Natural History. Stewardship. Sustainablility.
2006 TISCHER CREEK
TRANSPARENCY
Instead of sinking a secchi disk into a pond or lake to measure its transparency, stream water is poured into a transparent "turbidity tube" to determine the transparency of the stream water. A stream often isn’t deep enough to use a secchi disk, and the stream’s movement would also make using a disk difficult. Refer to the Hartley Pond Conditions 2006 link.
Transparency of streams and rivers is determined by measuring the length of a column of water in the tube over a standard miniature secchi disk at the bottom of the tube. The length is read when the disk is no longer visible looking down from above the column of stream water in the tube. The longer that column of stream water, the more transparent the water is. Dissolved colored material, suspended silt and clay from runoff from eroding soil, and suspended microscopic algae and aquatic animals will make this measured water column shorter in the tube.
The readings of Tischer Creek this year and last year were usually more than the length of the 100 centimeter-long tube. Because of the briefness of the 2005 reading record, only the 2006 data is shown in the chart. State-wide the transparency readings of northern Minnesota streams are generally much higher than those south of here, and Tischer Creek fits that northern pattern. A continuous sensing and recording device in the creek, downstream from the park and downstream of the Mt. Royal shopping center, where there is much impermeable surface, detected much lower transparencies from precipitation runoff events. Click to Minnesota Pollution Control Agency’s Lake Superior Streams web site.
In the park, an easily seen association between significant rain events and readings below 100cm wasn’t observed. The moisture content of the pre-rain permeable soil is a factor that easily hides that association. This year had little precipitation and so it took more precipitation to show up in increased depth, flow and turbidity. A few times this year however, the soil was moister.
The color of Tischer Creek water ranged from very light yellow to orange-brown; higher stream levels and spring time water tended to have greater amounts of color. The color of the stream water that flowed over Hartley Pond Dam into the creek is similar to the color of Hartley Pond’s water (2006 Hartley Pond Transparency).
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