Ecosystem impacts of three sequential hurricanes (Dennis, Floyd, and Irene) on the United States' largest lagoonal estuary, Pamlico Sound, NC

Three sequential hurricanes, Dennis, Floyd, and Irene, affected coastal Nor th Carolina in September and October 1999. These hurricanes inundated the r egion with up to 1 m of rainfall, causing 50- to 500-year flooding in the w atershed of the Pamlico Sound, the largest lagoonal estuary in the united S tates and a key West Atlantic fisheries nursery. We investigated the ecosys tem-level impacts on and responses of the Sound to the floodwater discharge . Floodwaters displaced three-fourths of the volume of the Sound, depressed salinity by a similar amount, and delivered at least half of the typical a nnual nitrogen load to this nitrogen-sensitive ecosystem. Organic carbon co ncentrations in floodwaters entering Pamlico Sound via a major tributary (t he Neuse River Estuary) were at least 2-fold higher than concentrations und er prefloodwater conditions. A cascading set of physical, chemical, and eco logical impacts followed, including strong vertical stratification, bottom water hypoxia, a sustained increase in algal biomass, displacement of many marine organisms, and a rise in fish disease. Because of the Sound's long r esidence time (approximate to1 year), we hypothesize that the effects of th e short-term nutrient enrichment could prove to be multiannual. A predicted increase in the frequency of hurricane activity over the next few decades may cause longer-term biogeochemical and trophic changes in this and other estuarine and coastal habitats.