A large-scale geographical coverage survey reveals a pervasive impact of agricultural practices on plankton primary producers

Abstract

Modern agricultural practices heavily rely on the use of agrochemicals. Glyphosate based herbicides are among the most widespread agricultural supplies. The massive application of glyphosate in conventional farming, provides continuous inputs of the herbicide into the environment, unintentionally placing non-target organisms at risk. Shallow lakes immersed in agroecosystems serve as integrators of human interventions in their watersheds. Autotrophic plankton, which are key components of biogeochemical cycles and food-webs, respond quickly to anthropogenic disturbances. Here, we assessed the environmental implications and ecological consequences of agricultural land use and glyphosate contamination on phytoplankton from 52 shallow lakes scattered over 180,000 km2 across the central pampas in Argentina, which lay on areas differentially impacted by glyphosate. Indicators of glyphosate usage positively correlated with lake turbidity and Cyanobacteria abundance, and were negatively associated with Chlorophyceae diversity. Glyphosate impact indicators were also associated with higher abundance of the small-sized representatives within each major algal class, which are assumed to be better adapted to poor light conditions. Detection of the presence of GLY-transporter genes (phnD) in seston samples was associated with higher picocyanobacteria biomass and lower pico-eukaryotic algae. Our results illustrate that the observed distribution patterns of phytoplankton can be explained by the combination of the watershed's agricultural profile, conductivity, and light quality.