Impact of P inputs on source-sink P dynamics of sediment along an agricultural ditch network. (1st March 2020)

• Record Type: Journal Article
• Authors: Ezzati, G.; Fenton, O.; Healy, M.G.; Christianson, L.; Feyereisen, G.W.; Thornton, S.; Chen, Q.; Fan, B.; Ding, J.; Daly, K.
• Is Part Of: Journal of environmental management. Volume 257(2020)
• Publication Date: 2020-03-01
• Subjects: Drainage water -- Farm pollution -- Phosphorus -- Soil -- Agriculture -- Sediment; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2019.109988
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Phosphorus (P) loss from intensive dairy farms is a pressure on water quality in agricultural catchments. At farm scale, P sources can enter in-field drains and open ditches, resulting in transfer along ditch networks and delivery into nearby streams. Open ditches could be a potential location for P mitigation if the right location was identified, depending on P sources entering the ditch and the source-sink dynamics at the sediment-water interface. The objective of this study was to identify the right location along a ditch to mitigate P losses on an intensive dairy farm. High spatial resolution grab samples for water quality, along with sediment and bankside samples, were collected along an open ditch network to characterise the P dynamics within the ditch. Phosphorus inputs to the ditch adversely affected water quality, and a step change in P concentrations (increase in mean dissolved reactive phosphorus (DRP) from 0.054 to 0.228 mg L −1 ) midway along the section of the ditch sampled, signalled the influence of a point source entering the ditch. Phosphorus inputs altered sediment P sorption properties as P accumulated along the length of the ditch. Accumulation of bankside and sediment labile extractable P, Mehlich 3 P (M3P) (from 13 to 97 mg kg −1 ) resulted in a decrease in P binding energies (k) to < 1 L mg −1 at downstream points and raised the equilibrium P concentrations (EPC0 ) from 0.07 to 4.61 mg L −1 along the ditch. The increase in EPC0 was in line with increasing dissolved and total P in water, demonstrating the role of sediment downstream in this ditch as a secondary source of P to water. Implementation of intervention measures are needed to both mitigate P loss and remediate sediment to restore the sink properties. In-ditch measures need to account for a physicochemical lag time before improvements in water quality will be observed. Graphical abstract: Image 1 Highlights: P inputs to ditch altered sorptive properties and accumulated in sediment. Low P binding and high equilibrium P in sediment acting as secondary P source. Measures needed to remediate ditch water and restore sediment P attenuation. Physico-chemical lag time expected for water quality measures.