A hydroecological model to assess the relative effects of groundwater abstraction and fine sediment pressures on riverine macro-invertebrates

To ensure that the environment is adequately protected and abstractors are fairly regulated, hydroecological assessment tools are needed that give local interpretation, indicate where ecological communities might not be resilient to current or future abstraction pressures, and take account of the effect of other stressors. These tools should ideally be transferrable across different river catchments. This study presents a hydroecological model indicating that macro-invertebrates were not resilient to long-term, steady-state levels of groundwater abstraction when flows at Q75 were reduced by more than 50% in unpolluted streams in the West Midlands of England. The proportion of silt and clay covering the substratum and distance from source were also significant predictors of ecological condition, but did not interact with the abstraction effect. Combinations of different biotic indices and supplementary field observations of catchment land use gave additional evidence of the impacts of excessive inputs of fine sediment overriding the effects of abstraction at some locations. This study has shown that regional hydroecological models can be used with existing environmental flow indicators and other local environmental information as a weight of evidence to identify where abstraction and excessive inputs of fine sediment need to be mitigated separately or together to achieve the full ecological benefits. Such regional hydroecological models can increase the certainty of regulatory decisions made at the local scale for licencing abstraction at current use and predicted future levels.