Response Of Small-Stream Biota To Sudden Flow Pulses Following Extreme Precipitation Events

Extreme discharge rate increases in small streams caused by sudden extreme precipitation events are classified as small-scale pulse-type disturbances. Small highland brooks in agricultural landscapes (arable land and meadows) are frequently characterised by extremely low flows during normal conditions, plus the rare appearance of high-flow events that periodically may reset their ecosystems. We studied two small highland brooks to assess the impact of extreme discharge rates (flow pulses) upon periphyton, macrozoobenthos, and fish assemblages. No distinct changes were recorded in composition of periphyton assemblage or fish (brown trout, Salmo trutta m. fario) occurrence following such flow pulses. Cyanobacteria, however, were absent following a flow pulse, while growth appeared to be boosted in green algae (Chlorophyceae). Similarly, there was no negative response observed in macrozoobenthos communities, with density, diversity, taxa richness, and saprobic indices remaining either more-or-less unchanged or considerably enhanced following high-discharge episodes. These observations were confirmed through Sorensen's similarity indices, which indicated no significant change in either periphyton or macrozoobenthos following such episodes.