Impact of P inputs on source-sink P dynamics of sediment along an agricultural ditch network

G. Ezzati, O. Fenton, M. G. Healy, L. Christianson, G. W. Feyereisen, S. Thornton, Q. Chen, B. Fan, J. Ding, K. Daly

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish (US)
Article number109988
JournalJournal of Environmental Management
Volume257
DOIs
StatePublished - Mar 1 2020

Keywords

  • Agriculture
  • Drainage water
  • Farm pollution
  • Phosphorus
  • Sediment
  • Soil

ASJC Scopus subject areas

  • Environmental Engineering
  • Waste Management and Disposal
  • Management, Monitoring, Policy and Law

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