Dilution of riverine heavy metal input concentrations by suspension of sediments and algal growth in the IJsselmeer

This study evaluates the effects of sediment erosion and primary production on the temporal and spatial variability of heavy metals concentration in settling solids in the lakes IJsselmeer and Ketelmeer. Settling solids were sampled fortnightly using sediment traps at two sites in the IJsselmeer and contents of clay, organic matter, calcium carbonate, six heavy metals and δ13C and δ18O values were measured. Wind speed and direction, suspended solids, organic matter, chlorophyll, phaeophytin and oxygen concentrations were measured in the water compartment, as was pH, temperature and Secchi depth. Regression and multivariate analyses were used to evaluate the relationships within the data set. Principal components analysis and stepwise multiple regression show that the variation in the heavy metals concentration in settling solids is related to the windspeed and clay content, both variables that are related to erosion of sediments; and to pH, chlorophyll and CaCO3, which are related to algal growth in the lake. This supports the hypothesis that the spatial gradient in the heavy metals concentrations in deposited solids in the IJsselmeer is the result of dilution of contaminated sediments due to erosion of older, less contaminated sediments and primary production related to algal growth.