Land use drivers of riverine methane dynamics in a tropical river basin, India

Abstract

Rivers are globally significant natural sources of atmospheric methane (CH4). However, the effect of land use changes on riverine CH4 dynamics, particularly in tropical zones, remain ambiguous, yet important to predict and anticipate the present and future contribution of rivers to the global CH4 budget. The present study examines the magnitude and drivers of riverine CH4 concentration and emission in the tropical Krishna River (KR) basin, India. The large spatial variability of CH4 concentration (0.03 to 185.34 μmol L −1) and emissions (0.04 mmol m−2 d−1 to 1666.24 mmol m−2 d−1) in the KR basin was linked to the site-specific features of the catchments through which rivers are draining. Several fold higher CH4 concentration and emission was observed for the urban river sites (64.63 ± 53.17 µmol L−1 and 294.15 ± 371.52 mmol m2 d−1, respectively) than the agricultural (1.05 ± 2.22 µmol L−1 and 3.45 ± 9.72 mmol m2 d−1, respectively) and forested (0.49 ± 0.23 µmol L−1 and 1.26 ± 0.73 mmol m2 d−1, respectively) sites. The concentrations of dissolved oxygen, total phosphorus, and Chlorophyll-a were significant hydrochemical variables strongly coupled with the dissolved CH4 concentrations. On the other hand, percentage of built-up area emerged as the most important landscape-level driver indicating that urbanization has an overriding effect on riverine CH4 concentration in the agriculture dominated KR basin. Our study supports the growing notion that tropical urban rivers are hotspot of CH4 emission. Furthermore, we show that the pattern of increasing in riverine CH4 concentration with built-up area (%) is a general feature of Asian river basins. As the urban land cover and population following an exponential increase, Asian rivers might contribute substantially to the regional and global CH4 budget.