Environmental Fluid Mechanics: Current issues and future outlook

All forms of life on earth are immersed in a fluid or another, either the air of the atmosphere or the water of a river, lake or ocean; even, soils are permeated with moisture. So, it is no exaggeration to say that life, including our own, is bathed in fluids. A slightly closer look at the situation further reveals that it is the mobility of fluids that actually makes them so useful to the maintenance of life, both internally and externally to living organisms. For example, it is the flow of air that our lungs that supplies oxygen to our blood stream. The forced air flow created by our respiration, however, is not sufficient; without atmospheric motion around us, we would choke sooner or later in our own exhaust of carbon dioxide. Likewise, most aquatic forms of life rely on the natural transport of water for their nutrients and oxygen. Our industrial systems, which release pollution on a continuing basis, would not be permissible in the absence of transport and dilution of nearly all emissions by ambient motions of air and water. In sum, natural fluid motions in the environment are vital, and we have a strong incentive to study the naturally occurring fluid flows, particularly those of air in the atmosphere and of water in all its streams, from underground aquifers to surface flows in rivers, lakes, estuaries and oceans. The study of these flows has received considerable attention over the years and has spawned several distinct disciplines: meteorology, climatology, hydrology, hydraulics, limnology and oceanography. Whereas the particular objectives of each of these disciplines, such as weather forecasting in meteorology and design of water-resource projects in hydraulics, encourage disciplinary segregation, environmental concerns compel experts in those disciplines to consider problems that are essentially similar: the effect of turbulence on the dispersion of a dilute substance, the transfer of matter or momentum across an interface, flow in complex geometries, the rise of a buoyant plume, and the impact of flow over a biotic system. The study of environmental flows is also fully integrated in the contemporary emphasis on environmental impacts and sustainable life on planet Earth. According to physicists, the world scientific community will be occupied during the 21st century in large part by problems related to the environment, particularly those stemming from the concern over climate change (Rodhe et al., 2000) as well as many other problems spanning a wide range of spatial and temporal scales. This marks the first time in the history of science that environmental problems lie at the forefront of scientific research. The following chapters of this book are illustrative of a number of these problems. The common points encourage interdisciplinarity to a degree that is increasing in proportion to the acuity of our environmental problems. This overlap between the various disciplines concerned with the environmental aspects of natural fluid flows has given rise to a body of knowledge that has become known as Environmental Fluid Mechanics. The interdisciplinary aspects become especially manifest in the study of processes at the interfaces between environmental systems.