Processes controlling the flux of legacy phosphorus to surface waters at the farm scale. (23rd December 2020)

• Record Type: Journal Article
• Authors: Barcala, Victoria; Rozemeijer, Joachim; Osté, Leonard; Van der Grift, Bas; Gerner, Laurens; Behrends, Thilo
• Is Part Of: Environmental research letters. Volume 16:Number 1(2021)
• Publication Date: 2020-12-23
• Subjects: legacy phosphorus -- leaching -- diffuse sources -- mitigation measures -- groundwater–surface water interactions -- agriculture -- eutrophication; Environmental sciences -- Periodicals; Human ecology -- Research -- Periodicals; Environmental health -- Periodicals; 333.7
• DOI: 10.1088/1748-9326/abcdd4
• Languages: English
• ISSNs: 1748-9326

Abstract

Abstract: Phosphorus (P) leaching from agriculture is a major driver of water eutrophication in downstream rivers and lakes. In drained lowland areas with intensive agriculture, a reduction in the fertilizer applications may be insufficient to improve the water quality in the short term as the P accumulated in the soil during decades of high fertilization may continue leaching for many years. A complementary approach to reduce P exports from agriculture is to implement edge-of-field mitigation measures at the farm scale. The selection of effective measures requires a detailed insight into the chemical and hydrological transport mechanisms. Here, we determined the main P sources, processes, and transport routes at the farm scale to support the selection of appropriate mitigation measures. We quantified the legacy P, the different P pools stored in the upper soil, and related it to the yearly P export downstream. To do this, we combined high-resolution monitoring data from the soil, groundwater, surface water, and ditch sediments. The legacy P in the topsoil was high, about 2500 kg ha −1 . The predominant subsurface flow and the subsoils' P sorption capacity retained the P mobilized from the topsoil and explained the relative moderate flux of P to surface waters (0.04 kg ha −1 during the 2018–2019 drainage season). The dissolved P entering the drainage ditch via groundwater discharge was bound to iron-containing particles formed due to the oxidation of dissolved ferrous iron. Once leached from the soil to the drainage ditch, resuspension of P-rich sediment particles during flow peaks were the most important P transport mechanism (78%). Therefore, we expect that hydraulic constructions that reduce flow velocities and promote sedimentation of P-containing particles could reduce the export of P further downstream.