Ecosystems can be defined very broadly to include almost every natural process that supports life.
For example, Cairns l 1996 states that
ecosystem services are those functions of ecosystems that society deems beneficial , including the maintenance of atmospheric gas balance, flood control, carbon storage, capture of solar energy, and subsequent production of food and fiber, maintenance of water quality, and maintenance of a genetic library that provides the raw material for improved foods, materials and drugs.
The art and science of environmental analysis has yet to reach the level where such functions can be readily analyzed in the context of a transportation study.
However, it seems likely that one day such issues will be an important foundation for environmental impact analysis [Wachs, 1999]
The following questions have been developed by the U.S. DOT to serve as the basis for any investigation of transportation-related impacts on the ecosystem [U.S. Department of Transportation, 1979a]