Mussels Serve as Water-Quality Sensors
Why would a mollusk wear a backpack?
For decades, IIHR has had a love affair with the freshwater mussel. Once students dig their first mussel from the Mississippi River mud, they are hooked. IIHR researchers have led countless mussel-based research projects, including efforts to re-establish endangered species in Midwestern rivers. At LACMRERS, a display of more than 40 different mussel species takes pride of place in the front lobby.
But why this special attraction to freshwater mussels? Well, says IIHR Research Engineer Anton Kruger, they are extraordinary creatures, and highly underestimated as well.
Mussels are filter feeders, and some species can live for 75 years or more. They move about and have preferences about where they choose to settle. Mussels draw in river water and pump it through their systems, filtering out nutrients. A large mussel bed, which can number in the millions, filters a lot of water. “They actually filter the amount of water that a major city, like Minneapolis, consumes on a daily basis,” Kruger explains.
All this has led to the question, what effect do mussels actually have on water quality?
Mussels with Backpacks
Kruger is leading a research project that aims to use mussels as water-quality sensors, equipping each mussel with a small “backpack” of electronic sensors to remotely transmit data at regular intervals. Funded by the Roy J. Carver Charitable Trust and IIHR, the project has developed into a true passion for Kruger.
“I am captivated with the idea of getting a backpack on a mussel,” he says.
Kruger, who is also an associate professor of electrical and computer engineering, says he and his team hope to create a remote wireless sensor network on the backs of the mussels in order to learn more about the nitrogen cycle in the river water. “The driver behind all this is the nitrogen cycle,” Kruger explains. Excess nitrates unintentionally exported from agricultural states in the Midwest to the Gulf of Mexico lead to algae blooms that deplete oxygen in the water and create the “Dead Zone.”
Friends and Collaborators
The concept of teamwork is an important one for Kruger. Each individual contributes essential skills and knowledge, and the project offers many opportunities for collaborations across disciplines. Besides Kruger, the team includes:
- IIHR Assistant Research Engineer Craig Just, an environmental engineer and assistant professor of civil and environmental engineering, with a strong interest in the nitrogen cycle in rivers and streams;
- Teresa Newton, a fishery biologist with the United States Geological Survey (USGS) and an expert on mussels;
- Nate Young, also an IIHR research engineer, who has a long-term interest in mussels;
- Postdoc Jim Niemeier, whose expertise in electronics and wireless sensor networks, combined with his approachable, easygoing personality, make him a go-to guy for students;
- Senior electrical engineering student Hannah Taylor, who designs and assembles the electronics;
- Gabriel Hart, a student and certified scuba diver, who tests the sensors in the UI diving pool;
- Jonathan Durst, who helped design and build the mussel microhabitat;
- Other students who designed enclosures for the electronics; and
- ECE faculty Raghu Mudumbai and Soura Dasgupta and their students.
This team has developed a nice synergy, Kruger says, and students play an important part in the research. Senior Hannah Taylor says she really likes being a part of the project, although it’s not always easy to explain to her friends. “When I say I put sensors on mussels, they all think I mean muscles,” she says. “They look at me like I’m insane.”
The backpack itself, which Taylor designed, contains all the electronics needed to make the measurements, as well as a small radio, but it is no bigger than a stack of quarters. Researchers glue the backpack to the mussel’s shell, and release the animal back into the river. No wires restrict the mussels’ movements. The goal is to make the sensors so inexpensive that they could be disposable.
The backpack-wearing mussels are currently still in a laboratory microhabitat, with pumps to bring in fresh river water and lights to create artificial day-night cycles. Cameras track the mussels’ every move. When the researchers are ready, they will release the mussels back into the Iowa River, where they can roam free.
The mussels chosen for the project are a large species known as “pocketbook” mussels. “We want a big mussel, so the backpack doesn’t impact them,” Kruger explains. “We don’t want to take a baby and weigh it down.” The team has designed a study to determine whether or not the backpacks affect the mussels’ behavior. So far, the answer seems to be no, although the study is ongoing.
The trickiest part of the equation is powering the sensors. Most batteries would die within a year, and researchers hope to gather data for five years or more. Another plan was to use the movement of the water to power the electronics. That, too, failed.
“Mussels don’t like fast-moving water,” Kruger explains. “They like to stay where there’s some water movement, but not too much, so that works against us.”
The most promising idea uses ions in the river water itself to power the instruments. Scientists place two dissimilar metals in the water, which generate a small current that can be put to use. Kruger says they initially planned to use copper and zinc — two inexpensive and easily obtainable metals. Luckily, mussel expert Teresa Newton cautioned against the use of copper, which is toxic to mussels. She potentially saved the team considerable wasted effort, Kruger says.
“When you know just enough to get yourself into trouble, then you talk to an expert,” he says.
Kruger says he is no expert, but he does love his mussels. “I’m quite fascinated by them,” he says.
Along with the rest of the team, he is part of a longstanding tradition at IIHR, where researchers are happy as clams to be working with mussels.