Genetic drivers of nitrous oxide flux in a polluted tropical river: the interplay of denitrifier communities, anthropogenic stress, and climate forcing

Abstract

ABSTRACT Schematic linking anthropogenic stress to climate forcing via a microbial genetic imbalance favoring nirS N2O production over nosZ N2 reduction. This study investigated the hypothesis that severe nutrient and organic pollution from untreated wastewater alters microbial genetics in Nigeria's River Ala, transforming it into a significant source of atmospheric nitrous oxide. Over a seven-month period, ninety-six (96) water samples were collected from the Ala River, Akure, and analysed via an integrated approach of physicochemical, bacteriological, and molecular methods. The findings revealed human-induced pressure on the river, as evidenced by high mean fecal coliform loads: 3.37 log10 (CFU) 100 ml−1 during the dry season to 3.60 log10 CFU 100 mL−1 in the wet season and a seasonal increase in nitrate concentrations, fluctuating from 6.43 mg L−1 to a peak of 42.25 mg L−1. Denitrifying bacteria, Pseudomonas and Achromobacter species, were isolated from highly contaminated water. Molecular screening confirmed that these bacteria possess genetic machinery for both nitrous oxide (nirS gene) and consumption potential (nosZ gene). High-nutrient conditions, driven by pollution, create a functional imbalance within the microbial community. This imbalance favours the production of nitrous oxide over its reduction to harmless nitrogen gas. There is compelling molecular-level evidence that localized water pollution is a potent driver of microbial community function, directly contributing to greenhouse gas emissions and impacting the global climate.