WATER QUALITY IN THE LOWER CAPE FEAR RIVER SYSTEM, 1996-1997

by

Michael A. Mallin, Martin H. Posey, Mary L. Moser, G. Christopher Shank,
Matthew R. McIver, Troy D. Alphin, Scott H. Ensign 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. Thirty-four stations throughout the estuary and the lower Cape Fear, Black, and Northeast Cape Fear Rivers were sampled monthly. Data were collected for a variety of physical, chemical, and biological parameters and results are presented within. A broad-scale analysis of the lower riverine and estuarine benthic invertebrate communities is also presented, as is a winter-spring analysis of the fish communities in the lower rivers.
    During both the summer of 1995 and 1996 there were substandard (< 5.0 mg/L) dissolved oxygen concentrations in the lower Cape Fear River and upper estuary, lasting several months. Data indicate that both industrial BOD and natural swamp water inputs contribute to this situation. Because of the well-mixed condition of the rivers dissolved oxygen vertical stratification does not occur; rather, hypoxic conditions are found throughout the water column. In 1996 this condition was exacerbated by Hurricane Fran, and levels at or approaching anoxia were found in some locations. Turbidity is another physical problem in the mainstem and the estuary, where both the freshwater and brackish water standards are exceeded at times. One major source of turbidity is non-point source runoff flowing into the mainstem and reaching the estuary following rain events upstream. Another source is estuarine dredging, which is permitted in winter. Turbidity can be problematic in that it interferes with rooted aquatic plant photosynthesis and feeding of fish and shellfish, and can transport fecal coliform bacteria, nutrients, and contaminants far downstream from their point of entry into the stream. The Black and Northeast Cape Fear Rivers maintain low turbidity as a result of their lowland origins and extensive streamside wetlands which filter the water.
    Inorganic nutrients (nitrate and orthophosphate) are general high in the mainstem of the Cape Fear, indicating significant non-point source inputs upstream. Nutrients in the blackwater tributaries were lower in concentration and had a greater percent in the organic form, demonstrating the value of riparian wetlands as filters and transformers of inorganic nutrients. Analysis of tributary streams showed instances where high concentrations of total nitrogen and phosphorus were contributed to the watershed by point sources from municipal (up to 7.6 mg/L TN and 1.5 mg/L TP) and industrial (up to 14.9 mg/L TN and 2.3 mg/L TP) wastewater effluents.
    Chlorophyll a concentrations were generally low to moderate in the Cape Fear system, because of high flow conditions, and elevated turbidity and water color reducing available light for photosynthesis. Additionally, the very well mixed nature of the river and estuary creates unfavorable conditions for surface algal bloom formation. Fecal coliform concentrations were usually within state standards for human contact waters in the riverine and estuarine stations. The lower estuary stations were often above the standard for safe shellfishing, however. Some tributary streams had problematic fecal coliform levels at times, including Little Rockfish Creek, Burgaw Creek, Browns Creek and Hammond’s Creek. Five-day biochemical oxygen demand (BOD5) was generally low at all stations tested in the mainstem Cape Fear and the two major blackwater tributaries. There was a 15% increase in BOD5 and a 17% increase in BOD20 between stations 3 miles upstream and 3 miles downstream of the International Paper mill in Riegelwood, indicating industrial inputs of BOD. BOD5 concentrations 6 times higher than normal occurred in the Northeast Cape Fear River following Hurricane Fran, but significant increases did not occur at the other stations.
    Analysis of waterborne metals indicated that arsenic, cadmium and lead concentrations were below state standards at all stations on all sampling occasions. Samples exceeding state standards for mercury were found on occasion throughout the system, and samples exceeding standards for iron and zinc were frequently encountered systemwide. Periodically some samples displayed elevated concentrations of chromium, copper and nickel, mainly in the lower estuary at locations near Sunny Point and Southport. Little Rockfish Creek was the tributary station which had the most problematic metals concentrations.
    The results of the first year of sampling infauna and epibenthos indicate that the species comprising these groups, their distributions, and seasonal patterns in the Cape Fear River Estuary are similar to those of other river-dominated estuaries in the southeastern and mid-Atlantic United States. As is typical of these estuaries, the fauna is dominated by a variety of widely occurring and opportunistic species that are capable of quick recovery from a variety of disturbances. However, strong responses in the infaunal and epifaunal communities to Hurricane Fran emphasize that the estuarine system was negatively affected by upstream inputs, possibly with strong ecosystem consequences, and that long-term trends in estuarine health need to be closely monitored.
    Variability in fish abundance and diversity was high during the short period of time that fisheries have been monitored thus far. Nevertheless, both gillnet and trawl collections indicated that fish abundance and diversity were lower in the Northeast Cape Fear River stations than in the mainstem Cape Fear River stations. Overall disease incidence was 2.1%. Disease incidence was higher (4.3%) in electroshock collections which targeted adult, resident species, and no disease was noted in trawl collections which target juveniles and non-resident species. The numerical dominance of non-native species in gillnet collections indicates that these species are proliferating throughout the drainage.
    The main impact of Hurricane Bertha on water quality was to cause reductions in dissolved oxygen, which subsequently recovered by late August to normal levels. Hurricane Fran, however, had a major systemwide impact on dissolved oxygen, BOD, nutrient concentrations, and water clarity. There was systemwide flooding of swampwater into main river channels during and after this hurricane. Analysis of data indicated that effects on the Northeast Cape Fear River were more severe and longer lasting than any of the other locations. In this watershed several swine waste lagoons breached or were inundated, introducing large quantities of labile BOD, phosphorus and ammonia into the river. The mainstem Cape Fear and the Black River were affected by millions of gallons of inadequately treated human sewage, routed into the rivers because of power losses to treatment facilities and pump stations. Benthic communities were variably affected by Hurricane Fran, with significant population reductions in the Northeast Cape Fear River and at a mid-estuary site. Effects on benthos were less severe and less long-lasting in the lower mainstem Cape Fear River and the lower estuary. There are no pre-hurricane fisheries data to make comparisons with. However, both gillnet and trawl data indicated higher fish abundance and diversity in the mainstem Cape Fear River than in the Northeast Cape Fear River. The severe and prolonged anoxia following Hurricane Fran in this tributary may be responsible for this difference.

Table of Contents

**Any tables or figures not included on this site are available in hard copy from the Center for Marine Science at the University of North Carolina at Wilmington**