LIMNOLOGICAL CHARACTERISTICS OF PAMPASIC PONDS (ARGENTINA)

A. FERNÁNDEZ CIRELLI, P. MIRETZKY Y V. CONZONNO

Melbourne, Australia

Congreso; Xth World Water Congress; 2000

International Water Resources Association

Pampasic ponds play an important role in the overall hydrological cycle of Buenos Aires Province, Argentinas richest agrarian region. Limnological and geohydrochemical studies provide the basic knowledge to prevent them from contamination by inadequate land management and can contribute to the sustainability of this catchment area of high economic relevance in our country. These ponds are permanent, lentic and shallow water bodies of different origin (combined fluvial and eolic processes), but without lakes as predecessors. Pampasic ponds in consideration are phreatic, that is to say, the local groundwater drainage supplies the base discharge of the pond?s waters. Therefore, in order to obtain a better understanding of the water chemistry of these ponds, it is necessary, first, to look for a mechanism that explains the chemical composition of groundwater. The main processes taking place in the drainage basin groundwater responsible for the Pampasic ponds hydrochemistry are: cation exchange process in the loessic sediments, that promotes an enrichment in sodium; and dissolution of halite sediments originated in Holocene marine intrusions that results in high equivalent amounts of sodium and chloride and aluminosilicate weathering that results in a release of mainly, sodium, calcium, magnesium, potassium, bicarbonate and silica. When the groundwater finally reaches Pampasic ponds, an evaporation-crystallization process takes place promoting calcite precipitation and an additional enrichment in sodium. The global understanding of these processes will let us predict the ecosystem?s response to anthropic activities.