Exxon Valdez Oil Spil Clean-Up Slowed Due to Lack of Oxygen and Nutrients for Biodegrading Organisms
19.01.2010 - Water & Oceans, Flora & Fauna, Arctic
Results of research on the biodegradation of the 1989 Exxon Valdez spill in Alaska has been published on the website of Nature Geoscience. The results show that the combination of low concentrations of oxygen and nutrients in the lower layers of the beaches slow down the aerobic biodegradation of remaining oil from the spill.
In the first five years after the spill, oil was found to disappear at a rate of approximately 70% a year, with calculations predicting it would disappear entirely within the following years. However about eight years ago, the disappearance rate had fallen to a mere 4% per year, leaving about 83,000 litres of oil on the shores in the region.
The beaches under study consist of two layers: a highly permeable upper layer and a layer with very low permeability. This means that on average, water moves through the upper layer up to 1,000 times faster than through the lower layer, which became more compacted through the movement of the tides over time, creating a sheltering effect on the oil that lies between 2.5 and 10 cm below the interface of the two layers.
Using groundwater hydraulic studies, the researchers were able to find that the outward movement of water through the lower layer deprived oxygen and nutrients from the micro-organisms responsible for the biodegradation of the oil. The team is now set to try and find a way to provide the micro-organisms with the oxygen and nutrients they need to spur aerobic biodegradation of the remaining oil in the affected areas.
