2.0
Physical, Chemical, and Biological Characteristics of the
Lower Cape Fear
River and Estuary
Matthew
R. McIver and Michael A. Mallin
Center for Marine Science
University of North Carolina at Wilmington
2.1
Introduction
This
section of the report includes a discussion of the physical, chemical, and
biological water quality parameters, concentrating on the 2002-2003 Lower Cape
Fear River Program monitoring period. These
parameters are interdependent and define the overall condition of the river.
Physical parameters measured during this study included water
temperature, dissolved oxygen, turbidity, salinity, conductivity and pH.
The chemical makeup of the Cape Fear River was investigated by measuring
the magnitude and composition of nitrogen and phosphorus in the water, as well
as concentrations of United States Environmental Protection Agency (US EPA)
priority pollutant metals. Three
biological parameters including fecal coliform bacteria, chlorophyll a
and biochemical oxygen demand were examined.
2.2
Materials and Methods
All samples and field parameters collected for the
estuarine stations of the Cape Fear River (NAV down through M18) were gathered
on an ebb tide. This was done so
that the data better represented the river water flowing downstream through the
system rather than the tidal influx of coastal ocean water.
Sample collection and analyses were conducted according to the procedures
in the Lower Cape Fear River Program Quality Assurance/Quality Control (QA/QC)
manual which has been approved by the NC Division of Water Quality.
Physical
Parameters
-Water
Temperature, pH, Dissolved Oxygen, Turbidity, Salinity, Conductivity
Field
parameters were measured at each site using a YSI 6920 (or 6820) multi-parameter
water quality sonde displayed on a YSI 610D (or 650 MDS).
Each parameter is measured with individual probes on the sonde.
At stations sampled by boat (see Table 1.1) physical parameters were
measured at 0.1 m, the middle of the water column, and at the bottom (up to 12
m). Occasionally, high flow
prohibited the sonde from reaching the actual bottom and measurements were taken
as deep as possible. At the
terrestrially sampled stations the physical parameters were measured at a depth
of 0.1 m.
Chemical
Parameters
-Nutrients
All nutrient analyses were performed at the UNCW Center for Marine Science (CMS)
for samples collected prior to January 1996.
A local state-certified analytical laboratory was contracted to conduct
all subsequent analyses except for orthophosphate, which is performed at CMS.
The following methods detail the techniques used by CMS personnel for
orthophosphate analysis.
-Orthophosphate
(PO4-3)
Water samples
were collected ca. 0.2 m below the surface in triplicate in amber 125 mL Nalgene
plastic bottles and placed on ice. In
the laboratory 50 mL of each triplicate was filtered through separate1.0 micron
pre-combusted glass fiber filters, which were frozen and later analyzed for
chlorophyll a.
The triplicate filtrates were pooled in a glass flask, mixed thoroughly,
and approximately 100 mL was poured into a 125 mL plastic bottle to be analyzed
for orthophosphate. Samples were frozen until analysis.
Orthophosphate analyses were performed in duplicate
using an approved US EPA method for the Technicon AutoAnalyzer (Method 365.5).
In this technique the orthophosphate in each sample reacts with ammonium
molybdate and anitmony potassium tartrate in an acidic medium (sulfuric acid) to
form an anitmony-phospho-molybdate complex.
The complex is then reacted with ascorbic acid and forms a deep blue
color. The intensity of the color
is measured at a wavelength of 880 nm by a colorimeter and displayed on a chart
recorder. Standards and spiked
samples were analyzed for quality assurance.
Biological
Parameters
-Fecal
Coliform Bacteria
Fecal coliform
bacteria were analyzed at a state-certified laboratory contracted by LCFRP.
Samples were collected approximately 0.2 m below the surface in sterile
plastic bottles provided by the contract laboratory and placed on ice for no
more than six hours before analysis.
-Chlorophyll
a
The analytical
method used to measure chlorophyll a is described in Welschmeyer (1994) and US EPA (1997) and was
performed by CMS personnel. Chlorophyll
a concentrations were determined
directly from the 1.0 micron filters used for filtering samples for
orthophosphate analysis. All
filters were wrapped individually in foil, placed in airtight containers and
stored in the freezer. During
analysis each filter is immersed in 10 mL of 90% acetone for 24 hours, which
extracts the chlorophyll a into
solution. Chlorophyll a
concentration of each solution is measured on a Turner 10-AU fluorometer. The fluorometer uses an optimal combination of excitation and
emission bandwidth filters which reduces the errors inherent in the
acidification technique.
-Biochemical
Oxygen Demand (BOD)
Five sites were chosen for BOD analysis.
One site was located at NC11, upstream of International Paper, and a
second site was at AC, about 3 miles downstream of International Paper (Fig.1.1). Two sites were located
in blackwater rivers (NCF117 and B210) and one site (BBT) was situated in an
area influenced by both the mainstem Cape Fear River and the Black River. For this sampling period additional BOD data were collected
at stream stations LVC, 6RC, LCO, GCO, BRN, HAM and COL.
The procedure used for BOD analysis was Method 5210 in Standard Methods (APHA
1995). Samples were analyzed for
both 5-day and 20-day BOD. During
the analytical period, samples were kept in airtight bottles and placed in an
incubator at 20o C. All
experiments were initiated within 5 hours of sample collection.
Samples were analyzed in duplicate.
Dissolved oxygen measurements were made using a YSI Model 57 meter that
was air-calibrated. No adjustments were made for pH since most all samples
exhibited pH values within or very close to the desired 6.5-7.5 range.
Several sites have naturally low pH and there was no adjustment for these
samples because it would alter the natural water chemistry and affect true BOD.
2.3 Results and Discussion
This section includes results from monitoring of the physical, biological, and
chemical parameters at all stations for the time period July 2002-June 2003. Discussion of the data focuses mainly on the river channel
stations, but poor water quality conditions at stream stations will also be
discussed. The contributions of the
two large blackwater tributaries, the Northeast Cape Fear River and the Black
River, are represented by conditions at NCF117 and B210, respectively.
The Cape Fear Region did not experience any significant hurricane
activity during this monitoring period (after hurricanes in 1996, 1998, and
1999); however, there was higher than average rainfall during the latter portion
of this sampling period, in contrast to the drought last year.
Therefore this report reflects mixed flow conditions for the Cape Fear
River and Estuary.
Water temperatures at all stations ranged from 3.9 to
30.5 oC and individual station annual averages ranged from 15.9 to
19.5 oC (Table 2.1). Highest
temperatures occurred during July (all station mean = 27.8) and lowest
temperatures during January (all station mean = 7.7).
Stream stations were generally cooler than river stations, most likely
because of shading and lower nighttime air temperatures affecting the shallower
waters.
Salinity at the estuarine stations ranged from 0.0 to
34.4 parts per thousand (ppt) and station annual means ranged from 2.4 to 26.0
ppt (Table 2.2). Lowest salinity
occurred in June 2003 (all stations mean = 2.6) and highest salinity occurred in
July 2002 (all stations mean = 22.1). Two
stream stations, NC403 and SAR, had occasional oligohaline conditions due to
discharges from pickle production facilities.
Annual mean salinity for 2002-2003 was higher than the eight-year average
for 1995-2003 at all stations (Figure 2.1).
-Conductivity
Conductivity at estuarine stations ranged from 0.1 to
52.3 mS/cm and from 0.0 to 7.7 mS/cm at the freshwater stations (Table
2.3).
Temporal conductivity patterns followed those of salinity.
Dissolved ionic compounds increase the conductance of water, therefore,
conductance increases and decreases with salinity, often reflecting river flow
conditions due to rainfall. Conductivity
may also reveal point source pollution sources, as is seen at BC117, which is
below a municipal wastewater discharge.
-pH
pH values ranged from 3.3 to 10.3 and stations annual
medians ranged from 3.7 to 8.0 (Table 2.4).
pH was typically lowest upstream due to acidic swamp water inputs and
highest downstream as alkaline seawater mixes with the river water.
Some unusually high pH values at LRC,BC117 and ANC are most likely due to
industrial discharges and or algal blooms (see also very high dissolved oxygen
concentrations). Low pH values at
COL predominate because of naturally acidic blackwater inputs.
-Dissolved Oxygen
Dissolved oxygen (DO) problems are a major water
quality concern in the Cape Fear River (Mallin et al. 1997; 1998a; 1998b; 1999a;
1999b). Concentrations ranged
from 0.1 to 16.8 mg/L and station annual means ranged from 3.4 to 10.6 mg/L (Table
2.5). Average annual DO
levels at the river channel stations were higher for 2002-2003 than the average
for 1995-2003 (Figure 2.2). Dissolved
oxygen levels were lowest during the summer (Table
2.5), often falling below the
state standard of 5.0 mg/L at several river and upper estuary stations.
Working synergistically to lower oxygen levels are two factors: lower
oxygen carrying capacity in warmer water and increased bacterial respiration (or
biochemical oxygen demand, BOD), due to higher temperatures in summer.
These hypoxic conditions could have negative impacts on the biota in the
Cape Fear River.
There is an oxygen sag In the main
river channel that begins at DP below a paper mill discharge and persists into
the mesohaline portion of the estuary. Mean
oxygen levels were highest at the upper river stations NC11 (9.0 mg/L) and AC
(8.6 mg/L) and in the middle to lower estuary at stations M42 (8.3 mg/L) and M23
(8.4 mg/L). Lowest DO levels were
at the lower river and upper estuary stations IC (7.4 mg/L) and NAV (7.5 mg/L).
Discharge of high BOD waste from the paper/pulp mill just above the AC
station, as well as inflow of blackwater from the Northeast Cape Fear and Black
Rivers, helps to diminish oxygen in the upper estuary.
As the water reaches the lower estuary higher algal productivity, mixing
and ocean dilution help alleviate oxygen problems.
The
Northeast Cape Fear and Black Rivers generally have lower DO levels than the
mainstem Cape Fear River (NCF117 mean = 6.5, B210 mean = 7.2).
These rivers are classified as blackwater systems because of their tea
colored water. As the water passes
through swamps en route to the river channel, tannins from decaying vegetation
leach into the water, resulting in the observed color.
Decaying vegetation on the swamp floor has an elevated biochemical oxygen
demand and usurps oxygen from the water, leading to naturally low dissolved
oxygen levels. Runoff from
concentrated animal feeding operations (CAFOs) may also contribute to chronic
low dissolved oxygen levels in these blackwater rivers (Mallin et al. 1998b;
1999a; Mallin 2000).
Several
stream stations were severely stressed in terms of low dissolved oxygen during
the year July 2002-June 2003. These
included ANC, NC403, BCRR and SR (Table 2.5).
Some of this can be attributed to low water conditions; however
point-source discharges also likely contribute to low dissolved oxygen at NC403
and possibly SR, especially via nutrient loading (Mallin et al. 2001; Mallin et
al. 2002).
-Field
Turbidity
Turbidity levels ranged from 0 to 140 nephelometric turbidity units (NTU) and
station annual means ranged from 2 to 28 NTU (Table
2.6).
Annual mean turbidity levels for 2002-2003 were lower than the 1995-2003
averages at the river stations and lower estuary, but higher at the mid-upper
estuary stations (Figure 2.3). Turbidity
was highest at the upper river stations, reaching a maximum at the upper
estuary, and declining toward the lower estuary.
Turbidity was lowest in the blackwater tributaries (Northeast Cape Fear
River and Black River).
Note:
The LCFRP uses nephelometers designed for field use, which allows us to acquire
in situ turbidity from a natural situation.
North Carolina regulatory agencies are required to use turbidity values
from water samples removed from the natural system, put on ice until arrival at
a State-certified laboratory, and analyzed using laboratory nephelometers.
Standard Methods notes that transport of samples and temperature change
alters true turbidity readings. Our
analysis of samples using both methods shows that lab turbidity is nearly always
substantially lower than field turbidity. We
therefore recommend that NCDWQ investigate the utilization of field rather than
laboratory turbidity in order to obtain data more representative of natural
conditions.
-Total
Suspended Solids
Total suspended solid (TSS) values ranged from 0 to 109 mg/L with station annual
means from 1 to 22 mg/L (Table 2.7). For
the river channel stations TSS was highest in the middle estuary at Marker 42
(mean = 22). Highest monthly means
for TSS occurred in winter and spring. Although
total suspended solids (TSS) and turbidity both quantify suspended material in
the water column, they do not always go hand in hand. High TSS does not mean high turbidity and vice versa.
This anomaly may be explained by the fact that fine clay particles are
effective at dispersing light and causing high turbidity readings, while not
resulting in high TSS. On the other hand, large organic or inorganic particles may
be less effective at dispersing light, yet their greater mass results in high
TSS levels.
-Light
Attenuation
The attenuation of solar irradiance through a water column is measured by a
dimensionless logarithmic function (k) per meter.
The higher this light attenuation coefficient is, the more strongly light
is attenuated (through absorbance or reflection) in the water column.
Light attenuation ranged from 0.66 to 5.63 k/m and station annual means
ranged from 1.51 to 3.70 k/m (Table 2.8). Annual
light attenuation means for this monitoring period were lower than for the
eight-year period 1995-2003 (Figure 2.4).
High light attenuation did not always coincide with high turbidity.
Blackwater, though low in turbidity, may increase light attenuation
through absorption of solar irradiance. At
NCF6 and BBT, blackwater stations with moderate turbidity levels, light
attenuation was high.
Compared to other North
Carolina estuaries the Cape Fear has high average light attenuation.
The high average light attenuation is a major reason why phytoplankton
production in the major rivers and the estuary of the LCFR is generally low.
Whether caused by turbidity or water color this attenuation tends to
limit light availability to the phytoplankton.
Chemical
Parameters – Nutrients
-Total Nitrogen
Total nitrogen (TN) ranged from 90
to 17,900 mg/L
and station annual means ranged from 541 to 9,233 mg/L
(Table 2.9). Mean total nitrogen
was higher this monitoring period than for the eight-year mean at all but one
channel station (Figure 2.5). Previous
research (Mallin et al. 1999a) has shown a positive correlation between river
flow and TN in the Cape Fear system. Total
nitrogen concentrations remained fairly constant down the river and declined
into the lower estuary, most likely reflecting uptake of nitrogen into the food
chain through algal productivity and subsequent grazing by planktivores as well
as through dilution. The pulp mill
above AC is a source of TN, increasing levels at this station over levels at
NC11. The blackwater rivers
maintained TN concentrations somewhat lower than those found in the mainstem
Cape Fear River. One stream
station, BC117, had a very high mean of 9,233 mg/L,
presumably from upstream wastewater discharge.
ROC has recently begun to show high levels of TN as well (mean 2,079 mg/L)
although the source is not known at this point in time.
Temporal patterns for TN were not evident.
-Nitrate+Nitrite
Nitrate+nitrite (henceforth
referred to as nitrate) is the main species of inorganic nitrogen in the Lower
Cape Fear River. Concentrations ranged from 5 (detection limit) to 16,800 mg/L
and station annual means ranged from 47 to 8,245 mg/L
(Table 2.10). Station annual means
for the 2002-2003 monitoring period were mostly higher than the eight-year means
(Figure 2.6). The highest riverine
nitrate levels were at NC11 (mean = 719 mg/L)
indicating that much of this nutrient is imported from upstream.
Moving downstream from NC11, nitrate levels decrease most likely as a
result of uptake by primary producers and tidal dilution.
The blackwater rivers carried low loads of nitrate compared to the
mainstem Cape Fear stations, though the Northeast Cape Fear River (NCF117 mean =
226 mg/L)
had higher nitrate than the Black River (B210 = 129 mg/L).
No clear temporal pattern was observable for nitrate.
Several stream stations showed
high levels of nitrate on occasion including SAR, NC403, PB, ROC, BC117.
NC403 and PB are downstream of industrial wastewater discharges and ROC
primarily receives non-point agricultural or animal waste drainage.
BC117, with high nitrate levels, exceeded the North Carolina State
drinking water standard of 10 mg/L on five occasions.
The Town of Burgaw wastewater plant, upstream of BC117, has no nitrate
discharge limits.
-Ammonium
Ammonium concentrations ranged from 10 (detection limit) to 1,180 mg/L
and station annual means ranged from 44 to 224 mg/L
(Table 2.11). This monitoring
period the mean ammonium levels were generally higher than the eight-year means
at the channel stations (Figure 2.6). Areas
with the highest ammonium levels this monitoring period included AC (mean = 199 mg/L),
which is below a pulp mill discharge, M61 (mean = 120 mg/L),
and M54 (mean = 125 mg/L)
in the middle estuary. Ocean
dilution accounts for decreasing levels down into the estuary.
At the stream stations, areas with high levels of ammonium include LVC,
ANC, BC117, PB, and BCRR.
-Total Kjeldahl Nitrogen
Total Kjeldahl Nitrogen (TKN)
is a measure of the total concentration of organic nitrogen plus ammonium.
TKN ranged from 50 to 3,420 mg/L
and station annual means ranged from 429 to 1,462 mg/L
(Table 2.12). Mean TKN for this
monitoring period was mostly higher than the eight-year mean at the channel
stations (Figure 2.8). TKN concentration drops down through the estuary,
likely due to ocean dilution and food chain uptake of nitrogen. Measured TKN levels in the blackwater rivers are usually
higher than in the mainstem Cape Fear River as a result of the high
concentration of organic materials dissolved in the water (Figure
2.8).
The stream stations typically have higher TKN as a result of the
influence of swamp water with high organic and ammonium content.
There were somewhat higher TKN levels during summer months.
-Total Phosphorus
Total phosphorus (TP)
concentrations ranged from 10 (detection limit) to 4,740 mg/L
and station annual means ranged from 35 to 1,563 mg/L
(Table 2.13). Mean TP for this
monitoring period was lower than the eight-year mean at all channel stations but
one (Figure 2.8). TP is
highest at the upper riverine channel stations and declines downstream into the
estuary. Some of this decline is
attributable to the settling of phosphorus-bearing turbidity, yet incorporation
of phosphorus into the food chain is also responsible.
A temporal pattern of higher summer TP is a result of increasing
orthophosphate, as the spatial pattern of TP is similar to that of
orthophosphate.
At the stream stations several areas had high TP including BC117, NC403,
and ROC. Some of these stations
(BC117, NC403) are downstream of industrial or wastewater discharges.
-Orthophosphate
Orthophosphate ranged from 0 to
3,740 mg/L
and station annual means ranged from 5 to 1,409 mg/L
(Table 2.14). The 2002-2003 annual
means at the channel stations were higher about half the time and lower half the
time than the eight-year means (Figure 2.9).
Much of the orthophosphate load is imported into the Lower Cape Fear
system from upstream areas, as NC11 typically has the highest levels.
The Northeast Cape Fear River had higher orthophosphate levels than the
Black River. Orthophosphate can
bind to suspended materials and is transported downstream via turbidity; thus
high levels of turbidity at the uppermost river stations may be an important
factor in the high orthophosphate levels. Turbidity
declines toward the estuary because of settling, and orthophosphate
concentration also declines. In the
estuary, primary productivity helps reduce orthophosphate concentrations by
assimilation into biomass. Orthophosphate
levels typically reach maximum concentrations during summertime, when anoxic
sediment releases bound phosphorus. Also,
in the Cape Fear Estuary, summer algal productivity is limited by nitrogen,
thereby allowing the accumulation of orthophosphate (Mallin et al. 1997; 1999a).
In spring, productivity in the estuary is usually limited by phosphorus (Mallin
et al. 1997; 1999a).
The stream stations BC117 and ROC
had very high orthophosphate levels while SAR and NC403 had moderately high
levels. NC403 and BC117 are strongly influenced by industrial and
municipal wastewater discharges, and SAR and ROC by agriculture/animal waste
runoff. There is a trend of
increasing orthophosphate at ROC since 1996, which will be investigated more
closely in the coming year.
Chemical Parameters -
EPA Priority Pollutant Metals
Aluminum levels in the Lower Cape Fear system were generally higher in the upper
river and decreased toward the lower estuary (Table
2.15).
Stream stations were generally low except COL which is considered
pristine swamp water. There is no
North Carolina aquatic standard for aluminum.
Arsenic, cadmium, and chromium all maintained concentrations below detection
limits at all stations (except two stations in February) throughout the year (Tables
2.16, 2.17, and 2.18).
Copper
concentrations periodically exceeded the state tidal saltwater standard of 3 mg/L
at some of the estuarine stations each month (Table
2.19).
The freshwater standard of 7 mg/L
was never exceeded at the upper river stations.
The
LCFRP is an iron-rich system (Table 2.20).
All of the freshwater stations except for NCF117, BC117, and COL
maintained average iron concentrations near or above the state standard of 1000 mg/L.
Iron concentrations generally decreased down-estuary.
Water-column concentrations of lead,
mercury, and nickel were below the analytical detection limit except for three
occasions for nickel (Table 2.21, 2.22,
2.23).
Zinc concentrations remained
below the state standard at all stations but showed highest values at BC117 (Table
2.24).
-Chlorophyll a
During this monitoring period
chlorophyll a was generally low at the
river and estuarine stations (Table 2.25). Chlorophyll a
ranged from 0.1 to 177.8 mg/L
and station annual means ranged from 1.0 to 22.4 mg/L.
Production of chlorophyll a
biomass is low to moderate in this system primarily because of light limitation
by turbidity in the mainstem and high organic color and low inorganic nutrients
in the blackwater rivers. Spatially,
highest values are normally found in the mid-to-lower estuary stations because
light becomes more available downstream of the estuarine turbidity maximum (Figure
2.11). Chlorophyll a
production is extremely limited in the large blackwater tributaries.
Highest chlorophyll a
concentrations were found during spring and summer.
There was no clear pattern of differences in mean annual levels at the
channel stations from the eight-year mean.
Substantial phytoplankton blooms do occur at the stream stations (Table
2.25). These streams are generally shallow, so mixing does not carry
phytoplankton cells down below the critical depth where respiration exceeds
photosynthesis. Thus, when flow
conditions permit, elevated nutrient conditions (such as are periodically found
in these stream stations) can lead to algal blooms. In areas where the forest canopy opens up large blooms can
readily occur. When blooms occur in
blackwater stream stations, they can become sources of BOD upon death and decay,
reducing further the low summer dissolved oxygen conditions common to these
waters (Mallin et al. 2001; 2002). Particularly
large stream algal blooms occurred this year at GS, PB, LRC, SR and BCRR, with
smaller blooms at ANC and LRC (Table 2.25).
-Biochemical
Oxygen Demand
For the main stem river, mean annual five-day biochemical oxygen demand (BOD5)
concentrations were highest at AC, on average about 30% higher than at NC11
suggesting influence from the pulp/paper mill inputs (Table
2.26).
BOD was somewhat lower during the winter.
A project aimed at assessing rural stream contributions to BOD was continued
this monitoring period. Results of
BOD in several stream stations can be seen in Table 2.26.
HAM showed the highest BOD5 and BOD20 levels, with very little difference
among the other stream stations. The
BOD studies are detailed in Chapter 4 of this report.
-Fecal Coliform Bacteria
Fecal coliform (FC) bacterial counts ranged from 0 to
4,360 cfu/100 mL and station annual geometric means ranged from 1 to 195 cfu/100
mL (Table 2.27). No clear temporal pattern is evident. The state human contact standard (200 CFU) was not exceeded
at the channel stations during any month. FC
counts this monitoring period were higher at the Cape Fear River stations but
lower at the estuary stations and the blackwater stations compared with the
eight-year average (Figure 2.12). FC
bacteria show a notable spatial trend of highest counts in the upper
estuary-lower river area bounded by IC, NAV, HB, and BRR.
Most stream stations surpassed the state standard for
human contact of 200 CFU/100 mL on at least one occasion.
BCRR, BC117, LRC, BRN, and HAM all had particularly high levels on at
least one occasion. LRC is
located below a point source discharge and the other sites are primarily
influenced by non-point source pollution.
2.4 References Cited
APHA.
1995. Standard Methods for the Examination of Water and Wastewater, 19th ed.
American Public Health Association, Washington, D.C.
Mallin,
M.A., L.B. Cahoon, M.R. McIver, D.C. Parsons and G.C. Shank. 1997. Nutrient
limitation and eutrophication potential in the Cape Fear and New River
Estuaries. Report No. 313. Water Resources Research Institute of the University
of North Carolina, Raleigh, N.C.
Mallin,
M.A., L.B. Cahoon, D.C. Parsons and S.H. Ensign. 1998b. Effect of organic and
inorganic nutrient loading on photosynthetic and heterotrophic plankton
communities in blackwater rivers. Report No. 315. Water Resources Research
Institute of the University of North Carolina, Raleigh, N.C.
Mallin,
M.A., L.B. Cahoon, M.R. McIver, D.C. Parsons and G.C. Shank. 1999a. Alternation
of factors limiting phytoplankton production in the Cape Fear Estuary. Estuaries
22:985-996.
Mallin, M.A. 2000.
Impacts of industrial-scale swine and poultry production on rivers and
estuaries. American Scientist
88:26-37.
Mallin, M.A., L.B.
Cahoon, D.C. Parsons and S.H. Ensign. 2001. Effect of nitrogen and phosphorus
loading on plankton in Coastal Plain blackwater streams. Journal
of Freshwater Ecology 16:455-466.
Mallin, M.A., L.B.
Cahoon, M.R. McIver and S.H. Ensign. 2002. Seeking science-based nutrient
standards for coastal blackwater stream systems. Report No. 341. Water Resources
Research Institute of the University of North Carolina, Raleigh, N.C.
U.S.
EPA 1997. Methods for the Determination of Chemical Substances in Marine and
Estuarine Environmental Matrices, 2nd Ed. EPA/600/R-97/072. National Exposure
Research Laboratory, Office of Research and Development, U.S. Environmental
Protection Agency, Cincinnati, Ohio.
Welschmeyer,
N.A. 1994. Fluorometric analysis of chlorophyll a
in the presence of chlorophyll b and
phaeopigments. Limnology and Oceanography
39:1985-1993.
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