The role of nutrient loading and eutrophication in estuarine ecology

Eutrophication is a process that can be defined as an increase in the rate of supply of organic mat-ter (OM) to an ecosystem. We provide a general ove rview of the major features driving estuarine eutrophication and outline so me of the consequences of that process. The main chemical constituent of OM is carbon (C), and therefore rates of eutrophication are expressed in unit s of C per area per unit time. OM occurs in both particulate and dissolved forms. Allochthonous OM originates outside the estuary, whereas autochthono us OM is generated within the system, mostly by primary producers or by ben thic regeneration of OM. The supply rates of limiting nutrients regulate ph ytoplankton productivity that contributes to inputs of autochthonous OM. Th e trophic status of an estuary is often based on eutrophication rates and c an be categorized as oligotrophic (< 100 g C m(-2) y(-1)), mesotrophic (100 -300 g C m(-2) y(-1)), eutrophic (300-500 g C m(-2) Y-1), or hypertrophic ( > 500 g C m(-2) y(-1)). Ecosystem responses to eutrophication depend on bot h export rates (flushing, microbially mediated losses through respiration, and denitrification) and recycilng/regeneration rates within the estuary. T he mitigation of the effects of eutrophication involves the regulation of i norganic nutrient (primarily N and P) inputs into receiving waters. Appropr iately scaled and parameterized nutrient and hydrologic controls are the on ly realistic options for controlling phytoplankton blooms, algal toxicity, and other symptoms of eutrophication-in estuarine ecosystems.