Decomposition of Standing Litter Biomass in Newly Constructed Wetlands Associated with Direct Effects of Sediment and Water Characteristics and the Composition and Activity of the Decomposer Community Using Phragmites australis as a Single Standard Substrate

In a large-scale field experiment in 18 basins in a three-year old constructed wetland (6 ha) in the Netherlands, we analyzed a wide range of environmental variables, grouped into variable groups, to determine the combined direct effect of the environmental variables and the resulting decomposer community on decomposition rates of standing litter biomass in newly constructed wetlands. The variability among the experimental units could only to a limited degree be explained by linear combinations of all 54 possible predictor variables (30 and 23% of variation explained after 6 and 12 months of decomposition). Moreover, models for decomposition after 6 months could not predict decomposition after 12 months. The poor predictions by our models are probably due to (sometimes large) variations in the predictor variables but small differences in decomposition rates between the different basins. Based on our results it seems that decomposition of standing litter biomass in newly constructed wetlands is relatively uniform when considered in time and space, with low explanatory power by variable groups from biotic and abiotic variables. Normally one would expect differences in decomposition rates with differing environments, but counterintuitively in newly constructed wetlands these differences are small.