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CHRONIC OIL POLLUTION IN THE GULF OF THAILAND

Computer technology has enabled to merge and visualize the previously unexplored SEAWATCH oceanographic data from the National Research Council of Thailand and the DDPH (dissolved and dispersed petroleum hydrocarbon concentration) data from Chulalongkorn University (Figure 1). 

Figure 1. A snapshot from a computer animation of the Gulf of Thailand showing observed net currents (blue arrows), wind (red arrows), the salinity at four depths from top to bottom (balls), the surface salinity (colored disks) and the dissolved and dispersed petroleum hydrocarbon concentration (DDPH, vertical bars). Adapted from Wattayakorn et al. (1998).

This has led to the discovery that the mean circulation in the Gulf of Thailand is forced by the South China Sea and not by the local wind as previously suspected, a phenomenon particularly marked during the Northeast monsoon when Mekong River water enters the lower Gulf (Wattayakorn et al., 1998). The visualization has also enabled spatial correlation analysis of the oceanographic and hydrocarbon data. This showed that the water currents control the fate of hydrocarbons in the Gulf. The animations of these data enabled oceanographers to realise for the first time that in the Southwest monsoon hydrocarbon-contaminated water from the Inner Gulf is slowly adverted towards the industrialized Eastern Sea Board, where more hydrocarbon is added in quantity. 

In the Northeast monsoon this contaminated water returns to the Inner Gulf where more hydrocarbons are discharged. Essentially these coastal waters mix but do not flush. As a result much of the inner Gulf and the Eastern Sea Board waters are chronically polluted by hydrocarbons. Indeed, in coastal waters of the Inner Gulf and the Eastern Sea Board, there were occasional acute pollution events (DDPH » 40 m g l^-1) superimposed 25% of the time upon chronic pollution (DDPH » 4 m g l^-1) and the presence of slightly contaminated water elsewhere (DDPH < 1.2 m g l^-1). Only the outer Gulf of Thailand seems relatively uncontaminated. The observed currents and DDPH data were used to drive an oil spill model, which predicted that acute contamination occurs at least once a year at any point in the Inner Gulf.

These findings have profound management implications. One cannot assume that the currents simply flush away pollutants so that a viable marine ecosystem will last in the Gulf of Thailand. Because of slow flushing hydrocarbon pollution is a serious, real threat. Indeed these animations were shown at the National Research Council of Thailand and were clearly pivotal in ensuring the passing of stronger oil pollution control laws.

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Last updated - October 20, 1999

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