Tungmetaller i en sedimentkärna från en sjö norr om polcirkeln-möjliga orsaker till haltvariationer i vertikalled

Sammanfattning: Changes in the accumulation of heavy metals (Cd, Cu, Hg, Fe, Mn, Ni, Pb, Zn), arsenic (As), and selenium (Se) in sediment of pristine lake in northern Sweden were studied by making measurements at different depths in a sediment core. The sediment core was extracted from the deepest part of the lake Sautusjärvi, close to the village Jukkasjärvi. The sediment samples were transported in a cooler to Lund University where they were kept in a cool room before being analysed. A potential local source of heavy metals to the atmosphere is the LKAB iron mine in Kiruna, one of the largest iron mines in the World. Sautusjärvi is a good lake for studying changes in atmospheric deposition of heavy metals because it receives no industrial effluent water and has little connection with other lakes and running waters. By slicing a 15 centimeter sediment core into 1-cm slices, it was possible to follow changes in heavy metal loads entering the lake. However, vertical changes in organic matter as well as other sediment constituents had to be taken into account when evaluating how the atmospheric deposition of the different heavy metals had changed over time. Almost all metals showed decrease in concentrations in the top layer of the sediment core, suggesting a general decline in metal concentrations in the atmosphere. Possibly, such a decline could be explained by less fossil fuel use, use of unleaded petrol, and better emission control by the use of improved filters that remove metals from exhaust gasses. However some of the studied elements (Hg, As, Se) increased in concentration towards the sediment surface. This may be the result of yearly increases in mining at LKAB, activities at the space facility Esrange or increased long-range atmospheric transport, e.g. from China or other growing economies in Asia.