Abstract. In this paper we present a model that can reconstruct water table position and soil temperature profiles to 3 m depth in boreal mixed mire systems using the readily available climate data on air temperature and precipitation as driving variables. The model simulates complete, multiple annual cycles including winter conditions and freeze-thaw processes. The major requisite for an accurate description of the soil heat flux in a mire is an accurate description of the water content of the profile because of the high porosity of the soil and the thermal properties of water. The soil moisture profile in this model is described as a function of water table position The necessity of correctly describing water content over time in modeling heat flows and ice formation in arctic soils was discussed by Waelbroeck [1993]. In peat-forming mires it is even more important to have a correct water content description for calculating heat fluxes because of the high water content in the saturated zone and the large variation of the water content in the unsaturated zone. Accurate water content de-

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Knowledge of natural, prepollution concentrations of heavy metals in forest soils and temporal trends of soil pollution are essential for understanding present-day pollution (ecotoxicological assessments) and for establishing realistic goals for reductions of atmospheric pollution deposition (critical loads). Soils not exposed to deposition of atmospheric pollution no longer exist and, for example, present lead (Pb) pollution conditions in northern European soils are a consequence of nearly 4,000 years of atmospheric pollution. We use analyses of Pb concentrations and stable Pb isotopes (206Pb/207Pb ratios) of ombrotrophic peat and forest soils from southern Sweden and a model for Pb cycling in forest soils to derive an estimate for the prepollution concentration of Pb in the mor layer of boreal forest soils and to back-calculate Pb concentrations for the last 5,500 years. While the present-day concentra tions of the mor layer are typically 40−100 μg g-1 (0.25−1.0 g m-2), Pb concentrations of pristine forest mor layers in Sweden were quite low, ≤0.1 μg g-1 (≤1 mg m-2). Large-scale atmospheric pollution from the Greek and Roman cultures (ca. 0 AD) increased Pb concentrations to about 1 μg g-1. Lead (Pb) concentrations increased to about 4 μg g-1 following the increase of metal production and atmospheric pollution in Medieval Europe (ca. 1000 AD).

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Soil processes in high-latitude regions during winter are important contributors to global carbon circulation, but our understanding of the mechanisms controlling these processes is poor and observed temperature response coefficients of CO 2 production in frozen soils deviate markedly from thermodynamically predicted responses (sometimes by several orders of magnitude). We investigated the temperature response of CO 2 production in 23 unfrozen and frozen surface soil samples from various types of boreal forests and peatland ecosystems and also measured changes in water content in them after freezing. We demonstrate that deviations in temperature responses at subzero temperatures primarily emanates from water deficiency caused by freezing of the soil water, and that the amount of unfrozen water is mainly determined by the quality of the soil organic matter, which is linked to the vegetation cover. Factoring out the contribution of water limitation to the CO 2 temperature responses yields response coefficients that agree well with expectations based on thermodynamic theory concerning biochemical temperature responses. This partitioning between a pure temperature response and the effect of water availability on the response of soil CO 2 production at low temperatures is crucial for a thorough understanding of low-temperature soil processes and for accurate predictions of C-balances in northern terrestrial ecosystems.