Environmental Factors Controlling Carbon Emission and Concentration Patterns in Siberian Taiga Rivers Across Seasons

Abstract

Despite the importance of small and medium size rivers of Siberian taiga in greenhouse gases (GHG) emission, important/major knowledge gaps exist regarding its temporal variability and controlling mechanisms. Here we sampled 11 pristine rivers of the southern taiga biome (western Siberia Lowland, WSL), ranging in watershed area from 0.8 to 119,000 km², to reveal temporal pattern and test main environmental factors controlling GHG emissions from the river water surfaces. Floating chamber measurements demonstrated that CO 2 emissions decreased about 2 to 4-fold from spring to summer and autumn, were independent of the size of the watershed and did not exhibit sizable (> 30%, regardless of season) variation between day and night. The CO 2 concentrations and fluxes were correlated with dissolved and particulate organic carbon, total nitrogen and bacterial number of the water column. The CH 4 concentrations and fluxes were correlated with phosphate and ammonia. Of landscape parameters, positive correlations were detected between riparian vegetation and CO 2 and CH 4 concentrations. Over the six months open-water period, the overall emissions of C from the watershed of 11 rivers were equal to the total downstream C export by rivers in this part of the WSL. Overall, this study suggest that sizable seasonal variations in GHG concentration pattern in boreal river waters are primarily linked to the terrestrial organic carbon supply, nutrient dynamics and biotic processes occurring essentially in the riparian zones. In particular, the fluxes are largely driven by riverine mineralization of terrestrial OC in the water column (both DOC and POC), coupled with respiration at the river bottom and riparian sediments. It follows that, under climate warming scenario, most significant changes in GHG regime of western Siberian rivers located in permafrost-free zone may occur due to changes in the riparian zone vegetation and water coverage of the floodplain.

Keywords: CO2, CH4, river, carbon, landscape, Siberia