East Fork Poplar Creek (EFPC), which runs through the city of Oak Ridge, Tennessee, is contaminated with mercury (Hg) which can be transformed into methylmercury (MeHg), a bioaccumulative neurotoxin, under anaerobic conditions by bacteria. To improve our understanding of the location where MeHg is produced this project investigates if physical and chemical characteristics of EFPC stream sediments can be used to predict microbial activity in the sediments. This information could be used to predict ‘hot spots’ of MeHg production. Microbial activity was assessed by measuring carbon dioxide (CO2) and methane (CH4) generation from sediments over time as a function of sediment grain-size. Sediments were further characterized by measuring loss on ignition (estimate of organic carbon content), pH, total and ferrous iron content, moisture content, wet bulk density, and particle size distribution. Across two independent sampling dates, silty sediments generated more carbon dioxide and methane than sandy sediments, indicating a higher level of microbial activity. We hypothesize that greater gas generation in the silty sediments is due to higher organic carbon content, which likely stimulates microbial activity. We hypothesized that there would be a negative relationship between sediment Fe content and CH4 production due to microbial Fe reduction being energetically more favorable than methanogenesis, meaning in high Fe sediments, iron-reducing bacteria will outcompete methanogens limiting CH4 production; however, we observed a positive relationship. After testing, MeHg is normalized by the total Hg, and data investigations reveal a positive relationship between percent MeHg and Fe content and CO2 generation and a negative relationship between percent MeHg and pH. Our next steps will be to look at additional variables like bacteria types, geographical elements, time of year, and sulfate content.

Relating soil geochemistry to microbial activity and methylmercury content in creek sediments

2019 Spring National Meeting

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