Instructional Activities:

Death Valley Scenario: Teacher Information

This is a partially fictitious scenario set up with the following premises and caveats.

1. The arsenic source is from a century-old abandoned gold mine. Exposed tailings with arsenic are leaching this toxic element down a canyon which spills onto an alluvial fan (a distinct blue color) in zoom out square H1. From there, it spreads across the alluvial fan until it enters the basin itself, where it is highly diluted. This is a POINT SOURCE. In their water management plan, students will (hopefully) include some mitigation strategy such as a dam or holding basin to contain and isolate the runoff from this alluvial fan. Show students the powerpoint which gives examples of the repercussions of mining.
2. The fresh water source is more diffuse and located in the northeast arm of Middle Basin where freshwater seeps into the floor of the basin. This is the deepest part of the basin, although the depth varies with precipitation and evaporation. The freshwater in-flow is crucial for keeping at least a small area below the 25% salinity level that would render the entire basin sterile. Brine shrimp and flies flourish here when salinity and temperature conditions are favorable.
3. For the purposes of this scenario, it’s considered possible to take water samples at each grid location – perhaps during one of the rare precipitation events. Actually, on most days of the year, there would be no possibility of taking water samples throughout most of the valley. In fact, on any given day, a visiting scientist could find Middle Basin completely dry, for any practical purposes. For that matter, simply taking samples at some of the points in the grid is often next to impossible, given that Middle Basin is often just a vast muddy salt flat. We’re glossing over all that, aren’t we? Have students read the case study.
4. The sample preparation template offers a loading plan, tied to the Middle Basin maps, for a 10 x 10 sample grid you can offer to your students. Notice that you can simply prepare 10 different stock solutions at different concentrations, load the requisite number of test tubes, THEN distribute them into the sample grid for students to analyze. Depending on the amount of time allotted to this entire activity, and your energy for preparing more samples, you may even consider allowing students to zoom in even closer to sample a specific area of Middle Basin.
5. While the simple version of this activity involves having students analyze and map distributions of 2 populations of extremophile microbes, there are numerous additional pieces of the activity we urge you to emphasize and incorporate into the work. It is in these pieces that students will experience the richness of the activity, and learn to think like scientists.
   • Students should have the experience of working with incomplete data. They should analyze their incomplete data at several stages, and take new additional data not based on a plan they made before they started, but based on what their first set of data tells them. Their investigation should be dynamic, changing to fit the conditions of the moment.
   • Students should have the experience of sharing data with other groups, and interpreting the data developed by other groups, in relation to their own data. As a teacher, you can create this type of communication at different levels, moving from meeting as a small lab group to a couple of lab groups, to summarizing the data at the end of the investigation with the entire class. Allow for this time as you plan your work flow.
   • Students should have the opportunity to do something with their data. In this scenario, we’ve suggested that students should write a watershed management plan for this part of Death Valley National Park. Depending on your students, you may wish to structure this final part as an assessment of the entire activity. You’ll want to think about how much of this “plan" you want to spell out for your students, or whether you want to leave it open-ended. A brainstorming session with your class would (hopefully) develop most of an outline for what the details of a watershed management plan might look like.