In 2002, the mid- Atlantic region experienced record drought levels. In September 2003, Tropical Storm Isabel produced large amounts of rainfall in the Chesapeake Bay region, and freshwater flow into the Chesapeake Bay was 400% above the long- term monthly average (http://chesapeake.usgs.gov/isabelinfo.html). Record drought conditions followed by a very wet year coincided with pulsed watershed nitrogen exports and one of the most severe zones of hypoxia, or “dead zones,” reported in the Chesapeake Bay.
Large pulses of contaminants such as this event may occur more often given evidence of increased variability of precipitation and hydrologic extremes occurring with climate change [Intergovernmental Panel on Climate Change (IPCC), 2007]. Conversion of land to human- dominated uses has increased contaminant loads in streams and rivers and further transformed hydrologic cycles [Vitousek et al., 1997]. Together, land use and climate change may interact in unexpected ways to alter the amplitude, frequency, and duration of contaminant pulses in streams and rivers (i.e., large contaminant loads that are transported over relatively short time scales).
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