Ecological Responses of the Neuse River-Pamlico Sound Estuarine Continuum to a Period of Elevated Hurricane Activity: Impacts of Individual Storms and Longer-Term Trends

摘要

Since the mid-1990s, the U.S. mid-Atlantic region has witnessed a sudden rise, in hurricane and tropical storm landfalls. In particular, eastern North Carolina has been impacted by eight hurricanes and six tropical storms in the past decade, and thisrelatively high frequency is forecast to continue for the next several decades. Each of the past storms exhibited unique hydrologic and nutrient loading scenarios for the Pamlico Sound, the United States' second largest estuarine system and its largest subestuary, the Neuse River estuary. This variability represents a challenge to nutrient management aimed at protecting water quality and ensuring optimal fisheries habitat conditions. Different rainfall amounts among hurricanes led to variable freshwaterand nutrient discharge and hence variable nutrient, organic matter, and sediment enrichment. These enrichments differentially affected physical and chemical properties (salinity, water residence time, transparency, stratification, dissolved oxygen), phytoplank-ton primary production, and phytoplankton community composition. The contrasting effects were accompanied by biogeochemical perturbations (hypoxia, enhanced nutrient cycling), benthic and planktonic habitat alterations, and possibly food web disturbances. Floodwaters from the two largest hurricanes, Fran (1996) and Floyd (1999), exerted multimonth to multiannual effects on hydrology, nutrient loads, productivity, biotic composition, and habitat condition. In contrast, relatively low rainfall coastal hurricanes like Isabel (2003) and Ophelia (2005) caused strong vertical mixing and storm surges but exhibited relatively minor hydrologic, nutrient, and biotic impacts. Both hydrologic and wind forcing are important drivers and must be integrated with nutrient loading in assessing short- and long-term ecological impacts of these storms. These climatic forcings cannot be managed but must be considered when developing water quality management strategies for these and other large estuarine ecosystemsfaced with increasing frequencies and intensities of hurricane activity.