Effects of mining on testate amoebae in a Finnish lake |
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Authors: | Susanna Kihlman Tommi Kauppila |
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Institution: | (1) Geological Survey of Finland, P.O. Box 96, 02151 Espoo, Finland;(2) Department of Geology, University of Turku, 20014 Turku, Finland;(3) Geological Survey of Finland, P.O. Box 1237, 70211 Kuopio, Finland |
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Abstract: | Sediment geochemistry and testate amoebae (thecamoebians) were used to track the spatial extent and temporal evolution of
mine loading and its impact on aquatic biota in Lake Pyh?j?rvi, central Finland. Pyh?salmi is an operating Zn-Cu–S mine, located
by Lake Pyh?j?rvi. Mine loading to the lake comes mainly from wastewater. Highest metal loading occurred in the 1970s and
1980s. Present loading consists mainly of Ca and S that nearly saturate dense wastewaters with gypsum. This affects oxygen
concentration in the lake’s northern basin, where effluent is presently discharged. Of 25 short sediment cores retrieved from
Lake Pyh?j?rvi, 10 came from sites ‘downstream’ and 15 from ‘upstream’ of the mine. Three sample levels from each core were
selected for further investigation after exploratory XRF metal analysis. Samples were chosen to represent lake conditions
before the mine impact, during the peak impact phase, and at present. Results from pre-disturbance deposits show that the
two lake basins are naturally different. The ‘downstream’ basin (Junttiselk?) has lower oxygen and a higher sedimentation
rate, which was revealed by concentrations of redox-sensitive and clastic-related elements, as well as faunal distributions.
The peak mine impact is reflected in the high concentration of S and metals Cu, Zn, Cd, Pb, which spread widely in the lake
and increased > 100% at sites near the tailings area. These concentrations have since decreased, but not to pre-disturbance
levels. The faunal response to peak metal concentrations was weak, spatially limited and masked by larger responses to other
environmental factors, including eutrophication, oxygen concentration, and increased clastic input generated by land-use changes.
These environmental factors and changes in mine water composition probably account for the reason that faunal assemblages
did not return to the pre-mine situation. Instead, the modern fauna reflects a third assemblage type that developed after
the peak-loading phase. Geochemical and thecamoebian analyses show that the mine has affected the two basins of the lake differently
during the lake history. Results suggest that mining impacts could be mitigated with good planning and management. |
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