No post-drought recovery of the macroinvertebrate community after five months upon rewetting of an irregularly intermittent Apennine River (Aterno River)

The combined effects of global changes and increasing water demand for human use are the main drivers of the increasing intermittence of most watercourses. The disruption of lateral, longitudinal and vertical connectivity during the dry phase in newly intermittent rivers may have dramatic effects on freshwater biota, ecosystem structure and processes and may extend its influence also after several months from the return of superficial flow. A few studies have systematically documented the dynamics of post-drought recovery of freshwater communities. In this paper we assessed the temporal dynamics of benthic in- vertebrate’s recovery starting from the first day after superficial flow resumption and for the successive five months. We demonstrated that the recolonization process of rewetted substrata was very low and partial, and after five months from the return of superficial flow the richness and abundance of post-drought re-colonizers were markedly lower if compared with the pre-drought community and with that of a near upstream perennial site. In this context, upstream drift, “seedbanks”and hyporheic refugia would be of mi- nor importance and the observed recolonization pattern may be mainly explained by the aerial dispersal from downstream perennial reaches of tolerant and generalist taxa. There- fore, former perennial Apennine rivers may be profoundly affected by modifications of the natural flow regime. Increasing intermittence of these watercourses may determine drastic changes in community structure and composition, with species loss and species substitu- tion. In addition, the high post-drought functional turnover may have negative effects on key ecosystem processes as leaf-litter breakdown and primary production.