ENVIRONMENTAL ASSESSMENT OF THE LOWER CAPE FEAR RIVER SYSTEM, 2001-2002

by

Michael A. Mallin, Martin H. Posey, Thomas E. Lankford, Matthew R. McIver, 
Heather A. CoVan, Troy D. Alphin, Michael S. Williams, and James F. Merritt

CMS Report Number 02-02
Center for Marine Science
University of North Carolina at Wilmington
Wilmington, N.C. 28409
November 2002

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Executive Summary

        Multiparameter water sampling for the Lower Cape Fear River Program (LCFRP) has been ongoing since June 1995.  The LCFRP currently encompasses 35 water sampling stations throughout the Cape Fear, Black, and Northeast Cape Fear River watersheds.  The LCFRP sampling program includes physical, chemical, and biological water quality measurements, analyses of the benthic and epibenthic macroinvertebrate communities, and assessment of the fish communities.  Principal conclusions of the UNCW researchers conducting these analyses are presented below, with emphasis on the period July 2001-June 2002.  The opinions expressed are those of UNCW scientists and do not necessarily reflect viewpoints of individual contributors to the Lower Cape Fear River Program.

        The mainstem lower Cape Fear River is characterized by reasonably turbid water containing high levels of inorganic nutrients.  It is fed by two large blackwater rivers (the Black and Northeast Cape Fear Rivers) that have low levels of turbidity, but highly colored water, with less inorganic nutrient content than the mainstem.  While nutrients are reasonably high in the river channels, algal blooms are rare because light is attenuated by water color or turbidity, and flushing is high.  Periodic algal blooms are seen in the tributary stream stations, some of which are impacted by point source discharges.  Below some point sources, nutrient loading can be high and fecal coliform contamination occurs.  Other stream stations drain blackwater swamps or agricultural areas, some of which periodically show elevated pollutant loads or effects. 

        During the 2001-2002 sampling period a prolonged drought had a significant effect upon water quality.  Parameters that are particularly subject to non-point source runoff (suspended solids, turbidity, and light attenuation) all showed considerable decreases compared with the long-term averages from 1995-2002.  Only 6% of the stations showed impairment for turbidity, and those did not show severe impairment.  However, nutrient concentrations during this sampling period were variable compared with previous years except for ammonium, which was higher this year at most stations compared with the long-term average, and organic nitrogen, which was lower.  Low dissolved oxygen remained a major problem in the LCFR basin, with 34% of the stations experiencing impairment, some stations (ANC, NC403, PB, and SR) severely.  The magnitude of the low dissolved oxygen problem was similar to that of previous non-hurricane years.  Additionally, 26% of the stations showed impairment by high fecal coliform counts.  The impaired locations were a mixture of areas impacted by point and non-point source inputs, with particularly high levels at LRC and BC117.  The number of stations impaired by fecal coliform contamination was lower than the past several years, undoubtedly a reflection of reduced non-point source pollution as a result of the drought conditions.  Chapter 3 provides an in-depth look at use support ratings for each subbasin, comparing the results of the North Carolina Division of Water Quality's 2000 Basinwide Management Plan with the LCFRP's assessments of the 2001-2002 sampling year.  The LCFRP utilized definitions used in part by the North Carolina Division of Water Quality for use support that consider a water body non-supporting (NS) of its designated use if the water quality standard for a given parameter is in violation > 25% of the time, and partially supporting (PS) if the standard is in violation between 11 and 25% of the time. 

        The benthic community of the Cape Fear River estuary is dominated by opportunistic taxa characteristic of mesohaline to oligohaline reaches of Mid Atlantic to southeastern U.S. estuaries. These taxa are quick to recolonize after disturbances and their dominance suggests the benthic community may be resilient to certain types of disturbance if that disturbance is short-lived and environmental conditions return to pre-disturbance levels. There are few long-term trends in diversity, abundance or species richness that have been consistent over the past 5 years. Similarly, there has been quick recolonization after disturbance and dominance by a relatively consistent group of species at each site over this time period. We interpret these results to indicate that the infauna in the Cape Fear River have been strongly affected by both natural and anthropogenic disturbances, leading to dominance by a restricted set of opportunistic species, and a paucity of groups such as larger bivalves or larger burrowing worms. However, the community does not currently appear to be exhibiting continued decline and the species present are likely to be able to tolerate or at least recover from water quality changes if these changes are not persistently severe.

        There continues to be a fundamental difference between the oligohaline mainstem Cape Fear site (NAV) and the oligohaline Cape Fear River site (NCF6). NCF6 has lower faunal abundances relative to NAV, with the only exception of summer 1999 (due to recruitment and later disappearance of a single polychaete species). NCF6 has higher diversity than NAV because of relatively similar densities among a suite of species at this low density site. In contrast, NAV has similar numbers of species as NCF6, but the community is dominated by only two taxa.

        Regarding the fisheries community, the lack of electroshocking data from this years survey has hampered our ability to closely monitor species richness and disease incidence.  Despite this, trawling catches of over five-thousand spots (Leiostomus xanthrus), and six-thousand Atlantic croakers (Micropogonois undalatus), created the largest trawling catch-per-unit-effort in the history of the survey. The large catches of estuarine dependent species further reinforces the important role the Cape Fear River system plays as nursery habitat.  With the data that are available, the drought has had little, if any effect on overall fish community structure, non-native percentages, or disease incidence.  Relative abundance, however, has been impacted by the large catch-per-unit-effort increases in the trawling survey.  Whether the increase was due to interannual variablilty, a large year-class, or simply due to the increased salinity caused by the severe drought North Carolina was experiencing, is a question that future surveys should investigate.  Although most of the trend analysis showed no discernable patterns in a positive or negative direction, a trend toward decreasing gillnetting catch-per-unit-effort and species richness in the summer/fall season may be developing and should be closely monitored in future surveys.

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Table of Contents

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