Geochemistry of the Kola River and Lake Imandra, northwestern Russia

• Main Author: Pekka, Larisa
• Format: Doctoral Thesis
• Language: English
• Published: Luleå tekniska universitet 2005
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16821

The impact from mining and large-scale agricultural activities on levels and migration of metals within the Kola River and Lake Imandra has been studied in detail. Evaluation of the pollution status in the Kola River is based on sampling of the dissolved (<0.22 µm) and suspended (>0.22 µm) fractions and also metal accumulation in aquatic bryophytes on 12 sites along the Kola River and its tributaries during an annual cycle. In Lake Imandra the sampling of dissolved (<0.45 µm) and suspended (<0.45 µM) fractions from 18 sampling levels within the water column was performed on three sampling occasions. Also, a sediment core and porewater were sampled. Major and trace elements (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr and Zn), total and particulate organic carbon (TOC and POC), N and P were analysed. The work was performed in close co-operation with Russian and Finnish scientists. An important and surprising result from the analyses of both water and bryophyte samples is the relatively low overall contamination in the Kola River, much lower than was reported in previous studies. In comparison with Swedish and Finnish reference data from the Kalix and Näätämöjoki Rivers, only Cu and Ni are elevated. The concentrations of As, Cu, Mn, Mo and Ni in bryophytes and water were highest close to the mine areas, relatively low in the middle parts of the Kola River, and elevated at the river mouth. Evaluation of the sampling methods and the analytical results obtained from the parallel sampling occasions in the Kola River performed by the Murmansk Area Department for Hydrometeorology and Environmental Monitoring (MADHEM) and by Luleå University of Technology (LTU) clearly indicated contamination problems during the fieldwork and transportation of samples by Russian partners, which may explain high trace-metal concentration data for the Kola River obtained in previous monitoring programmes. Results from the Lake Imandra study demonstrate the dominant role of Mn redox cycling in controlling distribution of several major and trace elements. Mn oxides act as a major scavenger and carrier for the non- detrital fraction of Al, Ca, K, Mg, P, Ba, Co, Cu, Ni, Mo and Zn in the bottom water. The Pb distribution appears to be totally dominated by the input of S-rich particles emanating from the industrial activities. Formation and dissolution of Mn particles most likely also control anaerobic ammonium oxidation to nitrate and reduction of nitrate to N2. Reaching the surface sediment the metals associated with Mn oxyhydroxides are released and diffuse along a concentration gradient downwards in the sediment and upwards into the overlying bottom water. The upward diffusion results in secondary enrichment of major and trace elements in the bottom-water suspended material by recycling with Mn (for Ni, up to 1% ashed weight), while downward diffusing As, Cd, Cu, Ni, Mo and Zn become associated with sulphides in the S-rich zone a few cm below the sediment-water interface. The near thirty-fold increase in anthropogenic supply of sulphur to the water column has resulted in a higher SO42- reduction in the sediment, which in turn favours the immobilization of trace metals by the formation of metal-sulphides. Ni shows highest enrichment (27 times) in the sulphide-rich sediment zone, compared with the pre-industrial values. The distribution of P, Sr, Ba and Co is less influenced by secondary processes in the surface sediment because of their major association with primarily particles from the apatite industry. The effects of expansion of the apatite and Cu-Ni mining industries beginning in 1955 are clearly seen in the sediment record. Concentrations of P, Sr, Ba (apatite mining) and S, Cu and Ni (Cu-Ni mining) have significantly increased compared to the pre-industrial levels, and the major element composition of the deposited particulate material has changed compared with the pre-industrial sediment. === Godkänd; 2005; 20061002 (ysko)