Sedimentary geochemical record of human–induced environmental changes in the Lake Brunnsviken watershed, Sweden

Abstract

Environmental changes in Lake Brunnsviken, its watershed, and the greater Stockholm region since the middle of the nineteenth century have left interpretable geochemical imprints in the bottom sediments. These human‐induced perturbations within the lake’s watershed included agriculture, urbanization, sewage and industrial disposal, and water column aeration. Smaller δ 15 N total values, high organic carbon mass accumulation rates, low C:N ratios, and larger δ 13 C org values identify periods of increased nutrient delivery and elevated primary productivity in the lake. C: S ratios that change from high to low trace the transition from an oxic hypolimnion to an anoxic one during the periods of high productivity. Accumulations of redox‐sensitive trace elements increase during the anoxic period and are further magnified during a time of industrial waste discharge into the lake. A recent decrease in black carbon concentrations in sediments reflects the conversion from wood and coal to cleaner forms of energy.