Exploring the Role of Microorganisms in Freshwater Ecosystems and Nutrient Cycling

Abstract

Freshwater ecosystems serve as critical biogeochemical engines but are threatened by a novel 'nutrient crisis' originating from widespread anthropogenic nitrogen and phosphorus inputs that disturb food web structures and promote eutrophication. While chemical monitoring provides insight, it cannot adequately convey the ecological processes underlying nutrient shifts. This work utilizes high-throughput metagenomic functional profiles coupled with geochemistry at human-impacted sites of the Kaveri River, providing an understanding of the functional roles of microbial communities in driving freshwater nutrient processing. A transition in the microbial community from niche-specialized oligotrophic to opportunist copiotrophic taxa was observed as urban pollution intensified. The model prediction accuracy of nutrient fluxes was substantially enhanced by incorporating functional gene abundances, particularly nifH and amoA markers, into these models; phosphorus-solubilizing microbial populations and soluble reactive phosphorus availability were positively correlated. Temperature and COD, the two strongest predictors of microbial metabolic plasticity, predicted a decrease in resilience above 28 °C. This study demonstrates that aquatic ecosystem function is critically driven by microbial consortia and advocates for the use of 'microbially-informed' resource management practices to improve aquatic ecosystem resilience to global change and anthropogenic pollution. Resource managers, moving beyond chemical time-slices, may now optimize interventions based on accurate predictions of nutrient dynamics, mitigating the human-impact on precious resources. This study closes the gap between microbial structure and function, suggesting new ways forward for a healthy future for freshwater bodies worldwide.