The thermal sensitivity of nitrification as a function of the concentration of nitrogen substrate

The joint influence of substrate concentration and temperature upon the rates of microbially mediated ammonia oxidation and nitrite oxidation is analyzed using rate laws reported in the literature. This analysis shows that (1) a family of substrate isoconcentrates is required to describe the thermal sensitivity of each oxidation step; (2) the optimum temperature of each step increases as the logarithm of its substrate concentration; and (3) the thermal rate-maximum of each step increases as its substrate concentration raised to a fractional power. From these relations and published parameter values, the progressions of optimum temperature and maximum rate with substrate concentration are calculated for each step. The thermal sensitivity of ammonia oxidation is thus seen to differ substantially from that of nitrite oxidation. The limits of validity and two potential applications of these results are discussed.