Determining Temperature-Normalized Decomposition Rates

Abstract

Temperature is a key environmental factor controlling rates of litter decomposition in streams and other ecosystems. Normalizing decomposition rates for temperature not only enables assessments of the importance of temperature effects but also facilitates comparisons of potential other controlling factors. This chapter describes procedures to achieve such normalization. In streams, temperature normalization of decomposition rates has almost invariably assumed a linear relationship. Accordingly, litter mass remaining at various time points after deployment of litter in the field is regressed against thermal sums (degree days) obtained from continuous temperature records. The same approach is taken when an exponential temperature dependency is assumed, commonly by using a Q10 model, with Q10 being assumed to take a given value, such as 2, or being fitted along with the decomposition rate coefficient. Here the thermal sums of the degree-day model are replaced by an integral that captures the exponential relationship. Worked examples of the calculations are provided in a supplementary spreadsheet and as computer code. Similar approaches to temperature normalization can be adopted based on dependencies encapsulated in the Arrhenius law used in the metabolic theory of ecology.