ABSTRACT
The 'hydrological cycle' is a well-known concept. (Should readers be unfamiliar with this concept, or with the basic hydrological terminology used below, they should refer to standard hydrological textbooks, such as Newson (1994), before proceeding.) The hydrological cycle describes the dynamic circulation
of water around, on and in the Earth. The most important phases of the hydrological cycle are:
• uptake of moisture from the Earth's surface (especially the oceans) to the atmosphere by evaporation and allied processes;
• transport of moisture around the planet in the form of atmospheric vapour;
• return of moisture to the Earth's surface in the form of precipitation (rain, snow, dew, etc.);
56 ENVIRONMENTAL COMPARTMENTS AND STRESSORS
• transport and storage of water over the Earth's surface in streams and lakes etc. ('surface runoff);
• transport and storage of water beneath the Earth's surface in aquifers ('groundwater flow');
• return of water via the latter two routes to the oceans.
