Natural Cleaning of Shorelines Following the Exxon Valdez Spill

Abstract

Field observations have identified a number of natural processes that contributed to the cleanup of the Exxon Valdez spill. This paper focuses on physical processes that remove oil residue from shoreline sediments. Data from shoreline surveys at 16 monitoring sites in Prince William Sound show significant reductions in both surface oil coverage and sediment oil content during the period from September 1989 to March 1990, while cleanup activities were suspended. Natural cleaning appeared to be dominated by wave action during storms. Changes in oiling conditions on high- and moderate-energy beaches can be explained as the result of wave action, based on beach profile data and time-lapse photography. However, observations from low-energy areas indicate that rates of change there were often as high as those from the more exposed and energetic wave environments. Studies of the oiled sediments have shown that interactions between the residual oil and fine mineral solids, such as clay particles, played an important role in the natural cleaning process. These interactions formed flocculated aggregates of a solids-stabilized emulsion in which small oil droplets are coated with micro-sized mineral fines and surrounded by seawater. In this form, the oil no longer sticks to the sediment surfaces so that it can be removed by low-energy waves or tidal washing. The large specific surface area of the flocculated oil promotes its eventual biodegradation by indigenous microorganisms.

Some environmental aspects of marine hydrocarbon bacteriology

“…The authors conclude that the elevated mineral potentials and increased bacterial numbers showed that degradation was enhanced even though they did not carry out direct chemical analyses. In contrast, other observers working in the Prince William Sound area, and around the same time, concluded that 'natural cleaning appeared to be dominated by wave action during storms' (Jahns et al 1991). It has also been claimed that surfactants formed by Pseudornonas aeruginosa were effective in cleaning gravel beaches following the 'Exxon Valdez' spill (Harvey et al 1990).…”

Ecological Effectiveness of Oil Spill Countermeasures: How Clean is Clean?

“…• Clay-oil flocculation-this process reduces adherence of oil to shore substrates and facilitates natural cleaning, as has been described for Prince William Sound after the Exxon Valdez spill [20];…”

TROUBLE ON OILED WATERS: Lessons from the Exxon Valdez Oil Spill

“…Oil traveled as far as 750 km from the spill site, contacting 1750 km of shoreline along the way (900 km in PWS) (76,100). Some beached oil was collected by cleanup crews, but much eventually ended up back in the water column, lifted off beaches when they were washed by humans or pummeled by winter waves (67,82,107,172).…”