A MODEL TO PREDICT GROSS SEDIMENTATION IN SMALL GLACIAL LAKES

This study is an attempt to quantify and rank variables of significance to predict gross sedimentation (i.e., net sedimentation plus resuspension) in small glacial lakes. Sediment traps were placed in 25 Swedish lakes and exposed for about 110 days during the summer for four years. Average values of rates of gross sedimentation in bottom traps were compared to catchment and morphometric parameters determined from different types of maps. Various hypotheses concerning the factors regulating gross sedimentation in lakes were formulated and tested. Different statistical tests were used to separate random influences from causal influences. The most important 'map parameters' were: the relative depth, linked to resuspension and the form and size of lakes, the forest and open land percent of the so-called near area (= the proximate area of the lake as determined by the drainage area zonation method), the distribution of mires and lakes in the catchment, the relief of the drainage area and the theoretical lake water retention time. Each of these variables only provides a limited degree of (statistical) explanation of the variability in gross sedimentation among the' lakes. The predictability of models for gross sedimentation can be markedly improved by accounting for the zonation problem, i.e., the distribution of the characteristics in the drainage area. The stability of the final model, which gives a r2-value of 0.78, has been tested with positive results. The model allows mean values of gross sedimentation to be estimated from readily available data of 'geological' characteristics of the lake and its drainage area. The variability in gross sedimentation from other factors/variables, such as temperature, precipitation, wind, and load of nutrients, may then be quantitatively differentiated from the impact of these 'geological' factors/constants.