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 stru ck by two hurricanes, with the second (Hurricane Fran) doing considerably m ore damage than the first (Hurricane Bertha). The Cape Fear watershed, larg est in North Carolina, suffered from severe water quality problems for week s following Fran, including a massive fish kill in the Northeast Cape Fear River. Post-hurricane flooding caused inputs of riparian swamp water to riv er channels, and sewage treatment plant and pump station power failures cau sed diversions of millions of liters of raw and partially treated human was te into rivers. Additionally, several swine waste lagoons were breached, ov ertopped, or inundated, discharging large quantities of concentrated organi c waste into the system, particularly into the Northeast Cape Fear River. D issolved oxygen (DO) decreased to 2 mg/L in the mainstem Cape Fear River, a nd fell to zero in the Northeast Cape Fear River for >3 wk. Biochemical oxy gen demand in the Northeast Cape Fear River was sixfold greater than in the other tributaries, probably as a result of anthropogenically derived input s. The Cape Fear Estuary also suffered from hypoxia for several weeks. Foll owing Hurricane Fran, ammonium levels in the Northeast Cape Fear River disp layed a distinct increase, and total phosphorus reached its highest concent ration in 27 yr. The benthic community, which is dominated by opportunistic species typical of oligohaline to mesohaline estuarine areas, showed a mix ed response. There was a significant decline in total benthic abundances im mediately after Hurricane Fran at an oligohaline station in the Northeast C ape Fear River, with recovery occurring in similar to 3 mo. An oligohaline station in the mainstem Cape Fear River, which had relatively rapid DO reco very, did not display significant declines. A mesohaline station 5 km below the confluence of these rivers showed broad and long-lasting benthic decli nes, but benthic declines were less severe in the lowest reaches of the est uary sampled. The natural hurricane effect of swamp water flooding into riv er basins led to reduced dissolved oxygen levels and increased light attenu ation. However, environmental damage was considerably increased by anthropo genic 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.