Loose One-Way Coupling of Land Use and Nutrient Emission Models to Assess Effects of Regional Development Scenarios on Catchment Water Quality

Nutrient enrichment and eutrophication can increase when urbanisation and intensification of agriculture production occurs without accompanying mitigation measures to offset impacts from land use transitions. The identification of measures to protect or restore water quality is a challenging exercise, particularly in the context of increasing population and urbanisation. Hence, decision-makers need adequate tools to better understand and evaluate the effects of policy interventions on water management and quality control in urban regions. A model integration method was developed to assess future scenarios of urban development on water quality using land use model Monitoring Land Use/Cover Dynamics and nutrient emission model Source Load Apportionment Model. A case study application investigated how projected changes in urban land use in the most populated region of Ireland, the Greater Dublin Region, impact on water quality. Results for all scenarios indicate increasing losses to water for both phosphorus (18–25%) and nitrogen (9–12%). However, as these scenarios assume that wastewater treatment efficiencies remain static into the future, this study highlights that the magnitude and distribution of investment in urban wastewater collection and treatment will have the greatest impact on changes in future nutrient emissions to water in this urban region. The differences between the development scenarios for diffuse nutrient losses were small in comparison, even though the location of specific land uses varied broadly across scenarios. It was found that the decline of agricultural land cover and replacement with urban development in Dublin region by 2026 as represented by four modelled scenarios resulted in substantial increases in diffuse phosphorus emissions, but only slight changes in diffuse nitrogen emissions. It was shown that the scales of impact from sources of nutrients vary from scenario to scenario and that these should be considered alongside planned mitigation of point sources of nutrient emissions to water. Such information can support physical planners, catchment managers and policy makers to plan accordingly to get the best possible environmental outcomes. The case study application demonstrated that the loose one-way coupling of a land use model and a nutrient emission model can be an effective and inexpensive approach to improve understanding of the effects of urbanisation on water quality and assist in the strategic planning of catchment management and infrastructure investment.