Abstract
Water covers 363 million square km, or 72% of the earth’s surface. The vast majority of this water is saline (96%), frozen (2%) or groundwater (1%). The 105\documentclass[12pt]{minimal}
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\begin{document}$$^3$$\end{document} of surface freshwater (0.008%) is in turn concentrated almost entirely in three large great lake systems (Fig. 3.1), with a vanishing small amount of surface freshwater forming lakes and rivers.