Decomposition of aquatic pioneer vegetation in newly constructed wetlands

Artificial wetlands are constructed around the globe for a variety of services, including wastewater treatment and carbon storage. To become a carbon sink, a newly constructed wetland must have a fully developed vegetation, consisting of species that can produce more organic matter than is being lost through decomposition. However, the effects of environmental conditions on the overall balance between production and decomposition might be complex. In this study, two large-scale field litterbag experiments were performed in a three-year old constructed wetland in the Netherlands, to separate the effects of litter characteristics and environmental conditions on decomposition rates of aquatic pioneer vegetation. Dimension reduction by principal component analysis was used to limit the number of variables for subsequent analyses in linear models. When transplanted to one common environment, litter characteristics alone could explain 52% and 26% of the variation in decomposition after 6 and 12 months, respectively. When both litter characteristics and environmental conditions were tested simultaneously and litter was decomposed in its original environment, 37% and 23% of the variation could be explained after 6 and 12 months, respectively. Both experiments showed two phases of decomposition: the initial leaching phase with an important role for litter characteristics and microbial communities in the model, and the second, slower phase, which is predominantly determined by litter characteristics and environmental conditions such as water quality. Model results could not be extrapolated to a fully developed reference area. Optimization of conditions in order to limit decomposition rates seems difficult and therefore we suggest using management options to influence biomass production and thereby fully exploit the use of newly constructed wetlands for carbon storage.