Pan-arctic flux of soil organic carbon to rivers by river bank erosion

Friday, December 14, 2018 - 08:25
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The migration of river channels simultaneously erodes and creates floodplain deposits. These deposits consist of both mineral and organic materials. While river bank erosion is recognized as a potential source for older carbon inputs to Arctic rivers its contribution to the cycling of carbon in permafrost regions has been unquantified to date. To constrain this contribution, we assessed bank erosion rates for >5,000 km of channels along 14 sections of 13 Arctic and sub-Arctic rivers with permafrost extent ranging from minimal to continuous. The analyzed rivers range in drainage area from 1,300 (Selawik) to 2.5 x 10^6 (Yenisei) km2, and in width from 50 (Selawik) to 6,500 m (Lena). Using our newly developed Python-based River and Basin Profiler (RaBPro) tool, we estimated channel slopes, delineated watersheds, and computed contributing basin statistics to develop an empirical model for river bank erosion rates in permafrost systems. This model, together with a pan-Arctic delineation of alluvial floodplains, and the Northern Circumpolar Soil Carbon Database, were used to estimate the pan-Arctic flux of soil organic carbon (SOC) into rivers due to bank erosion. Preliminary estimates suggest that the bank erosion flux of SOC may be as high as 38 Tg/yr--as large as the estimated flux of pan-Arctic riverine-transported carbon to the ocean. What fraction of eroded floodplain carbon reaches the ocean is unknown; significant fractions of the carbon may be redeposited downstream or released to the atmosphere.

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