Sedimentary diatoms in inferring trophic status and limnological changes in boreal lakes

Sedimentary diatoms in inferring trophic status and limnological changes in boreal lakes Miettinen, Juha O. Sedimentary diatoms in inferring trophic status and limnological changes in boreal lakes. – Analyses of sedimentary diatoms were used for inferring reference (pre-impact) conditions and limnological changes in eastern Fennoscandian lakes. Long-term limnological variation was studied from a sediment sequence covering the history of the last 10,000 years in Lake Pieni-Kuuppalanlampi, Karelian Republic, Russia. Diatom based transfer functions for total phosphorus (TP) concentrations and water colour in boreal lakes were developed using a new 78-lake training set in Finland, and validated using an independent test set of 30 lakes. These transfer functions were used for inferring background (reference) and recent TP concentrations and water colour in 27 lakes in East-Finland. In addition, trophic status development during the 20 th century was assessed for six lakes in Ladoga Karelia, Karelian Republic. In the area of Ladoga Karelia, relatively intensive agricultural land-use diminished as a consequence of the second world war, making it possible to study ecosystem recovery following relaxation of the human pressures. The results from the Lake Pieni-Kuuppalanlampi testify for the sensitivity of the lake and its diatom assemblages to both natural and anthropogenic, pollen-analytically inferred, changes in the vegetation of the catchment area. Diatom assemblages indicate long-term oligotrophication and decrease of pH in the lake during the Holocene, especially after spruce forests developed in the area. Early land-use, namely slash-and-burn cultivation, led to the eutrophication of the lake during the late Iron Age. Diatoms provide reliable estimates for TP concentrations and water colour in boreal lakes. The TP model yielded high correlations between predicted and observed values in the training set and in the test set, and low errors for the predictions. The colour model yielded lower, but reasonable, correlations between the predictions and the observations, and slightly higher errors for the predictions than the TP model. Squared chord distances between the background and recent diatom assemblages in the 27-lake dataset, combined with the diatom inferred TP and colour, indicate that in most lakes where the diatom assemblages have undergone significant changes, these can be attributed to changes in TP concentrations or water colour. The colour of the water, as well as the TP concentrations, has been subject to large changes in many lakes. The six lakes in Sortavala show different responses to changes in land-use practices. Two of the lakes recovered from the …