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Credit: PNAS
Researchers report the effects of nutrient reduction on coastal ecosystem recovery. Nutrient pollution causes widespread degradation of coastal ecosystems, yet the effectiveness of large-scale nutrient reduction efforts has not been empirically demonstrated. Jonathan Lefcheck and colleagues analyzed aerial surveys, biogeochemical data, historical land use information, and output from watershed models to evaluate the relationship between nutrient pollution and submerged aquatic vegetation (SAV) in Chesapeake Bay from 1984 to 2015. Models relating land use, nutrient loads, and SAV cover indicated that SAV cover decreased as nitrogen and phosphorus runoff loads increased. A model of interactions between SAV and local environmental conditions suggested that nitrogen directly reduced SAV cover, presumably by stimulating algal growth, whereas phosphorus indirectly reduced SAV by promoting phytoplankton blooms that block sunlight. The models also suggested a positive relationship between SAV species richness and total SAV cover, such that one additional species would increase SAV cover by 1.8-fold on average. Since 1984, mean water column nitrogen concentrations have declined by 23% and phosphorus concentrations by 8% on average. During the same period, SAV cover increased by approximately 17,000 hectares. The results suggest that reducing nutrient pollution can lead to long-term local ecosystem recovery, and that conservation or restoration of species diversity could further enhance recovery, according to the authors.
Article #17-15798: "Long-term nutrient reductions lead to the unprecedented recovery of a temperate coastal region," by Jonathan S. Lefcheck et al.
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