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Research article - Peer-reviewed, 2020

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

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


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.


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

Published in

Journal of Environmental Management
2020, volume: 257, article number: 109988

Authors' information

National University of Ireland Galway (NUI Galway)
Fenton, O.
Healy, M. G.
National University of Ireland (NUI) Galway
Christianson, L.
University of Illinois Urbana-Champaign
Feyereisen, G. W.
United States Department of Agriculture (USDA)
Thornton, S.
University of Sheffield
Chen, Q.
China Agricultural University
Fan, B.
China Agricultural University
Ding, J.
China Agricultural University
Daly, K.

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use

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