USGS uses watershed modeling to assess surface-water nutrient impairment across the Pacific

The region-wide, reach-scale results from a new study provide two new tools that might help water-quality managers. One is an estimate of the total contribution from point and diffuse sources to the loads delivered to nutrient-impaired water bodies. The other is a method to assess potential nutrient impairment based on estimated warm-weather dissolved oxygen and pH conditions. 

Like those throughout the country, state agencies responsible for managing watersheds within the Pacific region of the United States rely on many types of information to guide their assessments, management, and decision making. While it’s important that these agencies have access to readily available water-quality and watershed data that represent the time period in which they are interested, until recently these data were often incomplete, outdated, or non-existent. With the advent of large-scale spatial data sets that describe atmospheric, hydrologic, and terrestrial characteristics, detailed spatial and temporal analyses at the watershed level can now be performed to help inform management decisions.  

new report describes how recent SPARROW modeling results (representing water years 2000-2014) and other regional watershed data were used to assess surface-water nutrient impairment in the Pacific region. The results showed the contribution from both point and diffuse sources to instream nutrient loads and included estimates of warm-weather dissolved oxygen and pH conditions in free-flowing streams. These results can be used by water-quality managers to help identify potential impairment and inform water-quality management decisions needed to confirm and mitigate that impairment. The results described in this report contain the first complete estimates of nutrient, dissolved oxygen, and pH conditions for the Pacific region, and the techniques we used provide a framework for integrating watershed data to assess water-quality impairment across other large regions.