The River Derwent, Yorkshire, has a recognised fine-grained sediment problem and there is increasing realisation of the negative impact that Invasive Non-Native Species, such as Signal Crayfish, have on sediment budgets and geomorphic processes.
Janet Ricardson, an iCASP ITF, along side Helena Brown, Gareth Keevil, Alison Dunn and David Hodgson were funded under Yorkshire Waters AMP7 cycle to look at the impact of signal crayfish on the River Derwent sediment budget.
The project found that there is a lack of sediment data within the catchment, so modelling (using the Soil Water Assessment Tool) and monitoring via collecting samples each month were used to reduce the data gap. SWAT modelling showed that the Upper Rye and Upper Derwent are both contributing roughly the same volume to the sediment budget. Other areas of high yield relate to the north eastern border within the Lower Derwent around Pocklington. Overall, the modelling indicates that the Derwent could be contributing to roughly 12% of the overall Ouse sediment budget.
Twenty-three sites across the River Derwent were routinely sampled each month from February 2022 until November 2022. Samples were collected across the catchment, primarily from bridges to access the centre of the river and analysed at the Sediment, Soil and Pollutant Analysis Laboratory at the University of Leeds. The following factors were assessed at each site: grain size and shape of the suspended sediment (including percentage of silt and clay), conductivity, concentration, turbidity and nitrate concentration. The results show spatial and temporal variation in the datasets. Flow conditions appear to be the biggest driver of sedimentary changes in the catchment, however there are locally important factors, such as land-use impacting the sediment budget. Signal Crayfish activity was demonstrated using overnight pump sampler – where a clear overnight pulse of sediment was recorded. The pulse had reduced by early morning the next day. This highlights the importance of timing of sampling – for future work, pump samplers should be utilised. With regards to biosecurity, mitigation against burrowing and interventions regarding bank stability may be an option in the catchment.