The effect of environmental contamination on the decomposition of European frog-bit (Hydrocharis morsus-ranae L.) in natural conditions

Decomposition is one of the fundamental processes that influence the recycling of elements in the ecosystem. Environmental pollution and eutrophication may affect plant decay and, therefore, lead to disturbances in detritus-based food webs. The objective of the study has been to describe changes in biomass loss and macroelements (C, Ca, K, Mg, N, Na, P, S) and trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) contents during breakdown of Hydrocharis morsus-ranae L. (European frog-bit). The questions underlying the study were: Does element concentration in plant litter or the environment affect the rate and pattern of H. morsus-ranae decomposition? What are the chemical predictors of the H. morsus-ranae detritus decay rate? An in situ experiment on decomposition was conducted using the litter-bag technique. H. morsus-ranae was found to be a fast decomposing macrophyte. The Na, Mn and K release rates were the largest, and the concentrations of C, N, P, S and trace metals in litter increased during the decay. In study sites that differed in element concentrations in fresh plant material and water plants had different decay rates and final element contents. Both the inhibitory effect of contaminants (Cd and Ni) and/or stimulatory effect of nutrients (P, N) and essential elements, such as Fe, Mg and Mn, could cause variation in decomposition observed between the study sites.