Rising Global Riverine Deoxygenation Rates and <scp>GHG</scp> Emissions Driven by the Synergistic Effects of Warming and Anthropogenic Land Use Expansion

Global fluvial ecosystems are increasingly impacted by human activities, such as climate warming and land use changes; however, the combined effects of these pressures on river greenhouse gas (GHG) supersaturation and deoxygenation remain poorly understood. This study modeled past global trends (2002-2022) in river GHG saturation, dissolved oxygen (DO) levels, water temperature, and eight other water quality parameters using machine learning models powered by satellite observations. Our findings show significant global increases in river GHG supersaturation and deoxygenation, mainly driven by rising water temperatures (0.27°C ± 0.03°C per decade), increased precipitation, higher labile carbon and nitrogen inputs, and urban and cropland expansion. We estimate that anthropogenic GHG emissions from rivers due to these pressures totaled 1.5 Pg-CO₂-eq over the 20-year period. The increase in GHGs was accompanied by a global river deoxygenation rate of 0.058 ± 0.01 mg L^-1 per decade, suggesting rivers may be losing oxygen up to 2.5 times faster than lakes and oceans globally.