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WILLAMETTE BASIN SURFACE WATER ISOSCAPE (18O AND 2H) FOR INTERPRETING TEMPORAL CHANGES OF SOURCE WATER WITHIN THE RIVER.
Citation:
BROOKS, P. J. WIGINGTON JR, R. COMELEO, AND R. COULOMBE. WILLAMETTE BASIN SURFACE WATER ISOSCAPE (18O AND 2H) FOR INTERPRETING TEMPORAL CHANGES OF SOURCE WATER WITHIN THE RIVER. Presented at Isoscapes 2011 meeting, Purdue University, West Lafayette, IN, September 24 - 28, 2011.
Impact/Purpose:
Understanding how water sources for rivers are shifting spatially over time will greatly aid our ability to understand climate impacts on rivers.
Description:
Understanding how water sources for rivers are shifting spatially over time will greatly aid our ability to understand climate impacts on rivers. Because stable isotopes of precipitation vary geographically, variation in the stable isotopes of river water can indicate source water dynamics. We monitored the stable isotopes (18O and 2H) of river and stream water within the southern Willamette Basin in Western Oregon over two years. Within this basin, eighty-four percent of the isotopic variation in stream water from the small catchments could be explained by the mean elevation of the catchment, while seasonal variation was minimal. However, water within the Willamette River showed distinct isotopic seasonal patterns. This seasonal variation likely comes from a change in source elevation for water in the river. Willamette River isotopic values were at their lowest during summer low flow and at their highest during Feb/March when snow was accumulating in the mountains. We estimated that the mean elevation of the Willamette River source water shifted over 500 m seasonally. During winter when rain occurs in the valley and snow is accumulating in the mountains, the river reflects a mixture of low mountains and valley bottom precipitation. During the dry Mediterranean summer, 60-80% of the river water comes from the snow zone above 1200 m, which is only 12% of the land area and accounts for 15.6 % of the annual precipitation within the Willamette Basin. Reliance on high-elevation water during summer low flow highlight the vulnerability of this system to influences of climate change, where snowpacks in the Cascade Mountains are predicted to decrease in the future.