ABSTRACT
Freshwater input is an important determinant of the overall productivity of river-dominated estuaries (Snedaker et al., 1977; Cross and Williams, 1981). River flow into estuaries controls many factors that influence habitat structure, productivity, and food web interactions (Schroeder, 1978; Livingston, 1984a, 2000; Randall and Day, 1987; Gallegos et al., 1992; Mallin et al., 1993; Livingston et al., 1997). Basic features such as salinity, light penetration, stratification, dissolved oxygen (DO), sediment quality, nutrient loading, primary and secondary production, and food web structure are controlled in varying degrees by the cyclic changes in river discharges (Livingston, 2000). Freshwater input controls the long-term nutrient dynamics in river-dominated coastal systems (Livingston, 1981b, 1984a; Peterson and Howarth, 1987; Baird and Ulanowicz, 1989). Mallin et al. (1993) noted that primary production and algal bloom periodicity were directly related to rainfall in the watershed of the Neuse River estuary in North Carolina and consequent river influxes into the coastal system. River runoff was associated with eutrophication levels in the estuary to the point that the authors noted that episodic runoff should be taken into consideration in mitigation efforts to reduce nutrient loading to coastal areas. Under natural river flow conditions, the combination of high estuarine primary production and reduction of predation due to low/variable salinity contributes to rapid growth and enhanced productivity of eurytopic populations that are adapted to rapidly changing environmental conditions (Livingston, 1984a, 1991b, 2000). Climatological changes have biological effects on coastal systems that can be followed by population shifts over decades (Finney et al., 2000).
