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Health and Environmental Effects Research

NHEERL Researchers Report on Background Levels of Nutrients and Sediment in Great Rivers

NHEERL researchers’ significant analyses of background concentrations of nutrients and sediment in the Mid-Continent Great Rivers will be published in an upcoming issue of the Journal of the American Water Resources Association (JAWRA). The article is titled “Modeled Summer Background Concentration of Nutrients and Suspended Sediment in the Mid-Continent (USA) Great-Rivers” (by Angradi, Bolgrien, Starry, and Hill; 2012, JAWRA). Using data collected for the Great River Environmental Monitoring and Assessment Program, scientists at the NHEERL Mid-Continent Ecology Division used an empirical modeling approach to estimate the total phosphorus, total nitrogen, and total suspended sediment (TSS) concentration in the Lower Missouri, Upper Mississippi, and Ohio rivers. Natural longitudinal (downriver) variation in nutrients and TSS was removed using regression. The background concentration was determined as the y intercept of multiple regression models, using landscape stressor variables (urbanization, agriculture, and point sources) to predict corrected nutrient concentration. Background total nitrogen concentration was similar on the Upper Mississippi and Lower Missouri rivers. Background total phosphorus and TSS concentration were higher on the Lower Missouri River than on the Ohio River. The resulting background concentrations are useful to States’ assessment efforts as estimates of “pristine” or “reference” conditions that are independent from percentile-based water quality estimates, which are arbitrary and from biotic-response-based estimates that are extremely expensive to generate.

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