Effect of drought frequency and other reach characteristics on invertebrate communities and litter breakdown in the intermittent Mediterranean River Pula (Sardinia, Italy)

Benthic invertebrate communities were sampled in spring and fall, and breakdown of reed litter was measured in winter, spring, summer and fall, at 23 sites in an intermittent Mediterranean river basin (Pula, Sardinia, Italy), and their variations were related to drought frequency and other reach characteristics (altitude, order, stream channel width and depth, vegetation cover, sediment type, organic content, and water quality). 78% of the sites were affected by drought events, mainly in summer and fall. Benthic taxonomic richness was higher and most taxa were more widely distributed in spring than in fall. Canonical correspondence analysis showed that measured environmental variables accounted for 72% of the variance in invertebrate community structure. Reed decay rates varied among seasons, and during the dry season among stream orders as well. Drought events slowed down breakdown and explained 44% of spatial variability in decay rates (Stepwise multiple regression analysis), an additional 8% being explained by water chemistry. Results suggest that drought events affect ecosystem functioning (litter breakdown) more than structure (invertebrate communities)