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

Abstract

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 Ͼ3 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 ϳ3 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.

Temporal and spatial distribution of dissolved oxygen in the Pearl River Estuary and adjacent coastal waters

“…During July 2000, when there was a strong easterly wind event, the coastal plume was held back and the water column was almost homogeneously mixed (Yin et al, this volume B). Hurricanes have been reported to exert large impacts on hypoxia on the US's largest lagoonal estuary (Paerl et al, 1998;, Mallin et al, 1999. Consequently, the low DO waters in the bottom layer as observed in other years disappeared except near the water-sediment boundary layer (data not shown).…”

Water Quality Changes in the Guana Tolomato Matanzas National Estuarine Research Reserve, Florida, Associated with Four Tropical Storms

“…For example, in the estuarine environment associated with Pellicer Creek, commercial blood ark (Anadara ovalis), ponderous ark (Noetia ponderosa), and hard clam (Mercenaria mercenaria) populations were devastated by the multiple freshwater pulses associated with the 2004 storms and did not begin to recover in the region until 2006 (NUÑ EZ, personal communication). Situations of freshwater pulses affecting benthic community structure were also documented at Cape Fear, North Carolina, where six hurricanes in 4 years resulted in shifts of benthic infauna from marine to freshwater community structure (MALLIN et al, 1999).…”

Effects of Hurricane Katrina on Freshwater Fish Assemblages in a Small Coastal Tributary of Lake Pontchartrain, Louisiana

“…During a slow-moving storm, large amounts of rainfall can cause severe runoff pollution problems. For example, in 1996 when Hurricane Fran made landfall in North Carolina, local rivers experienced extensive fish kills caused by runoff pollutants (Mallin et al 1999). Saltwater storm surges can create devastating turbulence that not only causes direct fish mortality but also disturbs anoxic sediments that can create shortterm anoxic or hypoxic conditions in estuaries and intertidal zones (Mallin et al 1999;Buck 2005).…”

“…For example, in 1996 when Hurricane Fran made landfall in North Carolina, local rivers experienced extensive fish kills caused by runoff pollutants (Mallin et al 1999). Saltwater storm surges can create devastating turbulence that not only causes direct fish mortality but also disturbs anoxic sediments that can create shortterm anoxic or hypoxic conditions in estuaries and intertidal zones (Mallin et al 1999;Buck 2005). Hurricane winds can also uproot trees and produce 1.2-2.0 times the annual mean litterfall by defoliation, as was observed at an experimental forest in Puerto Rico after Hurricane Hugo struck in 1989 (Lodge and McDowell 1991).…”