Diatoms and chrysophyte stomatocysts from Medicine Lake.

Samples collected September 15-16, 1999.


John A. Barron, Sarah Spaulding, Scott W.Starratt


Sediment, rock and wood scraping, and macrophyte samples were collected from several locations around the perimeter of Medicine Lake. In order to document changes in the diatom assemblage over time, 26 samples were taken from Core 2.

Surface samples: All of the samples contain some diatoms. Generic diversity is variable ranging from five to sixteen. Species diversity within each genus has not been evaluated in detail. The following genera are represented:


Planktonic forms:
  • Aulacoseira
  • Cyclotella
  • Stephanodiscus (may be airborne contaminant from local Pleistocene diatomite deposits).


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Benthonic forms:
  • Brachysira
  • Craticula
  • Cymbella
  • Epithemia
  • Eunotia
  • Fragilaria
  • Gomphonema
  • Muelleria
  • Neidium
  • Pinnularia
  • Pseudostauosira
  • Stauroneis
  • Staurosira
  • Surirella
  • Tabellaria

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There are at least ten different chrysophyte stomatocysts. None of the cysts observed is known to have an affinity to a vegetative form of chrysophyte. Environmental interpretations using chrysophyte cysts are difficult to make owing to the lack of knowledge of the relationship between each stomatocyst and the physical and chemical parameters favored by its vegetative form.

The diatom taxa present suggest a cold, clear, circumneutral pH (most prefer a pH of around 7), mesotrophic (moderate level of nutrients) lake.

Downcore samples: Diatoms and chrysophyte stomatocysts are present in the upper 2-3 centimeters of sediment. Below 3 cm, the diatoms become increasingly sparse, due to solution in the silica-undersaturated pore water. Chrysophyte stomatocysts are more robust and continue in small numbers to a depth of about 12 cm.

Initial results indicate that there is potential for establishing a calibration data set for both diatoms and chrysophyte stomatocysts. This data set can then be used to evaluate environmental changes in downcore studies. Such studies will require a core collected in the deep center of the lake in order to minimize the silica solution problem inherent with shoreline studies in an environment where subaerial exposure can occur.

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