Date of Award

Winter 1992

Project Type

Dissertation

Program or Major

Earth Sciences/Geology

Degree Name

Doctor of Philosophy

First Advisor

W Berry Lyons

Abstract

Devils Lake is located in one of the largest closed basins in the northern prairies. Water and sediment samples were collected to characterize present and past hydrologic and climatic conditions in the basin.

Precipitation in North Dakota exhibits a wide range of stable isotopic compositions. Precipitation samples clustered along two segments of the meteoric water line, illustrating the strong seasonal component of precipitation. Low deuterium excess in summer precipitation was indicative of higher relative humidity of the air masses originating over the Gulf of Mexico. High deuterium excess in winter precipitation is similar to the values found at Canadian stations located on the northern prairies, indicating that the origin of winter precipitation is Arctic air masses.

The isotopic composition of ground-water in the Spiritwood aquifer is lighter modern precipitation, indicating that the water was recharged during colder, wetter periods. Surface water has experienced significant isotopic fractionation as a result of evaporation. Precipitation and runoff are not the only sources of recharge to Devils Lake. The intercept of the evaporation line for Devils Lake surface water and the precipitation, is more negative than precipitation and runoff.

Pore water in Devils Lake is enriched in major ions and nutrients. Two geochemical processes are primarily responsible for the large dissolved-solids and nutrient concentrations in the pore water: burial of saline sediments and pore water, and microbially-mediated sulfate reduction. Bottom sediment fluxes are the dominant source of major ions and nutrients to Devils Lake.

Based on, biogenic silica and the composition of organic matter (TOC, C:N, del C-13, and del N-15) in sediment cores, the paleobiologic conditions of Devils Lake can be described. High lake level stands are characterized by; increased primary productivity, increased input of detrital organic matter, and nitrogen unlimiting conditions, and low lake level stands by; decreased primary productivity, decreased input of detrital organic matter, where algal matter dominants the sedimentary organic matter.

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