This unique addition to reference literature provides an introduction to the major concepts and contemporary issues that are essential for students of environmental science and environmental studies to know. With over 200 entries authored by world-class names like Anthony Brazel, John Day and Edward Keller, this text is divided into six sections: Environmental Science, Environments, Paradigms & Concepts, Processes & Dynamics, Scales & Techniques, and Environmental Issues.
Thresholds are stages, or tipping points, for an environmental system at which the essential characteristics of the natural system's state change dramatically or where there is a significant impact on socioeconomic systems. Some environmental thresholds are well [Page 214]known, including the wilting point which occurs when plants can no longer extract water from the soil, the plant then starts to wilt and may die. In hydraulics there are values (Froude and Reynolds numbers) which define the conditions at which flow becomes supercritical or turbulent, and there also are threshold velocities that are necessary to move sediment particles of a particular size. As velocity increases the threshold velocity is when movement begins and later as velocity decreases there will be a threshold velocity at which movement ...