FIG. 1. Five examples of rising human pressures on the world’s freshwater ecosystems. A.—Global water withdrawals (after
Gleick 1993). B.—Number of large (.15 m high) dams (International Commission on Large Dams 2008). C.—Fisheries landings
from inland waters (Allan et al. 2005a). D.—Global inputs of anthropogenically fixed N. Input from all natural sources is
,110 Tg/y (Vitousek 1994, Galloway et al. 2008). E.—Number of known alien species in the Laurentian Great Lakes
(Ricciardi 2006).