Researchers report the contribution of historical phosphorus sources to river water quality. Management of agricultural phosphorus has been in effect for decades, with limited improvements in downstream water quality. Accumulated legacy, or historical, phosphorus sources can mobilize, serve as a persistent nutrient source, and mask efforts to improve surface water quality through reductions in contemporary agricultural inputs. Sarah Stackpoole, Edward Stets, and Lori Sprague estimated the potential contribution of legacy phosphorus, defined as phosphorus from anthropogenic inputs before 1992, to total river phosphorus export for 143 river sites in the continental United States. The authors compared river phosphorus exports to watershed agricultural phosphorus balances over the period 1992-2012. In two-thirds of the watersheds, agricultural inputs exceeded crop exports, indicating the accumulation of surplus phosphorus. Legacy contributions to river export could clearly be identified in 49 watersheds but could not be distinguished from large contemporary inputs in the remaining 94 watersheds, indicating that legacy contributions were likely small. The results also suggest that water quality responses to changes in agricultural management are highly variable. Therefore, the study calls for system-specific actions and accounting for long-term effects of total historical phosphorus storage as well as reductions in contemporary surpluses, according to the authors.
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Article #19-03226: "Variable impacts of contemporary versus legacy agricultural phosphorus on US river water quality," by Sarah M. Stackpoole, Edward G. Stets, and Lori A. Sprague.
MEDIA CONTACT: Mia Drane-Maury, United States Geological Survey, Water Mission Area, Reston, VA; tel: 703-648-4408; e-mail: mdrane-maury@usgs.gov
Journal
Proceedings of the National Academy of Sciences