The current status of a sample of english sites of special scientific interest subject to eutrophication

Abstract

Abstract Records for 102 Sites of Special Scientific Interest (SSSIs) in England were examined for eutrophic status and for symptoms of eutrophication using criteria established by the Department of the Environment (DoE). Seventy‐eight were found to be eutrophic or hyper‐eutrophic using total phosphorus criteria. Of the 102 sites, 85 cases (84%) showed symptoms of eutrophication. This had changed overtly the nature conservation interest in 69 cases. The 102 sites were contracted to 96 by listing together eight adjacent SSSIs in the Somerset Levels and treating another split‐site SSSI with separate catchments within it as two sites. Within these 96, 17 did not show symptoms of eutrophication and 79 (84%) did. Of the 79 cases, a major cause of the eutrophication in 35 (44%) was sewage effluent with a further five possible cases of effluent problems. The second most important cause (15 sites (19%) and potentially a further six, of the 79 sites) was attributed to the effects of common carp (Cyprinus carpio), and to a lesser extent common bream (Abramis brama), in mobilizing nutrients and increasing turbidity within the water body. Symptoms of deterioration were most frequently recorded in the aquatic plant communities, probably because these are most readily observed. Comparable changes should be expected in animal communities but these are infrequently monitored. There may have been unrecorded changes in some sites that had nonetheless suffered damage. It is likely that detailed studies of sites where there is clear evidence of eutrophication will reveal some deterioration in conservation interest. The primary management required to help restore the conservation interest in the 79 sites involves phosphorus removal from, or diversion of, sewage effluent in at least 30 cases. Of these two‐thirds (20) will fall outside the current arrangements being made by the DoE for the application of the Urban Waste Water Treatment Directive. Removal of carp and additional biomanipulative measures are suggested for at least 18 cases (23%) and fishery modifications in a further six, giving a total of 30% of sites where fish are a part of the problem. Further investigation is needed in nearly half of all cases where the situation is not entirely clear. The data available from statutory bodies to assess the trophic states of the sites examined were generally inadequate. Total phosphorus, a key variable in the currently recommended DoE scheme, and widely recognized as very important by the limnological community, is not routinely monitored by the National Rivers Authority (NRA), and methods used for soluble reactive phosphorus are not generally used with a sufficiently low detection limit.