Long-term trends in Loch Leven invertebrate communities

Detailed studies of the macroinvertebrate benthos and zooplankton communities in Loch Leven, the largest shallow lowland lake in Scotland, UK, were carried out from 1966 to 1973 as part of the International Biological Programme (IBP). The results revealed a reduction in species diversity that was attributed to increasing eutrophication. This work provides a baseline against which the response of the invertebrate communities to subsequent changes in management can be assessed. This article compares macroinvertebrate benthos and zooplankton data from the IBP study with the post-IBP era during which changes at Loch Leven included a 60% reduction in the phosphorus input from external sources and variations in fish stocking rates. Only in recent years has there been evidence of ecological recovery by the invertebrate communities: the number of macroinvertebrate and zooplankton taxa has increased (including taxa considered to be sensitive to nutrient enrichment) and invertebrate abundances have declined. These changes appear to reflect the improvements in water quality and habitat conditions at Loch Leven that have occurred as a result of the recent reduction in nutrient loads, albeit with a substantial delay before any ecological response could be detected. This time lag in recovery has important implications for assessing improvements in the ecological status of other lake systems, as is required by the EU Water Framework Directive