Water-quality trends in the nation’s rivers and streams, 1972–2012—Data preparation, statistical methods, and trend results

Abstract

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod/.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.Suggested citation: Oelsner, G.P., Sprague, L.A., Murphy, J.C., Zuellig, R.E., Johnson, H.M., Ryberg, K.R., Falcone, J.A., Stets, E.G., Vecchia, A.V., Riskin, M.L., De Cicco, L.A., Mills, T.J., and Farmer, W.H., 2017, Water-quality trends in the Nation's rivers and streams, 1972-2012-Data preparation, statistical methods, and trend results (ver. 2.0, October 2017): U.S. Geological Survey Scientific Investigations Report 2017-5006, 136 p., https://doi.org/10.3133/sir20175006. ISSN 2328-0328 (online) iii ForewordSustaining the quality of the Nation's water resources and the health of our diverse ecosystems depends on the availability of sound water-resources data and information to develop effective, science-based policies. Effective management of water resources also brings more certainty and efficiency to important economic sectors. Taken together, these actions lead to immediate and long-term economic, social, and environmental benefits that make a difference to the lives of the almost 400 million people projected to live in the United States by 2050. (http://water.usgs. gov/nawqa/applications/).In 1991, Congress established the National Water-Quality Assessment (NAWQA) to address where, when, why, and how the Nation's water quality has changed, or is likely to change in the future, in response to human activities and natural factors. Since then, NAWQA has been a leading source of scientific data and knowledge used by national, regional, State, and local agencies to develop science-based policies and management strategies to improve and protect water resources used for drinking water, recreation, irrigation, energy development, and ecosystem needs. Plans for the third decade of NAWQA (2013-23) address priority water-quality issues and science needs identified by NAWQA stakeholders, such as the Advisory Committee on Water Information, and the National Research Council as the Nation faces increasing challenges related to population growth, increasing needs for clean water, and changing land-use and weather patterns.Federal, State, and local agencies have invested billions of dollars to reduce the amount of pollution entering rivers and streams that millions of Americans rely on for drinking water, recreation, and irrigation. Tracking changes in the quality of these waterways over multiple decades is crucial for evaluating the effectiveness of p...

Effects of Antecedent Streamflow and Sample Timing on Trend Assessments of Fish, Invertebrate, and Diatom Communities

“…where Sen Slope is the median of the slopes computed from the data pairs used in the computation of the Kendall's tau from the Kendall-tau test for trend (Lorenz 2016), t 1 and t 2 are the start and end years, and M t1 is the predicted median value in year t 1 (equation 32, Oelsner et al 2017).…”

“…This approach was used as an alternative to traditional designation of trends as being significant or nonsignificant because it provides information on the certainty of the trend estimate, avoiding the binary significant vs. nonsignificant classifications imposed by an arbitrarily selected alpha value. Likelihood values below 0.85 were assessed "less than likely" and not further stratified into categories of certainty as in Oelsner et al (2017), Hirsch and De Cicco (2015), and Mastrandrea and Mach (2011) to simplify our results. We assessed a trend "likely" when the likelihood value was between 0.85 and 1.0.…”

“…BioData was queried for sites that met predetermined criteria to support trend analysis over the 2002-2012 trend period (Oelsner et al 2017). Sites were identified that had at least six annual samples of any assemblage (fish, invertebrate, or diatom) where samples were collected within one year of the start and/or end year and had less than a five-year gap.…”

Causal factors for pesticide trends in streams of the United States: Atrazine and deethylatrazine

“…The screening process to determine the sites with sampling representative of the trend period and chemicals with sufficient detections for trend analysis, as well as the data processing steps, was that described in Oelsner et al. (2017, p. 22). The trend analysis method was the seasonal wave model with adjustment for streamflow, SEAWAVE‐Q (Ryberg and Vecchia, 2013; Sullivan et al., 2009; Vecchia, Martin, & Gilliom, 2008).…”

“…Oelsner et al. (2017) completed an assessment of water quality trends for US rivers and streams that included pesticide trends for the periods 1992–2012 and 2002–2012. The pesticide concentration and streamflow datasets used to evaluate the pesticide trends, as well as the trend results, were published in a data release (Ryberg et al., 2017).…”