Nutrient enrichment of the coastal zone is a worldwide consequence of human population growth. Land clearing, fertilizer production and application, discharge of sewage and septic systems, and fossil fuel combustion have accelerated nitrogen and phosphorus loading to coastal ecosystems since the 1950's (Nixon 1995, Cloern 2001). Estuaries in the northeastern U.S. are particularly threatened by human disturbances within the densely populated coastal zone (Roman et al. 2000).