Groundwater Controls on DOC Transport to Arctic Streams and Rivers

The transport of carbon (C) stored in Arctic soils to aquatic ecosystems affects global cycles, but the mechanisms for delivery from land to surface waters are poorly understood. Hydrologic transport through the tundra is thought to occur dominantly via overland flow with minimal transport by groundwater. We have found that groundwater exchanges within the hillslope and riparian zone control C delivery to streams under highly variable hydrologic conditions. Groundwater transport driven by macro-topography is the sole mechanism for delivery during drier conditions. During saturated conditions and when overland flow inundates the surface, micro-topography drives the surface-to-subsurface exchange of water. These vertical exchanges explain the relatively constant instream C concentrations across a large range of stream discharge, and may influence the transport and fate of stored soil C in a warming Arctic.