Chemical composition of lake sediments along a pollution gradient in a Subarctic watercourse / Dauvalter V., Kashulin N., Sandimiriv S. [et al.] // Journal of Environmental Science and Health. Part A. - 2011. - Vol. 46. - P. 1020-1033.

Downloaded by [Vladimir Dauvalter] at 21:54 24 November 2013 1028 Dauvalter et al. observed in bo th large (lakes Im andra and Inari), and small lakes (Lake Chuna in the catchment basin o f Lake Im an ­ dra, Lake Kutsasjarvi, No rthern Sweden).[33,37,38] Maximal contents o f M n (exceeding Clarke (the average percentage o f an element in the earth crust) and background values with 10-50 times) were found in the surficial layer o f the sediment core o f the investigated lakes. Possibly, this is caused by the change o f oxidizing con­ ditions occurring in this top layer, as a reduction o f poorly soluble oxides M n4+ to dissolved M n2+ occurs at a higher redox-potential (i.e., at higher concentrations o f dissolved O2), than the reduction o f Fe3+ up to Fe2+. Hence, maximal contents o f Fe (exceeding Clarke and background values up to 10 times) in sediments can be marked at larger sediment depths, i.e., in conditions o f lower Eh value (at low concen­ trations o f dissolved O2). The better the benthonic layers o f water and surficial layers o f sediments are supplied with oxygen, the deeper in the sediments the accumulation of the poorly soluble oxides Fe3+ will occur.[37] The increase in Fe concentration in subsurface sediment layers (Fig. 5) is connected with processes o f molecular diffusion o f dissolved oxide iron forms (Fe2+) from the underlying sediment layers with anaerobic conditions and reduction potential, and upwards contact with the oxidized zone o f the water column, where oxidized iron again lose mobility and enrich the oxidized surficial sediment layer.[39] Dauvalter and Ilyashuk [39] proposed the assumption that accumulation o f Fe and Mn and formation o f ferro­ manganese nodules in sediments o f lakes o f No rth Fennoscandia can occur in the presence o f the following 0 50000 100000 Mn, ng/g three definitive conditions: 1) near neutral pH values o f water, and no processes o f lake acidification; 2) high content o f dissolved oxygen th roughout the entire water column to the bo ttom in absence o f processes o f lake eutrophication; and 3) sufficient depth o f lakes, about 15 m or deeper. Possibly, the above described lakes and their water areas meet these demands. In Ruskebukta and Vaggatem and two stations o f Lake Kuetsjarvi an increase in the contents o f P in surficial sediment layers was observed (Fig. 6). This suggests a development o f eutrophication processes in these lakes and an accumulation o f nutrients in the lake ecosystems, in­ cluding in sediments. According to ou r hydrochemical data the maximal weighted average concentration o f total phos­ phorus in water was found in Lake Ruskebukta, equalling 20-25 ^ g P /L in all study periods. The content o f phos­ phorus in water in this rather shallow lake (average depth 3 -4 m, maximal depth 15 m) is substantially defined by bioproduction, which are at a constant level.[17] The contents o f total phosphorus in Lake Kuetsjarvi changed in the range o f 4-31 ^ g P /L (average 17 ^ gP /L ). For the study period the concentration o f the to tal phos­ phorus in benthonic and surficial layers o f various water areas o f the Pasvik system changed in the range o f 3-39 ^ g P /L (average 11 ^ g P /L ). According to studies o f the chemical composition o f sediments, the maximum con ­ tents o f phosphorus in surficial layers and their maximum increase relative to background values (5.7 and 2.6 times, respectively) were found in sediments o f station Kuetsjarvi- 6 and Lake Ruskebukta (Fig. 6, Tables 1 and 2). Hence, the Fig. 5. Vertical distribution of concentrations of Fe and Mn (^g /g, dry weight) in sediment cores from lakes in the Inari-Pasvik watercourse.