Oregon Water Quality Index Report for North Coast Basin

Water Years 1986-1995

Land use, geology, hydrology, and water quality varies widely throughout the North Coast basin. Comparing minimum seasonal Oregon Water Quality Index (OWQI) values (Table 1), water quality ranges from excellent (upper Wilson River site) to very poor (Klaskanine River site). Water quality data were collected by the laboratory in 1985-1987 for the Tillamook Bay Tributaries special study, and regular quarterly ambient monitoring of all of the sites began in 1992.

Water quality is commonly impacted by the introduction of organic matter to streams. The presence of organic matter increases biochemical oxygen demand, which means less dissolved oxygen is available for aquatic life. The introduction of untreated animal or human waste increases the possibility of bacterial contamination of water, increasing the risk of infection to swimmers. Eutrophication is the process of enrichment of water with nutrients, mainly nitrogen and phosphorous compounds, which results in excessive growth of algae and nuisance aquatic plants. It increases the amount of organic matter in the water and also increases pollution as this matter grows and then decays. Employing the process of photosynthesis for growth, algae and aquatic plants consume carbon dioxide (thus raising pH) and produce an overabundance of oxygen. At night the algae and plants respire, depleting available dissolved oxygen. This results in large variations in water quality conditions that can be harmful to other aquatic life. While natural sources of nutrients can influence eutrophication, the introduction of nutrients strengthens the process. Sources of nutrients include wastewater treatment facility discharge and faulty septic systems, runoff from animal husbandry, fertilizer application, urban sources, and erosion. High water temperatures compound the decline in water quality by causing more oxygen to leave the water and by increasing the rate of eutrophication. Removal of streamside vegetation, among other factors, influences high stream temperature and, via erosion, increases sedimentation of streams.

Table 1. Seasonal Average OWQI Results for the North Coast Basin (WY 1986 -1995)

Summer: June - September; FWS ( Fall, Winter, & Spring): October - May
Scores - Very Poor: 0-59, Poor: 60-79, Fair: 80-84, Good: 85-89, Excellent: 90-100

Clatskanie Subbasin

The Clatskanie River is monitored at Highway 30 in Clatskanie. The Clatskanie River is impacted by occasional high levels of fecal coliform and total solids during periods of dry weather and low flows, indicating the presence of untreated animal or human waste. Low river flow has the effect of concentrating constituents in water. These conditions give the Clatskanie River poor water quality throughout the summer months (Table 1). Because flow increases and more dilution occurs during wet weather, water quality improves to good during the fall, winter, and spring.

Lower Columbia Subbasin

The Lower Columbia subbasin includes the Klaskanine, Youngs,Lewis and Clark, and Skipanon Rivers. As in the Clatskanie subbasin, lowflow conditions contribute to poorer water quality in the summer with improvementin the fall, winter, and spring.

The Klaskanine River at Youngs River Loop Road scores the lowest minimum seasonal average score in the North Coast basin. The summer samples include samples taken between (and including) June and September. In September, flow is very low in the Klaskanine River and it is likely that saltwater is intruding the river as far up as the convergence of the North and South Forks of the Klaskanine River. This is evident by the very high results for total solids, phosphates, and biochemical oxygen demand for each of the three samples taken in September. These high concentrations give very poor OWQI results during the summer. Samples taken during the fall, winter, and spring seasons typically exhibit good water quality (Table 1).

Youngs River at Youngs River Loop Road, just downstream of Youngs Falls, shows excellent water quality during the summer and good water quality during the fall, winter, and spring (Table 1). It is limited by occasional increases in nitrogen levels and biochemical oxygen demand during the wet season, indicative of the introduction of organic material to the river.

Lewis and Clark River at Stavebolt Lane shows good water quality in the summer and poor water quality during the fall, winter, and spring (Table 1). This seasonal decrease in water quality is due to a wide range of minor impacts on water quality: total solids, fecal coliforms, phosphates, and biochemical oxygen demand. Concentrations of these parameters are high because organic materials are washed from fields and stream banks into the river during periods of heavy or extended precipitation.

The Skipanon River is unique to the North Coast basin, and not just for its tea-like color. While it did not receive the lowest minimal seasonal average score, the Skipanon River has the most consistently poor water quality of all of the monitored streams in the basin (Table 1). Low dissolved oxygen concentration, high total solids, and high total phosphate concentrations consistently impact water quality, with the occasional influence of biochemical oxygen demand and high temperature. The Skipanon River has naturally occurring high levels of humus associated with surrounding marshes. This would contribute the majority of total solids and nutrients, which present a high demand on available dissolved oxygen.

Necanicum Subbasin

The Necanicum River is monitored at Riverside Lake Camp on Highway 101. Water quality during the fall, winter, and spring is excellent (Table 1). Water quality is impacted during the summer by the presence of fecal coliforms indicating the presence of untreated human or animal waste. The high concentration of fecal coliforms is compounded by low summer flows, meaning that less water is available for dilution. In the summer, water quality in the Necanicum River is slightly impaired, relative to the rest of the year, but still ranks as good (Table 1).

Nehalem Subbasin

The Nehalem River is monitored at Foley Road. In contrast to the trend established by the rivers to the north, the Nehalem River's good summertime water quality recedes to fair in the fall, winter and spring (Table 1). Impairments include elevated levels of nutrients (ammonia and nitrate nitrogen and total phosphates), biochemical oxygen demand, and total solids. In this case, rising water levels during heavy precipitation may be removing organic materials from fields, banks, and hillsides.

Tillamook-Nestucca Subbasin

The Tillamook-Nestucca subbasin includes the Miami, Kilchis, Wilson, Trask, Tillamook, and Nestucca Rivers. These rivers experience similar pressures and thus show similar impairments on water quality, although at different magnitudes. High levels of fecal coliforms, biochemical oxygen demand, nutrients (ammonia+nitrate nitrogen and phosphates), and total solids impact these waters during all seasons and flow conditions. This indicates the presence of untreated animal wastes in the rivers throughout the year. During the above-mentioned Tillamook Tributaries study, a comparison of upstream versus downstream conditions was made on the Wilson River. Results show that the upstream site (Highway 6 Bridge) had a higher average OWQI score compared to the downstream site (Highway 101 Bridge). The increase in fecal coliforms and total solids from upstream to downstream led to a deterioration from excellent to fair water quality (Table 1). The Tillamook River site had the most impaired water quality in the subbasin due to occasions of very high concentrations of fecal coliforms. Variations in OWQI scores for monitored rivers in this subbasin reflect differences in intensity of land use and differences in land management practices (Table 1).

References

Johnson, D. M., et al., 1985. Atlas of Oregon Lakes. Oregon State University Press, Corvallis, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1988. 1988 Oregon Statewide Assessment of Nonpoint Sources of Water Pollution. Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1988. Oregon's 1988 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1990. Oregon's 1990 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1992. Oregon's 1992 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1994. Oregon's 1994 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Written by Curtis Cude, Oregon Department of Environmental Quality, Laboratory Division