Date of Award

12-1-1973

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geography & Geographic Information Science

Abstract

Chemical analysis of water from 17 sites along the Devils Lake chain, starting with Mauvais Coulee and ending with East Stump Lake, and plankton and benthic analyses of East and West Stump Lakes, the two terminal lakes in the chain, were conducted from September 1969 to December 1972. A great degree of variation occurred along the chain with mineral content ranging from a minimum in groundwater to a maximum in East Stump Lake. Variations between lakes in the chain arise from physical characteristics such as isolation, permeability of basins, and reinundation.

Greatest mineralization r.as occurred in those lakes without outlets (East Devils and East Stump Lakes) where all inflow loss is by evaporation. West St trap Lake, having an outlet since separation from East Stump, has since become less mineralized.

Recent (1969-72) high discharges down Hauvais Coulee that overflowed from Main into Mission and East Bays in Devils Lake, reduced concentration of certain ions but initially increased that of others by pickup from dry bottoms. As rewatering moved down the chain, mineral pickup continued and heaviest ionic concentrations were in most recently watered areas. Uppermost bays lost mineral concentration with continued flow-through and marked reductions were achieved in Main and Creel Bays.

In alx lakes minerals tended to increase during summer evaporation, peak with winter freeze-out, and decrease with spring thaw. Sulfate crystals precipitated from solution in East Stump Lake as water cooled in autumn and gave a sudden decline in dissolved salts there.

Calciummagnesium ration wore affected by photosynthesis with more calcium than magnesium occurring in those waters *Lth little or no photosynthetic activity, such as groundwater and Mauvais Coulee in the spring. In all lakes, photosynthetic formation and precipitation of calcium carbonate leaves the more soluble magnesium carbonate in solution.

Ground and Mauv&is Coulee waters are sources of relatively lowly mineralized water to the chain; low minerality of the former being attributed to its lack of photosynthesizing organisms and its enclosed nature protecting it from climatic conditions such as evaporation. Lees mineralized condition of Mauvais Coulee is due to its transitory nature and high desiccation rates of lakes into which it flows.

Areal buildup and simultaneous decrease of orthophosphate in summer 1972 at all sites except East l>vils and West Stump Lakes are noteable but as yet unexplainable.

Variety of planktonic and benthic organisms has apparently increased in West Stump Lake with demineralization following its separation from East Stump Lake, in which number of species is quite low.

A recent water level increase has partially restored Devils Lake turning it once again into an attraction for sportsmen. The future of Devils Lake as well as other lakes in the c-.ain depends upon weather conditions and implementation of the Garrison Diversion Plan.

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