CE320 – Fate of Reactive Species in Environmental Systems The lab assignment associated with this lecture will be a tracer release experiment in the Fenton River performed on Thurs. April. 15. Directions to sample locations: The tracer test will begin with a Rhodamine WT dye release far enough upstream of the test reach that lateral mixing will have spread the dye plume across the channel. Two monitoring stations will be used to observed the dye plume. Observation will consist of collecting water samples a fixed sample location as a function of time. A fluorescence meter will be used to quantify the concentration of dye in the water sample. When the dye concentration reaches a maximum concentration at the sample location, a water sample will be obtained and sampled for nitrate, dissolved and total phosphate using colorimetric test kits. If the dye pulse can still be described as a rectangular pulse at your sample location, ratio of the reactive species concentrations (i.e. nitrate, dissolved phosphate or particulate phosphate) to the dye concentration should remain constant if only ‘loss’ mechanism is dilution. Planning Before conducting a tracer experiment, it is necessary to estimate the expected outcome approximately so that a sufficient number of samples can be collected to give adequate resolution in time and space. In class calculations performed before the release will be to estimate: 1. the mixing length in the Fenton River 2. the mass of dye to inject 3. approximate travel times to sample locations 4. expected duration of pulse at sampling location 5. proposed sample collection and measurement increment – since fluorometers are not flow through meters, discrete samples will need to be collected and measured after the dye plume has passed. Periodic samples can be measured in ‘real-time’ to roughly delineate the plume as it passes In addition, you will be given time to familiarize yourself with the measurement tools: 1. how to use fluorometer 2. how to use colourimetric test kitsPost-lab Write-up In addition to the standard lab write-up format be sure to address the following questions: 1. what was the average stream velocity at your location? 2. what was the average dispersivity of the study reach a. comment on the accuracy of your calculation b. comment on the factors that could affect the magnitude and difference between the two locations 3. what environmental reaction rate do you estimate for nitrate, dissolved and particulate phosphate? a. comment on assumption of constant ratio of reactive species to dye concentration? is it valid for your case? b. comment on whether plug flow assumption is valid c. comment on assumption that only N and P species enter reach at x=0 4. what improvements would you make to improve your parameter estimation a. if you were to re-do lab exercise b. if you were not constrained by man-power and time and could conduct a tracer experiment over a longer reach of the Fenton