Effects of moisture and temperature on carbon and nitrogen mineralization in mine tailings mixed with sewage sludge

Digested sewage sludge mixed with copper mine tailings was incubated for 3 mo at 16 combinations of temperature (-1, 5, 10, and 15 degrees C) and soil moisture content (2, 8, 14, and 24% by weight). Carbon dioxide evolution and net N mineralization were measured at increasing time intervals. A two compartment first-order kinetic model (refractory and labile C) was fitted to the time series of measured CO2 fluxes using nonlinear regression analysis. The dependencies of the rate constants on moisture and temperature could be well described by log-linear functions. The estimated Q10 value (the factor by which the rate is increased as temperature is increased 10 degrees C) was 2.55. Within the range of temperature and moisture considered here, which correspond to conditions occurring naturally in Sweden, CO2 evolution was more strongly controlled by moisture than by temperature. Less mineral N accumulated during the experiment at the lowest moisture or temperature. However, the dependency of net N mineralization on moisture and temperature in the remaining treatments was less clear than for C evolution, presumably due to denitrification at the higher temperatures and moisture contents. Nitrate was formed after around 2 wk but only at 10 and 15 degrees C.