USGS Study of Nutrients, Aquatic Plant Growth, and pH and Dissolved Oxygen Levels in the Lower Yakima River, Washington
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Lower Yakima River Eutrophication Study

Project Chief: Dan Wise

Cooperators: South Yakima and Benton Conservation Districts

BACKGROUND

Aquatic macrophytes

Macrophyte beds in the Yakima River

Since 2001, unusually dense and extensive patches of macrophytes (rooted aquatic plants) have been observed in the lower Yakima River (click opens PDF map, 0.8 MB) during the spring and summer. By 2003, this excessive plant growth was producing nuisance conditions in the lower river that impaired recreational use and was suspected of causing conditions (low dissolved oxygen concentrations and high pH) that might adversely affect fish.

In response to these concerns, the USGS and the South Yakima Conservation District conducted an assessment of eutrophication (nutrient enrichment) in the lower 116 mi of Yakima River during the 2004–07 irrigation seasons. This study evaluated the water-quality affects from algae and macrophytes in the Yakima River, and the results gained can be used by water-quality managers and other stakeholders in the Yakima basin during water-quality improvement efforts, such as Total Maximum Daily Load (TMDL) development and implementation.

OBJECTIVES

  • Characterize distinct reaches in the lower 116 mi of the Yakima River based on aquatic plant conditions, geomorphology, and habitat
  • Characterize nutrient and suspended-sediment conditions and calculate a load balance on nutrients and suspended sediment, including major tributaries, drains, and wastewater treatment plants to identify the major sources of nutrients
  • Characterize the extent and severity of exceedences of the State water-quality standards for water temperature, dissolved oxygen, and pH
  • Determine the important factors related to the spatial and temporal patterns in aquatic plant and water-quality conditions
  • Compare current aquatic plant and water-quality conditions to historical conditions

APPROACH

Continuous water-quality monitor

Continuous water-quality monitor in the Yakima River

The first year of the study (2004) was used to characterize the aquatic plant conditions, geomorphology, and habitat in the lower 116 mi of the Yakima River, characterize the nutrient and suspended-sediment conditions, calculate a load balance for nutrients and suspended sediment, and begin to characterize the extent and severity of exceedences of the Washington State water-quality standards.

During 2005–07, the aquatic plant conditions and the extent and severity of exceedences of the State water-quality standards in the Yakima River were characterized in more detail. The important factors related to the spatial and temporal patterns in aquatic plant and water-quality conditions were investigated by performing targeted studies in different reaches of the Yakima River and in the Naches River.

DATA

June 2004 reconnaissance data
Macrophyte biomass measured in the Yakima River, 2005–07

PUBLICATIONS

Wise, D.R., 2009, Assessment of Eutrophication in the Lower Yakima River Basin, Washington, 2000–07, U.S. Geological Survey Scientific Investigations Report 2009–5078.

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