Potential Microbial Load Reductions Required to Meet Existing Freshwater Recreational Water Quality Standards for a Selection of Mid-century Environmental Change Scenarios

Adapting to the impacts of environmental change (land use and climate), specifically on water quality, is one of the most pressing challenges for water policy globally. Currently, European Union and United States regulatory structures fail to explicitly account for the potential threats caused by environmental change to water quality in recreational freshwater. The objective of this study was to use watershed modelling to assess possible future load reduction measures and management strategies that may be required to meet existing microbial water quality standards in freshwater systems. The modelling work considers a suite of possible future environmental change scenarios for two watersheds in the west of Ireland and one watershed in Virginia, USA. Extensive reductions in microbial source loads (predominantly from point sources) for the Pigg (US) and Black (Ireland) watersheds were required to meet existing US Clean Water Act standards for the future scenarios simulated. Under the European Union Bathing Water Directive, all watersheds assessed were within the excellent classification for the various environmental change scenarios, indicating that this standard may be more achievable in future years. Outcomes of the work suggest that managing potential risks by adapting existing regulatory frameworks to explicitly plan for the effects of environmental change must become a critical component of watershed planning in the intermediate term. This will provide safe recreational water for use in society and protect public health.