SGER: Hurricane Isabel Impacts on Chesapeake Bay

点击翻译按钮获取中文摘要

Hurricanes are natural events that can impose a major perturbation to estuarineecosystems. Some effects of previous hurricanes on Chesapeake Bay (e.g., Agnes in1972) had lasting impacts on submerged aquatic vegetation (drastic decrease) and onfisheries (e.g. soft clam and oyster decline after Agnes). This SGER (Small Grant for Exploratory Reserch) project will examinethe effects of Hurricane Isabel on the hydrographic and food-web structure ofChesapeake Bay. Hurricane Isabel, which struck Chesapeake Bay on September 18,2003, provides a unique opportunity to document and evaluate effects of a significant.disturbance event.. Winds in excess of 70 mph vigorously mixed Bay waters. A stormsurge, 6.12 ft at the Bay mouth took 18 hours to move up the Bay to Baltimore wheremaximum water level was 7.36 ft above mean high water. This significant intrusion ofshelf water redistributed salt, plankton and fish within Chesapeake Bay. The 2003 WaterYear (WY), which includes rainfall associated with Isabel (Oct . Sept) represented thehighest WY freshwater input to Chesapeake Bay since 1937. The passage of Isabelduring the unusually wet 2003 provides a unique opportunity to evaluate effects of amajor perturbation on already enhanced freshwater input to the Bay ecosystem. The project will involved a 7-day cruise in early November, 2003 in which the samesampling procedures are followed that were designated during the six TIES years (1995-2000) and two BITMAX years (2001-2002) thus providing an essential contrast toconditions that observed in the wake of Hurricane Isabel. Investigators will intensively measure the hydrographic and ecosystem structure of the main stem ofChesapeake Bay. On leg 1 (3 days) they will conduct continuous mapping using a towedundulating recorder and surface mapping system which measures temperature, salt,oxygen, chlorophyll and zooplankton (Optical Plankton Counter) along a 350-km axialtransect down the main stem of Chesapeake Bay and with up to 24 cross-Bay transectsspaced 10 km apart. The vertical and horizontal resolution of these measurements will beapproximately 1 m and 200 m, respectively. Maps of physical and biological propertieswill provide an essential background for the hydrographic, plankton and fish surveys thatwill follow. On the second leg (4 days) they will conduct hydrographic stations (CTDs)and measurements of nutrients, phytoplankton biomass and production, zooplanktonpump and acoustic measurements, and fish abundance/distributions (Tucker trawl andmidwater trawl) on 26 Bay-transects. CBOS moorings, including the damaged stations,will be maintained through the interval.