Watershed determinants of terrestrial resource use by aquatic organisms across the world's freshwater hotspots

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North temperate regions hold much of the planet's freshwater, an essential ingredient for all life. But anthropogenic activities, such as land-use change, are dramatically altering these landscapes and threatening the delivery of key services provided by aquatic ecosystems, such as productive fish populations. Contemporary paradigms of aquatic conservation have emphasized inputs of pollutants and water resource development as causes of declining water security and biodiversity, but are failing when these two factors alone are improved. Increasingly, local watersheds are seen as critical controls of aquatic ecosystems. This is spurred by the recent discovery that pathways of energy mobilization upwards through aquatic food webs from microbes to fish rely on organic matter originating from terrestrial vegetation. In other words, new research is proving the adage that fish are in fact a "forest product".Any factor that changes the quality and quantity of organic matter exported from land into water will influence the delivery of aquatic ecosystem services. For example, human land use practices and emerging disturbances, such as fire and forest pathogens, will change the cycling of nutrients from terrestrial vegetation into aquatic ecosystems. But which of these factors are most important and consistently operating across different geographic regions is unknown. Identifying these drivers is critical for developing new watershed-level approaches for conserving freshwater that link actions on land to processes in water.Our research will test how different watershed characteristics control the use of terrestrial resources in aquatic food webs across lake-rich regions of the world. We will use our findings to forecast future changes in lake food webs associated with global change and recommend better practices for conserving freshwater resources. Our approach will be to bring together the leading international researchers studying terrestrial-aquatic linkages and synthesize available food web measurements from over 175 lakes. Using bioclimatic, vegetation, biogeochemistry, and land-use data extracted for each study lake, alongside cutting-edge statistical modelling techniques, we will predict the terrestrial drivers of lake food webs and link them to biomass accumulation by aquatic organisms.Outcomes of this research will be highly relevant to the UK and international policy around managing freshwater supplies by demonstrating strong linkages between terrestrial and aquatic ecosystems. A particular focus of our research is improving the Water Framework Directive (WFD), a piece of pan-European legislation designed to protect freshwater. We hope to use our research to impact policy associated with the WFD by engaging with the European Commission in a knowledge exchange symposium that we are organizing at the conclusion of our project. This project will also have many applications for improving regional land use planning and management, as well as restoring environmentally damaged landscapes. We are working closely with partners in the mining industry and government in associated NERC-funded projects and will use the results of this project to better inform these partners of the best practices for re-vegetating degraded watersheds.