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Spatial and Temporal Monitoring of Dissolved Oxygen in NJ Coastal Waters using AUVs (Presentation)
Citation:
Adams, D., J. Kohut, AND R. Schuster. Spatial and Temporal Monitoring of Dissolved Oxygen in NJ Coastal Waters using AUVs (Presentation) . Presented at MARACOOS 2012 Annual Meeting, Baltimore, MD, November 01 - 02, 2012.
Impact/Purpose:
Presentation to MARACOOS on AUV monitoring
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 paper we will present the results from a series of missions deployed from 2010 through 2013. 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 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. 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 strongest gradients were observed across the thermocline with surface waters usually much more oxygenated than the bottom waters. These gradients were weaker closer to the coast and broke down following several strong wind events. In late August 2011 the strongest of these wind events observed by the glider, Hurricane Irene, tracked directly over the inner New Jersey Shelf. Prior to the storm passing, we modified the glider mission to maintain a cross-shelf line coordinated so that the glider was in deeper water at the peak of the storm. In so doing we were able to capture the evolution of the hydrographic and dissolved oxygen fields before, during and after the storm. Irene rapidly mixed the water column, dramatically changing the structure of the hydrography and DO. Since this 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 responses across the region.
