No abstract

The growth of aquatic insects in a small mountain stream was studied with emphasis on water temperature. Growth of the five dominant species was examined in relation to degree-days. This measure accounts for time and the minimum temperature necessary for insect growth. All species showed reduced specific growth rates with lower temperatures, but some (Ephemerella dorothea, Leuctra tenella, Nemoura wui) did not stop growing at even the lowest water temperatures. Both Diplectrona modesta and Paraleptophlebia assimilis had minimum growth temperatures. Studies demonstrated that the growth of stream insects is directly proportional to the number of degree-days experienced by a population.

Chemical beach cleaners can facilitate cleanups of oiled shorelines by improving the efficiency of washing with water. The improvement is a result of reduced adhesion of the oil coating, which makes it easier to remove from shoreline surfaces, thereby reducing washing time and lowering the temperature of the wash water needed to clean a given area. The criteria established for use of chemical beach cleaners in the Exxon Valdez spill cleanup included demonstrating enhanced cleaning with low levels of toxicity to marine biota and with minimal oil dispersion. Since no commercially available products satisfactorily met these criteria for use in Alaska, a new product, Corexit 9580, was specifically developed in response to this need. This paper describes the successful development of this chemical, including both laboratory testing and field testing in Prince William Sound.

On November 11, 2005, the double-hulled tank barge (TIB) DBL 152 struck the submerged remains of a drilling platform that collapsed during Hurricane Rita in the northwestern Gulf of Mexico. The allision and eventual capsize of the barge caused the release of approximately 1.9 million gallons of low-API gravity slurry oil, which sank to the seafloor. Throughout the response, information on the concentration of submerged oil (volume per unit area) was sought to prioritize cleanup of multiple sunken oil patches. Numerous methods were employed to detect and assess submerged oil including, among others, divers to measure oil thickness and chain-weighted sorbent drags to delineate patch size. However, none of the techniques used were able to quantify the percent cover of oil, which emerged as a critical parameter for estimating oil concentrations. This paper presents the methodology for quantifying percent cover of submerged oil used during the long-term monitoring phase of this incident. Orthographic (downward-looking) images of the seafloor were obtained using an underwater drop camera. Full-motion video was digitally recorded using a laptop computer and video capture hardware. Imagery was georeferenced by overlaying GPS coordinates onto the streaming video using a video annotator. Still images were extracted from the video using frame-grabbing software during post-processing. Percent cover of oil was then manually determined for each image using two different methods: ocular estimation and point counts. Seafloor imagery was acquired at discrete sample points along drift transects, and when visibility allowed, continuously between sample points. Percent cover data obtained using these techniques, combined with oil thickness measurements and patch size information obtained using other methods, was used to estimate the volume of oil present within a discrete patch of submerged oil discovered in September 2006. Successful application of this technique demonstrated its viability as a cost-effective means of obtaining quantitative information about percent cover of submerged oil. Moreover, this relatively low-tech system was comprised primarily of off-the-shelf components that can be readily sourced, assembled and mobilized to a submerged oil spill response area.

A variety of methods and equipment were employed during the response and long-term monitoring phases of the DBL 152 incident to locate, track and quantify the nearly 2 million gallons of low-API gravity oil that sank in the western Gulf of Mexico approximately 30 nautical miles off the coast of Cameron, Louisiana. Methods and equipment used to survey submerged oil included: divers; stationary snare sentinels; chain-weighted snare drags using devices known as vessel-submerged oil recovery systems or V-SORS; remotely operated vehicles (ROVs), underwater video drop camera, sled-mounted towed video, side-scan sonar and Rox-Ann sonar. This paper will describe each method and associated equipment and its specific application to submerged oil detection and assessment for this incident. It will also explore the evolution and refinement of approaches used throughout the course of the response and the underlying rationale for these changes. Guidelines and relevant considerations for selecting among these methods will be suggested. Finally, strengths and limitations of each approach will be discussed with the goal of capturing and communicating the lessons learned so that future submerged oil response efforts may benefit from the practical experience gained during the DBL 152 response.