Sanctuary Integrated Monitoring Network
Monitoring Project

Land/Ocean Biogeochemical Observatory (LOBO)

Principal Investigator(s)

  • Ken Johnson
    Monterey Bay Aquarium Research Institute
  • Stephen Monismith
    Stanford University
  • Adina Paytan
    Stanford University
  • Marc Los Huertos
    University of California, Santa Cruz
  • Kerstin Wasson
    Elkhorn Slough National Estuarine Research Reserve
Start Date: October 27, 2003
End Date: July 31, 2008

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.

The first LOBO node is a mooring deployed in the main channel of the Sloughbetween the Hwy 1 bridge and Seal Bend. This node was deployed on October 27, 2003.

LOBO is supported by a BioComplexity Grant (ECS-0308070) from the National Science Foundation and by MBARI through a Grant from the David and Lucile Packard Foundation. The project will run through July 2008.

Summary to Date

The Relationship Between Nitrate Concentration and the Tidal Cycle

The nitrate concentration in Moss Landing Harbor and at the L01 mooring provides an illustration of how the tidal cycle creates significant changes in water properties of the main channel of Elkhorn Slough. Changes in nitrate, salinity, and temperature record the different water masses that pass the L01 mooring. Hypersaline water from the upper slough can be seen at low tide, while the incoming tide brings nitrate into the slough.

At least two different end-members contribute to the nitrate concentration of the water during the incoming tide. The first is via internal waves that bring deep, nitrate rich water from Monterey Bay to the near-shore surface, which is then advected into the slough with the tidal bore (Chapin et al, 2004). This water mass can be detected from the low temperature signal. The second is via the Old Salinas River that enters the South end of Moss Landing Harbor. The nitrate concentrations in these waters can be as high as 1500 ÁM. The high nitrate, low salinity waters are mixed with the incoming tide water, and exit on the following ebb tide. These waters reach the mouth of Elkhorn Slough during low tide, where they are mixed and transported up the main channel during the next flood tide.

Figures associated with this case study can be found at the LOBO website:

Study Parameters

  • N
  • Nitrates
  • P
  • Temperature
  • Salinity
  • Phosphate
  • Inorganic carbon
  • Precipitation

Figures and Images

Figure 1. The first mooring node was placed in Elkhorn Slough in October 2003.

Figure 2. Each mooring node is outfitted with several chemical sensors in addition to basic physical sensors. Sensors will monitor several variables, including phosphate, ammonia, iron, temperature, depth, salinity, and currents.

Figure 3. The mooring node is autonomous and can operate at near real-time for 3 to 4 months. Data are transmitted back to MBARI using a wireless Local Area Network (LAN).

Figure 4. Nitrate concentrations measured with an In Situ Ultraviolet Spectrophotometer (ISUS) developed at MBARI. Water depth and two salinities are also plotted.