USGS Scientific Investigations Report 2009–5078Assessment of Eutrophication in the Lower Yakima River Basin, Washington, 2004

Table 12. Comparison of nutrient and algal biomass results to suggested U.S. Environmental Protection Agency reference conditions and algal biomass nuisance levels for the lower Yakima and Naches Rivers, July 1–September 30, 2004–07.

[Suggested reference conditions are from U.S. Environmental Protection Agency (2000b). Shading indicates values greater than the suggested U.S. Environmental Protection Agency reference conditions. Phytoplankton nuisance level established by the State of Oregon (Oregon Administrative Code, 2006). Periphyton nuisance level established by the Province of British Columbia (British Columbia Ministry of Environment, 2001). Zillah-WADOE, results from sampling done by the Washington State Department of Ecology at Nob Hill (RM 111). Abbreviations: RM, river mile; num, number of samples collected; per, percentage of values greater than reference condition or nuisance level; med, median value for all samples; mg/L, milligram per liter; μg/L, microgram per liter; mg/m², milligram per square meter; –, no data]

Reach	Suggested USEPA reference condition												Nuisance level
	Nitrate plus nitrite  as nitrogen (0.072 mg/L)			Total Kjeldahl nitrogen (0.288 mg/L)			Total nitrogen (0.221 mg/L)			Total phosphorus (0.030 mg/L)			Phytoplankton chlorophyll a (15 µg/L)			Periphyton chlorophyll a (100 mg/m²)
	num	per	mean	num	per	mean	num	per	mean	num	per	mean	num	per	med	num	per	med
Naches River	12	25	0.031	12	8	0.135	12	17	0.166	12	50	0.032	2	0	1.5	6	0	44
Zillah-WADOE (RM 111)	12	58	0.095	–	–	–	12	33	0.201	12	50	0.030	–	–	–	–	–	–
Zillah (RM 116–72)	87	79	0.317	79	9	0.197	86	79	0.478	80	100	0.059	21	14	4.6	36	37	80
Mabton (RM 72–47)	11	100	1.095	11	82	0.373	11	100	1.468	11	100	0.144	20	20	13	0	–	–
Kiona (RM 47–4)	22	100	0.875	20	25	0.256	22	100	1.108	20	100	0.140	16	6	4.4	1	0	8

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