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

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 is addressing 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.