Trolls, etc

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Trolls, etc

Hi Dan - Julia again from the Polartrec course. I have two questions for you. You made a lot of references to trolls in your blog, but I never saw an explanation of what exactly trolls are (unless I missed it). I know there are trolls in Norway, but I have a feeling you're not talking about the kind that live under bridges or turn to stone if the sun rises on them... : )

Also, I'm curious about the salt discharge measurements. What is the point of doing that? To see how much mixing and dilution happens from where it is put into the stream to where you are measuring it? To get a standard reference? I have no idea - please explain! Thanks, Julia

Two Q's

Hi Julia,

The trolls we work with are much more agreeable. They are devices that are lowered by cable through the water column to measure temperature, conductivity, turbidity, pH, and dissolved oxygen. The cable is rather long for deep casts and connects up to a 'rugged reader' device that runs on a windows mobile platform, reading out your measurements live-time for in field recording but also logging the data on a small hard drive. These devices are incredibly useful for understanding the environmental parameters for all of the water bodies we've worked on.

The salt discharge is a way to measure stream discharge when a velocity meter based method doesn't work as well. Up at the glacier many salt discharges were done to calibrate the calculated discharge to the stage height of the stream as measured by a level-logger in the stream recording how much water was over the probe at any time. Basically, by putting a known amount of salt into the stream, timing how long it takes to be recorded as a conductivity rise measured by a troll, and then integrating the area under the conductivity rise curve (the total time the conductivity is registered by the reader as a graph of the data), you can calculate how much water is moving through the system.

Great Q's and hope I've made things a bit clearer!

-Dan

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Thanks for all the answers (I

Thanks for all the answers (I figured you were in transition), and I'm psyched to have figured out the graphs. I love puzzles! Much appreciated. I think I'd understand the salt discharge thing better if I could see it (the graphs, etc), but at least I know the purpose now.

Julia