2.0  Physical, Chemical, and Biological Characteristics of the
Lower Cape Fear River and Estuary

Matthew R. McIver, Michael A. Mallin, G. Christopher Shank

 

2.1  Introduction
   This section of the report includes a discussion of the physical, chemical, and biological water quality parameters, concentrating on the 1998-1999 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. 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.

Physical Parameters

Water Temperature, pH, Dissolved Oxygen, Turbidity, Salinity, and Conductivity
   Field parameters were measured at each site using a YSI 6920 Multiparameter 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, or until the cable connecting the datalogger with the sonde had been fully extended. High flow occasionally prohibited the probe from reaching the bottom. The instrument was calibrated prior to and after each sampling trip to ensure accurate measurements.

Chemical Parameters - Nutrients

    All nutrient analyses were performed at the Center for Marine Science Research for samples collected prior to January 1996. A local state-certified analytical laboratory was contracted to conduct all subsequent analyses (February 1996 through May 1999), except for the orthophosphate procedure that was performed at CMSR. The following methods detail the techniques used by CMSR 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 (1992) 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 with drierite granules, 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. 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. 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 June 1998–May 1999. Discussion of this data focuses mainly on the river channel stations, especially with respect to long term trends. 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. Conditions at the tributary stations are highly variable and often change rapidly as a result of localized weather phenomena, therefore, definable patterns and trends are not exhibited at these sites. Chronic water quality problems at tributary stations are discussed and possible causes are hypothesized. Hurricane Bonnie, which made landfall in the Cape Fear region on August 26, 1998, profoundly affected the Cape Fear River system, and is discussed in detail in Chapter 9.


Physical Parameters

Water Temperature
   Water temperatures at all stations ranged from 2.0 to 30.9 oC with individual station annual averages ranging from 17.0 to 20.8 oC (Table 2.1). Highest temperatures were found during July 1998 (all station mean = 28.7) and lowest temperatures were found during January 1999 (all station mean = 6.8). Tributary stations were generally cooler than the river channel stations; most likely a result of shading and low air temperatures at night.

Salinity
   Salinity at the estuarine stations ranged from 0.0 to 35.1 parts per thousand (ppt) and stations annual means ranged from 3.0 to 26.0 ppt (Table 2.2). Salinity was typically higher during the late summer/fall months and lower during the winter/spring months. Extremely low salinities in September are due to high rainfall from Hurricane Bonnie. The extreme low salinities had profound effects on the biota in the estuary (see Section 6 on benthic monitoring). Two tributary stations exhibited occasional oligohaline conditions. The Northeast Cape Fear River at NC403 and Panther Branch (PB) both receive salt-water effluent from pickle processing facilities.

Conductivity
   Conductivity ranged from 0.01 to 53.10 mS/cm at the estuarine stations and from 0.06 to 9.29 mS/cm at the tributary stations (Table 2.3). Temporal patterns for conductivity mimicked those of salinity. Dissolved ionic compounds increase the conductivity of surface waters; therefore, conductivity decreases with decreasing salinity, often reflecting river flow conditions concomitant with rainfall. Conductivity may also implicate point-source discharges of pollutants into the river. For instance, high conductivities at the PB station reflects the input of salt compounds by a pickle processing company. Also, at several freshwater stations located downstream of point-source inputs, conductivities are often higher than expected in non-saline surface waters: BC117 is below a wastewater treatment plant and AC is below a pulp mill discharge.

pH
    Values for pH ranged from 3.4 to 8.7 and station annual means ranged from 4.1 to 8.0 (Table 2.4). Median pH expectedly increased from the upper river (NC11- 6.3) into the estuary (M18 - 8.0), where low pH swamp water mixed with high pH seawater. The highest single measurement was taken in a freshwater tributary (LRC- 8.7), below a point-source discharge. The lowest single measurement was in a pristine blackwater tributary (COL - 3.4). However, pH can be naturally low in blackwater streams because of high concentrations of organic acids.

Dissolved Oxygen
    Dissolved oxygen (DO) concentrations ranged from 0.0 to 12.6 ppm and station annual means ranged from 3.3 to 10.1 ppm (Table 2.5). Mean annual concentrations at the channel stations were slightly higher than the four-year averages and remained above the North Carolina State standard of 5 ppm (Figure 2.1), yet dissolved oxygen problems are a major water quality concern for the Cape Fear River (Mallin et al. 1998a; 1998b). Dissolved oxygen levels at the channel stations are lowest during summer (Figure 2.2), with the four-year average falling below the NC state standard at several stations (Figure 2.3). 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 as well as increased allochthonous and autochthonous materials in the water. These hypoxic conditions could have negative impacts on the biota in the Cape Fear River (see Section 6). Natural hypoxia is most certainly exacerbated by effluent from a paper/pulp mill upstream of the AC station. Summer levels during 1998 were slightly higher than in 1997, until the arrival of Hurricane Bonnie (Figure 2.2).
    The Northeast Cape Fear and Black Rivers generally have lower dissolved oxygen levels than the mainstem Cape Fear River (Figure 2.4). 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 dissolve in 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 operations (CAOs) may also contribute to chronic low dissolved oxygen levels in these blackwater rivers (Mallin et al. 1998b). In the main river channel, mean oxygen levels were highest at the upstream stations NC11 (7.9 ppm) and AC (7.6 ppm) and at the lower estuary stations M23 (7.7 ppm) and M18 (7.6 ppm). Lower River and upper estuary stations DP (6.6 ppm), IC (6.0 ppm), and NAV (6.3 ppm) had the lowest DO levels. Discharge of high BOD waste from a paper/pulp mill just above the AC station (see Chapter 4), 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.
    Hurricane Bonnie caused DO levels to plummet to anoxic and hypoxic levels in September 1998; all channel stations had levels below 5.0 ppm (Table 2.3). The Northeast Cape Fear River suffered extremely low oxygen levels, becoming anoxic at NCF 117, where massive fish death occurred (see Chapter 9). The low dissolved oxygen levels resulting from Hurricane Bonnie were similar to the levels seen after Hurricane Fran hit the Cape Fear Region in September 1996. During both incidents, recovery of dissolved oxygen to normal levels, such as those seen in 1996, took nearly two months (Figure 2.2).
    Two tributary stations had chronic dissolved oxygen problems and annual means below the NC State standard of 5.0 ppm. NC403 at the headwaters of the Northeast Cape Fear River had an annual mean of 3.5 ppm. The pickle production facility upstream of this station is a likely source of BOD, yet the slow moving waters and the presence of several CAOs in the watershed may also contribute BOD. SR on the South River below the City of Dunn had an annual mean of 3.3 ppm, and although runoff from Dunn contributes significantly to BOD, there are likely other unknown sources of BOD in this watershed.

Turbidity
   Turbidity levels ranged from 0.0 to 130 NTU and station annual means ranged from 3 to 34 NTU (Table 2.6). Turbidities during this monitoring period were slightly lower than the four-year mean at most channel stations (Figure 2.5). The NC State standard for freshwater of 50 NTU was exceeded on seven occasions, most often at the upstream channel stations. The NC State standard for tidal saltwater of 25 NTU was exceeded on 26 occasions, most often in the upper estuary (Table 2.6). Although rainfall is positively correlated with turbidity in the Cape Fear River (see Chapters 3 and 4), turbidity peaks occur most often in winter and spring (Fig 2.6), the time of lowest rainfall in the Cape Fear Region. It is likely that decreased vegetation and decreased evapotranspiration during the cooler months lead to increased runoff and erosion. The contribution of turbidity by the Northeast and Black Rivers was very low. Typically, blackwater rivers carry a low turbidity load as a result of the settling action that occurs in the extensive riparian swamps bordering these rivers. At NCF117 the annual mean was 6 NTU and at B210 the annual mean was 8 NTU.
    The Cape Fear Region has endured the landfall of three hurricanes since 1996, usually accompanied by high rainfall totals. These events occurred in July 1996, September 1996, and August 1998; there were no high turbidity levels following these heavy rainfall events (Figure 2.6). It is likely that sediment loads were low because of dilution.
    The high levels of turbidity measured at NC11 (mean=29 NTU, maximum=130 NTU), indicates that a large portion of suspended material is being transported into the Lower Cape Fear River system from upstream areas (see also Chapter 3). Rainfall in the upstream areas of the Cape Fear River has a positive correlation with turbidity in the lower system (Mallin et al., 1998; see also Chapters 3 and 4 this report). Turbidity levels decline downstream before reaching the upper estuary at NAV, where increases turbulence may re-suspend turbidity particles. In the estuary, a turbidity maximum occurs as a result of electrochemical reactions in the water column due to the influence of charged ionic compounds (i.e. salinity). This leads to flocculation of particles (the turbidity maximum) and subsequent downstream settling. In the Lower Cape Fear River system the turbidity maximum occurs somewhere between M54 and M42 during normal flow conditions. Moving oceanward down the estuary, turbidities decline to a low at M18, a result of ocean dilution.

Note: The LCFRP uses nephelometers designed for field use, which allows us to acquire in situ turbidity from a natural situation. North Carolina Division of Water Quality uses turbidity values from water samples removed from the natural system, put on ice for a number of hours, and analyzed later using laboratory nephelometers. Standard Methods notes that transport of samples and temperature change alters true turbidity readings. Our analysis of samples read using both methods shows that lab turbidity is nearly always substantially lower than field turbidity, although the same process is used (nephelometry). We strongly recommend that NCDWQ begin utilizing 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 121 mg/l, with station annual means from 1 to 19 mg/l (Table 2.6). TSS was highest in the upper estuary at NAV and below a pulp mill outfall at AC. Lowest values were seen in the tributary stations and in the blackwater rivers. There was no definite temporal pattern for TSS, although, most of the high values occurred during early fall and winter. Unlike the 1997-98 monitoring period (Mallin et al 1998a), total suspended solids mimicked turbidity patterns fairly consistently. 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 inorganic particles may be poor at dispersing light, yet their greater mass results in high TSS.

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 0.99 to 10.49 k/m and station annual means ranged from 1.97 to 3.75 k/m. Light attenuation was typically highest at stations with high turbidity, yet the greater color in blackwater also increased light attenuation. At NCF6 and BBT, blackwater stations with moderate turbidity levels, light attenuation was very high (Table 2.8). Light attenuation during this monitoring period was somewhat higher than the four-year average at the river stations, but was lower than the four-year average in the estuary (Figure 2.7). Temporally, winter light attenuation was higher than other seasons, yet the highest monthly average was in September 1998, after Hurricane Bonnie. This was similar to results after Hurricane Fran, when light attenuation was highest system-wide because of flooding of highly colored swamp water into the main river channels (Mallin et al. 1999). 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

Ammonium
    Ammonium concentrations ranged from 5 (detection limit) to 960 m g/l and station annual means ranged from 29 to 223 m g/l (Table 2.9). Generally, the mean ammonium levels this monitoring period were lower than the four-year means at the channel stations (Figure 2.8). M35, M23, and M18, the three lowest estuarine stations, had annual means that were higher than the four-year means. Typically, sites with high ammonium levels were located below point source discharges. PB (mean = 223 m g/l) and NC403 (136 m g/l) are below pickle processing plants, LVC (130 m g/l) and AC (162 m g/l) are below industrial outfalls, and BC117 (146 m g/l) is below a municipal waste water treatment facility. ANC and COL are stations that represent relatively non-anthropogenically perturbed watersheds; however, annual means at these sites were moderately high (138 and 118 g/l, respectively). The reason for this may be that reducing conditions in these swamps retarded the conversion of ammonium to nitrate. The blackwater rivers had the lowest annual means (NCF117- 46 mg/l and B210 - 40 m g/l) of the riverine and tributary stations. Ocean dilution accounted for decreasing levels down into the estuary. There was a slight temporal pattern of lower ammonium during the cold winter months at the channel stations in 1996 and 1997. However, during 1995 and 1998, ammonium values during several winter months met or exceeded those of summertime (Figure 2.9). It is possible that higher levels of dissolved oxygen during colder months allow for rapid conversion of ammonium to nitrate. The unpredictability of ammonium levels on a seasonal basis is likely due to the multitude of variables that may affect ammonium levels including input/sources, oxygen conditions, bacterial activity, and algal productivity.

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 22,500 m g/l and station annual means ranged from 84 to 8,408 mg/l (Table 2.10). Station annual means for the 1998-99 monitoring period were about the same as the four-year means, except at several lower estuary stations (Figure 2.10). High nitrate levels at NC11 (mean = 738 mg/l) indicate 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 = 214 mg/l) had higher nitrate than the Black River (B210 = 164 mg/l). No clear temporal pattern is observable for nitrate (Figure 2.11). Two very low nitrate means during September 1996 and September 1998 followed hurricanes (with heavy rainfall) and may be a result of dilution and/or lack of oxygen, which would favor the ammonium nitrogen species over nitrate.
    Two tributary stations, LRC (average 1,523 mg/l) and BC117 (average 8,408 mg/l), carried extremely high levels of nitrate on several occasions, exceeding the North Carolina state drinking water standard of 10 mg/l six times. Both sites are strongly influenced by wastewater discharges upstream (see section below on Little Rockfish Creek). Nitrate at several other tributary stations was noticeably elevated. Most of these stations are in the Northeast Cape Fear River watershed and may be influenced by agriculture and/or factory-style livestock operations, which can contribute high nutrient levels to local watersheds. Silviculture may also affect nutrient levels (see Chapter 5).

Total Kjeldahl Nitrogen
    Total Kjeldahl Nitrogen (TKN) is a measure of the total concentration of organic nitrogen plus ammonium. TKN ranged from 60 to 5,230 mg/l and station annual means ranged from 368 to 1,218 mg/l (Table 2.11). Mean TKN for this monitoring period was lower than the four-year mean at all channel stations (Figure 2.12). Ammonium was also lower for the channel stations this monitoring period and this decline is reflected in the TKN values. Low TKN in the lower estuary highlights the fact that increasing primary productivity by phytoplankton increases uptake of inorganic nitrogen through the food chain into higher consumer organisms, and dilution with ocean water. Higher TKN at the tributary stations bolsters the idea as these sites usually have low phytoplankton productivity and are receiving streams for nitrate entering the system. Measured TKN levels in the blackwater rivers are higher than in the mainstem Cape Fear River as a result of the high organic materials dissolved in the water (Figure 2.12). There is somewhat higher TKN during summer months (Figure 2.13). TKN has steadily declined at the Lower Cape Fear River channel stations over the four monitoring periods, 1995-1999.

Total Nitrogen
     Total nitrogen (TN) ranged from 110 to 21,630 mg/l and station annual means ranged from 453 to 2,507 mg/l (Table 2.12). Mean total nitrogen was lower this monitoring period than for the four-year mean at all channel stations (Figure 2.14). 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 grazing by planktivores and dilution. The pulp mill above AC is a source of TN, increasing levels at this station (mean = 1416 mg/l). The blackwater rivers carried total nitrogen loads somewhat lower than those found in the mainstem Cape Fear River (NCF117 mean=893 mg/l, B210 mean=746 mg/l). Two tributary stations had incidences of elevated TN levels including LRC (2,507 mg/l, see Little Rockfish Creek section below) and BC117 (9,434 mg/l), both of which are strongly influenced by wastewater discharge. TN at these two stations occasionally reached alarming levels due to high levels of nitrate. Temporal patterns for TN are not evident (Figure 2.15), yet there is a conspicuous decline in TN in November 1997 that persists through this monitoring period. A similar decline in TKN (Figure 2.13) and the lack of a decline in nitrate or ammonium suggests that the declining constituent of TN is organic nitrogen. Reasons for this trend are unknown.

Orthophosphate
    Orthophosphate ranged from 5 (detection limit) to 4,717 mg/l and station annual means ranged from 11 to 1,395 mg/l (Table 2.13). At all of the channel stations the annual means this monitoring period were above the four-year means except in the lower three estuary stations and the blackwater rivers (Figure 2.16). A regression of orthophosphate for the four years of data collection at the channel stations indicates that levels of this nutrient have increased during the summer months (Figure 2.18). The reasons for this increase may be very complicated, yet increasing levels entering the system at NC11 indicate that much of the rise may be associate with activity in the upper and middle Cape Fear River watersheds. Much of the orthophosphate load is imported into the Lower Cape Fear system from upstream areas, demonstrated by NC11 (mean = 126 mg/l) having the highest levels. 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.
    The Northeast Cape Fear River had higher orthophosphate levels than the Black River. BC117 (average 1,395 mg/l) and LRC (average 436 mg/l) had very high concentrations of orthophosphate and SAR (131 mg/l), on the Northeast Cape Fear River, had moderately high orthophosphate levels. Although there is a textile discharge upstream, it is likely that the prodigious number of factory-style livestock farms in the area contribute as a source of this nutrient. Orthophosphate levels typically reach maximum concentrations during summertime (Figure 2.17), when anoxic sediment releases bound phosphorus. Also, in the Cape Fear River, summer algal productivity is limited by nitrogen, thereby allowing the accumulation of orthophosphate (Mallin et al 1997).

Total Phosphorus
    Total phosphorus (TP) concentrations ranged from 5 (detection limit) to 4,870 mg/l and station annual means ranged from 35 to 1,493 mg/l (Table 2.14). TP at the riverine channel stations was higher this monitoring period than the four-year mean (Figure 2.19), but the estuarine and blackwater stations concentrations were lower. A temporal pattern of higher summertime TP (Figure 2.20) is a result of increasing orthophosphate. TP was highest coming into the system at NC11 (mean=229 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. The spatial pattern of TP is similar to that of orthophosphate. LRC (mean=482 mg/l) and BC117 (mean=1,493 mg/l) exhibited high TP; wastewater discharge above these sites is the likely source (Table 2.14). Pickle plant discharge is the source of high TP levels at NC403 (mean = 298 mg/l) and PB (mean = 198 mg/l).

Organic versus Inorganic Nutrient Composition
   Organic nitrogen composition ranged from 47% to 76% of total N (Figure 2.21). The lowest levels were at NC11 (47%), increasing into the estuary at M54 (60%), and highest at the river mouth (71%). Organic nitrogen in blackwater rivers is naturally high (NCF117 = 75% and B210 = 76%) because of the complex dissolved compounds that derive from riparian swamps. The composition of phosphorus compounds (inorganic versus organic) was fairly constant at all stations, with organic phosphorus composition ranging from 53% to 69% of total P (Figure 2.22). In the Cape Fear River the lowest organic phosphorus composition was at NC11 (53%) with a gradual increase into the estuary at M54 (65%), and maximum percentages near the ocean at M18 (69%). Organic phosphorus composition was higher in the Black River (B210 - 64%) than in the Northeast Cape Fear River (NCF117 - 55% organic). Organic nitrogen percentages in the blackwater rivers were much higher than organic phosphorus (NCF117 - 75% vs. 55%, B210 - 76% vs. 64%). Higher ratios of organic versus inorganic compounds for both nitrogen and phosphorus in the estuary, along with higher algal biomass, reflect assimilation of nitrogen and phosphorus into the food chain via primary productivity.
    A clear temporal pattern is discernable for inorganic nitrogen to inorganic phosphorus ratios (Figure 2.23). The ratio is very high in winter, and during late summer dips below the Redfield ratio of 16:1 N:P. These ratios would theoretically lead to phosphorus limitation of primary productivity during winter and nitrogen limitation in summer. Our experimental data demonstrate that summer nitrogen limitation does occur, but in winter primary production is light-limited (Mallin et al. 1997). However, phosphorus limitation has been demonstrated experimentally in springtime (Mallin et al. 1997).

 

Chemical Parameters - EPA Priority Pollutant Metals

    There is no North Carolina State water-column standard for aluminum concentrations. Aluminum levels in the Cape Fear system were generally high at NC11 and decreased downstream to NAV, where levels were again elevated (Table 2.15). Stream stations were generally low except for BC117, which is below the Burgaw Wastewater Treatment plant outfall (Table 2.15). Arsenic, cadmium, and chromium all maintained concentrations below the state standard 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 m g/L at some of the estuarine stations in winter, and in the lower estuary in April (Table 2.19). The freshwater standard of 7 m g/L was rarely exceeded at the LCFRP stations except at BC117, which exceeded the standard in five out of twelve months and maintained average copper concentrations through out the year in violation of the state standard (Table 2.19).
    The LCFRP is an iron-rich system (Table 2.20). All of the freshwater stations except for NCF117 maintained average iron concentrations above the state standard of 1000 ug/L. Iron concentrations generally decreased down-estuary (Table 2.20). Water-column concentrations of lead and mercury remained below either the state standard or the analytical detection limit during 1998-1999 (Table 2.21, 2.22). Nickel concentrations remained below the state standard at all freshwater stations and only exceeded the salt water standard once in the estuary (Table 2.23). Zinc concentrations remained below the state standard at all of the estuarine stations and most of the freshwater stations during 1998-1999 (Table 2.24). However, Station BC117 exceeded the state standard twice last year and nearly did so on two other occasions (Table 2.24). Thus, station BC117 is problematic from a water quality standard based on several parameters. On the other hand, concentrations of several metals and nutrient species have decreased relative to previous years at LRC, evidently in response to the closing of the textile mill formerly upstream of that site (Mallin et al. 1997; 1998).

Note: The LCFRP has accumulated three and a half years of monthly water column metals at the present locations. From examination of the data it is our opinion that it is time to reallocate some of our metals efforts to other stations currently lacking such analyses, while maintaining analyses at those stations that are problematic or representative of a specific area.

Biological Parameters

Chlorophyll a
   During the June 1998 through May 1999 period chlorophyll a was generally low in the river and estuarine stations of the LCFRP (Table 2.25; Figure 2.24). 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. Highest chlorophyll a concentrations are typically found during the period June through September (Fig. 2.25). During the past year chlorophyll a was lower than the long-term average, possibly a result of Hurricane Bonnie causing extremely low levels in September 1988 (Table 2.25; Figure 2.25). Spatially, highest values are normally found in the mid-to-lower estuary stations (Figure 2.24), because light becomes more available downstream of the estuarine turbidity maximum. Chlorophyll a production is extremely limited in the large blackwater rivers (Table 2.25; Figure 2.24). However, substantial phytoplankton blooms do occur in the stream stations, particularly during summer months (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 (see Section 5) 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. 1998b).

Biochemical Oxygen Demand
   Average five-day biochemical oxygen demand (BOD5) concentrations were approximately 1.0 mg/L at stations NC11, B210 and NCF117 (Table 2.26). BOD5 and BOD20 were both considerably elevated at AC compared with NC11. Sources of this increased BOD are discharges from International Paper, and point sources and perhaps non-point source runoff within Livingston Creek. More detail is presented on BOD in Chapter 4. BOD concentrations at BBT are between that of NC11 and AC. This station receives inputs from both the river mainstem and the Black River. BOD displayed no discernable seasonal trend at any of the five stations sampled during 1998-1999 (Table 2.26). However, a major increase in BOD occurred at AC, BBT, B210 and NCF117 in September following Hurricane Bonnie. Sources for this BOD increase were swine waste inputs, malfunctioning human sewage systems, and increased non-point source contributions from swamp watersheds and agricultural areas.

Fecal Coliform Bacteria
   Fecal coliform bacterial counts in the LCFR system show a notable spatial trend of highest counts in the upper estuary-lower river area bounded by NAV, HB, and BRR (Figure 2.26). This is the result of several incidents during the years in which these stations showed unusually high counts (see November 1998 and April 1999, Table 2.27) for examples. This is most likely indicative of a malfunctioning point source discharge in this area. The mainstem river stations otherwise display relatively low counts (Table 2.27). The major exception to this was during September following Hurricane Bonnie, when high counts were found near Wilmington (HB, BRR, M61), and in the Northeast Cape Fear River. Improperly treated sewage discharges following power outages and swine waste from storage lagoons on floodplains were the principal sources for these inputs (see Section 9 this report). Many of the stream stations, particularly those draining watersheds rich in swine farms, also showed large increases in fecal coliform counts following Hurricane Bonnie (Table 2.27).
    The stream stations that yield chronically elevated fecal coliform counts are mainly those downstream of point sources. PB (below a pickle plant), LRC (below the site of the former Stevecoknit), and BC 117 (below the Burgaw wastewater treatment plant) all had geometric mean counts for the year exceeding the state standard for human contact of 200 CFU/100 mL (Table 2.27). BCRR had considerably lower counts than BC117, but was also in violation of the health standard. As there are no major point sources listed upstream of BCRR, non-point sources may be responsible for these high counts.

 

Little Rockfish Creek

    Station LRC, located on Little Rockfish Creek below the city of Wallace, has historically had egregious water quality problems including purple water coloration, and elevated nutrients, heavy metals, bacteria, and chlorophyll a (Mallin et al 1997,1998). Industrial and wastewater discharge from Stevecoknit, a textile facility, entered the creek upstream of LRC. The plant ceased operation approximately May 1998, though continued discharge to empty holding ponds may have continued for several months.
    Water quality improved after cessation of plant operations. Several parameters had noticeable reductions (June 1997-June 1998 versus May 1998-May 1999): turbidity 66%, TSS 78%, ammonium 79%, nitrate 97%, orthophosphate 97%, chlorophyll a 35%, aluminum 7%, chromium 99%, copper 93%, nickel 99%, zinc 79%. Although fecal coliform levels were reduced by 59%, levels occasionally reached numbers considered dangerous for human contact. Dissolved oxygen levels increased 15% and iron levels increased 6%. Although no quantification was made, freshwater clams became abundant at LRC during the summer of 1999.

 

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., 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., 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., M.H. Posey, G.C. Shank, M.R. McIver, S.H. Ensign and T.D. Alphin. 1999. Hurricane effects on water quality and benthos in the Cape Fear Watershed: Natural and anthropogenic impacts. Ecological Applications 9:350-362.

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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