Publication Date

5-2019

Advisor(s)

Johan Varekamp

Department

Earth and Environmental Sciences

Abstract

East Lake, one of the twin crater lakes at Newberry Volcano, Oregon, receives a gaseous flux of CO2, Hg0, and H2S from the hydrothermal system below. This work presents an initial model for the mercury and carbon cycles within the lake. The rate of Hg input into the lake is recorded in the lake sediments, whereas analyses of Hg in the water column provides the pathways. The carbon cycling is derived from analyses of the water and CO2 escape fluxes from the lake surface. Modeling of the surface fluxes as well as the carbon burial rate as a result of photosynthesis suggests a year-round input of ~25 tonnes CO2 day-1 from below. The lake has a gaseous zone (~10% of surface area) near the shoreline hot springs with elevated CO2 fluxes. Mercury travels with the CO2 bubbles from the hydrothermal system into the lake, with concentrations of 3-8 ng L-1 total Hg (dissolved and particulate bound), with 10s to 100s ng L-1 in the gaseous zone. Methylmercury levels reach up to 40% of total Hg. The sediment carries 1- 13 ppm Hg, with 5-13 ppm in core samples from the gaseous zone. The sediment Hg concentrations correlate with the abundance of Corg, except in the gaseous zone, which correlates with Stotal. It appears that two Hg pathways of fixation occur: (1) a largely inorganic pathway in the sediment/sediment-water interface in the zones of intense streaming H2S-CO2-Hg, and (2) an organic pathway in the lake waters that invokes oxidation of Hg, methylation, bioaccumulation, and deposition in association with Corg. Comparison of total water column Hg versus burial rate suggests a processing time of a few months between injection and extraction. The approximate depositional volume of Hg for the lake’s existence (6,500 years) is on the order of 10 tonnes of Hg. These results indicate that secular variations in CO2 fluxes can only be used when understanding the full chemical and physical lake system, given the large variations in monthly CO2. The data indicates that Newberry is a modest source of volcanic Hg, but is contained within the bounds of the lake.

Available for download on Monday, June 01, 2020

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