Computer models like the ones that recently simulated conditions in the Chesapeake bay in the US could alter opinions regarding the nature of environmental problems. But, there are limits to their dependability
computers are making their mark even in the field of environmental studies. Simulations of air, water and soil contamination are becoming popular methods for studying the environment. Such models are known to be precise and cheap. Recent work in the Chesapeake bay, in the us , indicates that computers can demonstrate complex interactions between various elements of the environment.
Contrary to the earlier view which blamed water-borne pollution for the environmental problems faced by the bay, the recent study has highlighted the role played by air pollution. Robin Dennis and his colleagues at the Environmental Protection Agency ( epa ) digitally recreated the atmosphere over the eastern us and combined it with another model that examines the flow of water into the Chesapeake. The group also simulated the movement of air across the country to study how nitrogen reacted with other airborne compounds and then dropped to the ground either directly or through the rain. Due to the fact that nitrogen descends fairly fast, earlier models had suggested that pollution from local sources had aggravated conditions in the bay. But the current models have provided a more detailed analysis of the problem and indicate that the problem is a much larger one and that 25 per cent of the nitrogen is still being carried aloft around 800 km from the source.
Although the testing of the bay's waters has helped monitor the problem, these models have shown how the pollution travels to the place. The pollution caused could be due to factory emissions in locations as far away as Ohio or Pennsylvania. Consequently, it has been suggested that some changes be incorporated into pollution control measures, as several years of regulations on water-borne pollution have failed to decrease the levels of nitrogen in the bay. More attention should now be given to air pollution, without abandoning measures to control water pollution.
The National Environmental Supercomputing Centre is where most of the work concerning the Chesapeake modeling was carried out. This three-year-old Centre set up by the epa is the only place in the world where such specific simulation facilities are available. Currently, the Centre has at least 40 different projects in hand. Instead of having to sample a huge region to determine where a toxic compound might reach if released by a factory, researchers need only a few samples to ascertain the same by using computers.
Computer programmes consider various aspects of a particular problem and work out the possible after-effects and solutions. For example, they can tell how certain compounds will degrade in the environment, how chemicals can percolate down to the water-table and how they can affect wildlife. Such programmes can take into account details down to the movement of atoms. Another advantage of techniques employing such simulation is that they save a lot of money. A project comparable to the one carried out in the Chesapeake bay, conducted in the early '80s -- to test the feasibility of a field experiment to study acid rain in eastern us -- cost around us $500 million. But the Chesapeake project has cost only around us $500,000.
In studies dealing with for instance, hazardous waste chemicals or forest fires (see Down To Earth , Vol 5, No 8), computer modeling can be used effectively. Maureen I McCarthy of the Pacific Northwest Laboratories has used computers to predict how radioactive contaminants might react with the local soil around the Hanford nuclear site in Washington. Simulation of the chemical processes in the environment helps in a realistic assessment of a particular situation while field experiments could be expensive, time-consuming and difficult to carry out.
But computer modeling does have its shortcomings. Models cannot always include every aspect of a natural system. Moreover, different approaches may yield different results for the same problem. For example, predictions about global warming have been controversial as varying results have come out of different models, based on distinct assumptions. Another difficulty with these models is the extent to which they are dependable. Absolute faith in a simulation of an environmental problem can be tough even for computer experts. Steven E Cabaniss of the Kent State University for instance, would prefer checking the results of toxicity experiments on animals before considering his tap water safe. Laboratory experiments involving mundane sampling cannot be done away with so easily.
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