Stuck in the mud: addressing the fine sediment conundrum with multiscale and interdisciplinary approaches to support global freshwater biodiversity

Environmental change is happening on a global scale. Freshwater ecosystems represent some of the most endangered habitats in the world, with declines in diversity (83% in the period 1970-2014) far exceeding that of terrestrial counterparts. One of the primary causes of reduced riverine ecosystem health is a loss of habitat associated with excessive fine sediment deposition (typically referred to as particles <2mm). Fine sediment is a natural part of river systems, however alterations to land use (e.g. intensive farming) and channelization / impoundment (via dams and reservoirs) have altered the quantity of fine sediment such that inputs now far exceed historic levels. Additionally, increasing hydrological extremes associated with climatic change, such as intense rainfall events, are likely to further increase the delivery of fine sediment to river channels.

Fine sediment deposition alters and degrades instream habitats making rivers unsuitable for flora and fauna to live in. Such changes lead to reductions in the biodiversity of riverine ecosystems and affects all components of the food web from fish and insects through to algae. Understanding the ecological implications of fine sediment is therefore imperative to be able to manage our rivers so that they can support and sustain healthy ecosystem functioning and support anthropogenic activities (e.g., fisheries, recreational activities). This is however challenging because a number of environmental factors control the consequences of fine sediment for flora and fauna. The proposed Fellowship aims to understand and quantify which environmental factors (e.g. land use, size of fine sediment and of the gravels within the river, time of year) influence the severity of fine sediment deposition for river communities. Specific objectives are to (i) quantify the trends between fine sediment loading and ecological responses in the UK and internationally; (ii) determine if there is a threshold of fine sediment loading before ecological degradation occurs and how this varies within individual rivers, (iii) develop understanding of how environmental controls (e.g. grain size, hydrological exchange) structure the effects of fine sediment and; (iv) outline a future research agenda to tackle the management of fine sediment in rivers.

In achieving these objectives, my Fellowship will provide a framework to determine which rivers types (e.g. highland or lowland, geology) are most at threat from fine sediment pressures internationally. The Fellowship will focus on macroinvertebrates (river invertebrates such as snails, insects and crustaceans) as a target organisms being abundant, diverse and occurring across the globe. The Fellowship represents a novel and exciting research programme with international reach and applicability that combines global datasets with multi-country field and artificial stream channel experiments (alpine and lowland) and laboratory experiments over different spatial scales to develop and validate theories spanning different environmental settings. The fellowship will lead to an exciting step-change in our understanding and will address unique fundamental research questions whilst working synergistically with UK statutory regulatory agencies and end-users such as the Environment Agency of England, Natural Resources Wales and Scottish Environmental Protection Agency. The research generated will have important ramifications for how stakeholders allocate resources to monitor and manage UK riverine ecosystems and will enable more efficient and targeted conservation and restoration plans.

The overall aim of the Fellowship is to provide valuable knowledge about how environmental controls structure the implications of fine sediment deposition for ecological communities. Specific impact goals of this research have been co-produced with stakeholders and are to:

1. Provide evidence as to where excess fine sediment may have an impact and how this varies spatially associated with river type / morphological degradation.
2. Provide policy makers with evidence as to a fine sediment threshold, which when crossed leads to biological impairment.
3. Provide key evidence to ensure that stakeholders continue to tackle fine sediment at the source rather than at drinking water treatment plants.
4. Provide policy makers with evidence as to how biological health is best assessed (via taxonomic, functional and biomonitoring tool approaches). The latter includes collaboration with the Environment Agency to test out new biological tools currently being refined.

Answers to these impact goals will enable stakeholders to allocate resources more effectively in monitoring and maintaining riverine ecosystem health globally. To achieve these impact goals, an advisory stakeholder panel will be formed consisting of key members of relevant stakeholder groups to ensure effective knowledge transfer exchange and impact. I will also work closely with the River Restoration Centre.

Who will benefit from this project and how?
i) National agencies including the Environment Agency, Natural England, Natural Resources Wales, Scottish Environmental Protection Agency, Northern Ireland Environment Agency, Environment and Climate Change Canada, and the United States Geological Survey who are responsible for the statutory monitoring and protection of the natural environment (medium to long term). These Agencies are supportive of the Fellowship from the outset, being actively involved in one or more of the work packages (medium to long-term).
ii) Organisations involved in developing environmental policies: Joint Nature Conservation Committee, Swiss Rivers group, British Hydrological Society and the British Ecological Society (BES), who seek to influence policy around threats to ecosystem biodiversity and functioning with results providing an evidence-base to inform policy (medium term).
iii) The research generated will be of international significance for regulatory management authorities and commercial water companies who have a role to play in mitigating the implications of fine sediment around the globe. At present many water companies invest resources on controlling fine sediment at the source and this Fellowship aims to provide evidence that supports this management practice (i.e. demonstrate the deleterious effects of fine sediment for aquatic biodiversity; medium term). The findings may inform management of key habitats and protected areas (medium to long term). Links will be made with the UK Water Industry Research (UKWIR; https://ukwir.org/).
iv) Stakeholders with an interest in river restoration schemes such as project partners the River Restoration Centre (consisting of 1047 agencies, trusts, practitioners) and local Rivers Trusts (medium to long term).
v) More generally, the results will be of interest to a number of conservation stakeholders such as Wildlife Trusts, Freshwater Biological Association, Rivers Trusts, local biodiversity teams of County Councils, The Department of Environmental Food and Rural Affairs (Defra) and Fisheries and Aquaculture Science who will also benefit from insights into the possible mechanisms and environmental controls of influencing fine sedimentation effects (medium term).
vi) The general public with an interest in conserving the natural environment and who pursue recreation activities or engage with rivers from time-to-time via other stakeholder interests such as angling clubs (short term, during the life of the Fellowship).