In harbors, waterfronts and shorelines around the world, sediments that have been contaminated by even small amounts of oil, chemicals, or other polluting substances could pose a health risk to both nature's fragile estuarine ecosystems, as well as to the rest of us. Sometimes this contamination is not even evident without testing. Traditionally, the solution has been to dredge (and place contaminated sediment in upland disposal areas where it must be further managed to prevent exposure to yet other ecological species), and presumably bring the quayside back to its pristine character. For many years, the Navy has looked at the best way to manage this contamination without disrupting an ecosystem that is fragile, but still functional.
Now, scientists funded by the Office of Naval Research have found there is evidence of a natural process called intrinsic bioremediation, whereby the resident bio-organisms in contaminated estuarine sediments can degrade or become a net sink for hydrocarbons and other organic pollutants, and thus may function as a filter within the ecosystem. In other words, the natural bacteria in the sediment - adapted by years of exposure to the problem - are doing a clean-up on their own. The natural bacteria metabolize (i.e. eat) the offending hydrocarbon pollutant (gas, oil, etc). Removal of the sediments that have microbiologically adapted to do this clean-up may actually increase the problem. If the dredging is done in estuaries with other industrial discharges occurring it doesn't take long for the system to again reach a contaminated state.
"What could happen," says Mike Montgomery of the Naval Research Laboratory, "is that we'd spend millions of taxpayer dollars to dredge the sediments, and end up doing more harm than good. We could create an even worse buildup of oil by removing the very elements that are solving the problem for us."
Research on this phenomenon funded by ONR and others continues in the Charleston Harbor Estuary (site of the former Charleston Navy Yard), around the Philadelphia Naval Complex Reserve Basin, San Diego Bay, and at other locations around the country. The strategy now is to learn how to identify sediments that may be undergoing intrinsic bioremediation, so that site clean-up programs can be planned accordingly.
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