Networked sensors provide reliable method for monitoring wetlands
Researchers and resource managers have long found it challenging to monitor frequent chemical changes in coastal wetlands because of the sporadic nature of traditional sampling techniques. When all samples are dependent on the researchers’ availability to be onsite, it can be difficult to catch the regular or episodic fluxes in and out of the ecosystem. The resulting under-sampling limits our understanding of processes and complicates the communication of results to information users, such as scientists, regulators, and the coastal community, because of the inevitable uncertainties that are always included.
To meet this challenge, MBARI’s Chemical Sensor Lab, led by Ken Johnson, designed the Land/Ocean Biogeochemistry Observatory (LOBO)—a network of sensors that continually collects data and relays the data back to shore in near real-time. LOBO includes an array of moorings deployed in the Elkhorn Slough National Estuarine Research Reserve.
The moorings are designed to monitor the concentration of nutrient chemicals, such as nitrate and phosphate, that pass from the agricultural lands of the Salinas Valley into Monterey Bay by way of the slough. Other sensors, including those measuring dissolved oxygen and chlorophyll, are used to assess the rates of respiration and photosynthesis by water column and benthic organisms in response to the nutrient flux.
The combination of complex estuarine characteristics, anthropogenic impacts, and many nutrient sources make Elkhorn Slough a challenging environment to accurately characterize biogeochemical processes using traditional monitoring methods. Therefore, the slough is an ideal place to demonstrate the potential of in situ nutrient sensor networks as an important new direction of the aquatic sciences.
Nitrate sensors in the LOBO array reveal a persistent nitrate concentration increase that spans two orders of magnitude from the already rich waters of Monterey Bay to the tidal region of the Old Salinas River Channel. The nitrate concentrations in the old river channel are at nearly 100 times higher than the largest values found in the ocean. The extreme nitrate levels in runoff that enters Elkhorn Slough fuels such high primary production rates that shallow slough ponds have been described as “hyper-ventilating.”
During daylight, photosynthesis raises oxygen to levels that are supersaturated as much as 200 percent, while respiration during the dark can deplete nearly all the oxygen from the system. Sensor nodes are placed closely together so that the propagation of these environmental signals can be monitored at multiple locations, and the biogeochemical processes that drive these transformations can be quantified.
The overarching goal of the LOBO project is to demonstrate that significant synergies accrue from operating a complete network of autonomous, biogeochemical sensors for extended periods. In this sense, the sensors and observing system are a pilot study for larger projects that are envisioned by the ocean community. The ability to study the interactions of the hydrological cycle, nutrient chemical cycles and human alterations of these cycles at the land/ocean boundary is a fundamental component of coastal zone management. The data collected by the observatory will be used by scientists from many institutions to study issues such as water quality, habitat, biodiversity, and invasive species in Elkhorn Slough.
This experiment is co-funded by the National Science Foundation BioComplexity in the Environment Program. The LOBO system has also been licensed to Satlantic, Inc., which has deployed LOBO networks in California, Florida, Oregon, and Nova Scotia. These networks form the backbone for a North American coastal observing system.
MBARI contributors to the LOBO project: Ken Johnson, Luke Coletti, Virginia Elrod, Steve Fitzwater, Hans Jannasch, Todd Martz, Joe Needoba, Josh Plant, Carole Sakamoto (with special thanks to the Moss Landing Marine Laboratories operations group.)