CO2 emission and microbial extracellular enzyme activities in sediment at land–water interface as influenced by metal pollution in the Ganga River

Abstract

Understanding the interactions of carbon and metal pollutants in anthropogenically impacted rivers is a prerequisite for determining the relative fates of these stressors. Here, through two sets of studies, we report carbon–metal pollutant interactions choosing the CO2 emission and sediment microbial extracellular enzyme activities as major determinants. The study, conducted along a 520-km main river and along a point source trajectory, showed a TOC-dependent but metal pollution-constrained CO2 emission. We found significant relationships (p < 0.05–0.001) between CO2 emission flux and its determinants: TOC, Cmic, FDAase and β-D-glucosidase. In the point source trajectory, CO2 emission flux was closely synchronous to these determinants. These relationships, however, were significantly constrained at the sites such as Knuj, Jjmu and Rjht where the concentrations of total heavy metal (∑THM) in the sediment exceed 347.44 µg g−1 indicating that the heavy metal pollution counteracted the C processing and consequently the CO2 emission flux. The study suggests that the excessive load of metal pollutants will eventually interrupt the C-cycling in the Ganga River inviting caution in C budgeting and C transport to coastal ocean. © 2024 Informa UK Limited, trading as Taylor & Francis Group.