Elizabeth Creech, MESc ’17, spent her summer knocking on doors. Ranging through Connecticut, Massachusetts, and Vermont, she asked landowners if she could take pictures of the sky from the middle of their streams. Creech studies how much light strikes the waterways—but in order to push the science forward she needed to convince landowners to let her into their water.
Creech, a recipient of a 2016 YIBS Master’s Research Grant, has 81 sites distributed through the three states: she won over dozens of residents. “I got into some really interesting discussions with farmers who were dubious about letting a Yale researcher onto their land. But they did seem to be interested in this idea that letting more light in or less light in could change what’s happening in the water.”
Rightly so. In many ways, light drives and defines the processes that take place in stream water. It fires the biological activity, it fires the decomposition of organic matter. It affects water temperature. These events and conditions tie into nutrient, and oxygen, cycling. Light influences entire food webs—as well as the lands downstream.
To help clarify these relationships, Creech set out to relate the amount of light hitting a stream with its size and bankside vegetation. She started with theory, moved to application, and then began site visits.
Trees, Creech knows, often catch light before the stream. “Really it’s the trees that affect the light, not the stream, the stream just happens to be there.” To prove the point, she needed a wide variety of sample sites.
“I said, ‘I want to find agricultural land, I want to find urban land, I want to find two distinct tree covers.’” And, she added, “I wanted them for specific stream orders, first through fifth.” Streams that range in size from small headwaters to watercourses just shy of rivers.
“I did a lot of mapping, looking at stream order, and I’d pull a location directly into google earth to see if it was accessible.” Then Creech drove north from New Haven to start her door-to-door campaign.
It took repeated effort to hone her technique. “I got rejected a few times. I said, ok, I need to read my person.” Creech talked water quality with some urban landowners, and mapping with some rural ones. She enjoyed a long conversation about beaver control. She walked through parks and waded through mud. More than people challenged her.
“A favorite site of mine was an ag site in northern Connecticut where a very nice woman let me into her cow pasture to take measurements at the stream running through it. The cows were fascinated by what we were doing. It was hard to get clear measurements at times because they were in the Pathfinder’s reflection or the PixPro’s view.” She needed measurements of light blocked by trees, not bovines.
To evaluate the light at each stream, Creech used tools that capture fisheye images of what lies above. She set up instruments—a PixPro camera and a reflecting tool called a Solar Pathfinder—at three points across the streams. She took shots from each bank and, wearing chest-high waders, placed the instruments upright in the center of the stream. The pictures she took of New England’s sky comprise her data.
The information, Creech thinks, could contribute to improving our knowledge of stream nutrient cycles.
“We know that organic matter in streams will decompose in two ways: it’s decomposed biologically and it’s decomposed with light. And though there are equations out there, we’re not sure how complete they are across stream types.” Creech works under the supervision of her advisor Dr. Peter Raymond in the Raymond Biogeochemistry Lab. He and his students study nutrient and carbon cycling in freshwater and coastal systems.
“We’re thinking that this data is going to be applied to better the scientific understanding of how light interacts with organic material in a stream. And how much of that breakdown of the organic material is done by the light.” Better, and more, data to improve the science.
Creech hopes to build a model that predicts light by stream size and vegetative setting. “My job, my piece of the puzzle, is really just to see if we can write a model.”
“If you know the order of a stream and you know the type of vegetation, do you know how much light is going to get through—is it predictable, or is it more complicated?”
Knowing how light works in a stream informs our understanding of the ecosystems within and around them. Eventually, the science may inform management by Creech’s landowners.
She noted that the process is collaborative. Other students in the Raymond lab work on the biological modeling. Creech brings the light.