In situ measurements of turbidity and Rhodamine WT dye concentration from an experiment conducted at the USGS Columbia Environmental Research Center, Columbia, MO, on April 2, 2019

This child data release includes in situ measurements of turbidity and Rhodamine WT dye concentration acquired during an experiment performed at the USGS Columbia Environmental Research Center, near Columbia, Missouri, on April 2, 2019.  The purpose of the experiment was to assess the feasibility of inferring concentrations of a visible dye (Rhodamine WT) tracer from various types of remotely sensed data in water with varying levels of  turbidity.  Whereas previous research on remote sensing of tracer dye concentrations has focused on clear-flowing streams, the Missouri River is much more turbid and the reflectance signal associated with the sediment-laden water could obscure that related to the presence and amount of dye.  This experiment thus provided an initial test of the potential to map dye concentrations from remotely sensed data in more turbid rivers like the Missouri, where tracer studies involving the release of a visible dye can provide insight regarding the dispersal of endangered sturgeon larvae. 
The experiment involved manipulating the turbidity and Rhodamine WT dye concentration in two water tanks.  The files included in this data release include the measurements of turbidity and Rhodamine WT dye concentration logged continuously in each tank to characterize variations in these quantities over the course of the experiment.  These data were recoreded with Turner Designs C3 submersible fluorometers and linked to the field spectra and hyperspectral and RGB images (available in related data releases) based on time stamps. 
Water sourced from a deep well and stored in a pond at CERC was pumped into two circular, 1.83 m diameter tanks and filled to a depth of approximately 0.5m. The tank interiors were painted black to minimize reflectance from the sidewalls or bottoms of the tanks. At the beginning of each experimental run, Rhodamine WT, a visible dye often used as a conservative tracer for dispersion studies in rivers, was added to the tanks and rapidly became well-mixed with minimal stirring. The amount of dye injected was calculated based on the known volume of water in the tank and each of six target dye concentrations: 0, 2, 6, 9, 12, and 20 ppb. Fine-grained sediment derived locally from the floodplain of the Missouri River by a commercial vendor near Jefferson City, Missouri, was added to each tank and agitated with pumps to place the material into suspension.  The turbidity of the water in the tanks then decreased gradually over time as the sediment settled out of the water column. 
A sample of the sediment was sent to the USGS Central Midwest Water Science Center to quantify the grain size distribution following standard USGS methods. This analysis indicated that the sediment was a sandy loam with 67.9% sand, 24.5% silt, and 7.6% clay, with a median particle size of approximately 0.15 mm. 
An in situ sonde, a Turner C3 submersible fluorometer, was placed within each tank and used to record time series of turbidity and dye concentration throughout the experiment with a 15 s logging interval.  The sondes were calibrated for sensing dye concentration as a function of fluorescence using a two-point calibration procedure (0 and 10 ppb) following the protocol established by the manufacturer. To create calibration solutions for fluorescence, the same pond water that was pumped into the tanks for the experiment was used to dilute a manufacturer-recommended standard. This calibration procedure was performed immediately prior to the experiment so that the calibration water would be representative of that used during data collection. A similar two-point procedure was used to calibrate the turbidity sensors within the sondes; sondes were calibrated at 0 (deioinzed water) and 100 NTU, using a calibration standard diluted with deionized water. Calibrations for each sensor in both sondes were tested and found to read within 5% for both low (1 ppb and 10 NTU) and high (30 ppb and 400 NTU) test dilutions of dye and turbidity standard. 
The turbidity and concentration measurements from throughout the experiment are compiled in a single zip file, SondeData.zip, that contains a separate text file named based on the nominal (i.e., target) dye concentration in each tank.  Each file contains columns with time stamps, Rhodamine WT dye concentrations in ppb (parts per billion), and turbity values in NTU (nephelometric turbidity units).  The nominal concentration levels were 0, 2, 6, 9, 12, and 20 ppb.

Tags: columbia, concentration, in-situ, missouri, remote-sensing, rhodamine-dye, sonde, tracer-tests, turbidity, usgs-5d6557c0e4b0c4f70ceeaf69
Organization: Department of the Interior