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OIL SPILL RESPONSE

It is generally agreed that mangroves are particularly sensitive to oil and that they are priority areas for protection.

The main protection options are:
++ mechanical recovery offshore from the mangroves;
++ dispersal (using oil spill dispersants) offshore; and
++ booming of mangrove shorelines and inlets.

Of these, it is the dispersal option which gives rise to the most debate. Experimental evidence concerning the effects of dispersed oil compared with untreated oil on mangroves is available, and is a useful input to contingency planning. The evidence points to the conclusion that mangrove trees tolerate dispersed oil better than untreated oil. If the objective is to protect the trees, the habitat they provide, and some wildlife species (notably water birds), then chemical dispersal offshore can be an effective measure under certain conditions (if the type of oil is dispersable and weather and sea conditions allow dispersant application). However, the possible effects on organisms in the water column need to be considered, and the advantages and disadvantages of offshore chemical dispersal weighed up as part of the contingency planning process. This subject is discussed more fully in the IPIECA report Dispersants and their Role in Oil Spill Response.

If oil enters mangroves, the main clean-up options are:
++ booming and skimming of oil on the water surface in mangrove creeks;
++ pumping of bulk oil from the sediment surface, depressions and channels; l
++ water flushing of free oil from sediment surface and mangroves, into areas where it may be collected;
++ use of absorbent materials, with subsequent collection and disposal.

There have recently been some promising experimental results using a newly developed chemical shoreline cleaner on trees oiled with heavy oil that covered the lenticels. The cleaner reduces oil adhesion with minimal dispersion. Difficulties are that some mangrove forests are virtually impenetrable, and heavy clean-up operations may cause physical damage. Moreover, if a large spill of relatively fresh light crude oil enters a forest, sediment penetration and toxic damage can occur very quickly, so that it is unrealistic to expect a clean-up operation to save many trees.

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