Date of Award

Spring 1-1-2010

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Geography

First Advisor

Mark W Williams

Second Advisor

Suzanne P Anderson

Third Advisor

Holly R Barnard

Abstract

Isotopic composition of precipitation, snow cover, snow melt, and stream flow were determined in three snow dominated headwater catchments to quantify the spatial variability and processes that alter stable isotope (oxygen-18, 18O and deuterium, 2H) composition across an elevational gradient and between open and under canopy environments. Across the three catchments there was no significant difference in δ18O in precipitation but a significant difference was found within the snow pack and snow melt. Within each of the catchments there was no significant difference in δ18O in precipitation landing in open and under canopy environments. At the two lowest elevation sites significant differences between open and under canopy snow pack δ18O were observed but there was no significant differences in δ18O of snow melt between open and under canopy settings at any location.

Additionally, isotopic (δ18O and 3H (tritium)) and geochemical (Na+, Si, and DOC) tracers were used to investigate residence times, source waters, and flow paths in four headwater catchments along a 2,310 m elevational gradient within the Boulder Creek Watershed. The amount and type of precipitation occurring across the elevational gradient was also produced. Precipitation totals from 2009 ranged from 563 mm at 1800 m to a high of 1214 mm at 3528 m. The precipitation was 85% snow at the highest elevation and only 32% snow at the lowest elevation. Application of a convolution integral to the δ18O values in precipitation and stream waters produced relatively short mean residence times ranging from 1.12 years in the alpine to 2.08 years in the lower montane ecosystem. Tritium analysis indicated relatively young surface water ages and supported the results from the residence time calculations. Two-component mixing models were run using δ18O to identify new and old waters and Silica (Si) to identify reacted and un-reacted waters. All streams consisted of greater then 50% old and greater than 50% reacted waters with the peaks in new and un-reacted water occurring during hydrograph recession. These results indicate that headwater catchments within Boulder Creek Watershed have relatively short groundwater residence times and that groundwater plays an important role in stream flow generation.

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Hydrology Commons

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