Department or Program



Pyramid Lake is a small, semi-closed lake thought to have formed 12000 – 13000 years ago, following the Green Lake Landslide at the end of the last glaciation. Recent records of watershed history indicate regional climate variability from natural and anthropogenic sources. Biogenic silica, stable isotopes (δ13C and δ15N), elemental carbon and nitrogen and compound-specific lipids (n-alkanes and carboxylic acids) were examined in two sediment cores, 28 and 36 cm, collected from Pyramid Lake to shed light on organic matter sources and primary production within the lake. Carbon isotopes ranged from -27.6‰ to -28.5‰ displaying a near constant trend up core while nitrogen isotopes ranged from 0.9‰ to 1.9‰, showing a slight enrichment up core. Biogenic silica ranged from 0.97% to 23.8% and increased towards to the top of the cores. Elemental carbon and nitrogen percentages both increase mid-core with values shifting from 7 to 14 percent and 0.5 to 1 percent, respectively. Compound-specific results suggest a high proportion of vascular plants with limited algal signatures. Ages were determined via 239+240Pu-dating and range from 1855 to 1963. Results in conjunction with C/N ratios suggest possible increases in littoral sediment redistribution and/or primary productivity beginning around 1923 in association with 20th century warming. By learning how the lake’s internal processes and conditions have changed in response to its environment, we can gain an understanding of the extent of human impact and predict how it could change in the future in the face of human-induced climate change.

Level of Access

Open Access

First Advisor

Beverly Johnson

Date of Graduation


Degree Name

Bachelor of Science

Number of Pages


Open Access

Available to all.