Statewide Nutrient Criteria Development
Background
Nutrients are naturally occurring and manmade chemicals, including nitrogen and phosphorus, that flow into surface waters. Nutrients are necessary to support aquatic life, but at high concentrations they can cause algal blooms, which sometimes result in low oxygen levels in the water that fish and other aquatic organisms need to survive. Excessive nutrients can also cause problems with taste, odor, and overall aesthetics, which impede recreation, reduce property values, and can lead to increased drinking water treatment costs.
What are nutrient criteria?
Water quality criteria set pollutant concentration limits that should not be exceeded if a waterbody is to continue to provide its uses to people and other organisms. In the case of nutrients, DWQ is deriving—through scientific and economic investigations—criteria for nitrogen and phosphorous that will establish nutrient levels that should not be exceeded if a waterbody is to retain its biological and recreation uses.
Why do nutrients need to be regulated?
Nutrients are necessary to support life; however, they can be a problem if concentrations get too high. This creates a biological imbalance via increased production (biomass) of algae and aquatic plants and increased abundance of microbes. These imbalances can create many related problems including:
- Low dissolved oxygen (DO) concentrations: Excess nutrients can cause an increase in the abundance of primary production. Large numbers of plants and algae photosynthesize during the day, producing large quantities of oxygen. At night, oxygen production ceases, whereas respiration (the use of oxygen in the process of building new cells) continues, which can cause anoxic (lack of oxygen) conditions. Further, these plants and algae eventually die and are decomposed by microbes who also consume oxygen. When excess nutrients are present microbes increase in abundance, resulting in higher rates of decomposition and oxygen consumption, which is often not an issue during the day (thanks to the plants and algae), but exacerbates low oxygen concentrations at night. These low DO concentrations are a concern because fish and other aquatic animals need to breathe, just like we do.
- Production of toxic phytoplankton: Toxic phytoplankton is a poor food source for other organisms and a threat to the health of humans and other organisms (e.g., the cows that died from drinking water at Matt Warner Reservoir).
- Loss of biodiversity, including many desirable organisms (i.e., trout) that are sensitive to low DO concentrations.
- Eutrophic waters and associated anoxic conditions often have "slimy" surface mats and smelly, mucky substrate, which greatly decrease aesthetics. This often results in decreases in the property and recreation values that these waters provide.
- Excessive algae growth leads to taste and odor problems, which can greatly increase drinking water treatment costs.
- Increased number of fish kills.