Title

Evaluating spatial and temporal variations of water chemistry and the impact of transient storage on solute transport in low-order mountain streams

Date of Award

2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor(s)

Donald I. Siegel

Keywords

Transient storage, Solute transport, Mountain streams

Subject Categories

Earth Sciences | Geochemistry | Physical Sciences and Mathematics

Abstract

Understanding how physical and chemical processes control water chemistry and water movement through watersheds lead to the ability to forecast how different watershed management approaches and climate change affects chemical mass flux in the systems. The purpose of my dissertation research was to complete a comprehensive hydrological and geochemical study of a third order stream in the transitional zone between wet high peaks and arid deserts of the Rocky Mountain region to evaluate the spatial and temporal variations of water chemistry and the influence of transient storage caused by geomorphic complexity on solute transport.

I first did a synoptic surface water and groundwater sampling of inorganic and isotopic geochemistry in Red Canyon Creek watershed to evaluate how mixtures of waters and selected geochemical processes modify stream water chemistry. I found that gypsum dissolution, carbonate precipitation, and the influx of tributary and ground water all affect stream water chemistry. To better understand how water chemistry changes temporally, I analyzed long-term sampling of streamwater and precipitation through a hydrologic year. Major solutes were diluted during snowmelt, as expected whereas δ 18 O varied little. This result suggests that snowpack preferentially leached out O-18 during the initial snowmelt and that later lighter melt mixed and dispersed with heavier recharge rain later in the season. Concentrations of NO 3 - showed distinct cycle related to biological uptake and the net annual export rate of nitrate from the watershed was lower than the median rate of watersheds in the nation and had values close to those in desert areas.

I also studied how channel complexity and reach scale may affect water transient storage and solute transport. I found from a series of small to large scale dye tracing tests that increased geomorphic complexity caused by natural obstructions, primarily beaver dams, leads to increases in transient storage and travel times of solutes in the system. The scaling of dispersion in low order streams seems analogous to scaling of hydrodynamic dispersion in groundwater settings. Multiple organic dye tracers were injected simultaneously, the comparisons among six different dyes indicated that Rhodamine WT and Sulforhodamine B can be used in dye tracing in long-reach surface water systems under sunlit conditions.

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