New research: barriers in our rivers – a death by a thousand cuts?

New research on the impact of barriers on fish populations and distribution is now underway in the Trent catchment. PhD candidate, Edward Dilks, talks about his transdisciplinary approach, including eDNA-analysis, mapping out the impacts of barriers on freshwater habitats in the Trent.

Over the past 50 years global freshwater populations have seen a dramatic decline of almost 84%. Much of this decline is linked to fragmentation of habitats and loss of connectivity, particularly in rivers. Habitat fragmentation is classified as the division of continuous, different types of environment, into single isolated patches of the same type. This is problematic as it prevents the movement of organisms between different habitats. Almost universally fragmentation reduces numbers of both different types and individual organism in a community, this has a knock-on effect of lowering nutrient retention and species persistence in an area.

Despite this close link, dams continue to proliferate, exacerbating the problem. Currently there are in excess of 58,000 large dams (taller than 15m and/or holding back 3,000,000m3 of water) and 16,000,000 small dams! Whilst small dams might be crossable, depending on the fish and dam in question, they are multiple orders of magnitude more abundant, often with multiple small dams over the course of a river, resulting in ‘fragmentation by a thousand cuts’. Within the UK this is a particular problem, with the legacy of industrial use present on many of our rivers, with mill dams, weirs, fords and culverts all contributing to only 1% of all rivers remaining free of artificial barriers.

What is being studied?
My work makes use of environmental DNA (eDNA) which is shed by all organisms. By taking a sample of water and looking specifically within this for fish DNA, I can determine the number of different species living within a river, and by making use of some pioneering techniques, get an idea of the abundance of each species. I can then take this information and build computer models which predict the ideal habitat for each species of fish that I find. In combination with this I aim to develop a number of computer models which account for multiple different environmental factors, such as how fast the river is flowing, how quickly DNA degrades, and number and height of barriers present, to quantify precisely which fish species, and how many of them, are living in different areas of the river. From a combination of these models I aim to be able to develop quantitative statistical rules linking barrier density to species-level impacts on fish populations.

What does this all mean?
In real terms, this will give us a much better understanding of what exactly the impacts of small barriers are on UK fish species, and will help us to develop more effective ways to protect and restore our rivers and their fish populations.

About the researcher
Edward is currently part of the NERC Envision DTP and graduated from Lancaster University with a BSc in Biochemistry before going on to study MSc Molecular Microbiology at Nottingham Trent University and MSc Environmental Leadership and Management at The University of Nottingham. His research interests lie in statistical and geospatial modeling, molecular ecology, and river restoration.

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