Assessment of Eutrophication in the Lower Yakima River Basin, Washington, 2004-07

Abstract

Creating the prolonged turbid and deep conditions during spring necessary to suppress macrophyte growth in this reach would not be possible in years with low streamflow. In addition, because of the relatively stable substrate present in much of this reach, the macrophyte root systems would likely not be disturbed under all but the most extremely high streamflows that occur in the lower Yakima River.

Yakima River Basin Water Column Respiration is a Minor Component of River Ecosystem Respiration

“…Large improvements in water quality draining to the Yakima River and its tributaries from agricultural wastewater drainages ("Wasteways") throughout 480 the Yakima River basin have decreased nutrient and TSS loads to these rivers (Appel et al, 2011). Total dissolved nitrogen (TDN; data not shown, see Grieger et al (2022)) concentrations throughout the basin (median: 0.19 mg L⁻ 1 , mean: 0.38 mg L⁻ 1 ) were within reference conditions (i.e., representing the least impacted conditions and intended to be protective of designated uses) set by the U.S. Environmental Protection Agency (EPA) for the lower Yakima River (1.468 mg L⁻ 1 ; Yakima River at Mabton); however, TDN concentrations exceeded reference conditions for the Naches River (0.166 mg L⁻ 1 ), a major tributary to the Yakima 485 River (Wise et al, 2009). Similarly, NO3-N concentrations (median: 0.07 mg L⁻ 1 , mean: 0.51 mg L⁻ 1 ) were within reference conditions for nitrite+nitrate for the lower Yakima River (1.095 mg L⁻ 1 ; Yakima River at Mabton) but exceeded reference conditions for nitrite+nitrate for the Naches River (0.031 mg L⁻ 1 ).…”

Long‐Term Disconnect Between Nutrient Inputs and Riverine Exports in a Semi‐Arid, Agricultural Watershed: Yakima River Basin 1945–2012

“…The area of river near Kiona specifically has become dominated by the native aquatic plant, water stargrass (Heteranthera dubia). Wise et al (2009) investigation into macrophyte's impact on Yakima river water quality did not find any noticeable uptake of N or P in the water column by water stargrass. However, they did find there was uptake of N and P from periphyton growth in some reaches (Wise et al, 2009).…”

“…Wise et al (2009) investigation into macrophyte's impact on Yakima river water quality did not find any noticeable uptake of N or P in the water column by water stargrass. However, they did find there was uptake of N and P from periphyton growth in some reaches (Wise et al, 2009). Additionally, Wise et al (2009) did not examine nutrient uptake from river sediments.…”

“…However, they did find there was uptake of N and P from periphyton growth in some reaches (Wise et al, 2009). Additionally, Wise et al (2009) did not examine nutrient uptake from river sediments. Fibrous water stargrass root systems grow from rhizomes and can extend well into the river bed, likely taking up nutrients stored in sediments (Hamel et al, 2001).…”

“…Finally, aquatic macrophytes are another unquantified, but potentially important, nutrient sink in the watershed. Beginning in 2001, dense patches of rooted plants starting growing in the lower reaches of the Yakima River (Wise et al, 2009). The area of river near Kiona specifically has become dominated by the native aquatic plant, water stargrass (Heteranthera dubia).…”