The hydrology of headwater catchments from the Plains to the Continental Divide, Boulder Creek watershed, Colorado

Cowie, Rory M.

Graduate Thesis Or Dissertation

The hydrology of headwater catchments from the Plains to the Continental Divide, Boulder Creek watershed, Colorado Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/qb98mf759

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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