Sedimentary geochemical record of human-induced environmental changes in the Lake Brunnsviken watershed, Sweden
Limnol. Oceanogr., 49(5), 2004, 1560-1569 | DOI: 10.4319/lo.2004.49.5.1560
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 lakes watershed included agriculture, urbanization, sewage and industrial disposal, and water column aeration. Smaller δ15Ntotal values, high organic carbon mass accumulation rates, low C:N ratios, and larger δ13Corg 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.