Summary


This regional assessment of surface-water nutrients used the National Hydrography Dataset Plus (NHDPlus) stream flow network and updated calibration data to develop refined SPARROW models for TN and TP for the PNW. These new models improve upon and supersede the earlier RF1-based models for the PNW. The PNW NHD SPARROW models were used to estimate mean annual nutrient conditions for 2002 and to identify the relative contribution of different sources to instream nutrient loads, both at established water-quality monitoring stations and in stream reaches where little or no monitoring data were available. The input data sets for the NHD models and the model results that resulted from them should be useful to researchers and water-quality managers when performing local nutrient assessments. The model results were used to show how the relative contributions from natural and anthropogenic nutrient sources (point sources and diffuse sources) change along two large rivers between their headwaters and mouths. Future SPARROW nutrient modeling for the PNW should be based on a more recent time period and could reflect mean seasonal as well as mean annual conditions. Additionally, sub-regional SPARROW models could be developed to help inform water-quality management decisions in specific areas of the PNW.


First posted July 17, 2013