The Anglesey lakes,Wales, UK—A palaeolimnological study of the eutrophication and nature conservation status

1. Palaeolimnological techniques were used to investigate recent environmental change in three shallow, coastal lakes (Coron, Dinam and Penrhyn) within biological SSSIs on Anglesey, Wales, U.K., where agriculture has influenced two sites while a third received sewage effluent. 2. The Penrhyn core was dated radiometrically and the timescale of the other two sites estimated by correlation. A range of palaeopigment, geochemical, diatom and chironomid analyses were made on the samples. 3. Results suggest that eutrophication has increased at all three sites in the last 50 years. Palaeopigment analyses indicate that Coron has had abundant blue–green algal populations, the Dinam sediments were highly organic and Penrhyn has been the most eutrophic. Trace metal profiles suggested significant sediment mixing. Although concentrations were sometimes low, diatom profiles from the sites include marked recent increases in Stephanodiscus, Cyclostephanos and Thalassiosira spp. 4. While there was a period of rapid eutrophication in Coron in the late-1960s, there are recent signs of reduced nutrient loading. Penrhyn appears the most enriched (and eutrophic from earlier time) and Dinam the least. Chironomid analyses suggest Coron has been the most enriched and two alternative explanations are put forward for the Chironomus loss in the recent sediments. Dinam has changed little, remaining mesotrophic and retaining the eutrophication-intolerant Pseudochironomus. In Penrhyn there has been a slow but progressive development of eutrophication, becoming mildly eutrophic at an early stage, with the loss of Pseudochironomus. 5. Environmental histories derived from sediment data of the three lakes have been related to specific catchment events and the significance of the relationship with lake ecosystem stability is discussed. The study shows the contribution of palaeolimnology to freshwater conservation.