Mary Shockley - Biogeochemistry Lab

College of William and Mary, Williamsburg, VA

Title:  Sulfate reduction and methanogenesis along the soil profile of a high salt marsh

At SERC’s elevated CO2 field site the biogeochemistry lab is studying the effects of elevated carbon dioxide levels on the respiratory pathways of microorganisms.  They’re making quite a bit of headway, gathering data on the two major pathways in this marsh - sulfate reduction and methanogenesis, but they’ve never studied respiration at a depth of greater than 20 cm.  Here’s where I came in.  Pat Megonigal has been wondering about what the bacteria are doing deep in the organic layer of the marsh.  Also, how deep does the organic layer extend?  To answer these questions we pulled a soil core that was about 6 m deep (this was no easy task).  We found that the organic layer extended for about 5.2 m and then we hit the mineral/clay layer below that.  So that answers one question – when you’re standing on the squishy, stinky surface of the salt marsh at the COsite, you’re standing on about 18 feet of decaying plant matter. 

We have found some interesting correlations between methanogenesis and sulfate reduction rate in our marsh.  It seems that when methanogenesis peaks, sulfate reduction rate also peaks, but a little deeper in the profile.  Also, we have found a strip of soil about 5 meters in depth where sulfate reducers and methanogens are fairly productive. 

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