2.0
Physical, Chemical, and Biological Characteristics of the
Lower Cape Fear River and Estuary
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 2001-2002 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 EPA priority pollutant metals.
Three biological parameters, fecal coliform bacteria, chlorophyll a
and biochemical oxygen demand, were examined to assess the effects of point and
non-point source loading of nutrients, organic materials, and other pollutants
on water quality.
2.2 Materials and Methods
All samples and field parameters collected for the estuarine stations of the
Cape Fear River (i.e. NAV down through M18) were gathered on an outgoing tide,
whenever possible. 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 procedures in
the Lower Cape Fear River Program QA/QC Manual, and approved by the NC Division
of Water Quality.
Physical Parameters
Water
Temperature, pH, Dissolved Oxygen, Turbidity, Salinity, and Conductivity
Field parameters were measured at each site using a YSI 6920 Multi-parameter Water Quality Probe (sonde) and displayed on a YSI 610D datalogger. Individual probes within the instrument measured water temperature, pH, dissolved oxygen, turbidity, salinity, and conductivity. At each station, physical parameters were measured at the surface, mid-depth, and bottom (up to 12 m). High flow occasionally prohibited the probe from reaching the bottom. The instrument was calibrated prior to each sampling trip and calibration points were checked upon return from each trip.
Chemical Parameters
Nutrients
All nutrient analyses were performed at the Center for Marine Science Research (CMSR,
now 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 (February 1996 through June 2002), except for the
orthophosphate procedure that was performed at CMS. The following methods detail the techniques used by CMS
personnel only.
Water samples were collected ca. 0.2 m below the surface in triplicate in amber 125 mL Nalgene plastic bottles. After collection, the samples were immediately placed on ice. In the laboratory, 50 mL of each triplicate was filtered through a separate 1.0 micron pre-combusted glass fiber filter, which were frozen and subsequently used for chlorophyll a analysis. The triplicate filtrates were pooled in a common glass flask, mixed thoroughly, and approximately 100 mL was poured into one 125 ml plastic bottle to be used for orthophosphate analyses. Filtered samples were stored in a freezer until time of analysis.
Orthophosphate
(PO4-3)
All orthophosphate analyses were performed in duplicate using an approved
EPA method for the Technicon AutoAnalyzer (Method 365.5).
In this technique, the orthophosphate in each sample reacts with ammonium
molybdate and antimony potassium tartrate in an acidic medium (sulfuric acid) to
form an antimony-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
Chlorophyll
a
The analytical method used to measure chlorophyll a is described in Welschmeyer (1994) and USEPA (1997). Chlorophyll a concentrations were determined directly from the 1.0 micron glass fiber filters used for filtering samples for nitrate+nitrite and orthophosphate analyses. All filters were wrapped individually in aluminum foil, placed in an airtight container and stored in a freezer. During the analytical process, the glass filters were separately immersed in 10 ml of a 90% acetone solution for 24 hours. The acetone extracts the chlorophyll a from the glass filters into solution. Each solution was then analyzed for chlorophyll a concentrations using a Turner AU-10 fluorometer. This method uses an optimal combination of excitation and emission bandwidths 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 all samples exhibited pH values within or very close to the desired 6.5-7.5 range.
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 2001-June 2002. 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 an extended drought during this sampling period. Therefore this report reflects relatively low flow conditions for the Cape Fear River and Estuary.
Water
temperature
Water temperatures at all stations ranged from 4.5 to 32.5 oC and
individual station annual averages ranged from 17.1 to 20.6 oC (Table
2.1). Highest temperatures occurred
during August (all station mean = 28.2) 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 0.1 to 36.2 parts per thousand (ppt) and station annual means ranged from 3.8 to 29.1 ppt (Table 2.2). Lowest salinity occurred in February (all stations mean = 8.2) and highest salinity occurred in November (all stations mean = 22.5). Two stream stations, NC403 and SAR, had occasional oligohaline conditions due to discharges from pickle production facilities. Annual mean salinity for 2001-2002 was much higher than the seven-year average for 1995-2002 at all stations (Figure 2.1), a result of drought and lower freshwater river flow conditions during this monitoring period. Many of the estuarine stations averaged about 5 ppt higher than the long-term average (Figure 2.1). The lower flow conditions during this sampling period influenced a number of parameters, as subsequent sections will show.
Conductivity at all stations ranged from 7.0 to 45.0 mS/cm at the estuarine stations and from 0.1 to 2.3 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 3.9 to 9.4 and stations annual medians ranged from 4.0 to 8.1 (Table 2.4). pH was typically lowest upstream due to acidic swampwater inputs and highest downstream as alkaline seawater mixes with the river water. Some unusually high pH values at LRC and BC117 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 (DO) problems are a major water quality concern in the Cape Fear River (Mallin et al. 1997; 1998a; 1998b; 1999a; 1999b). Concentrations ranged from 0.2 to 17.6 mg/L and station annual means ranged from 2.9 to 10.9 mg/L (Table 2.5). Average annual DO levels at the river channel stations were either similar to or slightly higher for 2001-2002 than the average for the six years 1995-2002 (Figure 2.2). Dissolved oxygen levels are lowest during the summer (Table 2.5, Figure 2.3), 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.
In
the main river channel there is an oxygen sag 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 (8.5
mg/L) and AC (8.3 mg/L) and in the middle estuary at stations M42 and M35 (8.0
mg/L). The estuary maxima were
higher upstream this year, reflecting the lower flow conditions.
Upper estuary stations NAV (6.2 mg/L) and HB and Marker 61 (6.8 mg/L) had
the lowest DO levels. 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 =
6.2, B210 mean = 7.1). 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 2001 – June 2002. These included ANC, NC403, PB 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, PB, and possibly SR, especially nutrient loading (Mallin et al. 2001; Mallin et al. 2002).
Turbidity
Turbidity levels ranged from 1 to 53 nephelometric turbidity units (NTU) and station annual means ranged from 2 to 21 NTU (Table 2.6). Annual mean turbidity levels for 2001-2002 were much lower than the seven year average for 1995-2002 at all river channel stations (Figure 2.3). Turbidity was high 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).
The lower levels of turbidity measured in the river and estuary stations indicates that the drought has considerably reduced the normally large portion of suspended material that is typically transported into the Lower Cape Fear River system from upstream areas. Rainfall in the upper and middle basins of the Cape Fear River has a positive correlation with turbidity in the lower system (Mallin et al. 1998a; 1999a).
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 1 to 41 mg/L, with station annual means from 1.8 to 14.1 mg/L (Table 2.7). For the river channel stations, TSS was highest in the lower estuary at Marker 18 (mean = 13.2). Again, these values are lower than those of previous years, reflecting the lower amounts of suspended sediments brought downstream due to the drought. Highest monthly means for TSS occurred in late winter and early 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 0.89 to 6.54 k/m and station annual means ranged from 1.46 to 4.18 k/m (Table 2.8). 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. Light attenuation during this monitoring period was lower than the seven-year average at all channel stations except NCF6 (Figure 2.4), probably a result of lower turbidity through lower river flow. Temporally, light attenuation was highest during fall through spring. Compared with 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 180 to 21,500 mg/L
and station annual means ranged from 339 to 9,403 mg/L
(Table 2.9). Mean total nitrogen
was equal to or lower this monitoring period than for the seven-year mean at all
channel stations (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 carried
total nitrogen loads somewhat lower than those found in the mainstem Cape Fear
River. One stream station, BC117,
had a very high mean of 9,403 mg/L,
presumably from upstream wastewater discharge.
ROC has recently begun to show high levels of TN as well (mean 2,410 mg/L)
although the source is not known at this point in time.
Temporal patterns for TN were not evident.
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 20,500 mg/L and station annual means ranged from 19 to 9,339 mg/L (Table 2.10). Station annual means for the 2001-2002 monitoring period showed no consistent pattern compared with the seven-year means (Figure 2.6). The highest riverine nitrate levels were at NC11 (mean = 761 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 = 175 mg/L) had higher nitrate than the Black River (B210 = 109 mg/L). No clear temporal pattern was observable for nitrate.
Several stream stations carried high levels of nitrate on occasion (ANC, NC403, PB, ROC, BC117). NC403 and PB are downstream of industrial wastewater discharges and ROC primarily receives non-point agricultural or animal waste drainage. The source of nitrate at ANC is currently not known. 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 concentrations ranged from 5 (detection limit) to 1,720 mg/L and station annual means ranged from 31 to 227 mg/L (Table 2.11). Generally, the mean ammonium levels this monitoring period were higher than the seven-year means at the channel stations (Figure 2.6). This might be a concentration effect from point sources discharging into waters affected by the drought. Areas with the highest ammonium levels this monitoring period included AC (mean = 191 mg/L), which is below a pulp mill discharge, M54 (mean = 135 mg/L), and M61 (mean = 136 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 ANC, BC117, and BCRR (Table 2.11). PB also maintains relatively high ammonium levels.
Total Kjeldahl Nitrogen
Total Kjeldahl Nitrogen (TKN) is a measure of the total concentration of organic nitrogen plus ammonium. TKN ranged from 60 to 3,950 mg/L and station annual means ranged from 289 to 1,348 mg/L (Table 2.12). Mean TKN for this monitoring period was lower than the seven-year mean at all channel stations (Figure 2.7). Ammonium was generally higher for the channel stations this monitoring period and therefore organic nitrogen species must have been somewhat lower to account for low TKN. This was likely because of lower runoff of organic-rich swampwater and non-point source organic N from concentrated animal operations and other agricultural sources. 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 2.7). 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 5 (detection limit) to 3,550 mg/L and station annual means ranged from 30 to 1,461 mg/L (Table 2.13). TP at the riverine channel stations downstream into the upper estuary at BRR was slightly higher this monitoring period than the seven-year mean (Figure 2.8), and TP in the middle and lower estuary was lower. TP was highest coming into the system at NC11 (mean = 224 mg/L) and declined into the estuary toward the ocean. 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, BCRR, PB, and ROC. Some of these stations (BC117, NC403 and PB) are downstream of industrial or wastewater discharges.
Orthophosphate
Orthophosphate ranged from 0 to 3,550 mg/L and station annual means ranged from 10 to 1,681 mg/L (Table 2.14). The 2001-2002 annual means at the channel stations were considerably higher than the seven-year means down into the lower estuary and at the blackwater tributaries (Figure 2.9). In the lower estuary the averages this period were slightly lower than the seven-year averages.
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.
Aluminum levels in the Lower Cape Fear system were generally higher in the upper river, with a peak in the upper estuary at NAV, and decreased toward the lower estuary (Table 2.15). Stream stations were generally low except for BC117, which is below the Town of Burgaw wastewater treatment plant outfall, and COL, which is 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 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 in August, October, and June (Table
2.19).
The freshwater standard of 7 mg/L
was never exceeded at the upper river stations. Copper levels at BC117 exceeded the standard in four
out of six months, and the annual mean at this station was above the state
standard.
The LCFRP is an iron-rich system (Table
2.20). All of the freshwater
stations except for NCF117 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 (Table 2.21, 2.22,
2.23).
Zinc
concentrations remained below the state standard at all stations but were
elevated at BC117 on several occasions and during October at 6RC (Table
2.24).
Chlorophyll a
During this monitoring period chlorophyll a was generally low to moderate at the river and estuarine stations (Table 2.25). 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 2.10). 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 seven-year mean (Figure 2.10).
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 LRC, BC117
and BCRR, with smaller blooms at ANC and PB (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 40% higher than at NC11 suggesting influence from the pulp/paper mill inputs (Table 2.26). BOD displayed no discernable seasonal trend at any station.
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.
Fecal Coliform Bacteria
Several stream stations surpassed the state standard for human contact of 200
CFU/100 mL on at least one occasion. The
stream stations LRC and BC117 had geometric mean counts for the year exceeding
this standard. ANC, GS, BCRR,
BC117, LRC, 6RC, and SR all had particularly high levels on at least one
occasion. LRC and BC117 are
located below point source discharges, and the other sites mainly have problems
with non-point source pollution. The
total number of stations impaired by fecal coliform contamination (standard
exceeded in >10% of samples) was lower than in previous years, reflecting
reduced runoff conditions as a result of the drought.
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., M.H. Posey, M.L. Moser, G.C. Shank, M.R. McIver, T.D. Alphin, S.H. Ensign
and J.R. Merritt. 1998a. Environmental Assessment of the Lower Cape Fear River
System, 1997-1998. CMSR Report No.
98-02. Center for Marine Science Research, University of North Carolina at Wilmington, Wilmington, NC.
Mallin,
M.A., M.H. Posey, M.L. Moser, G.C. Shank, M.R. McIver, T.D. Alphin, S.H. Ensign
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98-02. Center for Marine Science Research, University of North Carolina at Wilmington, Wilmington, NC.
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., M.H. Posey, G.C.
Shank, M.R. McIver, S.H. Ensign and T.D. Alphin. 1999b. Hurricane effects on
water quality and benthos in the Cape Fear Watershed: Natural and anthropogenic
impacts. Ecological Applications 9:350-362.
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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