Trout Lake Research Rewind: Monitoring Macrophytes & Crushing Chlorophyll

by Riley Steinbrenner

Week Eleven

After spending the first part of their summer working with the Citizen Lake Monitoring program—which recruits lakeside-dwelling citizens to monitor water clarity using a Secchi disk—the Aquatic Invasive Species crew have spent their last few weeks recording plant populations on surrounding lakes by taking point-intercept surveys, or sampling at predetermined GPS locations based on a lake’s littoral (near shore) zone, depth and surface area. With a completion rate of two days per lake, the crew has completed surveying eleven lakes, and have one more left for the summer.
I joined AIS crew on their second day of surveying Little Bearskin Lake in Hazelhurst. Linden and Rosie raked each point at a depth of 15 feet, identifying every aquatic plant species they pulled up. Carol also recorded the depth, dominant sediment type where the plants were taken from and the density of each plant caught on the rake using a number scale system, as well as visual sightings of aquatic plants spotted nearby but not caught on the rake. These PI surveys are important in monitoring the aquatic-plant densities on lakes, especially if they contain invasive species like Eurasian Watermilfoil.
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Week Twelve

Back when undergrads Camryn Kluetmeier and Sydney DeMets of LTER base crew sampled Trout Tower, one of the samples they collected was chlorophyll—the pigment in aquatic plants like algae that makes them green. They do this by running a lake’s water into a tube and then through a paper filter that catches the microscopic chlorophyll pigments.
My last week on station, I joined Camryn in the “chloro room”—a dark room in the basement of station—to see just how they take these samples to measure the “green-ness” of lakes. For the next two days, Camryn would be running the samples from FLAMe (Fast Limnological Automated Measuring), another crew on station that samples on several lakes in the area. On Monday, Camryn started by taking a test tube with the chlorophyll-saturated filter paper and methanol—a preservation solution—and grinding it in a machine that frees the chlorophyll out of the plant cells. Plants, like humans, have cells that make up its tissue, so in order to release the pigment that makes it green, the cells have to be broken up. Then, she placed the test tubes of crushed filter paper, freed chlorophylls and methanol in a fridge for preservation.
The next day, Camryn began the steps to measure the green-ness!.The big question of the day would be: Which of the lakes the FLAMe crew sampled were the most green? Each test tube contains the crushed chlorophyll from a different lake, but the first thing Camryn had to do was run them through a centrifuge. A centrifuge is a machine that spins at 3,000 rotations per minute and separates the methanol and chlorophyll solution—the part Camryn wants—from the loose pieces of filter paper still inside the test tube. Next, she pipetted the methanol/chlorophyll solution from each test tube into a different test tube. Camryn put each of these inside of a spectrophotometer, which blasts light through the solution. Since chlorophyll is green, it reflects green wavelengths—all others color, like red, are absorbed. This is how Camryn measures the green-ness of the samples, by seeing which absorbed the most amount of red wavelengths of light—that is what the spectrophotometer measures.
Observing the computer screen attached to the spectrophotometer, Camryn pointed out the seven lines that indicate the seven different lakes that FLAMe crew sampled from. The taller the lines peak, the more red wavelengths it absorbed. That means this lake was the most “green”—or contained the most aquatic plants like algae—compared to the rest of the sample lakes.
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