Date of Award

Spring 5-2015

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Geography and Geology

Committee Chair

Omar Harvey

Committee Chair Department

Geography and Geology

Committee Member 2

Franklin Heitmuller

Committee Member 2 Department

Geography and Geology

Committee Member 3

Alan Shiller

Committee Member 3 Department

Geography and Geology

Abstract

Accounting for all possible sources of atmospheric CO2 is a pressing issue today due to the increasing effects of climate change. Estimates suggested that on the order of 1.3 million tons of dissolved pyrogenic carbon (pyDOC) could be entering the northern Gulf of Mexico annually. Assessing the fate of pyDOC in aquatic systems is crucial to understanding ecosystem impacts and potential feedback to climate change. Current research indicates that despite a generally lower susceptibility to biodegradation than their unpyrolyzed equivalents, pyrogenic carbon is not environmentally inert. While the role of microorganisms on the fate and transformation of dissolved pyrogenic carbon is well understood, very little research has been conducted to quantify contributions of abiotic processes such as photodegradation. The purpose of this study was to assess photodegradation of pyDOC and quantify its byproducts (specifically, CO2 evolved). The study consisted of a complimentary mix of laboratory-scale and controlled field-scale experiments with objectives of: 1) To assess the influence of solar irradiance on photodegradation of dissolved pyrogenic carbon and the nature of the degraded byproducts, 2) To assess spatiotemporal variation in photodegradation of pyDOC in a freshwater and saltwater system, and 3) To assess the impact of salinity and depth below the water on photodegradation rates.

Natural charcoal was collected from a prescribed burn site, dissolved, and diluted to create a stock solution for testing. A sampling apparatus was made to hold the samples in a stable position at the water surface. Samples were exposed to natural light with repeated experiments on days of varying irradiance (cloudiness). Variations in spatiotemporal influences were assessed by placing samples at different distances from shore both in a freshwater lake and in the Mississippi Sound. Experiments took place over three days with samples being collected every four hours. Following exposure, samples were tested using UV visible spectrophotometry, gas chromatography, as well as pH and electrical conductivity. Results indicated that photodegradation accounts for a 50% loss of dissolved pyrogenic carbon with the amount of photodegradation being proportional to solar irradiance. As a byproduct of photodegradation, the samples exposed to light were found to have on average more than twice as much headspace CO2 as the dark control samples. This could be a sizable unknown source for atmospheric CO2. Side by side tests of samples in a saline solution and samples in a distilled water solution were exposed and were found to degrade at similar rates and produce equal quantities of CO2[CB1] . Samples were also exposed at different depths below the surface of the water at 3, 6[CB2] , and 12 inches. Samples at 3 inches lost 14%, while samples at 12 inches lost only 6% after one day of exposure with a total of 6.2 kW h/m2. A curve was then constructed to predict the loss of dissolved pyrogenic carbon at a certain depth with 6.2 kW h/m2 in one day.

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