A GEOCHEMICAL STUDY OF THE TEANAWAY RIVER AND ITS TRIBUTARIES, CENTRAL WASHINGTON

This geochemical study examines the Teanaway River and its tributaries over a 6-month period from May 2021 to November 2021. The Teanaway River, located near Cle Elum, WA, is one of the Yakima River’s largest tributaries and lies within the Columbia River Basin. The Teanaway River is a critical resource for the local community and has recently been targeted for habitat and stream restoration through the formation of the Teanaway Community Forest. The goal of this study is to characterize the natural variations in stream water chemistry through comparison of major element compositions and stable isotope ratios, measured using an Inductively Coupled Plasma Optical Emission Spectrometer (ICPOES) and Cavity Ring-Down Spectroscopy, respectively. These methods allow for the analysis of weathering reactions in tributary watersheds and how they alter the chemistry of river water, as well as the determination of mixing relationships between snowmelt and different surface waters. Three forks of the Teanaway (North, Middle, and West) were reviewed in this study as well as five smaller tributaries. Thus far, we have observed that the West and Middle Forks are similar both isotopically and in terms of major elements compared to the North Fork. These differences can be explained by differences in east-west position and geology of the subbasins drained. The West and Middle Forks drainages are further west accounting for the heavier isotope signatures. The North Fork drainage includes the ultramafic Ingalls Complex which might account for the higher Mg concentrations in its waters. Seasonal variations in water chemistry reveal highest concentrations in August and September when streamflow is dominated by baseflow and snowmelt contribution is minimal.