Methane and nitrous oxide fluxes in the polluted Adyar River and estuary, SE India

We measured dissolved N2O, CH4, O2, NH4+, NO3- and NO2- on 7 transects along the polluted Adyar River–estuary, SE India and estimated N2O and CH4 emissions using a gas exchange relation and a floating chamber. High NO2- implied some nitrification of a large anthropogenic NH4+ pool. In the lower catchment CH4 was maximal (6.3 ± 4.3 × 104 nM), exceeding the ebullition threshold, whereas strong undersaturation of N2O and O2 implied intense denitrification. Emissions fluxes for the whole Adyar system ∼2.5 × 108 g CH4 yr−1 and ∼2.4 × 106 g N2O yr−1 estimated with a gas exchange relation and ∼2 × 109 g CH4 yr−1 derived with a floating chamber illustrate the importance of CH4 ebullition. An equivalent CO2 flux ∼1–10 × 1010 g yr−1 derived using global warming potentials is equivalent to total Chennai motor vehicle CO2 emissions in one month. Studies such as this may inform more effective waste management and future compliance with international emissions agreements.