Environmental Effects of Aquifer Overexploitation: A Case Study in the Highlands of Mexico MARIA VICENTA ESTELLER* CARLOS DIAZ-DELGADO Centro Interamericano de Recursos del Agua Facultad de Ingenieria, Universidad Autonoma del Estado de Mexico Cerro Coatepec, S/N. C.U. 50130 Toluca (Estado de Mexico) Mexico ABSTRACT / There are several environmental processes occurring under aquifer overexploitation conditions. These processes include groundwater table decline, subsidence, attenuation and drying of springs, decrease of river flow, and increased pollution vulnerability, among others pro- cesses. Some of these effects have been observed on the Upper Basin of the Lerma River. The Lerma River begins in the SE of the Valley of Toluca at 2,600 m asl, in the wetland known as Lagoons of Almoloya del Rı ´o. This wetland is made up of a group of lagoons, which are an important aquatic system from an environmental point of view. The water inflow of this wetland is a discharge of springs, which occur between the fractured volcanic material of the moun- tain range and granular volcanic– continental deposits of the Valley of Toluca aquifer. The intensive exploitation of the Valley of Toluca aquifer to supply urban and industrial water to Mexico City and Toluca began in 1950 and is responsi- ble for a steady decline of piezometric levels of 1–3.5 m/yr. Other effects of this exploitation—the drying of the wetland, the decrease of river flow and the land subsidence— caused serious ecological and social impacts. The authori- ties declared this aquifer as overexploited in order to re- duce the exploitation and preserve the availability of water resources in this important region. The environmental impacts of aquifer overexploita- tion have been observed in numerous places around the world (Llamas 1992). In these places, the adverse consequences have been proven, one of the most im- portant being the desiccation of wetlands and rivers, with subsequent loss of the aquatic ecosystem, which is of great ecological value due to its wide biodiversity (Rodriguez-Estrella and Lopez-Bermudez 1992, Mar- tinez-Alfaro and others 1992, Cruickshank 1995). Other effects are a decline in the groundwater level, subsidence, the drying-up of springs, a decrease in river flow and a deterioration of water quality, among others (Martinelli and others 1998, Celik and Afsin 1998, Scott and others 1999). The region of the Upper Course of the Lerma River (Central Mexico) is a representative example of the overexploitation problem. The Upper Course of the Lerma River, giving rise to the Upper Basin of the Lerma River, is situated in an area known as the Mex- ican Highlands (Figure 1). This area is an important center for industrial and agricultural activity, with a high population density and enormous demands for water, which are being met almost exclusively from groundwater. Moreover, added to this problem, is the exportation of groundwater from this basin to Mexico City, for part of the city’s water supply. This water exportation to Mexico City is done at a rate of 14 m 3 /sec, a volume taken from the aquifers of the valleys of Toluca and Atlacomulco-Ixtlahuaca, both located in the Upper Basin of the Lerma River. Of these two valleys, the one subject to greater exploitation is the Valley of Toluca (CCRECRL 1993). The lagoons of Almoloya del Rio are located in the Valley of Toluca (SE sector), giving rise to the Lerma River, and make up the only natural wetland of the Upper Basin of the Lerma River, situated at an altitude of 2237–2600 m asl. These lagoons have, for many centuries, represented a way of life for the inhabitants of the area as their activities were based on hunting, fishing, and gathering of aquatic flora and fauna. On the other hand, this area is an important natural reserve, because of its biodiver- sity (Albores 1995, CCRECRL 1997, Boehm and Sando- val 1999). The deterioration of the ecosystem of the Lagoons of Almoloya del Rio is related to the exploitation of the groundwater resources at rates higher than the natural recharge, giving rise to the overexploitation of the Val- ley of Toluca aquifer. This paper aims to establish, in the most pragmatic possible way, the effects of the overexploitation of the KEY WORDS: Water resources exploitation; Water table decline; Dimi- nution of river flow; Wetland; Ecological impact; Social impact *Author to whom correspondence should be addressed; e-mail: esteller@coatepec.uaemex.mx DOI: 10.1007/s00267-001-0024-0 Environmental Management Vol. 29, No. 2, pp. 266 –278 © 2002 Springer-Verlag New York Inc.