Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes

[摘要] The continental shelf of the northern Gulf of Mexico receives high dissolved inorganic nitrogen and phosphorus loads from theMississippi and Atchafalaya rivers. The nutrient load results in high primary production in the river plumes and contributes tothe development of hypoxia on the Louisiana shelf in summer. While phytoplankton growth is considered to be typicallynitrogen-limited in marine waters, phosphorus limitation has been observed in this region during periods of peakriver discharge in spring and early summer. Here we investigate the presence, spatio-temporal distribution and implications ofphosphorus limitation in the plume region using a circulation model of the northern Gulf of Mexico coupled to a multi-nutrientecosystem model. Results from a 7-yr simulation (2001–2007) compare well with several sources of observations and suggest that phosphoruslimitation develops every year between the Mississippi and Atchafalaya deltas. Model simulations show that phosphorus limitationresults in a delay and westward shift of a fraction of river-stimulated primary production. The consequence is a reduced flux ofparticulate organic matter to the sediment near the Mississippi delta, but slightly enhanced fluxeswest of Atchafalaya Bay. Simulations with altered river phosphate concentrations (±50%) show thatsignificant variation in the spatial extent of phosphorus limitation(±40% in July) results fromchanges in phosphate load.

[学科分类] 地球化学与岩石