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Title: Phosphorus legacy: overcoming the effects of past management practices to mitigate future water quality impairment

Author
item SHARPLEY, ANDREW - University Of Arkansas
item JARVIE, HELEN - Centre For Ecology And Hydrology
item Buda, Anthony
item MAY, LINDA - Centre For Ecology And Hydrology
item SPEARS, BRYAN - Centre For Ecology And Hydrology
item Kleinman, Peter

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2013
Publication Date: 9/5/2013
Citation: Sharpley, A., Jarvie, H.P., Buda, A.R., May, L., Spears, B., Kleinman, P.J. 2013. Phosphorus legacy: overcoming the effects of past management practices to mitigate future water quality impairment. Journal of Environmental Quality. 42:1308-1326.

Interpretive Summary: Billions of dollars have been spent on programs to reverse the water quality impairment known as “eutrophication,” the biological enrichment of water derived from excess nutrient inputs. Conservation and nutrient management programs have had mixed success in reducing loads of phosphorus to eutrophic water bodies, the key nutrient controlling freshwater eutrophication. A key factor affecting the success of mitigation programs is the contribution of legacy phosphorus, that is, phosphorus that is stored in soils and sediments and derives from historical activities. This study defines the range of phosphorus legacies that can be found, using case studies to elucidate the range of processes and settings in which legacy phosphorus can be a concern.

Technical Abstract: A slower and smaller than expected water quality response to implementation of conservation measures across watersheds has led many to question the efficacy of these measures and calls for stricter land and nutrient management strategies. In many cases, this limited response is due to the legacies of past management, where sinks and stores of phosphorus (P) along the terrestrial-fluvial continuum can mask reductions in edge-of-field losses of P. Accounting for legacy P along this continuum is important to correctly apportioning sources and for development of successful watershed remediation. Here we examine the drivers of legacy P at the watershed scale; the physical cascades and biogeochemical spirals of P along the continuum from soil to rivers and lakes, via surface and subsurface flow pathways. Terrestrial P legacies encompass prior nutrient and land management that have built up soil P to levels exceeding crop needs and modifying the connectivity of terrestrial P sources to fluvial transport. River and lake P legacies encompass a range of physical and biogeochemical processes controlling retention and remobilization of P, which are linked to water and sediment residence times. We provide case studies that highlight the major processes and varying timescales over which legacy P continues to contribute to receiving waters and discuss how these P legacies could be managed in future conservation programs. We show how previously recommended N-based applications of manure have built up a large P legacy in soils and have increased the risk of P runoff, especially where site hydrology can overwhelm P sources and convert a modest source of P into a major legacy P load. however, we do see a relatively rapid legacy P recovery in some fluvial systems; in the River Lambourn, UK, river bed sediments continued to release legacy P into the overlying river water for only c.6 months after point source remediation. With longer water and sediment residence times in standing waters, several European lakes took from 10 to 20 years to transition from eutrophic to mesotrophic states. In attempting to live with P legacies, we highlight the need for innovative management practices. We show that sources and sinks of P along the land-water continuum are closely related to organic carbon (C) turnover, thus nutrient management for water body remediation needs to address management of organic C, as well as nutrient sources.