Potential impacts of offshore oil spills on polar bears in the Chukchi Sea

Sea ice decline is anticipated to increase human access to the Arctic Ocean allowing for offshore oil and gas development in once inaccessible areas. Given the potential negative consequences of an oil spill on marine wildlife populations in the Arctic, it is important to understand the magnitude of impact a large spill could have on wildlife to inform response planning efforts. In this study we simulated oil spills that released 25,000 barrels of oil for 30 days in autumn originating from two sites in the Chukchi Sea (one in Russia and one in the U.S.) and tracked the distribution of oil for 76 days. We then determined the potential impact such a spill might have on polar bears (Ursus maritimus) and their habitat by overlapping spills with maps of polar bear habitat and movement trajectories. Only a small proportion (1 -10%) of high-value polar bear sea ice habitat was directly affected by oil sufficient to impact bears. However, 27-38% of polar bears in the region were potentially exposed to oil. Oil consistently had the highest probability of reaching Wrangel and Herald islands, important areas of denning and summer terrestrial habitat. Oil did not reach polar bears until approximately 3 weeks after the spills. Our study found the potential for significant impacts to polar bears under a worst case discharge scenario, but suggests that there is a window of time where effective containment efforts could minimize exposure to bears. Our study provides a framework for wildlife managers and planners to assess the level of response that would be required to treat exposed wildlife and where spill response equipment might be best stationed. While the size of spill we simulated has a low probability of occurring, it provides an upper limit for planners to consider when crafting response plans

Validation of Oil Trajectory and Fate Modeling of the Deepwater Horizon Oil Spill

Trajectory and fate modeling of the oil released during the Deepwater Horizon blowout was performed for April to September of 2010 using a variety of input data sets, including combinations of seven hydrodynamic and four wind models, to determine the inputs leading to the best agreement with observations and to evaluate their reliability for quantifying exposure of marine resources to floating and subsurface oil. Remote sensing (satellite imagery) data were used to estimate the amount and distribution of floating oil over time for comparison with the model’s predictions. The model-predicted locations and amounts of shoreline oiling were compared to documentation of stranded oil by shoreline assessment teams. Surface floating oil trajectory and distribution was largely wind driven. However, trajectories varied with the hydrodynamic model used as input, and was closest to observations when using specific implementations of the HYbrid Coordinate Ocean Model modeled currents that accounted for both offshore and nearshore currents. Shoreline oiling distributions reflected the paths of the surface oil trajectories and were more accurate when westward flows near the Mississippi Delta were simulated. The modeled movements and amounts of oil floating over time were in good agreement with estimates from interpretation of remote sensing data, indicating initial oil droplet distributions and oil transport and fate processes produced oil distribution results reliable for evaluating environmental exposures in the water column and from floating oil at water surface. The model-estimated daily average water surface area affected by floating oil \u3e1.0 g/m2 was 6,720 km2, within the range of uncertainty for the 11,200 km2 estimate based on remote sensing. Modeled shoreline oiling extended over 2,600 km from the Apalachicola Bay area of Florida to Terrebonne Bay area of Louisiana, comparing well to the estimated 2,100 km oiled based on incomplete shoreline surveys

Photochemical oxidation of oil reduced the effectiveness of aerial dispersants applied in response to the Deepwater Horizon spill

Author Posting. © American Chemical Society, 2018. This is an open access article published under an ACS AuthorChoice License. The definitive version was published in Environmental Science and Technology Letters 5 (2018): 226–231, doi:10.1021/acs.estlett.8b00084.Chemical dispersants are one of many tools used to mitigate the overall environmental impact of oil spills. In principle, dispersants break up floating oil into small droplets that disperse into the water column where they are subject to multiple fate and transport processes. The effectiveness of dispersants typically decreases as oil weathers in the environment. This decrease in effectiveness is often attributed to evaporation and emulsification, with the contribution of photochemical weathering assumed to be negligible. Here, we aim to test this assumption using Macondo well oil released during the Deepwater Horizon spill as a case study. Our results indicate that the effects of photochemical weathering on Deepwater Horizon oil properties and dispersant effectiveness can greatly outweigh the effects of evaporative weathering. The decrease in dispersant effectiveness after light exposure was principally driven by the decreased solubility of photo-oxidized crude oil residues in the solvent system that comprises COREXIT EC9500A. Kinetic modeling combined with geospatial analysis demonstrated that a considerable fraction of aerial applications targeting Deepwater Horizon surface oil had low dispersant effectiveness. Collectively, the results of this study challenge the paradigm that photochemical weathering has a negligible impact on the effectiveness of oil spill response and provide critical insights into the “window of opportunity” to apply chemical dispersants in response to oil spills in sunlit waters.This work was supported, in part, by National Science Foundation Grant OCE-1333148, Gulf of Mexico Research Initiative Grants 015, SA 16-30, the DEEP-C consortium, and the Clark Family Foundation, Inc. EPA funding was provided to R.N.C. from the Oil Spill Liability Trust Fund

Oil fate and mass balance for the Deepwater Horizon oil spill

Based on oil fate modeling of the Deepwater Horizon spill through August 2010, during June and July 2010, ~89% of the oil surfaced, ~5% entered (by dissolving or as microdroplets) the deep plume (\u3e900 m), and ~6% dissolved and biodegraded between 900 m and 40 m. Subsea dispersant application reduced surfacing oil by ~7% and evaporation of volatiles by ~26%. By July 2011, of the total oil, ~41% evaporated, ~15% was ashore and in nearshore (\u3c10 m) sediments, ~3% was removed by responders, ~38.4% was in the water column (partially degraded; 29% shallower and 9.4% deeper than 40 m), and ~2.6% sedimented in waters \u3e10 m (including 1.5% after August 2010). Volatile and soluble fractions that did not evaporate biodegraded by the end of August 2010, leaving residual oil to disperse and potentially settle. Model estimates were validated by comparison to field observations of floating oil and atmospheric emissions

Recommendations for the advancement of oil-in-water media and source oil characterization in aquatic toxicity test studies

During toxicity testing, chemical analyses of oil and exposure media samples are needed to allow comparison of results between different tests as well as to assist with identification of the drivers and mechanisms for the toxic effects observed. However, to maximize the ability to compare results between different laboratories and biota, it has long been recognized that guidelines for standard protocols were needed. In 2005, the Chemical Response to Oil Spills: Ecological Effects Research Forum (CROSERF) protocol was developed with existing common analytical methods that described a standard method for reproducible preparation of exposure media as well as recommended specific analytical methods and analyte lists for comparative toxicity testing. At the time, the primary purpose for the data collected was to inform oil spill response and contingency planning. Since then, with improvements in both analytical equipment and methods, the use of toxicity data has expanded to include their integration into fate and effect models that aim to extend the applicability of lab-based study results to make predictions for field system-level impacts. This paper focuses on providing a summary of current chemical analyses for characterization of oil and exposure media used during aquatic toxicity testing and makes recommendations for the minimum analyses needed to allow for interpretation and modeling purposes.publishedVersio

Scaling restoration of American lobsters: Combined demographic and discounting model for an exploited species

Ecological theory does not currently allow precise predictions of the consequences of ecological restoration. Ecological restoration and species enhancement projects could be profitably used to test theoretically based predictions, but only if theory were first applied to develop quantitative predictions suitable for testing. Here, we review what is known about factors limiting population size and production of the American lobster Homarus americanus, and use that information to construct a demographic life-table model of population dynamics. We then use the model to evaluate alternative options for enhancing lobster population size and production. Because this species represents an example of a population subjected to intense human exploitation as a target of commercial fisheries, which has stimulated much research on its biology, demographic modeling is facilitated. Furthermore, intervention into the fishery provides a viable restoration option available only to exploited species. We apply the economic concept of discounting (of future pay-back in the form of restoration, analogous to being paid interest on a loan) to allow quantification of the scale of restoration needed to compensate for both the magnitude of the estimated loss of American lobsters and the time lags between loss and restoration following a major oil spill. Quantification of benefits is rarely performed for restoration projects to guide compensation for natural resource damages caused by environmental incidents. The methods and approach developed here can help address this past failure in order to provide compensating ecological and human services equal to those lost. The approach represents a significant step forward in conceptually and quantitatively addressing restoration needs. The methods may be applied to other species, especially those that are exploited by humans, but also others that can feasibly be restored to mitigate impacts of adverse environmental events

Restoration that targets function as opposed to structure: replacing lost bivalve production and filtration

ABSTRACT: Abundant suspension-feeding bivalves have a dominant organizing role in shallow aquatic systems by filtering overlying waters, affecting biogeochemical processing, and diverting production from the water column to the benthos. In degraded aquatic systems where bivalve populations have been reduced, successful restoration of ecosystem functions may be achieved by targeting the revival of bivalve populations. The ‘North Cape’ oil spill on the coast of Rhode Island (USA) provides an opportunity to demonstrate the feasibility of scaling bivalve restoration to meet quantitative goals of enhanced production. After this oil spill, mortalities of bivalves were estimated by impact assessment modeling of acute toxicity, and results were confirmed by comparisons with counts of dead and moribund animals on local beaches. Computation of lost bivalve production included future production expected from affected animals, had they lived out their expected life spans. This calculation of production forgone required a demographic model that combined age-specific mortality with individual growth. Application of this modeling approach to surf clams Spisula solidissima, the species that comprised 97% of the total loss of bivalve production from the spill, illustrates the detailed implementation of scaling restoration to match estimates of losses. We consider the factors known to limit abundance and production of surf clams and other marine bivalves (hard clams, American oysters and bay scallops) and review the advantages of hatchery stocking, transplantation, habitat restoration, and reduction of fishing pressure in selecting a reliable and efficient restoration action. Age-specific estimates of the scale of population enhancement required to restore production showed that fewer additional animals were needed when larger (older) animals were added, but at the expense of greater grow-out requirements. Relaxation of fishing was most effective for hard clams. Accurate scaling of restoration was most sensitive to mortality rate, and the most efficient restoration involving seeding of small bivalves would be accomplished using surf clams. Monitoring of the restoration option chosen to compensate for the bivalve loss following the ‘North Cape’ oil spill can serve to test the underlying demographic assumptions and accuracy of the restoration scaling

Modeling Distribution, Fate, and Concentrations of Deepwater Horizon Oil in Subsurface Waters of the Gulf of Mexico

Oil spill modeling of the 2010 Deepwater Horizon discharge was performed to evaluate the fate of the oil in subsurface waters of the Gulf of Mexico. The oil fate model Spill Impact Model Application Package (SIMAP) was used to estimate rise rate of oil droplets, dissolution of oil constituents, movements of oil droplets and dissolved components, and degradation of hydrocarbon components in the deep-sea. As sampling during April-July 2010 was primarily performed within 20. km of the spill site, model predictions were compared to field data from within a 25-by-25-km box centered on the wellhead. Concentrations of soluble and semisoluble hydrocarbon components predicted by the model agreed well with chemical measurements when compared as frequency distributions within varying depth zones of the water column. The results showed that the soluble hydrocarbons primarily dissolved near the release depth, while semisoluble compounds were partially dissolved at depth and as droplets rose

Validation of Oil Spill Transport and Fate Modeling in Arctic Ice

Reliability of oil spill modeling in Arctic waters for response planning and risk assessments depends on the accuracy of winds, currents, and ice data (cover and drift) used as input. We compared predicted transport in ice, using ice and ocean model results as input, with observed drifter trajectories in the Beaufort Sea and an experimental oil release in the Barents Sea. The ice models varied in ice rheology algorithms used (i.e., Elastic-Viscous-Plastic [EVP], presently used in climate models, versus a new Elasto-Brittle [EB] approach in pack ice) and the time averaging of their outputs, which were provided as input to oil spill models. Evaluations of model performance (skill) against drifters showed improvement using EB instead of EVP rheology. However, model skill was degraded by time-averaging of ocean and ice model vectors before input to the oil spill model. While the accuracy of individual oil model trajectories projected weeks to months into the future is expected to be low, in the event of a spill, forecasts could be updated frequently with satellite and other observations to improve reliability. Comparisons of modeled trajectories with drifters verified that use of the ice-ocean models for ensemble modeling as part of risk assessments is reliable.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author