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> July 26, 2006 - Sediment Filtration Lab
post Jul 26 2006, 04:17 PM
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The "wet lab" is set up in a spare dorm room in Polarbrakka, where the students live. Christina was teaching Eric and Heather how to filter the samples today and I was able to get some pictures of what they were doing.

First, they measure each sample in a graduated cylinder. This gives a fairly accurate reading of the starting volume. This sample is everything sucked up by the tube positioned in the river at either the lower or upper ISCO sampler.

Using the Graduated Cylindar
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A small round piece of filter paper is positioned between the top and bottom part of the filter bottles. The sample is poured into the apparatus, and a vacuum pump helps pull the water through the filter paper. There are 4 filters set up, so four of our samples can be worked at once.

Pouring the Sample into the Filter System
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It takes 20-30 minutes to get the water through! The vacuum makes a whirring noise and eventually the water goes through drop by drop, leaving just the sediment on the filter. It is kind of like draining spaghetti, where the water passes through the holes in the colander while the pasta stays on top. Each set of 4 samples takes about 40 minutes to process, so with 48 bottles to work every 2 days, this adds up to 8 hours of filtering!

The Filtering System
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Then the filter can be taken our and set to dry. Although the paper tends to curl up, it has a bit of a static charge to it and the sediment does not come off. The cabinet helps keep anything bad from happening to the samples!

The Samples Set to Dry
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Once the sample is dry, itís mass will be figured in this very sensitive balance. It can figure mass to 0.001 grams! This will tell us how much sediment is in the water at each 2 hour interval for every day that we sample it. The mass of the filter paper will be subtracted from the total mass, giving us just the data for the sediment. That is like you weighing yourself in heavy ski boots, and then weighing the boots so you could subtract that weight to get just your weight.

Christina Using the Sensative Balance
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Question of the day: What do you expect to see in this data? Will there be more sediment on a sunny day, or in the afternoon, during a rain storm or in the middle of the night? Why? (Remember, we still enjoy 24 hours of sunlight here right now, although the sun is dipping down more and by mid August will dip below the horizon at night for the first time since April).

Let me know what you hypothesize by sending an email or posting on the ďask the teacherĒ forum. We will let you know what we find!
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