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Environmental Monitoring


March 2011 Issue

Stereo Vision System Provides Precise Way to Monitor Waves
Engineers have created a new type of stereo vision to study ocean waves as they pound against the shore, providing a better way to understand and monitor this violent, ever-changing environment. The approach, developed at Oregon State University (OSU), uses two video cameras to feed data into a computer system that can observe large areas of ocean waves in real time and help explain what they are doing and why.

'We're trying to achieve with cameras and a computer what human eyes and the brain do automatically—see the way that near-shore waves grow, change direction and collapse as they move over a seafloor that changes depth constantly,' said David Hill, an associate professor of coastal and ocean engineering at OSU.

This is the first attempt to use stereo-optical imaging in a marine field setting on such a large scale, Hill said, and offers the potential to provide a constant and scientifically accurate understanding of what is going on in the surf zone. It is also a form of remote sensing that does not require placement of instruments in the pounding surf environment.

Hill said recent advances in computer science made it possible to incorporate and make sense out of what a dynamic marine environment is doing at the moment it happens.

'A wave is actually a pretty difficult thing for a computer to see and understand,' Hill said. 'Some things like speed are fairly easy to measure, but subtle changes in height, shape and motion as the waves interact with a changing ocean bottom, wind and sediments are much more difficult.'

Researchers at OSU and the Technical University of Delft in The Netherlands published their research in Coastal Engineering.

Gulf Dispersant Study Suggests Prolonged Deepwater Fate
To combat last year's Deepwater Horizon oil spill, nearly 800,000 gallons of chemical dispersant were injected directly into the oil and gas flow coming out of the Macondo wellhead. Scientists report that a major component of the dispersant was contained within an oil-and-gas-laden plume in the deep ocean and had not degraded three months after it was applied.

While the results suggest the dispersant did mingle with the oil and gas flowing from the mile-deep wellhead, they also raise questions about what impact the deepwater residue of oil and dispersant might have had on the environment and marine life.

The study, published in Environmental Science — Technology, is the first peer-reviewed research published on the gulf spill dispersants.

'The results indicate that an important component of the chemical dispersant injected into the oil in the deep ocean remained there and resisted rapid biodegradation,' said University of California, Santa Barbara, geochemist David Valentine, whose team collected the samples for Woods Hole Oceanographic Institution chemist Elizabeth B. Kujawinski.

Kujawinski and the other researchers found one of the dispersant's key components, dioctyl sodium sulfosuccinate (DOSS), was present in May and June in parts-per-million concentrations in the plume from the spill more than 3,000 feet deep. The plume carried the DOSS in a southwest direction, where it was detected at lower (parts-per-billion) concentrations in September.

'Over 290,000 kilograms ... of DOSS was injected into the deep ocean from April to July,' Kujawinski said. 'That's a staggering amount, especially when you consider that this compound comprises only 10 percent of the total dispersant that was added.'

Using a new, highly sensitive chromatographic technique, Kujawinski reports those concentrations of DOSS indicate that little or no biodegradation of the dispersant substance had occurred. The deepwater levels suggest any decrease in the compound could be attributed to dilution. They found further evidence that the substance did not mix with the 1.4 million gallons of dispersant applied at the ocean surface and appeared to have become trapped in deepwater plumes of oil and natural gas.

Though the study was not aimed at assessing the possible toxicity of the lingering mixture—Kujawinski said she would 'be hard pressed to say it was toxic'—it warrants toxicity studies into possible effects on corals and deep-water fish such as tuna, she said. The Environmental Protection Agency and others have already begun or are planning such research, she added.

Kujawinski cautioned that 'we can't be alarmist' about the possible implications of the lingering dispersant. Concentrations considered 'toxic' are at least 1,000 times greater than those observed by Kujawinski and her colleagues, she said. But because relatively little is known about the potential effects in the deep ocean, she added, 'we need toxicity studies.'

Digital Images of Humboldt Bay and Eel River Estuary Available
New full-color, digital aerial photographs and benthic habitat maps of Humboldt Bay and Eel River Estuary are now publicly available through California Sea Grant and NOAA Coastal Services Center's Digital Coast.

The images, all orthorectified and geographic information system-compatible, provide the first detailed (0.5-meter resolution) inventory of the region's intertidal and subtidal bottom habitats, such as tidal mud flats, salt marshes and eelgrass meadows.

The imagery was collected with the goal of furthering ecosystem-based management of the bay, while addressing specific topics of interest such as endangered species conservation, nonnative species control, wetlands restoration and climate change adaptation, as part of the Humboldt Bay Initiative.

The geosciences company Photo Science (Oakland, California) that collected the aerial images waited nearly three years for the requisite weather and tidal conditions. One constraint that made the project such a painstaking process was the need to capture images during an extreme low tide, in order to expose normally submerged vegetation and substrate.

The scientists also preferred surveying the bay and estuary in summer when plant growth is at or near a seasonal maximum. In addition, the photos had to be taken in the morning and with clear skies and calm winds (no small feat in fog-soaked Humboldt).


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