Water quality trends in the Entiat River Watershed

A large, multiagency effort is underway in the interior Columbia River basin (ICRB) to restore salmon, trout, and char listed as threatened or endangered under the 1973 federal Endangered Species Act. Water quantity and quality are widely recognized as important components of habitat for these depleted salmonid populations. There is also broad concern about maintaining a high-quality water supply for other societal and ecosystem uses. A particularly active salmonid habitat restoration program is being conducted in the Entiat River, which drains a portion of the eastern slope of the Cascade Mountains in central Washington state. There, routine monitoring by the Washington Department of Ecology identifies pH and water temperature as water quality parameters of concern. In response, the U.S. Forest Service, Pacific Northwest Research Station is testing a more intensive approach to water quality monitoring that uses multiparameter data-logging instruments at four locations to measure fundamental water quality parameters (pH, water temperature, dissolved oxygen, and specific conductivity). This report presents results from the first 4 years of the study and discusses variation in water quality parameters with season, river discharge, and location. We demonstrate that unattended data-logging instruments effectively provide high-resolution data, which facilitate identification of forcing mechanisms such as direct solar radiation, air temperature, and river discharge. Results complement ongoing, broad-scale salmon recovery monitoring by quantifying concurrent changes in water quality. Although exploratory in nature, this study can inform future, more intensive monitoring programs.