Citation:

SHIRAZI, M. A. Predicting synoptic water quality indicators of wadeable streams in the U.S. using National Soil Database. Presented at American Society of Agronomy, San Antonio, TX, October 16 - 19, 2011.

Impact/Purpose:

Nationwide assessment of water quality is a goal of the United States Environmental Protection Agency (USEPA), and the EPA’s Wadeable Stream Assessment (WSA) was developed in response to that goal.

Description:

Nationwide assessment of water quality is a goal of the United States Environmental Protection Agency (USEPA), and the EPA’s Wadeable Stream Assessment (WSA) was developed in response to that goal. The observed chemical, physical, and biological water quality indicators (WQI) from WSA offer a synoptic estimate of all the nation’s waters based on 1392 probability sites sampled across the conterminous United States. The analysis and extrapolation of this assessment to sites elsewhere in the U.S is aided by a nationwide soils data base of potential predictors of the observed WQI. The U.S. soil characteristics (SC), and SC environments, spatially define soil map units, which we obtained from the U.S. Natural Resources Conservation Service to describe the watersheds of the 1392 sites by their SC. We then used the SC as independent predictors of one or more WQI in our models, whereas the remaining WQI served as co-predictors. We calculated the SC squared distance metrics (SC_sqrd) to link WSA watersheds with map units, and ran the models to predict the distribution of WQI in the 9551 (STATSGO) and 253,060 (SSURGO) soil map units of the conterminous United States. The relative errors of prediction of four land-use-dominated WQI, NO3, total P and suspended solid, and turbidity, were >>100%, and of 14 physical, chemical, and biological WQI, were <78%. This nationwide synoptic view provides a useful management tool for estimating the expected “natural” water quality locally and regionally in the conterminous U.S.

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