Dennis Helsel

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Trends in environmental variables are often investigated within a study region at more than one site. At each site, a trend analysis determines whether a trend has occurred. Yet often also of interest is whether a consistent trend is evident throughout the entire region. This paper adapts the Seasonal Kendall trend test to determine whether a consistent(More)
INTRODUCTION Throughout the United States increasing demands for safe drinking water and requirements to maintain healthy ecosystems are leading policy makers to ask complex social and scientific questions about how to assess and manage our water resources. This challenge becomes particularly difficult as policy and management objectives require scientific(More)
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Objective 1—Identify the human and natural factors associated with occurrence of pathogens and indicators from fecal sources.. Objective 2—Characterize the quality of streamwater and ground water in relation to beneficial uses for(More)
Previously reported dendrochemical data showed temporal variability in concentration of tungsten (W) and cobalt (Co) in tree rings of Fallon, Nevada, US. Criticism of this work questioned the use of the Mann-Whitney test for determining change in element concentrations. Here, we demonstrate that Mann-Whitney is appropriate for comparing background element(More)
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