DOM Associates with Greenhouse Gas Emissions in Chinese Rivers under Diverse Land Uses

Growing evidence indicates that rivers are hotspots of greenhouse gas (GHG) emissions and play multiple roles in the global carbon budget. However, the roles of terrestrial carbon from land use in river GHG emissions remain largely unknown. We studied the microbial composition, dissolved organic matter (DOM) properties, and GHG emission responses to different landcovers in rivers (n = 100). The bacterial community was mainly constrained by land-use intensity, whereas the fungal community was mainly controlled by DOM chemical composition (e.g., terrestrial DOM with high photoreactivity). Anthropogenic stressors (e.g., land-use intensity, gross regional domestic product, and total population) were the main factors affecting chromophoric DOM (CDOM). DOM biodegradability exhibited a positive correlation with CDOM and contributed to microbial activity for DOM transformation. Variations in CO2 and CH4 emissions were governed by the biodegradation or photomineralization of dissolved organic carbon derived from autotrophic DOM and were indirectly affected by land use via changes in DOM properties and water chemistry. Because the GHG emissions of rivers offset some of the climatic benefits of terrestrial carbon (or ocean) sinks, intensified urban land use inevitably alters carbon cycling and changes the regional microclimate.