Marine and Aquatic Communities, Stress from Eutrophication

Abstract

Most lakes, estuaries, and coastal ocean regions in the proximity of large human populations have experienced significant nutrient enrichment when contrasted to more “pristine” conditions. This stress of nutrient enrichment is viewed as the cause of eutrophication, with classical symptoms of subsurface water oxygen depletion from excess algal production and proliferation of noxious algal species. The typical eutrophication phenomenon has been defined in lakes as a direct cause-and-effect relationship to a single macronutrient, usually phosphate. For both ecological research and resource management, this lake concept has been extended to estuarine and coastal waters, with some incorrect conclusions. Estuaries and coastal waters, as well as lakes, have complex microbial communities of phytoplankton algae plus heterotrophic bacteria and protozoa that together act as the beginning of the food web. The response of different members of these communities to different stimuli as well as differences of grazer pressure on different ecosystems must be taken into consideration. In estuaries and coastal waters, more complex biogeochemical reactions and tides and currents further complicate understanding the impact of nutrients. Ratios of the macronutrients nitrogen and phosphorus to each other and to silicon vary in both time and space, exerting varying influences on the microbial response. In addition, trace nutrients, which are often considered unimportant in lakes, probably have a major influence on estuarine and coastal primary production. Trace metals and organic compounds also have potential contaminant influences on the overall microbial response. Eutrophication as a stress in estuarine and coastal marine waters is not a simple cause-and-effect phenomenon.