Aquatic geochemistry of small lakes: Effects of environment changes

This paper reports the results of an extensive investigation of water chemistry in the small lakes of European Russia and Western Siberia along a climatic gradient. It was demonstrated that small lakes unaffected by any direct contamination can be used as indicators of natural geochemical conditions of water formation, as well as global and regional fluxes of airborne pollution and climate warming. A novel concept was developed for within- and between-zone variability in water chemistry over vast areas of tundra, taiga, forest, and steppe, and contributions of natural and anthropogenic factors to its formation under present-day conditions were estimated. A proposed predictive scenario showed that climate warming will result in an increase in water salinity in southern regions and ubiquitous phosphorus enrichment in terrestrial waters; the hydrologic and geochemical conditions of water formation in northern Siberia will change significantly in response to permafrost thawing. Zonal features in the development of anthropogenically-induced processes in terrestrial surface waters (acidification, eutrophication, and metal enrichment) were determined. It was demonstrated that, in addition to naturally acidified lakes with high contents of humic acids, acid lakes of anthropogenic origin occur over the whole humid region discussed here, and acidification processes were characterized for each subregion. The trophic status of lakes and limitation of their bioproductivity with respect to nutrients were estimated. The concentrations and distribution of trace elements were analyzed in terrestrial waters from various climatic zones of European Russia and Western Siberia, and the first estimates were obtained for the mean concentrations and coefficients of migration of a wide range of elements in terrestrial freshwaters. We distinguished a group of metal (Mo, As, U, Bi, Sb, Cd, Ag, Se, Re, Pb, Cd, W, etc.) the enrichment of which in natural waters results from their global dispersion in the environment. Experimental results and natural observations are presented on the processes of metal ion complexation with humus substances, and sequences of their increasing activity in competing for organic ligands were derived. Data are presented on the speciation of metals depending on natural water chemistry in the tundra, taiga, and steppe zones. The pioneering investigations on the geochemistry of natural waters allowed us to substantiate new regional norms for water quality.