Geomorphic Factors Related to the Persistence of Subsurface Oil from the Exxon Valdez Oil Spill

Abstract

I www.JCRonline.org Nixon, Z.; Michel, J.; Hayes, M.O.; Irvine, G.V., and Short, J., 2013. Geomorphic factors related to the persistence of subsurface oil from the Exxon Valdez oil spill.Oil from the 1989 Exxon Valdez oil spill has persisted along shorelines of Prince William Sound, Alaska, for more than two decades as hoth surface and suhsurface oil residues. To hetter understand the distribution of persistent subsurface oil and assess the potential need for further restoration, a thorough and quantitative understanding of the geomorphic factors controlling the presence or absence of subsurface oil is required. Data on oiling and geomorphic features were collected at 198 sites in Prince William Sound to identify and quantify the relationships among these geomorphic factors and the presence and absence of persistent subsurface oil. Geomorphic factors associated with the presence of subsurface oil were initial oil exposure, substrate permeability, topographic slope, low exposure to waves, armoring on gravel beaches, tombolos, natural breakwaters, and rubble accumulations. Geomorphic factors associated with the absence of subsurface oil were impermeable bedrock; platforms with thin sediment veneer; fine-grained, well-sorted gravel beaches with no armor; and low-permeability, raised bay-bottom beaches. Relationships were found between the geomorphic and physical site characteristics and the likelihood of encountering persistent subsurface oiling at those sites. There is quantitative evidence of more complex interactions between the overall wave energy incident at a site and the presence of fine-scale geomorphic features that may have provided smaller, local wave energy sheltering of oil. Similarly, these data provide evidence for interactions between the shoreline slope and the presence of angular rubble, with decreased likelihood for encountering subsurface oil at steeply sloped sites except at high-angle sheltered rubble shoreline locations. These results reinforce the idea that the interactions of beach permeability, stability, and site-specific wave exposure are key drivers for subsurface oil persistence in exposed and intermittently exposed mixed gravel beach and rocky shoreline environments. ADDITIONAL INDEX WORDS:Exxon Valdez, oil persistence, subsurface oil. Prince William Sound, Alaska, USA, geomorphology.

Long-Term Ecological Impacts from Oil Spills: Comparison of Exxon Valdez, Hebei Spirit, and Deepwater Horizon

“…39 Upon landfall, oil percolated through the highly permeable boulder armoring and became entrained in fine grained sediments located below. Natural breakwaters and headlands protect these beaches from wave exposure, 41 and limited hypoxic groundwater flow through the relatively impermeable fine sediments minimizes the potential for microbial degradation of the oil. 42 Most of the subsurface oil is currently found in Prince William Sound below 10−20 cm of clean sediments.…”

The Role of Detailed Geomorphic Variability in the Vulnerability Assessment of Potential Oil Spill Events on Mixed Sand and Gravel Beaches: The Cases of Two Adriatic Sites

“…According to Nixon and Michel (2018), these oil residues are typically located in finer-grained sand and gravel sediments, often under an armor of cobble-or boulder-sized clasts, in areas with limited groundwater flow and porosity. According to Nixon et al (2013) the oil persistence, nearly 20 years after the Exxon Valdez oil spill on the intermittently exposed gravel beaches, is due to a complex interaction between small-scale geomorphic features (e.g., armoring) that proved shelter from the local incident wave energy. They documented subsurface oiled layers down to an average burial depth between 13.6 and 18.6 cm.…”

Predictive Modeling of Subsurface Shoreline Oil Encounter Probability from the Exxon Valdez Oil Spill in Prince William Sound, Alaska

“…Many studies have identified factors that affect the behavior and persistence of oil on the shorelines of PWS and the Gulf of Alaska in the more than 20 years since the spill. − As part of these studies, the presence of both surface and subsurface oiling and the presence of geomorphic factors that led to oil persistence have been documented at discrete locations; however, these studies are largely descriptive, and limited quantitative extrapolation was possible. We used survey data describing the presence of subsurface oil in excavated pits together with synoptic predictor variables to derive a series of models for use in generating calibrated probabilities of encountering subsurface oil of various types at all locations.…”

“…Review of previous investigations − indicated that the primary drivers of control of long-term oil persistence after oil has been stranded are initial oil loading, shoreline geometry and geomorphology, and wind wave exposure. Based on this review, we derived a series of raster layers describing oiling and physical variables thought to influence and control the presence and persistence of subsurface oil in PWS.…”