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Siesta Lake Eutrophication

A cache by TerryDad2 Send Message to Owner Message this owner
Hidden : 01/04/2011
Difficulty:
3 out of 5
Terrain:
1.5 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

Siesta Lake was created by a glacial moraine blocking a minor stream. Since its formation sediment has been slowly filling it in and it will one day become a meadow. This natural process is called eutrophication.

As you embark or continue your journey to discover and explore beautiful and historic rocks, waterfalls, peaks, creeks and other wonders, please keep in mind that these places need to remain wild and protected so that they may be enjoyed by others for generations to come. Please be diligent in respecting these sites by doing the following:

  1. Please keep trash with you at all times, do not leave it behind in these pristine places.
  2. Bury human waste 6 inches deep, make certain you are at least 50 paces away from any water source and PLEASE bring your toilet paper and sanitary items back out with you.
  3. Keep food and all scented items on your person at all times.
  4. Support wildlife by allowing them to find their own food, do not feed them.
  5. Allow plants to grow and water to stay clean by staying on trails, bike paths and roads.
Thank you, Yosemite Wilderness Management

There is a small area to pull off the road and have a look at Siesta Lake. Be careful of the highway traffic. Tioga Road is closed in the winter.

During one of the last glaciations, a glacier flowed through this area stopping at about this point. The road is built through the terminal moraine of this glacier. This moraine blocked the flow of a stream forming Siesta Lake.

From the moment it formed, the lake began filling with sediment. The rate at which this happens is related to the how much sediment is transported into the lake and the organic content of the lake. Each spring, melting snow erodes sediment off the surrounding mountains and transports it to the streams that fill the lakes of the Dinkey Lakes Wilderness. While in the streams, the water flow is fast enough to keep the sediment moving. When the water reaches a lake, the speed of the water slows depositing the sediment in the lake. This sediment begins to fill the lake from the point where the stream enters the lake, forming a delta. This process alone will bring enough sediment to eventually fill the lake from its side. However, the in-filling process can be greatly increased by elevated biologic activity in the lake.

Biologic activity includes shore plants, underwater plants, freshwater plankton, algae, aquatic life, among other things. As these things die, they settle to the bottom of the lake filling it in and providing nutrients for more biologic growth. This process generally fills the lake in from the bottom up as material settles to the bottom.

Three stages of lake development have been developed by limnologists to describe the aging of a lake. These stages are called trophic states, oligotrophic, mesotropic, and eutrophic. These states are most easily recognized by the amount of biologic activity in the lake. Oligotrophic lakes are clear with little biologic activity. Eutrophic lakes look cloudy and have a lot of biologic activity. Mesotropic lakes are somewhere in between.

Urban and agricultural runoff can contain various nutrients that can greatly increase biologic activity. The increased biologic activity then increases the rate of eutrophication of the lake. This artificial increase is called cultural eutrophication.

All the stages of eutrophication are natural processes and each has its own benefits. Oligotrophic lakes would be great swimming lakes and provide beautiful picturesque landscapes. An eutrophic lake would probably be an excellent fishery and wildlife habitat.

Logging questions:

  1. The text "GC2M29C Siesta Lake Eutrophication " on the first line
  2. The number of people in your group.
  3. What stage of eutrophication is Siesta Lake?

The following sources were used to generate this cache:

  • Matthes, Francois. 1930 USGS. Geological Survey Professional Paper 160 Geologic History of the Yosemite Valley. http://www.nps.gov/history/history/online_books/geology/publications/pp/160/index.htm Last Updated: 28-Nov-2006
  • Kiver, Eugene and David Harris. 1999. Geology of U.S. Parklands Fifth Edition, John Wiley & Sons, Inc.
  • Yosemite Association, 1942 Yosemite Road Guide, Revisions made in 1956, 1963, 1965, 1970, 1976, 1981, and 1989.
  • NPS Informational Pannel.

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