Publication Date

April 2016

Advisor(s)

Johan Varekamp

Major

Earth and Environmental Sciences

Language

English (United States)

Abstract

East Lake is one of two twin-crater lakes located in the Newberry Volcano, 30 miles south of Bend, Oregon. It has volcanic geothermal inputs largely composed of CO2, but also including H2S and Hg. These volcanic inputs establish unique sediment and water chemistries in the lake and the surrounding ecosystem. Sediment analyses reveal that East Lake sediment is predominantly composed of biogenic silica (~60%) followed by organic carbon (8-12%) with the remainder consisting of volcanic ash. East Lake is terminal. Its water level is dependent upon meteoric water inputs and evaporation. The surface water pH varies between 6.5 and 7 and waters are HCO3- dominant with an average concentration of about 130 ppm. East Lake has a higher internal PCO2, compared to the atmospheric PCO2, producing a diffusive loss of CO2 from the surface of the lake. Data collected from CO2 measurements taken from the surface of the lake during the summer of 2015 in conjunction with sequential Gaussian simulation, estimate a lake surface loss of about 44 tonnes of CO2/day. The diffusive CO2 loss at the lake surface is the main cause of an exaggerated d13C gradient of dissolved carbon with depth. East Lake is a moderately productive lake with CO2 and silica volcanic inputs providing nutritive reactants to photosynthetic organisms. Such organisms consist of phytoplankton, various Nostoc species (cyanobacteria) and aqueous vegetation. All new data collection for this study occurred during the summer of 2015.

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