Metals in Lakes: Field and Modeling Results on Remedial Strategies with a Focus on Mercury and Radiocesium

Abstract

There are many chemical threats to the aquatic ecosystem today, e. g., eutrophication from nutrients, contamination from halogenated organics, radioisotopes and metals, and acidification. Pollutants reach lakes via different pathways: wet and dry atmospheric deposition on the catchment and the lake surface, direct emissions from, e. g., industries and urban areas and internal loading from contaminated sediments. The spread, retention and biouptake vary from substance to substance (Forstner and Miiller 1974; Forstner and Wittmann 1981; Salomons and Forstner 1984; Vernet 1991), but the fundamental principles and processes regulating the distribution and biouptake are more or less the same for all toxic substances, and could be modeled in the same manner by means of generic, massbalance models, but with different rates and model variables for different substances. For metals dissolved in the water or absorbed to very fine carrier particles, the distribution of these may be widespread and revealed as elevated concentrations in water, in suspended materials, in sediments and in biota over vast areas. However, elevated concentrations in abiotic compartments is one thing - biological uptake and increased ecological effects on the ecosystem level may be quite another (Hakanson 1984; Meili 1991a; Peters 1991). Thus, a fundamental question concerns the actual and potential ecological effects: How can one detect, describe and predict ecological effects at the ecosystem level?