Studies of complex, biogeochemical processes in oceans, lakes and rivers are often hindered by a lack of sensor systems that can be deployed for long-term, continuous observations. This is particularly true for chemical sensors. While a variety of chemical sensor systems have been demonstrated, there are few that can operate unattended for long periods (>3 months) in aquatic systems. Here, we propose to develop and refine a variety chemical sensor or sampler systems for extended endurance, autonomous observations. The operation of these instruments will be verified by deploying them in an experimental Land/Ocean Biogeochemical Observatory (LOBO) in the Elkhorn Slough National Estuarine Research Reserve (ESNERR) at the head of Monterey Bay. LOBO will be an array of moorings equipped with autonomous chemical and physical sensors and water samplers that will be operated in near real-time. A key element of this project will be verification of the long-term performance of the sensor systems by utilizing the observatory to perform fundamental observations of biogeochemical cycles. The initial operation of the observatory system will be demonstrated with two nitrate sensor systems, which we have developed, that can operate for 3 to 4 month periods without intervention. These sensors will be augmented with additional detection systems for phosphate, silicate, ammonia, iron, pH and CO2 that are in various stages of development. The observatory will consist of an array of 6 mooring 'nodes' deployed along a transect from the ocean into and along the channel of Elkhorn Slough. Each mooring will incorporate several chemical sensors, as well as basic physical (T, S, depth, Acoustic Doppler Current Profiler) sensors. In-situ water samplers will also be mounted on the moorings to collect samples for chemical concentration and isotope analyses that will allow us to independently validate sensor measurements and the biogeochemical processes that are inferred from the observations. A coupled hydrodynamic model of Elkhorn Slough will allow us to calculate mass balances and source and sink terms for chemical cycling. The sensor array will be linked to the Internet in near real-time through a wireless Local Area Network.
The work proposed here can be generalized to a broad range of coastal environments, many of which are subject to coastal environments. As such, our system should be considered a pilot project to assess the feasibility of operating biogeochemical observatories for scientific, environmental management and educational purposes. "The network is the sensor". Our goal is only met when we demonstrate this to be true with substantial and novel results that enhance our ability to study, manage and utilize ecosystems for education. In order to accomplish this, we must design a chemical sensor network that can operate continuously, remain in calibration, and assimilate data within short enough periods to facilitate focused studies and training exercises. Such a real time system will provide unique educational opportunities to inform the public about biogeochemical processes in the coastal zone, and will provide valuable data to be used for wetland management purposes.
