Water Quality Assessments

We provide predicted total nitrogen (TN), total phosphorus (TP), and specific conductance (EC) for streams in the western US. Our models to enable resource managers to compare the expected to observed values for all 3 water chemistry indicators. These models have adapted from those described in (Olson and Hawkins 2012 and 2013) to avoid shifting baseline issues by using stationary climate predictors (i.e., values are not adjusted for the effects of human-caused climate change).

  1. Total nitrogen (TN): Nitrogen can be present in freshwater in several forms including ammonia (NH3), nitrites (NO2) and nitrates (NO3). These can occur naturally, or they can be derived from anthropogenic sources such as fertilizer. Although nitrogen is biologically critical, an excess in freshwater systems can lead to excess algal or plant growth. These blooms can lead to shifts in community structure and have negative impacts on ecological condition and function.
  2. Total phosphorus (TP): Phosphorus is most commonly present as phosphate (PO4) and is also an essential biological nutrient. Phosphorus does have natural sources but can more often derive from anthropogenic sources. Like nitrogen in an aquatic system, an excess of phosphorus can lead to excess algal and plant growth. This eutrophication has negative impacts on aquatic communities and functions.
  3. Electrical conductivity (specific conductance) (SC): Ionic compounds such as dissolved salts can conduct electricity in water. Conductivity data enable us to better understand the salinity of streams and rivers and potentially identify the presence of an anthropogenic source of salt. Freshwater invertebrates possess different tolerances to salinity; elevated dissolved salt content can impact invertebrate community structure. 
  4. Stream temperature: The thermal regime is among the most important abiotic drivers of biological patterns and processes in river systems. Over evolutionary time, organisms have evolved strategies to maximize fitness in response to different thermal regimes, while in the short term temperature constrains the distribution, development, and growth of aquatic organisms. Consequently, activities such as grazing, dams, and water diversions that alter thermal regimes represent primary threats to lotic ecosystems. In addition to the above water quality constituents, NAMC has built models for predicting reference stream temperature (Hill et al 2013). There is no need to request these values from NAMC though because they are publicly available for every segment of the National Hydrography Dataset (NHD). These predictions have now been incorporated into the StreamCat dataset for 2008-2009 and 2013-2014 time periods. These predicted natural stream temperature can also be compared to predicted stream temperatures in the NorWest dataset for most of streams in the west.

Literature Cited

  • Olson, J. R., and C. P. Hawkins. 2013. Developing site-specific nutrient criteria from empirical models. Freshwater Science 32:719-740.
  • Olson, J. R., and C. P. Hawkins. 2012. Predicting natural base-flow stream water chemistry in the western United States. Water Resources Research 48:W02504.
  • Hill, R. A., C. P. Hawkins, and D. M. Carlisle. 2013. Predicting thermal reference conditions in USA streams. Freshwater Science 32:39-55.