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Sediment Tubes

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1. Stream Science in Antarctica: During the 2001-02 summer season, the streams in Taylor Valley had the highest flow in recorded history. Before the high flow, lots of green algae was observed, but the next year there was none. Why would that be? ( Scoured from the rocks by the fast moving water? Covered by sediment?) Wolman Pebble Counts were taken at each stream. 100 random pebbles were measured both across their longest and shortest sides to determine an average of the streambed characteristics. Scientists are looking for a relationship between the streambed and the algae that grows there.

2. Parcticle settling is governed by Stoke's Law, which says that settling is linearly dependent on parcticle density and quadratically dependent on diameter. In other words settling is proportional to the square of the diameter of the parcticle and directly proportional to parcticle density.

3. The parcticles will be carried laterally by water currents and will settle depending on their size and density. Some of the parcticles that settle out along the way will stay permanently on the bottom, but sediments can be reintroduced into the water by turbulence. This resuspension tends to occur when there are strong currents and also in shallower areas when wind mixes grains from the banks and causes additional turbulence on the surface. Sediment deposits tend to form in low energy, or slow moving water areas such as pools or on the inside bends of meandering streams.

3. Agricultural Run-off: As rain hits fields, smaller grains of sediment and soil are mixed with the water and the run-off brings it to the stream. The stream becomes full of sediment. Too much sediment can change the stream eco-system functions. It can cover the natural bottom sediment and the invertebrate habitats. Invertebrates feed the fish, so they are also impacted. The water column becomes murky and not enough light can penetrate allowing photosynthesis of algae to occur. In many agricultural streams, Riparian Buffer strips have been planted, a row of trees and grasses along a bank to slow the run-off as it approaches the stream. The grasses slow the water movement, and the sediment falls out before entering the stream.

Resources and Reference Materials
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=7272 (nice images of the Dry Valleys)

You might want to take a look at some of my Antarctic journal entries and images: ../../huffman/1.11.2003.html


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