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Monitoring Dissolved Oxygen in New Jersey Coastal Waters Using Autonomous Gliders
Citation:
Kohut, J., C. Haldeman, AND J. Kerfoot. Monitoring Dissolved Oxygen in New Jersey Coastal Waters Using Autonomous Gliders. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-13/180, 2014.
Impact/Purpose:
The coastal ocean is a highly variable system with processes that have significant implications on the hydrographic and oxygen characteristics of the water column. The spatial and temporal variability of these fields can cause dramatic changes to water quality and in turn the health of the ecosystem. While low Dissolved Oxygen (DO) concentrations are not uncommon in the coastal ocean, what is less understood is how the location and size of these low DO regions vary and what impact that variability has on ecosystem health. Therefore alternative sampling strategies are needed to continuously map these low DO areas in a way that quantifies this variability. This project applies a series of Autonomous Underwater Vehicle (AUV) deployments from Sandy Hook to Cape May, NJ to address this need by mapping the subsurface DO concentration in near real-time within the near coastal ocean.
Description:
The coastal ocean is a highly variable system with processes that have significant implications on the hydrographic and oxygen characteristics of the water column. The spatial and temporal variability of these fields can cause dramatic changes to water quality and in turn the health of the ecosystem. While low Dissolved Oxygen (DO) concentrations are not uncommon in the coastal ocean, what is less understood is how the location and size of these low DO regions vary and what impact that variability has on ecosystem health. Therefore alternative sampling strategies are needed to continuously map these low DO areas in a way that quantifies this variability. This project applies a series of Autonomous Underwater Vehicle (AUV) deployments from Sandy Hook to Cape May, NJ to address this need by mapping the subsurface DO concentration in near real-time within the near coastal ocean. The long endurance capability combined with the required sawtooth pattern propulsion make the glider an ideal platform for continuously mapping sub-surface ocean conditions at high resolution and in near real-time. In this project we completed 6 glider missions along the New Jersey coast in 2011 and 2012. Each glider was specifically setup to complete these nearshore missions that focus the monitoring specific to the needs defined by the Environmental Protection Agency (EPA) and the New Jersey Department of Environmental Protection (NJDEP). All the glider missions were completed in accordance to the operating procedures described in the Quality Assurance Project Plan (QAPP). The QAPP was approved by the project participants at EPA, Rutgers, and NJDEP. The document clearly states the pre- and post-deployment steps needed to ensure the quality of the data collected during each mission. By following these specifications we documented the required quality assurance steps for the AAnderra Optode, SeaBird CTD (pumped and unpumped) and the glider platform itself. The missions were carried out with a predefined path that was adjusted through consensus of the project partners (Rutgers, EPA, and NJDEP) to capture the variability in the magnitude and structure of dissolved oxygen patterns in the coastal ocean. Consistent with previous discrete sampling, each glider mission observed DO concentrations below 5 mg/L. These lower concentrations were limited to the bottom layer. The unique sampling provided through the glider AUV showed that the DO concentrations were highly variable in the vertical, horizontal, and through time. The scales of variability of the DO concentration observed over these two seasons were on the order of 60-80 km in space and 3-4 days in time. The strongest gradients were observed across the thermocline with surface waters usually much more oxygenated than the bottom waters. These vertical gradients were weaker closer to the coast and broke down following strong wind events. Since sampling was all done in real-time, the monitoring data was immediately available to NJDEP and EPA to inform their response to these events. Based on these missions, we have begun to sample the dynamic coastal ocean environment at the scales of known variability. The results show that while there are persistent patterns in the dissolved oxygen fields off our coasts, rapid changes can occur with varied effects across the region.