Agricultural runoff fuels large phytoplankton blooms in vulnerable areas of the ocean

• Published in: Nature 2005-03, Vol.434 (7030), p.211-214
• Main Authors: Beman, J.M, Arrigo, K.R, Matson, P.A
• Format: Article
• Language: English
• Subjects: Agricultural ecosystems; Agricultural land; Agricultural production; Agricultural runoff; Agriculture; algal blooms; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Biomass; California; chlorophyll; Chlorophyll - analysis; Chlorophyll - metabolism; coastal water; Ecosystem; Ecosystems; Ecotoxicology, biological effects of pollution; Fertilizers; Fertilizers - analysis; Fuels; Fundamental and applied biological sciences. Psychology; Humanities and Social Sciences; letter; Marine; Marine and brackish environment; Marine ecology; Marine ecosystems; multidisciplinary; Nitrogen; Nitrogen - analysis; Nitrogen - deficiency; Nitrogen - metabolism; nitrogen fertilizers; Nutrient concentrations; Nutrient removal; Oceans; Oceans and Seas; Phytoplankton; Phytoplankton - growth & development; Phytoplankton - metabolism; Plankton; remote sensing; Runoff; Science; Science (multidisciplinary); seawater; Seawater - chemistry; Seawater - microbiology; Surface water; Tropical Climate; Tropical environments; Water column; water pollution; Water Pollution - adverse effects; Water Pollution - analysis
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature03370

Biological productivity in most of the world's oceans is controlled by the supply of nutrients to surface waters. The relative balance between supply and removal of nutrientsincluding nitrogen, iron and phosphorusdetermines which nutrient limits phytoplankton growth. Although nitrogen limits productivity in much of the ocean, large portions of the tropics and subtropics are defined by extreme nitrogen depletion. In these regions, microbial denitrification removes biologically available forms of nitrogen from the water column, producing substantial deficits relative to other nutrients. Here we demonstrate that nitrogen-deficient areas of the tropical and subtropical oceans are acutely vulnerable to nitrogen pollution. Despite naturally high nutrient concentrations and productivity, nitrogen-rich agricultural runoff fuels large (54-577 km2) phytoplankton blooms in the Gulf of California. Runoff exerts a strong and consistent influence on biological processes, in 80% of cases stimulating blooms within days of fertilization and irrigation of agricultural fields. We project that by the year 2050, 27-59% of all nitrogen fertilizer will be applied in developing regions located upstream of nitrogen-deficient marine ecosystems. Our findings highlight the present and future vulnerability of these ecosystems to agricultural runoff.