Coastal Zones

Biography

Biography: Gilbert Rowe

Abstract

The generally accepted causes of hypoxia (oxygen concentrations < 2 mg/Liter) in the coastal zone are 1. eutrophication resulting from nutrient loading, 2. Water column stratification created by a freshwater plume and 3. Excess terrestrial organic matter, but the relative importance among these varies between ecosystems and likewise has been the subject of intense debate. The consequences of hypoxia are 1. preservation of organic matter in the sediments, 2. Elimination of both sessile and motile megafauna, and 3. A decrease in mean animal size and diversity among sediment dwelling invertebrates. Enhanced production of trace gases from anaerobic metabolism and diminished fisheries production may also be significant but remain open to question. Blooms of sediment-dwelling sulfide-oxidizing bacteria may prevent toxic sulfide from diffusing into the water column. Mitigation strategies include reducing nutrient loading, reducing freshwater flow and altering freshwater flow into wetlands, but there is wide-spread disagreement on which of these is most effective or even tractable. Climate change and human impacts in the coastal zone may increase the frequency and extent of hypoxia by increasing nutrient loading. Sea level rise may exacerbate loss of wetlands. Diminished supplies of freshwater to estuaries may increase salinities in estuaries and shrink the length of the fresh to salt water gradient in estuaries and near-shore, while flooding and sea level rise may extend the fresh-to-salt zonation pattern and increase stratification, thus enlarging areas of hypoxia. Increases in temperature will enhance vertical stratification and metabolic rates, both of which would add to the geographic areal extent of hypoxia and biological stresses. 'Ecosystem services' must be considered when remedial actions are to be considered, but these will differ depending of the ecosystem in question.