Quantifying the combined nutrient enrichment, pathogenic, and ecotoxicological impacts of livestock farming on UK rivers

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Livestock farming is the dominant farming type and source of organic matter pollution in UK freshwaters, with over 9.65M cattle and 32.7M sheep on 10M hectares of grassland, representing 57% of all agricultural land in the UK. When organic matter from livestock excreta is flushed to waters it drives changes in their physical, chemical and ecological quality and function. These include changes to the turbidity (and therefore light penetration), conductivity, benthic substrate character and oxygen regimes of the receiving waterbody, the delivery of agrochemicals including anti-microbial (antibacterial, antifungal, antiparasitic and antihelminth agents) and hormone compounds, both natural and derived from veterinary pharmaceutical use, all of which are likely to drive ecotoxicological impacts in receiving waters. They also contain nutrient-rich dissolved and particulate organic matter likely to drive eutrophication impacts in freshwater ecosystems, while also presenting a significant challenge for waters abstracted for human consumption. Pathogens, including bacteria and viruses, add to this portfolio of stressors, presenting a persistent problem for recreational water use, fisheries and shellfisheries in livestock farming areas. These stressors are likely to be present in most livestock excreta, but the extent to which different production systems and manure handling practices remove or reduce their concentration prior to their transfer to freshwaters is poorly understood. Nor do we understand the impact of the environmental character of the receiving waterbody on these ecotoxicological and nutrient enrichment impacts and pathogen persistence. Climate change-induced increases in water temperature and alterations in flow regime may then accelerate biological processing of this material, while the increased frequency of rainfall events predicted for the UK may overwhelm on-farm storage capacity, confounding efforts to reduce livestock impacts on freshwaters. There is thus an urgent need to understand interactions between these stressors, environment and management in driving changes in UK freshwater quality.QUANTUM will address this substantial knowledge gap, allowing us to better understand livestock farming as a key driver of changing UK quality in the livestock-dominated catchments of Wales, Scotland and Northern Ireland, and throughout the north and west of England. This new knowledge will help us create models that can better predict how UK freshwater quality functions in the presence of these multiple stressors, and how it is likely to change in future in response to climate change and mitigation efforts.We will achieve this by:1. Developing evidence on the composition of livestock excreta, how this varies according to manure handling and management, and their chemical and microbiological persistence in freshwaters, which will provide a new framework to define and contextualise pressures they exert on UK freshwaters.2. Exploring how different freshwater biota respond to this portfolio of stressors, allowing us to develop a predictive understanding of likely ecosystem responses to livestock management practices across the UK.3. Understanding how livestock excreta perturb the state of freshwater ecosystems, and how the multiple stressors in these fluxes interact with each other and environmental character, which is essential if we are to understand how these freshwater communities assemble, function and respond to changing livestock farming practices, under current, mitigated and climatically-altered conditions.4. Identifying the livestock production practices and management approaches likely to generate the lowest possible impacts on freshwater chemistry and ecosystems, which will provide critical underpinning for the developing policy and practice by our project partners, to minimise livestock farming impacts on UK freshwaters under ambient and changing climate.