CLIMATE-DRIVEN RESPONSE OF GROUNDWATER INPUT TO THE YUKON RIVER

Evaluation of groundwater input to North American rivers is generally confined to smaller rivers because flows in most large rivers are regulated, rendering it difficult to estimate base flow. The Yukon River Basin provides a unique environment to study groundwater contribution to a large, natural river system in a permafrost-dominated watershed. We develop a conceptual model of dynamic groundwater-stream interaction along the >3,000 km unregulated course of the Yukon River through various physiographic and climatic regions from southwestern Yukon, Canada and across central Alaska, United States, draining 831,400 km². This study complements other ongoing U.S. Geological Survey (USGS) work addressing changes in chemical exports from the Yukon River Basin to the Bering Sea in response to climate warming. Analysis of streamflow measurements performed by the USGS since the 1950s enables quantification of groundwater to the Yukon River. Our results indicate that groundwater presently contribute as much as 45% of the annual flow in the headwaters region and about 20% downstream where it incises the Yukon Plateau. The data also suggest a shift towards increased groundwater input to the Yukon River, especially pronounced in the headwaters, that is coincident with climate warming in northern latitudes over the past 50 years. Currently, groundwater comprises about 20% of the water in the Yukon River that empties into the Bering Sea and contributes 5-8% of the dissolved organic carbon (DOC)and 35-45% of the dissolved inorganic carbon (DIC). We hypothesize that the fraction of groundwater input to total annual flow in the Yukon River has increased in response to climate change, supporting a decrease in DOC export to the Bering Sea and an increase in DIC export.