Effects of wetland management on aquatic biodiversity and water quality of Sites of Special Scientific Interest on the Somerset Levels and Moors

The Somerset Levels and Moors (SLM) consists of the largest area of lowland wet grassland and wetland habitat in the UK. Covering approximately 70,000 ha, the Somerset Levels catchment encompasses the approximately 35,000 ha combined area of the catchments of the River Parrett, River Tone, River Brue, and River Axe, and their associated tributaries. Since at least the 1400’s, the SLM has undergone draining activity and land reclamation facilitated in part by digging ditches, locally referred to as rhynes. In the present day the landscape is dominated by artificially drained, irrigated and otherwise modified rivers and wetlands. Designations of the SLM include being listed as a Ramsar Site (under the Ramsar Convention), as a Special Protection Area (SPA), and the presence of many Sites of Special Scientific Interest (SSSI). These designations generally cover the same areas and are owing to the site’s internationally important wetland features such as assemblages of plants, insects, and breeding birds.

The balance of evidence indicates that the designated protected areas of the Somerset Levels and Moors are at risk due to excessive levels of phosphorus within the water system, with associated biological evidence of eutrophication. Within the SLM, phosphorus is considered the limiting nutrient causing eutrophication, the process which occurs when an abundance of nutrients enters a watercourse. These nutrients can cause increased growth of surface flora, such as algae or duckweed, resulting surface blooms which decrease the supply of sunlight for plants below the water surface, reducing oxygen production in the water. As these blooms die their bacterial decomposition uses up oxygen, further causing oxygen levels in the water to drop, resulting in loss of aquatic life such as fish and invertebrates.

To assess wetland and ditch management options which reduce the ecological impact of high nutrient exposure.
To explore and evaluate opportunities to minimise the floating plant dominance in the Somerset Levels and Moors Ramsar ditch network which are driven by nutrient enrichment and will be impacted by climate change