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Ranking connectivity risk for phosphorus loss along agricultural drainage ditches
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2020-02
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Moloney, T., Fenton, O., Daly, K. Ranking connectivity risk for phosphorus loss along agricultural drainage ditches, Science of The Total Environment, 2020, 703, 134556. DOI: https://doi.org/10.1016/j.scitotenv.2019.134556
Abstract
Agricultural drainage systems comprising both in-field pipe drains and surface ditches are typically
installed to remove excess water from agricultural land. These drainage networks can provide
connectivity between phosphorus (P) sources and surface waters thereby increasing the risk of P loss
to rivers and streams. The objective of this study was to derive a farm-scale drainage ranking that
categorises drainage ditches in terms of P loss risk based on connectivity and physic-chemical
characteristics. Ten pilot farms were selected to characterise drainage networks through ground
survey and, sediment and water sampling. Five drainage ditch categories were derived based on
landscape setting and connectivity. Each category recorded soluble and reactive P concentrations
above environmental water quality standards. To assess the risk of surface ditches as a connectivity
vector between agricultural P and surface waters ditches were ranked in order of P loss risk by
integrating landscape position and sediment P chemistry. Elevated sediment P with high equilibrium P
concentration (EPCo) were associated with ditches connected to farm yards, and in sediment sampled
at ditch outlets, suggesting P deposition over time indicative of a legacy P source. The greatest risk of
P loss was attributed to ditches connecting farm yards to streams, and ditches that connected the
drainage network to surface waters, or Outlets. These results rank connectivity risk for P loss along
agricultural drainage ditches for farm level risk assessment to target P loss mitigation measures to
the appropriate locations.