The influence by point sources on carbon, nitrogen and metals in two sedimentary environments

Sediments in two aquatic environments have been investigated. Both are anthropogenically affected and polluted. The focus has been on stable carbon and nitrogen isotopes, C/N ratios, and heavy metals. The first site is Höggarnsfjärden Bay in the inner parts of the Stockholm Archipelago, Sweden, where a garbage dump releases treated leach water. The effect on carbon and nitrogen in the sediment close to the discharge is large, but 1200 m downstream the effect is diluted by the background discharge of the town of Stockholm and the Lake Mälaren, which drains into the archipelago. The main source of the studied metals is not the garbage dump itself. The sediment close to the discharge shows high enrichment factors due to high sedimentation rate and adsorption, and low decomposition of organic matter. The metal enrichment factors of downstream sites are not higher than the upstream sites. The second site is Lake Verkasjön close to the north part of Lake Vättern, in the county of Örebro, Sweden. River Salaån flows through Lake Verkasjön on the way through a former mining area to Lake Vättern. Upstream of Lake Verkasjön an ore dressing plant site was used in 1877-1881 for extraction of zinc. During that period the sediment of Lake Verkasjön received high loadings of sulphidic tailings. Normal sedimentation after the event has lead to that the polluted sediment is found as a distinct layer at 18-22 cm. The layer is characterized by elevated metal concentrations, decreased organic matter content and increased stable carbon composition. The sediment that has accumulated above 18 cm works as a physicochemical barrier that seals the waste from the overlying sediment. At the time of the event the signal of aquatic production in the sediment changed; the sediment above the layer has an increased proportion of aquatically produced material, implying changed land use in the catchment area