• Lough Melvin: Developing cost-effective measures to prevent phosphorus enrichment of a unique aquatic habitat

      Schulte, Rogier P.; Doody, Donnacha G.; Byrne, Paul; Cockerill, C.; Carton, Owen T.; Lough Melvin Nutrient Reduction Programme (School of Agriculture, Food Science and Veterinary Medicine, University College Dublin in association with Teagasc, 2009)
      Lough Melvin, located on the border of Leitrim (Republic of Ireland) and Fermanagh (Northern Ireland), is unique among Irish lakes, supporting a fish community typical of a natural post-glacial salmonid lake, and has been designated as a Special Area of Conservation (SAC). The biodiversity of the lake is vulnerable to changes in water quality resulting from eutrophication, and over the last 15 years, phosphorus (P) concentrations have increased to the upper range of mesotrophic classification. Agriculture has been reported as one of the main contributors of P loadings to the lake, which poses an apparent paradox in light of the low-intensity nature of farming practices in the catchment. The objectives of the project reported on here were to identify the dominant P pressure and pathway risks governing P loss in the catchment, and to evaluate and select potential mitigation measures, based on an assessment of cost-effectiveness and farmer preference. Throughout this project, we employed an explicitly participatory approach, with farmer stakeholders inputting directly into the identification and evaluation of mitigation measures. We identified risks on 50 survey farms by using the modified P Ranking Scheme. A suite of 25 potential mitigation strategies was identified from the literature and on-farm interviews. For each measure, we derived the order of magnitude of potential costs, impact, and cost-effectiveness, and measures were preferentially ranked by 25 participating farmers. The resulting ranking of measures showed that support for nutrient management planning and soil analysis was the most cost-effective and popular measure aimed at reducing P pressures in the long term, while installation of sediment traps in drainage ditches was the most cost-effective and popular measure aimed at reducing P transport vectors in the short term. We demonstrate that through this careful evaluation and selection of mitigation measures, over 50% of potential total reduction in P loss can be achieved at c. 5% of potential total cost. In addition, we show that measures commonly proposed to mitigate against “high-visibility risks” are not necessarily cost-effective or acceptable to farmer stakeholders. The results of this study are specific to the biophysical environment and farming context of the Lough Melvin catchment, however, we suggest that the approach taken in our project may be used as a template for the formulation of regional catchment management plans, such as the draft river basin district management plans required under the Water Framework Directive.