DESCRIBING THE GEOCHEMICAL LANDSCAPE OF NORTHWESTERN WISCONSIN, USA

A data set of multi-element geochemistry for soils, stream sediments, and lake-bottom sediments for a 2 degree x 4 degree area of northwestern Wisconsin is used to examine trends in geochemical distribution across a landscape glaciated by Wisconsinan and older ice advances. Each sample medium shows a different statistical population for most elements. Geochemical surveys using a single medium are not good quantitative predictors of the composition of other media, even those close to sample sites. Compositions of C-horizon soils reflect their parent glacial materials. Variability is caused both by the mode of deposition of the glacial materials (e.g., lodgement till vs. ice-margin moraines vs. outwash, etc.) as well as the composition of bedrock source terranes. Compositions of A-horizon soils are determined by these same factors but also show the influence of anthropogenic inputs for elements such as mercury and lead. Pedogenic processes that formed the A-horizon also produce differences from C-horizon compositions and homogenize small-scale spatial variability shown by C-horizons. Stream sediments have compositions that qualitatively mimic the spatial variability of soil compositions, but quantitatively are compositionally distinct from soils for most elements. We can use the large stream sediment database for the study area to predict soil compositions by applying a correction based on the smaller soil data set. The technique has varying levels of accuracy for different elements and appears best suited to estimating background soil composition rather than anomalous concentrations, which are poorly predicted. Lake sediment compositions are largely independent of the composition of surrounding soils. Compositional variability is controlled in large part by the character of the lakes. Seepage lakes have a large biogenic component and detrital components are subordinate. Drainage lakes and especially impoundments have compositional variability determined largely by varying amounts of detrital mineral particles.