As water moves north in the bottom layer of the Chesapeake Bay it runs out of oxygen and then accumulates hydrogen sulfide from bacteria using sulfate respiration in the sediments and the water column. Yesterday we found the sweet spot between these two conditions, and so for today we moved north just a little ways to collect water that only recently (in the last week or so?) started accumulating sulfide. Jeff Cornwell and I got up early to do some “sniffing” around with his spectrophotometer. We cast the CTD at a couple stations and measured sulfides at the bottom and near the top of the deep layer of water. We settled on station CB5.1 off the mouth of the Patuxent R. where bottom water sulfide concentration was about 1 micromolar.
The team was very efficient today, and we finished our standard sample collection (sediment samples at three depths and water samples at eight depths) by lunchtime and had a relaxed afternoon processing the samples. After dinner we broke down the experiment we started last night. My team sampled the BOD bottles for bacterial production rate and ribosomal RNA to see if the active microbial community changed during the incubation.
Ian Hewson’s team sampled the large 2-liter BOD bottles for messenger RNA to see if there was a change in the genes expressed by the microbial community. Jeff Cornwell’s team sampled the 300ml BOD bottles for respiration rate (as change in oxygen and change in CO2), and for concentrations of oxygen, CO2, nitrate, and sulfide. Unfortunately we have to wait until we get home to get most of these results, but we did learn that no sulfides accumulated in the bottles, which is good. Tomorrow we will repeat this experiment using sulfidic water from near the Chesapeake Bay Bridge. If our hypothesis is correct, the bacteria in that old sulfidic water will not have the genetic tools to handle higher energy electron acceptors, and so microbial growth and respiration will not change or might even decrease with the addition of nitrate and oxygen. That would be sweet.