Multiple-stressor effects on river biofilms under different hydrological conditions.

We studied the relative importance of environmental factors (river flow, nutrients, dissolved organic matter) and organic micro-pollutants [herbicides, insecticides, industrial organic compounds, personal care products, antibiotics and pharmaceuticals, (PhCs)] to the structure and function of epilithic biofilms under various hydrological conditions and land uses., Biofilms from four river basins in the Iberian Peninsula (Llobregat, Ebro, Júcar and Guadalquivir) were analysed in summer-autumn during a wet period and base-flow conditions. The sites experienced different levels of pollution., We used variance partitioning (Redundancy Detrended Analysis, RDA) to link environmental stressors to the structure and function of biofilms, which were assessed as diatom community composition, algal biomass, photosynthetic activity, bacterial density and extracellular phosphatase activity., RDAs showed that industrial organic compounds, herbicides and PhC products were the pollutants most strongly associated with measures of biofilm structure and function, whereas dissolved inorganic nitrogen, dissolved organic carbon and hydrological variability were the environmental factors most strongly associated with biofilm responses., Thicker biofilms developing during base flow were most affected by pollutants and nutrients. In contrast, thinner biofilms developing during periods of high river flow were less affected by chemicals. [ABSTRACT FROM AUTHOR]