Drilling for oil can lead to accidental discharges that are harmful to local ecosystems. Likewise, spills of oil in transit or from routine operations are a serious hazard that can have devastating effects on marine and freshwater systems. The delayed as well as the prompt effects vary. The refining of oil and the release of pollutants in its combustion may have widely dispersed effects. Pipelines may promote erosion and, when overland, may hinder species migration. That suitable planning can prevent such untoward effects is now being tested by the operation of the Alaska pipeline. The overall ecosystem effects of oil are less serious than those of coal for corresponding energy production levels. Automobile emissions affect not only human health and comfort but also agricultural and plant life systems. (See “Agriculture and Plant Life.”)
The extraction and delivery of natural gas can threaten natural habitats. Pipeline leaks, by blanketing with natural gas and thus excluding oxygen, may leave an area barren for several months after the leak has been stopped. Fires and leaks from receiving facilities in marine areas are particularly hard on estuary life. The combustion of natural gas is indirectly damaging to ecosystems through the accompanying oxidation of atmospheric nitrogen. The nitrogen oxides thus formed are an important factor in acid precipitation (discussed under “Water and Climate”). In association with the photochemical-oxidant system or sulfur dioxide, they can be toxic to plant life (as previously noted). In total, however, the effects are much less severe than those of coal.
The ecological effects of coal-derived fuels are much the same as those for coal itself. On the other hand, the production of oil from shale carries with it the threat of considerably more ecological damage than conventional production of oil. The attractive oil shale resources in the United States are located in limited areas of the western states that are ecologically fragile and that are short of water, of which large quantities would be needed. Solid-waste disposal is a problem. Experimentation has been initiated on conversion of oil shale in situ, a technique that might or might not be less damaging ecologically than retorting in aboveground plants but that may involve serious aquifer disruption.