A magnetic sensor for predicting seafloor oxygen depletion

In aquatic environments receiving high input rates of organic matter (e.g., intensive mariculture, domestic sewage outfalls, dredged material/industrial waste disposal), the ability to monitor sediment oxygen demand ( = SOD) associated with detritus breakdown is critical. Certain species of bacteria are magnetotactic and microaerophilic, and tend to thrive in the redox boundary layer ( = RPD) of aquatic sediments where they secrete intracellular magnetite (Fe₃O₄) particles. These particles posses single domain magnetic properties and are only secreted when the interstitial porewater contains 3-5% dissolved oxygen. The ability to measure the magnetic signal ( = magnetometry) from ambient populations of such magnetic bacteria would allow the relative position of the RPD within the sediment column to be determined over long periods of time. A magnetic sensor is superior to redox probes as electrodes tend to become chemically contaminated and microbially 'fouled' when left in the sediment for a long period of time. A magnetometer has been developed and validated that will register the relative position of the RPD in marine sediments as inferred from the presence of ambient populations of magnetotactic bacteria. The sensor system consists of the following integrated elements: Bacterial magnetic field detection - Signal amplification - Electronic signal to noise reduction/filtration - Signal transformation - Data read out/storage. It is proposed that this device can be used either as a surveying tool or deployed as a full time alarm emplacement alerting to high instances of SOD and associated overlying water column hypoxia. The ability to predict water column hypoxia is especially critical for the protection of fisheries and mariculture activity.