ENVIRONMENTAL ASSESSMENT OF THE LOWER CAPE FEAR RIVER SYSTEM, 1999-2000

by

Michael A. Mallin, Martin H. Posey, Matthew R. McIver, Scott H. Ensign,
Troy D. Alphin, Michael S. Williams, Mary L. Moser and James F. Merritt

Report Number 00-01
Center for Marine Science
University of North Carolina at Wilmington

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 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 June 1999-May 2000. The opinions expressed are those of UNCW scientists and do not necessarily reflect viewpoints of individual contributors to the Lower Cape Fear River Program. This report focuses on the period June 1999 through May 2000.
    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 tidal 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.
    Several stations were in violation of North Carolina water quality standards based on percent of samples in violation during the year June 1999 – May 2000. Definitions used by the North Carolina Division of Water Quality for use support 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. Based on this, Station M42 was NS for turbidity, and Stations NAV, HB, BRR, M61, M54, M31, SPD, LRC and BCRR were PS. Stations that can be considered non-supporting for dissolved oxygen (4.0 in blackwater stations and 5.0 in estuarine stations) were NAV, DP, IC, NCF117, ANC, SAR, GS, N403 and SR. Stations considered partially supporting for dissolved oxygen include HB, M61, M54, SPD, BBT, B210, ROC, BCRR, GCO and HAM. Stations in which fecal coliform concentrations exceeded 200 CFU/100 mL >25% of the time (NS) were N403, PB, LRC, BC117, BCRR and HAM. Those considered PS for fecal coliforms include LVC, GS, ROC, GCO and BRN. Copper was the only problematic waterborne metal, with Stations NAV, HB, M54, M42, M31, LRC and BC117 rated PS.
    The LCFRP carried out an extensive program to analyze short-term (24 hr, or diel) variability in water quality in 1998-1999. This was done at five locations on 4-6 occasions each. A diel signal for dissolved oxygen change was not seen in three of the stations, and occurred only twice at NC11 and twice (faintly) at M42. Diel signals were common only for water temperature among all stations, with increased temperatures in the afternoons and lowest at night or early morning. Short term dissolved oxygen variability in the LCFR system was primarily controlled by tidal movement, at locations where tidal movement was strong. Near and in the estuary, the incoming tide coincided with increased dissolved oxygen, pH, salinity, specific conductance, and bottom water turbidity pulses. In the riverine stations the waters appeared well mixed, with stratification generally confined to the estuary where dissolved oxygen and pH were associated with higher salinity waters. These data confirm an earlier study by the LCFRP in which discrete depth water samples were collected at the surface and bottom for chemical parameters and statistically compared. It was also plain from this study that both diel and tidal variability can be overwhelmed by hurricane forced changes in water quality, particularly in the Northeast Cape Fear River.
    For the 1999-2000 Cape Fear River report, the benthic sampling and analyses emphasized analysis of site characteristics, annual and seasonal variations in community structure, variations in species richness and diversity, and effects of multiple hurricanes on the Cape Fear River benthic community. These analyses are preliminary in nature, based upon only 4 years of data (3 of which were affected by hurricanes) and only 4 sampling sites. Additional sites will be required to adequately address spatial patterns. However, the 4 sites sampled provide insights into biotic community structure in the lower Cape Fear River system. Basic findings for this report are:

• The Northeast Cape Fear River and Cape Fear River oligohaline sites (NCF6 and NAV) are similar in terms of numbers of species present, with low to moderate relative species richness at both sites. However, they differ in several important aspects. The NCF6 site is characterized by higher diversity, low faunal densities, and seasonal variability in abundances. In contrast, the NAV site is characterized by lower diversity, higher total faunal density, and a tendency towards winter or spring peaks in faunal abundance and seasonal replacement of dominant species. Such differences indicate fundamentally different processes controlling these communities.
• Lower estuarine sites (M54 and M31) are characterized by moderate species richness and faunal abundances. They are dominated by taxa typical of other river-dominated mid Atlantic and southeastern estuaries, though clams continue to be much less common than reported in many other studies.
• Although abundances fluctuated among years at all sites, overall diversity, number of species and the identity of dominant taxa remained relatively persistent over the 4 years, with some variations related to seasonality. The only exception was a gradual trend towards lower species richness over time at M31.

Hurricane effects varied among sites. However, there were few unequivocal long-term effects of multiple hurricanes on faunal abundance (though, as noted above, there were some potential effects on species richness).
    Fish diversity and abundance were decreased in the 1999 summer/fall sampling period relative to the two previous years. While species richness showed no seasonal or spatial trend during 1999, an alarming trend is the steady drop in species richness over the last three fall seasons. The June-December samples have demonstrated declines from 70 species in 1997, to 65 species in 1998, to 56 species in 1999. An area of concern is the drop in post-larval croaker in 1999. Loss of nursery habitat in the Cape Fear could have negative impacts on recruitment of commercially important marine species. Non-native abundance has increased in the gill net catch this season. Through competition, hybrid striped bass may be depressing the native striped bass (Morone saxatalis) population. Another area of concern is the increase in the number of grass carp (Ctenopharyngodon idella) captured. This species feeds on aquatic vegetation that is used as nursery habitat for juvenile fish and aids in erosion control. An increasing population of this species could have negative impacts on future recruitment of fisheries resources in the Cape Fear. Overall, external signs of fish disease remain low in the Cape Fear (1.6%). Bowfin (Amia calva), however, are exhibiting a 50% infection rate. That this resident species continues to exhibit an abnormally high infection rate warrants concern and future tissue sampling for contaminant loading.
    In recent years, both Hurricanes Fran and Bonnie caused massive fish kills in the Northeast Cape Fear River from severe hypoxia and anoxia caused by the heavy BOD loads. That was not the case with Hurricane Floyd in 1999. The hypoxia after Floyd was both delayed and milder than that following the other two hurricanes, and the effect on fish appeared to be much less severe. The largest fish kill we found occurred three weeks after Floyd, and consisted of only 18 carcasses at NCF117, the scene of large-scale kills on other occasions. We suspect that the flooding caused the smaller fish to move up over the floodplain, where abundant food sources are found while dilution of BOD-causing materials in the river channels ameliorated the effect of hypoxia on the larger fish in the channels.
    To summarize responses by the benthic community to the recent multiple hurricanes in the Cape Fear River system, long-term declines in species richness occurred at the lowest site (M31) and there were short-term, though variable, effects on species composition and abundance at most sites. However, the benthic community appeared remarkably resilient to repeated hurricane events with few major long-term changes apparent. This is probably related to the opportunistic lifestyle of the dominant species found in this estuary. Maranzellaria, Mediomastus, the dominant insect larvae, and oligochaetes are well-known to be opportunistic taxa that can quickly colonize an area after a disturbance and exhibit rapid recovery in population numbers. The dominance of these taxa in the Cape Fear estuary is typical of many river-dominated estuarine systems, but may also reflect the long history of disturbance from channelization, dredging, and upstream development and agricultural runoff that has occurred. The benthic community in the Cape Fear estuary may reflect those taxa that have already undergone selection for periodic, strong disturbance events.
    Floodwaters in the lower rivers and estuary showed low fecal coliform counts when examined three weeks after Hurricane Floyd. In contrast, many LCFRP stations exhibited high fecal coliform counts one week following Hurricane Bonnie, demonstrating that there is an important human health concern in post-hurricane water bodies. Additionally, watersheds within the Wilmington City limits showed very high fecal coliform counts a week after Floyd’s passage. Post-hurricane sources of fecal coliforms in the rivers include swine waste from flooded or breached lagoons, runoff from sprayfields, and rerouted human sewage that was incompletely or not treated following failure of main power supplies. Sources in the city include sewage overflows and urban runoff (likely from dogs and other animals). We recommend that civic health authorities post warnings at all public boat ramps and in the newspapers that water may not be safe for human contact for a period of at least three weeks following hurricane events.
    To summarize, Hurricanes Fran and Bonnie, and to a lesser extent Floyd, caused water quality degradation and increased risk of human exposure to potential microbial pathogens. The lower Cape Fear watershed contains many point-source sewage outfalls and the largest concentration of industrial-style swine farms (CAOs) in North Carolina. Hurricane impacts to these pollutant sources have led to large inputs of nutrients, oxygen-consuming organic wastes (BOD) and fecal bacteria into the river system. Following the hurricanes the most severe damage (as measured by water quality indicators, losses in the benthic community, and fish kills) was in the Northeast Cape Fear River. This tributary hosts both point sources and numerous CAOs. Additionally, lower flows than the Cape Fear mainstem combined with tidal action helps to retain pollutants for extended periods in this tributary. While the river hydrology cannot be changed, better management of animal wastes from CAOs on the floodplain and independent backup generating systems for wastewater facilities lacking them will help reduce post-storm pollutant impacts to the biotic communities. 

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