Habitat structure and Trichoptera diversity in two headwater flood plains, NE Italy

Two headwater flood plains in tributaries of the Tagliamento catchment (ICE. Italy) were investigated to compare and contrast floodplain morphology, aquatic habitat structure, physico-chemical characteristics, and Trichoptera community relationships. The two flood plains (one stable and forested, the other dynamic and open) were similar with respect to position along the longitudinal continuum, elevation, stream order, and geological material. However, the two flood plains differed greatly in aquatic habitat structure, physico-chemical character, and Trichoptera abundance, distribution, and richness. The forested reach had lower slope, finer sediment, more standing waterbodies, significantly higher benthic organic matter standing stocks, and a closed canopy of predominantly Alnus incana. Trichoptera abundance in the forested flood plain was higher, as was taxa richness (27 taxa), than in the open flood plain (16 taxa). Differences in Trichoptera composition and richness were due to the presence of several species of Limnephilidae, which were correlated with benthic organic matter. These findings are discussed in the context of species-abundance relationships, environmental factors, and reach-specific morphological characters. Results illustrate the dependence of habitat type and invertebrate community response to reach scale factors (i.e., geomorphology and hydrology) that may be uncoupled from position along the longitudinal continuum.