Mesh size and site effects on leaf litter decomposition in a side arm of the River Danube on the Gemenc floodplain (Danube-Dráva National Park, Hungary)

In forested floodplain ecosystems, leaf litter represents an important energy source for aquatic organisms, and its decomposition is a key ecosystem process. In this paper, we investigate the decomposition dynamics of Salix alba, Populus hybrids in the depositional zone of a side arm of the River Danube, and of Fraxinus angustifolia, Ulmus laevis, Quercus robur in the erosional zone. To estimate the effect of small-sized invertebrates, we used litter bags with two mesh sizes (0.04 and 1 mm), and to evaluate the site effects the F. angustifolia leaves were exposed in both sites. Willow and poplar leaf litter decomposed at an intermediate rate; ash and elm decomposed quickly, and the oak decomposed slowly. The faunal exclusion experiments revealed the importance of Chironomidae larvae, which formed the dominant macroinvertebrate taxon in the medium-mesh bags. The initial quality of the leaf litter, especially the N:P ratio, affected the activity of microorganisms, the density of chironomids, and was positively correlated with the breakdown rates. The site conditions had a significant effect on the decay rate and nutrient dynamics. We concluded that the leaf litter decomposition processes and the associated nutrient dynamics are affected by nutrient availability, consumer activity and site conditions.