Ammonia is a naturally occurring form of nitrogen. As aquatic plants and animals die, bacteria decompose nitrogen-containing proteins into ammonia. Sewage, however, is a much more significant source of ammonia than decomposing organic matter. A high concentration of ammonia in a river system may be an indicator of a recent sewage release to the river. High levels of ammonia can be toxic to aquatic life.
Water quality criteria for ammonia are dependent on temperature, pH, and the presence of salmonids. Assuming pH = 7.5, temperature = 15 oC, and salmonids are present, the current water quality criteria for ammonia (expressed as total ammonia) are:
-Acute criteria for protection of aquatic life: 15 ug/L
-Chronic criteria for protection of aquatic life: 130 ug/L
Dissolved Oxygen (DO)
The majority of the oxygen in water comes from the atmosphere; however, a large amount comes from photosynthesis of aquatic plants. Decay of organic wastes such as sewage and dead plants and animals are the main cause for decreases in dissolved oxygen in river systems. If decay causes the dissolved oxygen levels to drop too far, the water will no longer be able to sustain aquatic plant and animal life. The current water quality criteria for dissolved oxygen, which are also indicated in (Table 3), are:
-30-day mean maximum criteria for cool water: 6.5 mg/L
-7-day minimum mean criteria for cool water: 5.0 mg/L
-Absolute minimum for surface samples criteria for cool water: 4.0 mg/L
Nitrate + Nitrite-nitrogen
Nitrate and nitrite are naturally occurring forms of nitrogen in the environment. As aquatic plants and animals decompose, bacteria convert nitrogen-containing proteins into ammonia, which can then be converted to into nitrites and nitrates by bacteria. Sewage and fertilizers, however, are far more significant sources of nitrates and nitrites to the environment. Elevated nitrite and nitrate in a river can be an indication of a sewage release in the area. Excessive nitrates or nitrites also stimulate algae growth. A significant increase in algae growth leads to increases in decaying organic matter in a water body. The decay process uses up oxygen from the water, sometimes to the point where insufficient oxygen is present to support fish.
The current water quality criteria for nitrate, which are also indicated in (Table 3), are:
-Water and fish ingestion criteria for protection of human health: 10 mg/L
-Drinking water Maximum Contaminant Level: 10 mg/L
Temperature affects the amount of dissolved oxygen the water can hold, the rate of photosynthesis, the metabolic rates of aquatic animals, and the sensitivity of aquatic species to pollutants. Temperature increases can result from industrial discharges, heat absorption by suspended solids, and urban storm water runoff from sun warmed impervious surfaces. Reduction of natural vegetative cover and replacement with impervious surfaces is a primary cause of water temperature increases in urban areas. Removal of riparian vegetation and tree cover along streams can increase water temperatures. Disruption of hyporheic flow through development of floodplain areas is a significant cause of tempreature increase.
Oregon’s temperature standard is based on biologically based temperature criteria (OAR 340-041-0028(4), the superseding cold water protection criteria (OAR 340-041-0028(11), or the superseding natural condition criteria as described in OAR 340-041-0028(8), or site-specific criteria approved by EPA.
The main stem of the lower Willamette River is identified as having a migration corridor (OAR 340-041 Figure 340A) and the following criterion applies: The seven-day-average maximum temperature may not exceed 20.0 degrees Celsius (68.0 degrees Fahrenheit).
In addition, the lower Willamette River must have coldwater refugia that are sufficiently distributed so as to allow salmon and steelhead migration without significant adverse effects from higher water temperatures elsewhere in the water body. If the department determines through the TMDL process that the natural thermal potential of all or a portion of the lower Willamette River exceeds the biologically-based criteria, the natural thermal potential temperatures supersede the biologically-based criteria and are deemed to be the applicable temperature criteria for that portion of the water body.
Total Phosphorus (TP)
Phosphorus occurs naturally in the environment in various forms, but sewage and fertilizers are also significant sources. Phosphorus is an essential nutrient for plant growth, but excessive phosphorus loading to a water body can lead to increased algae growth, with subsequent increases in algal decay and oxygen depletion.
No numeric water quality criteria exist for total phosphorus.
Total Suspended Solids (TSS)
Suspended solids in river systems come from riverbed erosion, soil erosion, waste discharges, and turbidity from aquatic animal activity. Urban sources of solids include accumulated street litter, construction sites, localized erosion, airborne deposition, and vehicle traffic. Elevated suspended solids in water can increase heat absorption, resulting in temperature increases and oxygen reduction. Suspended solids can also reduce sunlight penetration, resulting in reduced photosynthesis and further oxygen reduction. In addition to the indirect effect on aquatic life from the reduced oxygen levels, suspended solids can directly affect aquatic species by clogging the gill of fish and smothering fish eggs and aquatic insects.
No numeric water quality criteria exist for total suspended solids.
The optimal pH range for most aquatic species is approximately 6 to 8, and the tolerance to change in pH for many species is very low and can result in death. Excessive algae growth can increase pH, which causes increased removal of carbon dioxide from the water through the photosynthesis process. High pH can result in higher concentrations of some metals, which may be toxic to aquatic species. Levels of pH below 6.3 can affect soil structure and cause leaching of metals from soil particles. Spills from industrial activities can cause severe changes in pH. The current water quality criteria for pH, which are also indicated in (Table 3), are :
-Minimum allowable pH: 6.5
-Maximum allowable pH: 8.5