TO most people the ocean is the personification of depth and immensity. For this reason its pollution seems impossible. But for rivers, it's an entirely different story. While oceans belong to no one, rivers belong to nations and their people.

River water is less dense than ocean water. Oil with a density greater than one gram per cubic centimeter will sink in the river, but float in the ocean. Hence, oil spills in rivers are of great concern because they will threaten not only surface resources, but also a wide range of subsurface aquatic organisms linked in a complex food chain.

Ever since it was announced that a coal-fired power plant will be built within a stone's throw of the Sundarbans, environmental scientists and activists at home and abroad have raised alarms about the disastrous effect it will have on the ecologically sensitive bio diverse rainforest.

Unfortunately, all the warnings fell on deaf ears.

The recent sinking and spillage of more than 350,000 liters of furnace oil in a river in Mongla, 40 km NNE of the Sundarbans, should ring the alarm bell anew. Otherwise, it will be the prologue of the tragic play The Death of a Rainforest, scripted by the energy Czars and directed by the Government of Bangladesh.

What happens to the oil that is spilled in the water? All oils, regardless of types, contain some volatiles. About 25% of the volatiles evaporate within three months, becoming an air pollutant. Nearly 60% of the remaining mass, relatively nonvolatile compounds that are lighter than water float on the surface, where they are broken down over the next few months by bacterial decomposition and photooxidation. The remaining 15% is a dense asphaltic substance that sticks together and sinks to the bottom in huge globs. It is these black, tarry lumps that will wash up on the banks

of the Sundarbans.

How will oil spill affect the Sundarbans? Vast stretches of the unique mangrove swamps will be blackened.Mangrove forests are

highly sensitive to oil toxicity. They can be further damaged by cleanup activities. Because they grow so slowly, replacing a mangrove tree can take decades. Consequently, animals

that depend on the mangrove environment for their survival will die.

Oil will kill plants and animals in the estuarine zone of the Sundarbans. If the layer of the spill is thick enough, it will smother creatures unable to move out from under it. Especially hard hit will be the barnacles, mussels, crabs and rock weed (a type of algae). Their recovery after an oil spill may take two to ten years. Oil will also washup on the banks, killing organisms that live there.

Water birds will be affected differently. Swimming and diving birds will become covered with oil, reducing their buoyancy and impairing flight. The insulative value of feathers will be lost and the birds will quickly die of exposure to cold water.As for the water-dwelling mammals, such as dolphins and porpoises, they will have unusual lung damage and adrenal hormone abnormalities.

Although injury to the vegetated above ground habitat is often the most visible impact, the effects of oil spills

on bottom-dwelling or benthic organisms are of paramount concern because of the multiple ecological processes and ecosystem functions that these organisms support. Oil will kill the benthic organisms, such as crabs. However, those benthic organisms that survive may accumulate oil in their tissue, making them inedible. Oil spill will also contaminate the flesh of the commercially valuable fish, thereby endangering the livelihood ofthe fishermen.

The ocean is large, the nights are dark and detection of oil spill is difficult. The rivers are narrow, they are shallow and any oil dumped into a river, even in the darkness of night, will become visible after sunrise. And if the spills occur frequently in the waters of the southwestern part of Bangladesh, the last act of the play The Death of a Rainforest will be staged sooner than later.

The writer is Professor of Physics at Fordham University, New York.