Faunal community change in the sediment impacted Bovington Stream and the River Frome (Dorset, UK) between 1998 and 2016

Bovington Camp has been a main training area for armoured vehicles since 1916. Over the years, this has resulted in the erosion and mobilisation of soil particles into watercourses draining the area. Sediment-rich water from a main tributary, the Bovington Stream, discolours the River Frome during high flows. Regulatory agencies and angling groups were concerned that the quality of the river was being affected by run-off from the military ranges. Macroinvertebrate communities were studied between 1998 and 2016 at two sites on the Bovington Stream above and below a sediment trapping pond and two sites on the River Frome above and below the confluence. Samples were collected in Spring and Autumn and ecological quality was assessed using the River Invertebrate Classification Tool (RICT). There were marked increases in the ecological quality of the Bovington sites over time with most change occurring in the period 1998 to 2004. The two Frome sites were consistently classed as high quality throughout the study period. Increases in taxon richness between 1998–2004 and 2011–2016 were significant in the Bovington Stream but no change was observed in the River Frome. Faunal abundance at all sites fluctuated but there were no significant trends. The Combined Fine Sediment Index (CoFSI), assesses the impact of fine sediment pressure on the macroinvertebrate community. Low CoFSI scores were recorded in the early years of the study (1998–2000) at both Bovington sites but showed a steady increase until around 2010–2011, suggesting a degree of improvement/recovery from fine sediment pressure. No similar changes in CoFSI scores occurred in the River Frome. In the absence of any major disturbances in the Bovington catchment other than sediment remediation we conclude that the observed ‘improvements’ in the Bovington Stream are in large part due to the sediment control measures (sediment trapping and diversion) implemented since 1998. The project has shown how relatively simple sediment control strategies can improve ecological quality and has provided information on long-term faunal responses which can help managers plan the extent and timing of effective mitigation measures.