Physical, chemical, and biological results from a Lagrangian study of water and sediment transported by Powder River in central Wyoming and southeastern Montana, between June 27 – July 3, 2019

A Lagrangian study was conducted in 2019 that followed two water masses in the Powder River from central Wyoming to southeastern Montana. The study characterized the changes of the in-stream transport of sediment and associated chemical and biological constituents. Depth-integrated water samples (using an isokinetic nozzle) and river bottom sediment samples were collected at six mainstem and three tributary locations. Measurement of the depth-integrated water samples included physical, chemical, and biological constituents associated with the water, the large-grain suspended sediments (> 63 or 53 µm), and the fine-grain suspended sediments (< 63 or 53 µm). Field samples were collected as the two separate water masses were tracked from tributary sources to a downstream location on Powder River. In stream field measurements included discharge, temperature, pH, and specific conductance. Suspended-sediment concentrations were determined for the large- and fine-grain size fractions, whereas river bottom sediments were analyzed for mean particle size. Depth-integrated water samples were analyzed for alkalinity, dissolved organic carbon, total dissolved nitrogen, major anions, cations, and metals. Unfiltered water samples and suspended sediment fractions were analyzed for metals. Differences in microbial community composition and abundance were determined for the free-living planktonic community, whole-water community, and the large- and fine-grain size suspended sediment communities.