ORIGINAL ABSTRACT

Agricultural practices significantly influence riparian landscapes, increasing contaminant inputs into aquatic ecosystems, with profound effects on biodiversity and ecological processes. This study evaluated the structural and functional responses of autotrophic biofilms to nitrogen (10 µg/L as urea fertilizer), glyphosate (8.64 µg/L of active ingredient, Green II Herbicide Soluble Concentrate GREEN-GO®), and their combination in a 15-day laboratory microcosm experiment conducted during May and June 2021. The experiment used 1.5 cm × 1.5 cm frosted glass substrates, which were colonized in the laboratory with a natural algal community inoculated from the Chocancharava River, Córdoba, Argentina (33°03'14″ S, 64°22'23″ W). We assessed total biomass, chlorophyll a, algal community structure, and metabolic activity under four treatments: control, nitrogen, glyphosate, and nitrogen-glyphosate. Glyphosate significantly reduced taxa diversity and altered community structure, leading to a decline in diatoms and the dominance of Monoraphidium minutum, likely due to its tolerance mechanisms. Nutrient enrichment and glyphosate exposure simplified algal assemblages, favoring tolerant taxa. The density of Monoraphidium minutum significantly influenced net primary production, underscoring its functional role under stress conditions. These findings demonstrate how tolerant species drive biofilm responses to diffuse pollution, with implications for trophic connectivity and ecosystem functioning due to community simplification.