Temperature models for nitrification and denitrification in lake sediments

During this century the Intergovemmental Panel on elimate ehange (IPeC) predicts the global climate to change significantly with temperature increases o f 3 to 5 oe in the Danish region, with highest increases in winter (HouGHTON et al. 2001). ehanges in wind climate and hydrology and their effects on temperature and mixing regimes must be modelled to present a complete picture of consequences of climate changes. We focused on the direct effects of temperature on key process rates. In general, the rates of physical, chemical, and biological processes increase with temperature. ehemical equilibrium studies describe temperature influence on process rates as: Q10 = (~1/~2) <2-ei) (VAN'T HOFF 1884), where ~1 and Jl2 are process rates at 2 temperatures 8 1 and 8 2, respectively; or by a more theoretically founded expression and introduction of an activation energy: kT = Ae-Ea/RT (ARRHENIUS 1889), where kT is a rate constant at the absolute temperature T, A is a frequency factor, Ea is an activation energy, and R is the gas constant. These equations, however, are only valid over small temperature intervals. Strong deviations occur at low temperatures and especially at high temperatures, where the proteins of enzymes are denaturised. In many studies these exponential equations have been routinely applied, although careful inspections have shown a temperature dependence not statistically different from a simple linear response (COUSSINS & BOWLER 1987, MONTAIGNES et al. 2003). To study the effect of climate changes on the nutrient metabolism in lakes we measured nitrification and denitrification rates over the temperature range 0-60 oe in sediment sarnples from Frederiksborg eastle Lake and applied a number of temperature models to the data. The most predictive model was used to describe the acclimatisation o f the processes, and the model was calibrated and verified on sediments from a series of mesocosms run with various climate scenarios.