Chapter 2 . Lakes of Argentina Section 1 . Classification and State of the Environment of the Argentinean Lakes 1

Due to the great climatic variety and the peculiar north-south orographic distribution, Argentinean lake systems include a wide diversity of aquatic environments. The deepest lakes are situated in the Patagonian Andes and Tierra del Fuego, and range from ultraoligotrophic to oligotrophic. Patagonian Plateau lakes are shallower than Andean lakes and usually range from mesotrophic to eutrophic. All lakes in the Pampa Plain are very shallow and range from eutrophic to hypertrophic or salt lakes. Most of the lakes situated in the central-western and northwestern arid regions are reservoirs or salt lakes, and range from mesotrophic to eutrophic. More than half of the northwestern reservoirs have very low dissolved oxygen concentrations in the hypolimnion during mid-summer. Argentina has more than 400 lakes with surface area > 5 km2, but for some of them not even major ion data are available. Because of the wish to synthesize and to extract general characteristics and patterns, issues have been selected which adequately reflect the character of the lake environment in Argentina. We divided Argentina according to geographical regions into six major divisions: 1) Puna, 2) Chaco-Pampa Plain, 3) PeriPampean Sierras, 4) Andean Patagonia, 5) Patagonian Plateau, and 6) Brazilian Shield related systems. Most of the lakes situated in Patagonia are low disturbed lakes. However, the Pampa Plain lakes are usually lightly impacted by agricultural operations. Moreover, most of the reservoirs located in the Argentinean arid "corridor" are highly impacted by agriculture. Other lakes in both north and south Argentina range from salt lakes, through dark humic-stained lakes and large river floodplain lakes, to dilute high altitude glacial lakes. Argentina still has a larger proportion of its lake waters in natural conditions. However, expected developments for natural resources indicates that Argentinean goals for lake water management should include the preservation of some proportion of pre-european natural lake environment, and the evolution of a stable, managed lake environment in the more developed regions. 1 Paper presented at ILEC Workshop on Sustainable Management of the Lakes of Argentina, San Martin de los Andes, Argentina, 24-25 October, 1997.