Publication Date


Document Type


Committee Members

Songlin Cheng (Advisor), Chad Hammerschmidt (Committee Member), Rebecca Teed (Committee Member)

Degree Name

Master of Science (MS)


Crystal Lake showed distinct biogeochemical patterns, which were governed by thermal stratification, photosynthesis, and sulfur redox processes. Field parameter measurements and water and Planktothrix rubescens samples were collected in May, August, and October, 2013 at the deepest point in the lake, to better understand these processes. At the metalimnion-hypolimnion boundary, P. rubescens produced chlorophyll and turbidity maxima. Photosynthesis produced oxygen-rich and nutrient-poor surface waters. The decay of organic matter produced anoxic, nutrient-rich water in the hypolimnion. Sulfate concentrations were high in the epilimnion and metalimnion, with a maximum at the layer of P. rubescens, and decreased with depth in the hypolimnion. Sulfide was absent in the epilimnion and metalimnion and increased with depth in the hypolimnion. Sulfur isotopic composition changed with depth in the hypolimnion due to Rayleigh Fractionation. It can be concluded that P. rubescens play a major role in the sulfur cycle and sulfur isotopic composition changes.

Page Count


Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded