Lima Megacity's Influence on Aquatic Microbial Communities in the Rímac River: Dominance Over Spatial and Seasonal Variations.

The Rímac River, a vital watershed on the Peruvian coast, is confronted with substantial environmental challenges stemming from intensive exploitation and widespread contamination. As the primary source of water for Lima, supplying approximately 80% of the city's needs, the river is heavily impacted by pollutants from domestic, hospital, industrial, and mining effluents. These contaminants introduce microbiota that pose significant public health risks. This study utilizes 16S rRNA gene metabarcoding to characterize the bacterial communities along the Rímac River, examining both spatial (upper, middle, and lower basins) and temporal (dry and rainy seasons) variations. Over a year-long sampling period, DNA sequencing revealed pronounced microbiological differences between the Metropolitan and Regional zones, primarily driven by anthropogenic activities. Key findings include a significant reduction in microbial diversity and an increase in pathogenic bacteria within the Metropolitan zone, while the influence of seasonal variations and altitudinal gradients was comparatively minor. Betaproteobacteria emerged as the most abundant class across most samples. Notably, Aliarcobacter cryaerophilus, an indicator of fecal contamination and a potential public health hazard, was predominantly detected in the Metropolitan zone. These results underscore the necessity for comprehensive monitoring of the Rímac River's microbiota, incorporating advanced molecular techniques to effectively track and mitigate pollution. The study emphasizes the urgent need for robust water quality management strategies to protect this critical resource, ensuring the health and sustainability of Lima and its surrounding regions.