Abstract:

The Macando oil spill three years ago released an unprecedented amount of oil into the Gulf of Mexico. The environmental impacts of this massive influx oil are still being studied today. This project focuses on the effects oil has on microbes in deep-sea anoxic sediments. In the anoxic sediments, three major microbial zones exist due to competitive-substrates. The primary microbes studied within each of the three zones respectively are the sulfate reducing bacteria, the methanotrophs, and the methanogens. In this experiment, oil was added to the top of sediments in cores and incubated at 25 degrees Celsius. Incubations were done to produce a time series for each zone tracking the changes in concentration of sulfate. Sulfate reduction was inferred by the drawdown of sulfate concentrations. It was hypothesized that the addition of oil would cause sulfate to be depleted faster in the sulfate reduction zone and methane to be produced sooner in the methane production zone. Methane production zone was defined as the sediment section below the sulfate reduction zone. The results showed that sulfate remained constant throughout the time series despite oil being added.

Suggested Citation:

Laura Lapham. 2016. Sulfate reduction over time with and without the addition of oil, June 2013 to August 2013. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7XW4GTT

Purpose:

To determine if the addition of oil will cause sulfate to be depleted faster in the sulfate reduction zone, indicating consumption of the oil.

Data Parameters and Units:

time (days), sulfate concentrations (mM)

Methods:

An initial evaluation of sulfate profile allowed three zones to be partitioned from the core and the sediment placed in an air-tight plastic bag. The first zone contained sulfate (sulfate reduction zone), the second zone was where methane and sulfate were both low (sulfate methane transition zone) and the third and final zone contained no sulfate but high concentrations of methane (methane production zone). Two treatments of each zone were the control and one containing 5:1 volume ratio of sediment to MC252 crude oil. Bags were slurried and placed in an anoxic glove bag. The experiment ran for 10 weeks, and every 2-5 days, a subsample was collected to be measured for sulfate concentrations.

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