Carbon dioxide emission and its regulation at land–water interface downstream of a point source at Ganga River (India)

The streams and rivers are considered hotspots of CO 2 exchange; and representative direct CO 2 emission measurements are essential for a correct regional estimate. We measured CO 2 emission flux at 15 sites at land–water interface downstream of a point source during low flow for three consecutive months for the year 2017. The general range of CO 2 efflux observed here was close to the results of regional studies, although values near the point source were disproportionately high (>350 mg/m 2 /h). CO 2 emission flux showed strong dependence on total organic carbon (TOC; R 2  = 0.96; P  < 0.001),NH 4 +( R 2  = 0.88; P  < 0.001), soluble reactive‐P (SRP; R 2  = 0.91; P  < 0.001) and microbial activity measured in terms of fluorescein diacetate activity (FDAase; R 2  = 0.92; P  < 0.001) and substrate induced respiration (SIR; R 2  = 0.96; P  < 0.001). Because point source‐associated interfaces provide heterogeneous habitats, our study suggests the need for large scale monitoring of CO 2 emission at land–water interface of major rivers for more correctly presenting the regional scale CO 2 budget.