Apr 27, 2016In Iowa, more than 2 billion pounds of nitrogen fertilizer are used to grow corn, and roughly 20 percent of the nitrogen, in the form of nitrate, runs off into lakes and rivers. Nitrate is food for the algae and plankton that live in these waterways, leading to excessive growth of these organisms. After they die, the decomposing organisms deplete the water of oxygen, killing fish.
Two University of Iowa colleagues—Anton Kruger, professor of electrical and computer engineering, and Craig Just, assistant professor of civil and environmental engineering—were discussing how to monitor the impact of nitrate in the Iowa River and reduce the amount of nitrate that flows down into the Mississippi Delta. They decided to equip freshwater mussels, which consume algae and phytoplankton, with tiny sensors and radio transmitters and use them to monitor the health of Iowa rivers. They also wanted to show that mussels can help remove nitrate from the water. The mollusks' excrement contains ammonia and urea; the urea more readily deposits to the riverbed than the water, Just says, and bacteria convert the ammonia into nitrogen gas that bubbles harmlessly to the surface.
For the study, a team of students attached a magnet to one side of each mussel's shell and a sensor connected to a wireless transmitter to the other side. The tiny battery-powered sensor can detect changes in the magnetic field each time a mussel opens and closes its valve. If the valve opens and closes more often, it means there is more food in the water, which could mean more nitrate.
The data was sent via a radio transmitter to a base station. The team used radios that operate in the 400 MHz range, and can transmit 10 feet or so in the river.
The researchers hope to obtain funding to develop the prototype sensors into ad hoc mesh networks that could communicate with receivers on buoys, so the data could be relayed by a Wi-Fi or cellular network to researchers in the lab. If they can show the mussels improve the water quality, they might be able to convince government agencies and businesses to help restore the freshwater mussel population, which is an endangered species. "The mussels are analogous to the canary in the coal mine," Kruger says. "If they are healthy, the water is healthy. If they are not doing well, then you know there is a problem."