Leaf litter decomposition rates in freshwaters differ by ecosystem

Decomposition rates of leaf litter in freshwaters are often used as a proxy for ecosystem function; however, there are many sources of variation in decomposition rates within and between freshwater ecosystems that still have not been tested. In particular, the variation in decomposition rates between different freshwater ecosystems has rarely been addressed.

Here we compared decomposition rates of red alder (Alnus rubra) leaf litter in streams, ponds and lakes within a single forest, while controlling for water temperatures. Using coarse-mesh and fine-mesh bags we found that when accounting for degree days, decomposition rates were higher in streams than ponds, and twice as high in streams than lakes, for either mesh size. The overall densities of invertebrates per leaf pack or per gram of leaf litter were very similar between the three ecosystems.