Fluvial biofilms from upper and lower river reaches respond differently to wastewater treatment plant inputs

Abstract

We examined how wastewater treatment plant (WWTP) inputs affect fluvial biofilm functioning and structure developing on river surface sediments in two different reaches characterized by different anthropogenic pressures. The upper reach includes one site before and one after Palautordera WWTP (Pref and P, respectively); the lower reach includes one site before and one after Tordera WWTP (Tref and T, respectively). We performed an ex situ translocation experiment which resulted in four treatments (Pref-P, Pref-T, Tref-T, Tref-P) and in three different impact grades according to a translocation gradient defined by water chemical changes between sites, being Tref-T the lowest translocation gradient, Pref-P and Tref-P the medium translocation gradient, and Pref-T the highest translocation gradient. After receiving WWTP inputs, upper reach communities (Pref-P and Pref-T treatments) had a decrease in live bacteria and an inhibition of extracellular enzyme activities, while lower reach communities (Tref-T and Tref-P treatments) showed an increase of enzyme activities. Treatments with the highest and lowest translocation gradients resulted in different metabolic fingerprints. Results suggest that the origin and sensitivity of the receiving community determines its functional response and also reinforce the idea that the impact level is an influential aspect to consider when analyzing community responses to anthropogenic impacts