Hurricane Effects on Water Quality and Benthos in the Cape Fear Watershed: Natural and Anthropogenic Impacts

In the summer of 1996, southeastern North Carolina, United States, was struck by two hurricanes, with the second (Hurricane Fran) doing considerably more damage than the first (Hurricane Bertha). The Cape Fear watershed, largest in North Carolina, suffered from severe water quality problems for weeks following Fran, including a massive fish kill in the Northeast Cape Fear River. Post-hurricane flooding caused inputs of riparian swamp water to river channels, and sewage treatment plant and pump station power failures caused diversions of millions of liters of raw and partially treated human waste into rivers. Additionally, several swine waste lagoons were breached, overtopped, or inundated, discharging large quantities of concentrated organic waste into the system, particularly into the Northeast Cape Fear River. Dissolved oxygen (DO) decreased to 2 mg/L in the mainstem Cape Fear River, and fell to zero in the Northeast Cape Fear River for >3 wk. Biochemical oxygen demand in the Northeast Cape Fear River was sixfold greater than in the other tributaries, probably as a result of anthropogenically derived inputs. The Cape Fear Estuary also suffered from hypoxia for several weeks. Following Hurricane Fran, ammonium levels in the Northeast Cape Fear River displayed a distinct increase, and total phosphorus reached its highest concentration in 27 yr. The benthic community, which is dominated by opportunistic species typical of oligohaline to mesohaline estuarine areas, showed a mixed response. There was a significant decline in total benthic abundances immediately after Hurricane Fran at an oligohaline station in the Northeast Cape Fear River, with recovery occurring in -3 mo. An oligohaline station in the mainstem Cape Fear River, which had relatively rapid DO recovery, did not display significant declines. A mesohaline station 5 km below the confluence of these rivers showed broad and long-lasting benthic declines, but benthic declines were less severe in the lowest reaches of the estuary sampled. The natural hurricane effect of swamp water flooding into river basins led to reduced dissolved oxygen levels and increased light attenuation. However, environmental damage was considerably increased by anthropogenic practices, including the lack of backup generating systems for waste treatment systems and subsequent sewage diversions into rivers, as well as accidents occurring at swine waste lagoons sited on river floodplains.