One of the most extensive manifestations of anthropogenic mismanagement of nitrogen is eutrophication of the northern Gulf of Mexico. Leaching and runoff transport excess agricultural fertilizer via the Mississippi River to the Gulf where phytoplankton multiply exponentially, then die and decay at the sea floor resulting in critically low dissolved oxygen levels. This hypoxia kills fish and other organisms creating so-called dead zones that can cover 6,000–7,000 square miles. Dead zone mitigation plans call for coupling management actions with enhanced monitoring, modeling, and research on nitrogen delivery to, as well as processing within, the Mississippi River. Native freshwater mussels are known to remove nitrogen containing algae and phytoplankton, but not enough is known about the behaviors of freshwater mussels or the impacts these behaviors may have on the aquatic nitrogen cycle.
Our vision is to create a living biosensor network of native freshwater mussels in a major river to monitor, comprehend, and ultimately model key components of the nitrogen cycle. Native freshwater mussels are a guild of long-lived, suspension feeding bivalves that perform important ecological functions in aquatic systems. Mussels can influence nutrient cycling, because they transfer nutrients from the water column to the riverbed. Nutrients excreted by mussels can stimulate primary and secondary production. Thus, in high mussel-density areas, mussels may cycle appreciable concentrations of nutrients—although this has not been explicitly tested.
Our multidisciplinary team is performing a series of laboratory experiments exploring the feasibility of using freshwater mussels as sensors. For sensing, we place Hall-effect sensors on mussels to monitor the rhythmic opening and closing of their valves (gape). One shortcoming of previous work is that mussels were monitored in artificial conditions: glued fast in laboratory flumes, or tethered in constrained settings. To overcome this shortcoming, our team has built a mussel microhabitat with a constant river water feed stock, solar simulator, and Hydrolab DS5 water chemistry sondes equipped with chlorophyll a, ammonia, nitrate, temperature and dissolved oxygen sensors. A main thrust of our work is to develop the technology to monitor mussel gape untethered/wirelessly using inexpensive, unlicensed radios and wireless sensor network concepts. If successful, this will enable us to monitor mussels untethered in their natural environment.