Tolerant species drive the response of autotrophic biofilms to non-point pollution by nitrogen and glyphosate

Abstract

Agricultural practices signifcantly infuence riparian landscapes, increasing contaminant inputs into aquatic ecosystems, with profound efects on biodiversity and ecological processes. This study evaluated the structural and functional responses of autotrophic bioflms 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 signifcantly 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 simplifed algal assemblages, favoring tolerant taxa. The density of Monoraphidium minutum signifcantly infuenced net primary production, underscoring its functional role under stress conditions. These fndings demonstrate how tolerant species drive bioflm responses to difuse pollution, with implications for trophic connectivity and ecosystem functioning due to community simplifcation.