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Catchment Models and Management Tools for Diffuse Contaminants (Sediment, Phosphorus and Pesticides): DiffuseTools Project

Published in Irish EPA Technical Reports, 2021

Recommended citation: Thomas I., Bruen M., Mockler E., Werner C., Mellander P., Reaney S., Rymszewicz A., McGrath G., Eder E., Wade A., Collins A. and Arheimer B. 2021: “Catchment Models and Management Tools for Diffuse Contaminants (Sediment, Phosphorus and Pesticides): DiffuseTools ProjectIrish EPA Research Report no. 396. ISBN: 978-1-84095-011-8

Agricultural pollution continues to be a major cause of eutrophication of waterbodies and water quality degradation in Ireland and internationally, with the success of mitigation measures hampered by the diffusivity of pollution sources and pathways. Ireland must meet international water quality obligations set by the EU Water Framework Directive (WFD), with the aim of achieving “good ecological and chemical status” in all and high status in some High Status Objective (HSO) waterbodies by 2027. For surface waters, S.I. 272 sets out the required standards. Good ecological status is assessed using environmental quality standards, including an annual mean unfiltered reactive phosphorus (P) concentration not exceeding 0.035mgl –1 in Irish rivers. The WFD includes provisions from the Nitrates Directive that aimed to protect waterbodies from agricultural nitrogen and P pollution by implementing a Nitrates Action Programme and S.I. 605, Good Agricultural Practice for Protection of Waters Regulations. The most recent Environmental Protection Agency (EPA) water quality assessment over the period 2013–2018 found that 52.8% of surface waterbodies assessed are of good or high ecological status (a decline of 2.6% compared with 2010–2015), with the remaining (47.2%) being of moderate, poor or bad ecological status. This has given rise to concerns that the current mitigation measures, which in the past have been heavily source focused, do not go far enough, and has led to renewed interest in the development of decision support tools (DSTs) for P loss management. These can spatially map P, sediment and pesticide losses from agricultural land to waterbodies at high resolution and are needed by farmers, catchment managers, policymakers and water agencies to improve cost-effective targeting of pollution mitigation measures. The University College Dublin (UCD)-led DiffuseTools project has developed such modelling tools suitable for implementation nationally to estimate P and sediment losses from diffuse sources and their delivery points to surface waters using the latest data, science and geographical information systems (GISs).

Here we develop high-resolution quantitative modelling to

  1. Support better targeting and prioritising of diffuse pollution mitigation measures and thereby increase their cost-effectiveness;
  2. Inform engineering designs (flow volumes) and interventions required to meet WFD targets;
  3. Improve functional land management and inform farm practices (e.g. where to spread excess fertiliser); and
  4. Facilitate modelling the effects of climate change.

Note that this work focuses on surface runoff transport, and subsurface pathways are not considered here.

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