Portneuf River Water Quality


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The Portneuf River
Geography	Discharge	Floods	Groundwater	Water Quality

Monitoring Water Quality

   Water quality can refer to many aspects of a water body, including the amount of sediment, nutrients, bacteria, algae, plant material, and chemical contaminants that are present in the water. Different aspects of water quality are of particular interest for different organisms or uses. For example, water temperature and the concentration of dissolved oxygen are important to cold water fishes, high concentrations of bacteria pose a threat to human uses such as swimming, high sediment loads can be detrimental to certain species of aquatic insects, and high concentrations of nutrients can result in nuisance growth of aquatic plants.
   Several contaminants have been identified as problematic in certain reaches of the Portneuf River. During the summer, when flows are low, high water temperatures and low dissolved oxygen concentrations pose threats to cold water fishes such as trout. During spring runoff large amounts of sediment may be washed from urban streets into the Portneuf, contributing to high sediment loads. High concentrations of bacteria, exceeding standards set by the Idaho Department of Environmental Quality, have been found in the Portneuf within the concrete channel in Pocatello. Some of the springs bringing groundwater into the Portneuf between Batiste and Siphon Roads have very high concentrations of dissolved phosphorus, which are almost certainly contributing to the large quantities of aquatic plants that accumulate in the channel in that portion of the river.
   There are several types of monitoring that are being done to track water quality in the Portneuf River. There are sondes, instruments recording multiple water quality parameters, permanently installed at 6 locations in the Portneuf and at one location in Marsh Creek. These sondes record water temperature, turbidity, pH, conductivity, and dissolved oxygen at 15 minute intervals; data from these sondes can be viewed on line at the Rapid Creek Research web site. The Pocatello sewage treatment plant does regular sampling of water that it releases into the Portneuf River. Students in the General Ecology class at Idaho State University, in cooperation with the ID DEQ, have sampled water at various points along the Portneuf River in fall 2002 and spring 2003. Water samples were analyzed for nutrient, sediment, and bacterial concentrations; data from the fall samples are plotted here.

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Threats to
our river

E. coli

Efforts to
Protect our Water

Dissolved phosphorus – this is the nutrient that most commonly limits primary production in freshwater aquatic systems. Adding phosphorus to a river or lake will often stimulate rapid growth of aquatic plants such as algae and macrophytes. Excessive plant growth can reduce that attractiveness of a water body for activities such as boating and swimming, and when large amounts of vegetation die in a water body the decomposing organisms can greatly reduce the concentration of oxygen in the water.
Dissolved phosphorus levels in the Portneuf River were relatively low at all sample locations upstream of Siphon Road. Springs that enter the river between Batiste and Siphon Roads have high concentrations of phosphorus that probably is the result of leaching of phosphorus from slag piles at the Simplot and former FMC refineries.

Nitrogen Nitrogen is often the second limiting nutrient after phosphorus in freshwater aquatic ecosystems. The addition of large amounts of nitrogen can result in eutrophication, similar to the effects of excessive phosphorus. Two common forms of inorganic nitrogen in fresh water are ammonia (NH₄) and nitrate (NO₃). Nitrogen concentrations in the Portneuf River were relatively low at all sample sites in fall 2002.

Suspended Sediments – Sediment in a river or lake reduces the clarity of water. At very high concentrations sediments can interfere with visual predators, like trout, and filter feeders, such as some aquatic insects. The amount of sediment that a river can carry depends on the volume of water in the river and the amount of energy that water has. Water that is flowing swiftly can carry more sediment, and sediment will stay in the water column longer in water that is very turbulent compared to calm water. As sediment falls out of the water column it will cover the river bottom. Large amounts of sediment can destroy spawning and overwintering habitat for fish by filling in the space between stones and gravel. Sediment loads in rivers like the Portneuf are typically higher in spring, when snowmelt increases the volume of water in the river. As flows drop, the water’s energy drops as well, and it cannot keep as much sediment in suspension.

The sondes in place along the Portneuf estimate sediment load by measuring the degree to which a beam of light is scattered by material (sediment) in the water column. With proper calibration measurements, these turbidity measurements can provide a good estimate of sediment load in the river. The relationship between turbidity and sediment load can vary from one location to another depending on the type of materials that make up the suspended sediments. This figure shows relationships between turbidity and sediment load at the Edson Fichter Nature Area and at Batiste Road. The difference in these relationships is probably due to differences between silty sediments at the Edson Fichter site and more mineral sediments that result from sanding materials used on Pocatello streets during the winter.

Bacteria
Bacteria play many key roles in ecosystems, but they are a concern with respect to water quality because some bacteria can cause disease. Escherechia coli, E. coli, is a bacterium found in the digestive tract of all warm-blooded animals. It is often used as an indicator of contamination by sewage or fecal material, and the Idaho Department of Environmental Quality has established standards for the concentration of E. coli that is permitted in water used for various activities. More information on E. coli in the Portneuf River can be found here.