News Photo by Darby Hinkley Cecilia Howard, left, and Diana Velazquez, both Ph.D. candidates at the University of Michigan Department of Earth and Environmental Sciences, stand by the sediment trap they just cleaned after it was pulled up from Middle Island Sinkhole.

ALPENA — Sinkhole science is happening in the Thunder Bay National Marine Sanctuary, and two researchers are taking samples from the bottom of underwater sinkholes to be analyzed at the University of Michigan lab.

Cecilia Howard and Diana Velazquez are both Ph.D. candidates at the University of Michigan Department of Earth and Environmental Sciences. They conducted similar research last year in Thunder Bay, and they came back this past week for more sample collection.

“We retrieved this yesterday,” Howard said on Tuesday of the sediment trap, a large yellow, funnel-shaped piece of equipment. “It was deployed over winter. We redeployed it in October, and now we are cleaning it up. This is a sediment trap, which collects particulate matter that’s falling down in the water column and funnels it down into a bunch of bottles, and, on a schedule, we’ll rotate the bottles, so you can get samples that were collected over this time period.”

Those samples will then be analyzed at the U-of-M lab to determine any changes or new discoveries about the sediment.

“We’re really interested in how the low-oxygen conditions in Middle Island Sinkhole impact nutrient cycling of essential elements like carbon and nitrogen,” Velazquez said. “So we’re basically tracing, what are the sources that make their way into the sediments and are ultimately preserved in Middle Island Sinkhole.”

She continued: “The sinkhole is full of microbial mats, which are primarily composed of cyanobacteria.”

“A lot of proteobacteria, too,” Howard added. “One of the things I’m looking at, actually, is what’s going on with those microbial communities. The microbial mats on the surface are really distinctive and super cool-looking. They’re, kind of, purple and white and will sometimes form little gaseous fingers that stick up from the sediments. But then there are also super diverse communities down in the sediments, themselves. So one of the aspects that I’m looking at in the sinkhole is, how are those communities changing through time? Because we’ve been sampling down here for quite a lot of years, at this point.”

Howard said others have been sampling prior to them coming up to do the most recent fieldwork and research.

“One of the aspects I’m looking at is, actually, how are those microbial communities being affected by, for example, changes in ice cover and temperature in the lake above?” Howard said. “Because the material that is falling down is ending up in the sediment, so that changes from year to year.”

“We also got some Lake Huron sediments, which would be in the oxygenated region of the lake, for a form of comparison,” Velazquez said, adding that those samples will also be analyzed. “We want to compare not only how the conditions in Middle Island Sinkhole are changing through time, but also Lake Huron, in general.”

Howard explained the purpose of this research.

“One aspect of it is that, because we have been sampling here for a long time, anoxic sediments are generally thought of as preserving climate signals and signals of life really well, because stuff doesn’t decay very well when there’s no oxygen, because a lot of the organisms that might be eating all of that organic matter can’t live down there because there’s no oxygen,” Howard said. “Looking at Middle Island Sinkhole, because we have these year-upon-year samplings, we can look at how things are changing, and how that’s being influenced by the lake as a whole. It’s potentially got better preservation of it than you might get where there is oxygen and where you have worms and shellfish mixing up the sediments a lot more. So you can look at how those climate and environmental signals are changing through time.”

Howard added: “We have pretty consistent sediment coring since around 2012.”

Stephanie Gandulla, resource protection coordinator with Thunder Bay National Marine Sanctuary, talked about the importance of that research being done in the Sanctuary.

“The Sanctuary is always excited to facilitate different kinds of science out here in Lake Huron,” Gandulla said. “Scientists from all over the world have been drawn to the unique environment in the Middle Island Sinkhole since the Sanctuary’s designation. What Cecelia and Diana and their colleagues’ work is doing is really putting Alpena and the Sanctuary on the map as a place to do cutting-edge science.”

Darby Hinkley is Lifestyles editor. She can be reached at 989-358-5691 or dhinkley@thealpenanews.com.