Carbon processing in the Kolyma River Watershed and the role it plays in CO2 outgassing

The Kolyma River watershed in Northeast Siberia is the largest watershed underlain by continuous permafrost, storing vast amounts of organic carbon and nutrients, which if thawed will become available to microbial processing or transport downstream. Understanding the internal hydrological processes and outgassing across large Arctic river watersheds is crucial if we are to better refine estimates of GHG emissions. Previous conceptual models treated waterways as simple pipes, transporting water from land to ocean without internal processing but current research makes it evident that we must acknowledge them as possible active processors. In July and August 2010, a survey spanning 260 km of the Kolyma River Watershed was conducted to examine the rates of carbon processing in a diverse set of subwatersheds. A total of 23 subwatersheds (eleven streams, and twelve rivers) and nine mainstem locations were sampled at which water samples were collected for measurements of partial pressure of Carbon dioxide (pCO2), dissolved organic carbon (DOC), chromophoric dissolved organic matter (CDOM) and biological oxygen demand (BOD). Spatially, pCO2 concentrations decrease along flowpaths from small streams to the Ocean with the greatest variation between small streams and large rivers. Measurements of DOC concentrations and bioavailability indicate small streams are higher in the total amount and lability of DOC compared to larger tributaries. The results of this study suggest the headwater streams in the Kolyma River watershed are actively processing carbon during the summer at a more significant rate compared to larger tributaries and the Kolyma mainstem. Understanding the relationship between watershed size and carbon processing is critical for predicting how future warming will likely impact the Arctic carbon cycle. This study is part of the Polaris Project, an NSF-funded undergraduate field program based out of the Northeast Science Station in Cherskiy, Northeast Siberia (www.thepolarisproject.org).