The effect of river plume nutrient input on ocean chlorophyll levels

River runoff has a great effect on the biogeochemical cycles of nutrients in the oceans. These nutrient inputs have been increasing in recent years due to anthropogenic activities such as the use of fertilizer, runoff of sewage, and the burning of fossil fuels. This nutrient increase enhances phytoplankton production, which can stress ecosystems if oxygen is depleted. We seek to examine the effect of river plume nutrient inputs on oceanic chlorophyll values. Monthly SeaWiFS satellite estimates of surface chlorophyll concentration were examined in the vicinity of large river plumes in the oceans over a six year period. A particular focus was the equatorial Atlantic region, as it receives the largest nutrient inputs from rivers. We defined a study region in the western equatorial Atlantic (~76.5E - 36.5W, 3.5S - 20.5N). Three large regions drain to this area bringing substantial nutrients to the ocean (the Amazon, Orinoco, and Tocantins rivers). In this western equatorial Atlantic region, we find that river-plume nutrients increase chlorophyll concentrations over about 25% of the total area during summer months, declining to ~ 10% during winter. Chlorophyll levels in the plume and coastal waters are about 14 times greater than those in the open ocean. Riverine nutrient inputs significantly impact ocean biogeochemistry in the tropical Atlantic Ocean.