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OXYGEN REGIMES IN ESTUARIES: IMAGING ANOXIA THROUGH NORMOXIA
Citation:
Cicchetti, G, L Coiro, J S. Latimer, W Nelson, B J. Bergen, AND S Rego. OXYGEN REGIMES IN ESTUARIES: IMAGING ANOXIA THROUGH NORMOXIA. Presented at Sediment Profile Imaging Colloquy of Experts, Galway, IR, April 7-9, 2004.
Description:
The U.S. EPA, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, is developing empirical stressor-response models linking nitrogen loading to near-bottom dissolved oxygen (DO) concentrations in semi-enclosed coastal systems. Sediment profile cameras offer many advantages when used as a proxy for direct measurements of near-bottom DO in these models. Sediment profile camera metrics integrate oxygen regimes over time, and allow wide spatial coverage via rapid sampling and analysis. But, sediment profile image measures have not previously been directly or quantitatively linked to near-bottom oxygen regimes in our geographic area. Therefore, prior to using this technique as a regulatory tool, we set out to quantify and verify the relationships between measured near-bottom DO and sediment profile camera metrics in shallow estuarine soft sediments of the Northeast United States. We designed and built a camera system consisting of a camera frame, a 27-degree prism, and a 1.4 megapixel digital camera that records directly onto a laptop computer through 120 feet of firewire cable. We captured sediment profile images biweekly at four continuously monitored DO logger stations in Narragansett Bay between July and November 2002. These stations spanned a range of sediment types and oxygen regimes. We used Nilsson and Rosenberg's "BHQ" method of sediment profile image analysis, and found that these camera measures (BHQ) reliably tracked DO over time. The best correlations were found when DO was evaluated 1) as the percent of time under or over a hypoxic threshold, and 2) over time scales of three weeks or more (by examining DO regimes over the time period preceding each camera deployment). The camera was effective at identifying stations that had experienced high or low DO regimes over the preceding three weeks across a wide range of sediment types. Based on these data, we submit that sediment profile camera imagery can be a useful tool for environmental managers interested in quantitative estimates of near-bottom DO regimes.