YUKON RIVER TRIBUTARIES SUM TO TOTAL BASIN EXPORT BASED ON SOLUTE LOADS

Investigations of hydrology and hydrochemistry of remote river basins are hampered by the lack of spatially and temporally integrated discharge and chemistry data. In large basins, a further issue is unraveling landscape and other controls on solute loads. This study uses the solute chemistry of tributaries to the Yukon River to assess spatial patterns in annual solute yields. First we show that annual discharge of the Yukon River can be computed by summing calculated annual discharges from 42 predominantly ungaged tributaries based on basin area and average annual precipitation specific to that area [1]. The success of this calculation shows that groundwater inputs are integrated throughout the tributary basins and that storage is a minor component of Yukon River discharge. Next, annual inorganic solute fluxes for each tributary were determined by combining annual discharge with point measurements of solute concentrations. The summed contributions of tributary waters show that the Yukon River discharges ~33 x 10^12 g of total dissolved solids each year at Pilot Station. The solutes are dominated by cations calcium and magnesium (~7.2 and ~1.8 g /m^2/yr) and anions bicarbonate and sulfate (~21 and ~7 g /m^2/ yr). The calculated yields compare well with yields determined from daily discharge and instantaneous concentration data at the USGS gage at Pilot Station, the most downstream gage on the Yukon River. Almost all calculated yields were within 10% of measured yields. Only bicarbonate and chloride showed higher discrepancies, of 17 and 13% respectively. These findings show that annual solute yields for a major subarctic river can be determined from tributary basins using calculated discharges and distributed point measurements of solute concentration. This work provides the basis for analyzing the spatial controls on solute yields within the Yukon River basin, such as the distribution of rock types, permafrost, vegetation zones, and tributary size.

[1] Parks et al, 1985, Estimation of selected flow and water-quality characteristics of Alaskan streams: USGS WRI Report 84-4247