|Title||Recent diatoms from Douglas Lake, Cheboygan County, Michigan|
|Year of Publication||1976|
|Degree||Doctor of Philosophy|
|Number of Pages||419 pp.|
|University||University of Michigan|
|City||Ann Arbor, MI|
A short core of 1.7 m was taken from South Fishtail Bay in Douglas Lake for examination of the recent sedimentary record of diatoms and pollen. The pollen data indicate the modification of the vegetation by man's activities. The diatom record chronicles the lake's response to the terrestrial manipulation. In the lower portion of the core the diatom assemblage remaines relatively stable with respect to number of taxa present and species composition. Above this relatively stable zone the pollen data indicates removal of the pine forest and an increase in the non-arboreal pollen types. Concurrently, the diatom assemblage undergoes dramatic changes. The initial response of the diatom assemblage suggests that the removal of the forest did not appreciably alter the environment for the diatoms but that near the end of the lumbering period a major terrestrial event drastically altered the environment for the diatoms as evidence by Melosira granulata gamma-status. A period of adjustment followed this event until it was altered by cultural eutrophication. Taxa intolerant of pollution either drop out of the assemblage or are severely depressed above this level of alteration of the lake environment. Pollution tolerant taxa increase in abundance toward the surface and assume roles as dominant taxa at the surface. The diatom assemblage has been altered in such a way that it can never return to its former state. A total of 376 diatom taxa were encountered in the core and are presented in a taxonomic list. Data analysis was handled in two ways: the traditional depth vs. abundance profiles and with principal components analysis (PCA). The PCA segregated the core into six strata (by depth). These depth clusters suggest diatom responses to ecological conditions at the time of deposition. Also, the PCA strongly supports the irreversable change in the diatom assemblage. Abundance profiles of the 183 most common taxa are included.