By Robb Jacobson, June 27, 2016
Missouri River scientists started the first phase of the pallid sturgeon free embryo drift study by employing a standard method to understand how hydraulic processes vary the rate of downstream transport of dissolved constituents and particles. On June 26 they released 50 liters of rhodamine-WT dye (figure 1) into the Missouri River about 10 miles downstream of Fort Peck Dam, Montana (about 1.75 miles downstream of the Milk River confluence). The downstream dispersion of dye is being recorded through a network of fluorometers distributed through about 84 miles of the river. Rhodamine-WT is a harmless but very visible dye (figure 2) that is frequently used to study time of travel in river systems, usually to assess contaminant transport rates.
The experiment is being helped a great deal by collaboration with US Army Corps of Engineers and Western Area Power Administration, who have arranged for near-steady flows for the duration of the experiment.
The initial effect of putting the dye in the river is dramatic, as nearly the entire river turned bright red (figure 3). With continuous dilution, the bright red faded to burnt umber after drifting about 6 miles. After 20 miles it was no longer visually identifiable, although the instruments have been able to detect the dye to concentrations as low as 1 parts per billion.
Information from the dye trace is being used in near-real-time to refine the sampling strategy for the companion free embryo-drift experiment taking place in the afternoon of June 27. More about the collaborative free embryo drift experiment in subsequent posts.