidal variations at Havre de Grace.
1
0.5-
0-
-0.5-
-1
15 16 17 18 19 20 21 22 23 24 25
June 1993
^ 0.5-
0)
Q
0-
-0.5 -I
-1
i i i i T i i r i i i ^ i \
1 2
i i
3 4 5 6 7 8 9 10 11 12
August 1993
0.5-
0-
-0.5-
-1
i i i i i
345
i i r ir T i
6 7 8 9 10 11 12 13
October 1993
-------
Appendix B3. Physical data from Station 1, Havre de
Grace, 1993.
15
rain Y thunder storms
10-1
O)
O
0
8.5-
8-
y_
6.5-
6
^325
i
o
|275H
•a
c
8
250
35-
030-
o
Q.
20
15 16 17 18 19 20 21 22 23 24 25
June 1993
-------
Appendix B4. Physical data from Station 2, Havre de
Grace, 1993.
20
rain Y thunder storms
O)
010-
Q
i i
8.5-
8-
7*>-
I -o
7-
6.5-
6
i r i i r i i i i r i
n r
375
§300
o
i i i r
35
030-1
20
15
16 17 18 19 20 21 22 23 24 25
June 1993
-------
Appendix B5. Physical data fromStation 2, Havre de
Grace, 1993.
15-
rain X thunder storms
o> 9-
0
3-1
0
10-
9.5-
9-
5.8-5-
8-
7.5-
7
T 375
o
•1325-
13
§300-
I I I I I I I I T I I I I I I I 1 I I I I T I
20-L-r-T
1 2 3 4 5 6 7 8 9 10 11 12
August 1993
-------
Appendix B6. Physical data fromStation 3, Havre de
Grace, 1993.
rain thunder storms
15
ra 9-
0
\ i i i i i i i i i i i i i r i i i
1 2 3 4 5 6 7 8 9 10 11 12
August 1993
-------
Appendix B7. Physical data fromStation 1, Havre de
Grace, 1993.
ram
10
9.5-
9-
8-
7.5-
7
25
920-
Q.
E 15-
0) IO i
10-
3 4 5 6 7 8 9 10 11 12 13
October 1993
-------
Appendix B8. Physical data fromStation 2, Havre de Grace,
1993.
20-
O)
010-
Q
9.5
I
Q.
9-
8.5-
8-
7.5-
-375
O
^
T3
o300
25
020-
o
Q.
10
rain
i i r
*e
4 5 6 7 8 9 10 11 12 13
October 1993
-------
Appendix B9. Physical data fromStation 3, Havre de
Grace, 1993.
ram
20
I
Q.
8.5-
8-
7.5-
7-
6.5
i i i i
E 350
o
3.325-j
£ 300-
o
275
o
25
QL
10
i i r
345
i i
i i i i i i i i
6 78 9 10 11 12 13
October 1993
-------
Appendix B10. Weather Observations at BWI Airport. Arrows indicate
rain, * indicates thunderstorms.
90-
80-
® 70-
§60-
-o 50-
o 4C
o 30-
S5 20-
10-
0-
25
o20-
cu +r
Q. 1L
T3 c j
c o-
0
31-
i r
O)
I
E
£
§30-1
0)
2
CO
^3
29-
35-
i \ r
O
O)
a>
30-
25-
§20^
2 15-1
0)
|10^
? 5^
0
15 16
17 18 19 20 21 22 23 24 25
JUNE 1993
-------
Appendix B11. Weather Observations at BWI Airport. Arrows indicate
rain, * indicates thunderstorms.
3 4
5678
AUGUST 1993
-------
Appendix B12. Weather Observations at BWI Airport.
Arrows indicate rain.
o>
I
E
E
CO
.0
29-
6 7 8 9 10
OCTOBER 1993
11 12 13
-------
Appendix B13. Daily average light attenuation and
standard error at Havre de Grace monitoring stations,
1993.
Station 1
Station 2
Station 3
4.0-
16 17 18
19 20 21
June 1993
22 23 24
567
August 1993
8 9
10
3.5-
3.0-
2.5-
2.0-
1.0-
0.5-
0.0
789
October 1993
10 11 12
-------
Appendix B14. Total suspended solids at Havre de
Grace monitoring stations, June 1993.
70
60-
50-
40-
30-
20-
10-
0-
70
Station 1
•_ 60-
O) 50-
£ 40-
(/) o
0) J
H 20-
10-
0
Station 2
n i i i i
12
10-
8-
6-
4-
2-
0
Station 3
15 16 17 18 19 20 21 22 23 24 25
June 1993
-------
Appendix B15. Total suspended solids at Havre de
Grace monitoring stations, August 1993.
300
O)
E,
(f)
V)
50
40-
30-
20-
10-
0
Station 3
i i i i i i i
2 3 4 5
i i i i i
7 8 9
10 11 12
August 1993
-------
Appendix B16. Total suspended solids at Havre de
Grace monitoring stations, October 1993.
O)
450
400
350
300
250
200
150
100
50
0-
Station 2
45
40-
35-
30-
25-
20-
15-
10-
5-
0
Station 3
ww^^^
I I I I I I ™ I I I I I I I I I I I I I I
3 4 5 6 7 8 9 10 11 12 13
October 1993
-------
Appendix B17. Chlorophyll a concentrations at Havre de
Grace monitoring stations, June 1993.
25
20-
15-
10-
5-
0
Station 1
25
20-
* 10-1
6 5-\
0
25
Station 2
20-
15-
10-
5-
0
Station 3
i i i i i i i i i i i i i i i i r i i i i
15 16 17 18 19 20 21 22 23 24 25
June 1993
-------
Appendix B18. Chlorophyll a concentrations at
Havre de Grace monitoring stations, August 1993.
0
30
25-
20-
15-
10-
5-
0
Station 3
1 2 3 4 5 6 7 8 9 10 11 12
August 1993
-------
Appendix B19. Chlorophyll a concentrations at
Havre de Grace monitoring stations, October 1993.
u>
(0
O
40
35
30
25
20-
15
10
5-
0-
40
35
30
25
20
15
10
5
0
Station 1
Station 3
3 45 6 7 8 9 10 11 12 13
October 1993
-------
Appendix B20. Dissolved inorganic nitrogen concentrations
at Havre de Grace monitoring stations, June 1993.
200
150-
100-
50-
0
Station 1
2.5
2
•1.5
1
0.5
0
200
150-
100-
50-
200
150-
100-
50-
0
Station 3
i i i i i i i i i i i i i i i i i i i i i r
15 16 17 18 19 20 21 22 23 24 25
2.5
2
-1.5
1
0.5
0
June 1993
-------
Appendix B21. Dissolved inorganic nitrogen concentrations
at Havre de Grace monitoring stations, August 1993.
100
90
80
70
60
50
40-
30-
20-
10.-
0-
100-
90-
80-
70-
60-
50-
40-
30-
20-
10-
0-
100-
90-
80-
70-
60-
50-
40-
30-
20-
10-
0-
1.4
Station 1
t i i i i r
\ r
Station 2
T i i i i i r
i i i i i i i r
Station 3
1234
5678
August 1993
9 10 11 12
-1.2
-1
-0.8
-0.6
-0.4
-0.2
-0
1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
-0
1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
-0
3
CD
-------
Appendix B22. Dissolved inorganic nitrogen concentrations
at Havre de Grace monitoring stations, October 1993.
100
80-
60-
40-
20-
0-
100
^ 80-
3. 60-
5 40-
Q
20 -J
0
100-
80-
60-
40-
20-
0
Station 1
i i i r
Station 2
i r
i r
Station 3
6 7 8 9 10 11
October 1993
i i i
12 13
1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
o
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
3
CD
-------
Appendix B23. Ammonium concentrations at Havre
de Grace monitoring stations, June 1993.
60
50-
40-
30-
20-
10-
0
60
50-
40-
30-
20-
10-
0
Station 1
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
15 16 17
18 19 20 21
June 1993
22
24 25
-------
Appendix B24. Ammonium concentrations at Havre de
Grace monitoring stations, August 1993.
10-
8-
6-
4-
2-
Station 1
0-
i r
10-
8-
6-
4-
2-
Station 2
0-
i i \
i i i i r
0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
-0
0.14
-0.12
-0.08 (Q
-0.06 ~J
-0.04
-0.02
0
1 2 3 4 5 6 7 8 9 10 11 12
August 1993
-------
Appendix B25. Ammonium concentrations at Havre
de Grace monitoring stations, October 1993.
5-
4-
3-
2-
1-
0-
5
3.3
?2
Z1.
0-
5-
4-
3-
2-
1-
0
Station 1
i i
i \ i
i r
i i
Station 2
r r
i r
i i
i \ i
i \
\ i
Station 3
0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
i i i
3 4
i i i i i
6 7 8
-0
0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
i i i r i i i r
10 11 12 13
0
October 1993
-------
Appendix B26. Nitrate concentrations at Havre de
Grace monitoring stations, June 1993.
150-
100-
50-
0
150
Station 1
-2
-1.5
1
-0.5
i i i i i i i i i i i i i i i i i i i i i r
0
0
150-
100-
50-
0-
Station 3
o
-2
-1.5
-1
-0.5
i i i i i i T r i i i r i i i r r \ i i i r
15 16 17 18 19 20 21 22 23 24 25
June 1993
0
-------
Appendix B27. Nitrate concentrations at Havre de
Grace monitoring stations, August 1993.
100
80-
60-
40-
20-
0
Station 1
I I I
\ I
1 I
1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
100
s801
360-
CO
O 40-
Z
20-
0
100
80-
60-
40-
20-
0
Station 2
I I
I I I I I
I I
I I I
Station 3
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
i r
-0
1.4
45678
August 1993
i i i i i r T
9 10 11 12
-1.2
-1
-0.8
-0.6
-0.4
-0.2
-0
3
CD
-------
Appendix B28. Nitrate concentrations at Havre de
Grace monitoring stations, October 1993.
100
80-
60-
40-
20-
0-
100
1.4
^ 80-
3 60-
0*40-
20-
0-
100
Station 1
i i i i
i i r
i i i i i
i i \r
Station 2
80-
60-
40-
20-
0
Station 3
i i
\ r
-1.2
-1
-0.8
-0.6
-0.4
-0.2
-0
-1.4
-1.2
-0.8
-0.6
-0.4
-0.2
-0
•1.4
i r r i
-1.2
-1
-0.8
-0.6
-0.4
-0.2
-0
6 7 8 9 10 11 12 13
October 1993
-------
Appendix B29. Nitrite concentrations at Havre de
Grace monitoring stations, June 1993.
5
4-
3-
2-
1-
0
Station 1
CM
4-
3-
2-
1-
0
Station 2
0.07
rO.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
i i i i i \ i i i i i i i \ \ i i i i r
0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
5
4-
3-
2-
1-
0
Station 3
i r i i i ii i i i i T^ i i i i riii i
15 16 17 18 19 20 21 22 23 24 25
0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
June 1993
-------
Appendix B30. Nitrite concentrations at Havre de
Grace monitoring stations, August 1993.
8
7-
6-
5-
4-
3-
2-
1-
0
Station 1
\ r
\ i r
\ i i r
-0.1
-0.08
-0.06
-0.04
-0.02
0
8
^ 7
^ 6
«3 5
CM 4-
O o
Z J
2-
1-
0
8-
7-
6-
5-
4-
3-
2-
1-
0
Station 2
i i i r i i
i i i i i
Station 3
-0.1
-0.08
-0.06 g
-0.04 ^
i
-0.02
0
\ i i i i i i
1234
i i i r
5 6 7 8
August 1993
i i i i i i i r
9 10 11 12
-0.1
-0.08
-0.06
-0.04
-0.02
0
-------
Appendix B31. Nitrite concentrations at Havre de
Grace monitoring stations, October 1993.
6 7
October 1993
i i i r
10 11 12 13
-------
Appendix B32. Discharge at Conowingo Dam, Susquenna
River, 1993.
60000
^50000-
^40000-
CD
E? 30000-
-§ 20000-
co
"6 10000^
0
JU
i i r
15 16 17 18 19 20 21 22 23 24 25
June
10000
W 8000-
M—
"oT 6000-
S>
_g 4000-
~ 2000-
0
I I I I I I I I ! n I TIIFFI \ \ I I
2 3 4 5 6 7 8 9 10 11 12
August
60000
50000-
CD
E? 30000 -I
•g 20000 ^
~ 10000H
0-
i i i i i i i i i i r
\ i i r
4 5 6 7 8 9 10 11 12 13
October
-------
Appendix B33. Phosphate concentrations at Havre de
Grace monitoring stations, June 1993.
15 16 17 18 19 20 21 22 23 24 25
June 1993
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
-------
Appendix B34. Phosphate concentrations at Havre
de Grace monitoring stations, August 1993.
i i r
-0.003
-0.002
-0.001
0
2345678
August 1993
9 10 11 12
-------
Appendix B35. Phosphate concentrations at Havre
de Grace monitoring stations, October 1993.
i i i i i r
3456
0.0012
-0.0010
-0.0008
-0.0006
-0.0004
-0.0002
0.0000
0.0012
-0.0010
-0.0008 g
-0.0006 <£.
-0.0004 '
rO.0002
0.0000
0.0012
-0.0010
-0.0008
-0.0006
-0.0004
-0.0002
0.0000
7 8 9 10 11 12 13
October 1993
-------
Appendix C
-------
Cl: Water column nutrient concentrations for the control and
dissolved continuous experimental treatments.
AMMONIA
I
z
1
£.3 -
2 -
1.5-
1 -
0.5-
n -
A.
T
D
*
D DISSOLVED CONTINUOUS
* CONTROL
1 ° ° i S «? s
* s *
*
T
S
i
i
T I
±
NITRATE & NITRITE
OJ
0
°3
to
i
1 _
0.75-
0.5-
0.25-
n -
B.
T
o n
-L
T
T
D
a
5 T
j- a
*
n - P
- 1
* * 5
=F
_L
n
g
^
PHOSPHATE
1.5-
0.5-
n-
C.
. I = i '
ft o 1 • 2 J-
7 ^ T t T * * 1
3 I
a
r *
c
*
6 7
WEEK
10
11
12
-------
C2: Time series water column nutrient concentrations for the
dissolved pulse experimental treatments.
AMMONIA
. 0
200
NITRATE & NITRITE
PHOSPHATE
11 AUGUST
14 SEPTEMBER
25 OCTOBER
-0.25
168
-------
C3: Macrophyte growth rate for control and experimental
chambers for the twelve week fall 1993 experiment.
PARTICULATE
PULSE
DISSOLVED
PULSE
DISSOLVED
CONTINUOUS
i i i i i i i i i i i
0123456789 10 11 12
WEEK
Growth (cm shoot-1 week-1)
-------
C4: Summary of the autotrophic component biomass at the
end of the experiment.
zw-
150-
100-
50 -
PHYTOPLANKTON
o-1 —
4
3 -
2 _
1 -
o
4-
MACROALGAE
T
25
20 .
IS .
10 .
5 .
0 _
1 1
4»
T
1
EPIPHYTE
T
T
2.5 -
2 _
1.5 -
1 _
0.5 _
0 _
—
-JU.
J.
T
1
SEDIMENT
06
05 -
0.4 -
0.3 -
0.2 .
0.1 _
0 _
n. - - ,
i
PLANT
T
T
A
' Jt '
T
*
T
1 ' '!
CONTROL
PART PULSE
DISS PULSE
DISS CONT
-------
C5: Nitrogen budget for the autotrophic components in the
experimental chambers.
IB
2
30
20-
10-
PLANT
3 MACROALGAE
;] SEDIMENT
~] PHYTOPLANKTON
EPEPHYTE
CONTROL PARTICULATE
DISSOLVED
PULSE
DISSOLVED
CONTINUOUS
------- |