The global abundance and size distribution of lakes, ponds, and impoundments

One of the major impediments to the integration of lentic ecosystems into global environmental analyses has been fragmentary data on the extent and size distribution of lakes, ponds, and impoundments. We use new data sources, enhanced spatial resolution, and new analytical approaches to provide new estimates of the global abundance of surface-water bodies. A global model based on the Pareto distribution shows that the global extent of natural lakes is twice as large as previously known (304 million lakes; 4.2 million km2 in area) and is dominated in area by millions of water bodies smaller than 1 km2. Similar analyses of impoundments based on inventories of large, engineered dams show that impounded waters cover approximately 0.26 million km2. However, construction of low-tech farm impoundments is estimated to be between 0.1% and 6% of farm area worldwide, dependent upon precipitation, and represents .77,000 km2 globally, at present. Overall, about 4.6 million km2 of the earth’s continental ‘‘land’’ surface (.3%) is covered by water. These analyses underscore the importance of explicitly considering lakes, ponds, and impoundments, especially small ones, in global analyses of rates and processes. Although lakes are of global importance, most analyses of functional processes in freshwater ecosystems have either emphasized regional similarities (Thienemann 1925; Naumann 1929; Kalff 2001) or have adopted an ecosystemspecific emphasis. The few global analyses of lacustrine processes have been limited because knowledge of the number and size distribution of lakes has been incomplete (Alsdorf et al. 2003; Lehner and Döll 2004). Further, Limnol. Oceanogr., 51(5), 2006, 2388–2397 E 2006, by the American Society of Limnology and Oceanography, Inc.