Quantifying mercury reduction kinetics in soils
Date
2013-01-24
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Degree Level
Doctoral
Abstract
Mercury emissions from soils significantly contributes to the global Hg cycle; however there is little research on the fundamental biotic and abiotic factors (soil temperature and moisture) controlling Hg reduction kinetics in soils. Specifically, it is not clear if biological processes contribute significantly to mercury reduction in soils. The development of controlled chambers and an inter-comparison of methods for studying soil Hg reduction kinetics is also an important research need in order to better quantify the effects of environmental variables on Hg reduction process. I succeeded in developing a simple, portable and accurate laboratory quartz flux chamber system that can be used to precisely and accurately measure the effect of different environmental parameters on Hg reduction kinetics.
The effects of soil temperature, percent water filled pore space, and sterilization on the kinetics of Hg(0) formation in 10 different boreal soils of Nova Scotia, Canada were quantified using the developed quartz beaker system. This system was used to quantify pseudo-first order Hg(0) formation rate constants under a range of environmental conditions by fitting an integrated pseudo first order reaction equation to the data for cumulative Hg(0) formed in soil over a 24 hour period (r2 = 0.90 to 0.99, p<0.001, n = 10). The cumulative mass of Hg(0) formed and the k values increased linearly with increasing soil temperature (278 to 303 K) both in non-sterilized and sterilized soils. Sterilizing soils significantly (p<0.05) decreased the percent of total Hg reduced to Hg(0), with sterile soils on average reducing 3.4% of total mercury as compared to 6.8% for non-sterile soils with increasing soil temperature. The cumulative mass of Hg(0) formed in soils and the reduction rate constants attained a maximum at 60 percent water filled pore space and decreases thereafter in non-sterilized and sterilized soils. Hg(0) formation did not occur at 80 percent water filled pore space.
This research finds biotic contributions to be highly significant in the process of Hg reduction and my results confirm the key role played by soil temperature and moisture in the production of Hg(0) in natural forested soils of Atlantic Canada.
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Keywords
Mercury, Soils, Microbes, Reduction, Percent water filled pore space, Temperature
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Soil Science
Program
Soil Science