Drastic flow reduction modulates the response of fluvial biofilms to Triclosan exposure

PROIA, L; VILCHES, CAROLINA; BONINNEAU, C; GUASCH, H; ROMMANI, A; SABATER, S

Girona

Congreso; VII Simposium for European Frehwaters Sciences; 2011

Consequences of global change on rivers are, among others, alterations of flow regime and entrance of compounds potentially toxic for the biota. Indeed, in water scarcity situations, reduced dilution capacity may amplify the effects of chemical pollution. Therefore, studying the response of natural communities to both flow reduction and toxicants is a key issue in the assessment of global change impacts on river ecosystems. This work aims to investigate the influence that an episode of drastic flow reduction may have on the response of biofilms to pulses of Triclosan (TCS). Specific objectives were: i) the assessment of the separated effects of flow and TCS and, ii) determine the potential interactions between the two factors. Three-week old biofilms were subsequently exposed to flow reduction (1 week), flow interruption (2 days) and TCS pulses under restored flow conditions (2 days). Biofilms were later left for two weeks under steady flow conditions to describe late responses and recovery. Several descriptors of biofilms were analyzed previously and after every manipulation. Biofilms responded to flow interruption with a slight increase of phosphatase activity (+25.3% above controls) and a marked increase in the biomass of green algae (+118.5%). Pulses of TCS severely affected biofilms, leading to a significant decrease in photosynthetic efficiency (-17.4%), live/dead bacteria ratio (-28.6%) and phosphate uptake rate (-32.8%) in exposed biofilms respect to controls. Late effects evidenced significant interaction between the two stressors. In particular, one week after the end of exposure, phosphate uptake capacity and diatoms fluorescence of biofilms submitted to both flow reduction and toxicant exposure resulted significantly lower than controls indicating an enhancement of TCS toxicity by flow reduction. Finally, two weeks after TCS exposure, biofilms in general recovered. In conclusion, our study demonstrated how the negative effects of TCS on biofilms can be worsened under water scarcity situation.