Researchers at the University of Iowa are recruiting an unusual test subject in their quest to reduce harmful nitrates in Midwestern waterways. Instead of humans, robots, or lab rats, the team is using freshwater mussels with 3D-printed backpacks to study the nitrogen cycle in the Mississippi River watershed area.
Nitrogen is a major issue in the area due to the agricultural application of fertilizers in Iowa and other nearby states. These nitrates enter local rivers, lakes, and streams, where they’re eventually carried to the Gulf of Mexico. This nitrogen loading can produce algal blooms as large as 6,000 square miles that deplete oxygen in the water and create dead zones that kill fish and other aquatic organisms.
Researchers are interested in mussels because of their unique role in the nitrogen cycle. They are filter feeders — taking in gallons of water each day, filtering out the nutrients, and then pumping the fluid out of their bodies. During this process, the bivalves remove excess nitrogen from the water column, preventing it from reaching the Gulf of Mexico and decreasing the likely hood of deadly algal blooms. A healthy population of mussels can transfer a large amount of nitrates out of a waterway.
In these studies, the University of Iowa are using the muscles as an indicator of declining water quality, a water-based version of the “canary in a coal mine.” The electronic mussel backpack will communicate one important piece of data to researchers — the real-time measurement of a mussel’s gape. The gape is the rhythmic opening and closing of the mussels valve, which remains regular unless there is a disturbance. When the gape patten changes, researchers will know there has been a disturbance in the environment. Each backpack will include a magnetic sensor to monitor the mussel’s gape, a microcontroller to manage data that is sent to researchers, a 3D-printed shell, and a battery to power the device.
The 3D printed backpack will transmit gape data for a year, after which it will become inert, remaining attached to the mussel but not interfering with its daily activities. The data collected in this single year will provide valuable insight into the mollusk lifecycle and the water quality of areas being studied. Researchers hope this information can be used to find solutions that will reduce harmful nitrates in Midwestern waterways.