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TSS quantifies solids by weight and is heavily
influenced by stream flow and land disturbing activities. Mountain streams in undisturbed forested
areas remain clear even after a moderately heavy rainfall event, but streams in
areas with disturbed soil will become highly turbid after even a relatively
small rainfall. Deposition of silt into a stream bottom can bury and destroy
the complex bottom habitat. Consequently, the habitat for most species of
aquatic insects, snails, and crustaceans is destroyed by stream siltation. The
absence of these species reduces the diversity of the ecosystem. In addition,
small amounts of bottom-deposited sediment can severely reduce the hatch rate
of trout eggs. There is no legal standard for TSS, but values below 30.0 mg/l
are generally considered low, and values above 100 mg/l are considered high. A
good measure of the upstream land use conditions is how much TSS rises after a
heavy rainfall.
These
graphs show median turbidity levels and total suspended solids concentrations
for each site compared with the average median for the eight-county VWIN
region. In the past year sample
collection occurred twice at a period when rains affected the streams. On several other occasions the streams were
high from rains that had occurred in previous days, but the streams had already
had sufficient opportunity to clear before samples were collected. On the two occasions when samples were most
affected by sediment runoff, the sites most affected were Mill Creek, Pine Creek,
and Cedar Creek. Mill Creek and Pine
Creek are at the northwestern end of the lake and Cedar Creek is at the
southeastern end. Hurricane Creek, the
upstream site on Norton Creek and Glenville Creek have been relatively
unaffected by sediment runoff. The
downstream site on Norton Creek has been only slightly affected by sediment
runoff.
Cedar
Creek also exhibits the highest median turbidity levels and sediment
concentrations and also exceeds the average median for the region in both
categories. The median sediment
concentrations at Mill Creek also exceed the average median for the
region. The sources of sediment to these
streams should be investigated.
Regionally, the most common sources are unpaved roads, construction
sites, bank erosion, and agriculture, particularly livestock.
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