Original paper

Macrozoobenthos communities from two types of land-water transition zones in a European lowland dam reservoir

Poznańska, Małgorzata; Kobak, Jarosław; Wolnomiejski, Norbert; Kakareko, Tomasz

Abstract

We investigated the abundance, diversity and taxonomic composition of macrozoobenthos from the land-water interfaces of a lowland dam reservoir developing on sandy and organic-rich substrata. We also checked the possibilities of the occurrence of the edge effect consisting in increased abundance and diversity of the community developing in the transition zone between two habitats, as well as in the presence of taxa specific for only that zone. The study area was the middle part of the Włocławek Reservoir (the lower Vistula River, central Poland). In 2002-2003, we sampled air-exposed (above the water line, at the water line) and submerged (0.5 m and 1 m depth) sites from a sandy area situated in the flooded part of the reservoir and a small cove overgrown with macrophytes, with sediments rich in organic matter. In the organic-rich sediments, biodiversity and abundance were higher at the exposed sites than at the submerged ones. Furthermore, we found numerous specific taxa, which occurred only in the land-water interface of the organic-rich habitat (semi-terrestrial Diptera, terrestrial and amphibious Oligochaeta, Endochironomus sp. (impar group), Valvata cristata, Anisus contortus and Coleoptera larvae). Thus, all symptoms of the edge effect were observed there. On the other hand, the sandy shore was a simple transition zone. Some symptoms of the edge effect appeared (high biodiversity and the presence of a few amphibious taxa) but the abundance was extremely low compared with that found at the submerged sites. Individuals inhabiting the sandy transition zone formed accidental assemblages, widely differing from one sample to another. The homogeneous unstable land-water interface on the sandy shore is a poor habitat for macroinvertebrates, which are washed out by wave action, have no protection against air exposure and freezing, and their substratum may be totally destroyed in winter by ice drifting downstream. On the other hand, organic-rich sediments are more stable and provide much better protection and food conditions for the fauna living near the water line.

Keywords

macroinvertebrate communityecotoneedge effectwater level fluctuationssubstratum typeair exposure