Nutrient-enhanced productivity in the northern Gulf of Mexico: past, present and future

摘要: Nutrient over-enrichment in many areas around the world is having pervasive ecological effects on coastal ecosystems. These include reduced dissolved oxygen aquatic systems and subsequent impacts living resources. The largest zone of oxygen-depleted waters United States, entire western Atlantic Ocean, found northern Gulf Mexico Louisiana/Texas continental shelf influenced by freshwater discharge nutrient load Mississippi River system. mid-summer bottom areal extent hypoxic (<2 mg 1−1 02) 1985–1992 averaged 8000 to 9000 km2 but increased up 16000 20 700 1993–2001. system dominant source fresh water nutrients Mexico. concentrations loading adjacent have changed last half 20th century. average annual nitrate concentration doubled, mean silicate was 50%. There no doubt that flux nitrogen (per unit volume discharge) from 1950s 1980s, especially spring. considerable evidence nutrient-enhanced primary production causally related depletion lower column. Evidence long-term data sets sedimentary record demonstrate historic increases riverine inorganic loads over 50 years are highly correlated with indicators productivity overlying column, i.e. eutrophication waters, worsening stress waters. associates ocean changes landscape use management resulted enrichment receiving A steady-state model, calibrated different observed summer conditions, used assess response reductions inputs. reduction surface layer chlorophyll an increase a either or phosphorus loading, being greater for reductions.