WATER QUALITY IN THE LOWER CAPE FEAR RIVER SYSTEM, 1995-1996

by

Michael A. Mallin, G. Christopher Shank, Matthew R. McIver
and James F. Merritt

Executive Summary

    Under the auspices of the Cape Fear River Program a broad-scale water sampling program in the Cape Fear watershed was begun in June 1995. Sixteen stations throughout the estuary and the lower Cape Fear, Black, and Northeast Cape Fear Rivers were sampled monthly, with the number of stations increased to 34 in February 1996. Data were collected for a variety of physical, chemical, and biological parameters.
    The mainstem Cape Fear River was characterized by high inorganic nutrient concentrations, moderate chlorophyll a biomass, high turbidity levels, and summer-early fall substandard dissolved oxygen levels. The main blackwater tributaries (the Black and Northeast Cape Fear Rivers) have much lower inorganic nutrient concentrations, low chlorophyll a biomass, very low turbidity levels, and low summer-fall dissolved oxygen levels. These blackwater rivers also differ from the mainstem Cape Fear in that most of the nitrogen and phosphorus (particularly nitrogen) is in the non-biologically available organic form rather than the inorganic species (nitrate, ammonia, orthophosphate). The extensive riverine wetlands bordering these blackwater systems appear to serve as efficient pollutant filters.
    The Cape Fear Estuary was characterized by moderate to high nutrient concentrations, moderate to high chlorophyll a biomass, periodic pulses of high turbidity, and summer-fall low dissolved oxygen in the upper estuary. The higher chlorophyll a concentrations (up to 29 ug/L) were found in the mid-to-lower estuary during the summer months. The high turbidity pulses were caused by non-point source runoff in the mainstem Cape Fear River watershed, and also from periodic dredging activities in the estuary. Causes of the river-upper estuary dissolved oxygen sag appear to be a combination of BOD loading from the pulp and paper industry along the mainstem Cape Fear River and contributions from oxygen-poor swamp waters draining into the blackwater tributaries.
    Vertical profiles and surface and bottom sampling results indicated that the riverine water column was well-mixed. There were no significant overall physical differences and few significant chlorophyll or nutrient differences (less than 20% of the time) between surface and bottom. The estuarine water column was likewise usually well-mixed, with occasional elevated salinity and turbidity near the bottom in mid-estuary. Chlorophyll and nitrogen concentrations showed no consistent vertical differences in the estuarine water column. Total phosphorus and ammonia showed periodic higher bottom-water concentrations (TP 34% of the time and ammonia 27% of the time). The well-mixed nature of the river and upper estuary prevented the formation of anoxic bottom waters. However, this same phenomenon also cause low dissolved oxygen levels (2-5 mg/L) to be maintained in the surface as well as bottom waters.
    Several animal waste lagoon spills occurrd in the Cape Fear watershed during summer 1995. We extensively sampled two of these, a 8.5 million gallon poultry lagoon rupture in the Northeast Cape Fear watershed in Duplin County and a two million gallon swine waste lagon leak near Town Creek in Brunswick County. The spills caused high nutrient loads to enter receiving waters (particulary amminia and orthophosphate), algal blooms, fish kills, and high turbidity concentrations. The BOD introduced by the spills caused low dissolved oxygen problems in local receiving streams and a dissolved oxygen sag in the Northeast Cape Fear River that registered its lowest reading 55 miles downstream of the waste input into the river. Elevated nutrients from the spill were also found at this downstream location. The spills also introduced high concentratins of fecal coliform bacteria and other pathogens to the receiving waters. The potential of environmental damage from the growing number of waste lagoons in the watershed is considerable, partcularly under adverse weather conditions (nor’easters, tropical storms or hurricanes).

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