Stream Water Quality in the Slapton Catchments: Analysis of Key Trends since 1970

There was concern in the 1960s that Slapton Ley, a freshwater coastal lagoon and the largest natural body of fresh water in south-west England, was becoming increasingly eutrophic. To be able to quantify inputs of water, sediment and nutrients into the lake, a programme of continuous stream discharge monitoring and weekly water quality sampling was initiated by Slapton Ley Field Centre: water quality data are available for the main streams that flow into the lake from September 1970. The sampling regime included both the two larger (higher-order) rivers flowing into the lake and two first-order streams. In total, the catchment area is 46 km2 of which 81% is gauged. This study reviews this 50-year study of small catchment hydrology. Weekly monitoring of water quality has shown that the lake remains eutrophic despite clear improvements in waste-water treatment. The long-term monitoring has provided the context for process studies of hillslope hydrology and delivery of sediments and nutrients into the stream system. Beyond eutrophication, long data series of the type presented here are a rich source for generating new ideas or testing existing hypotheses.