11. Agriculture, Water Mismanagement and Ecosystem Transformations in the Cuatrociénegas Valley in the Chihuahuan Desert, Mexico

Due to water overexploitation mainly related to agricultural activities, water levels are diminishing in the Churince System, one of the wetlands of the Cuatrociénegas Valley, in the Chihuahuan Desert of northeastern Mexico. Soil subsidence is increasingly frequent, leading to the formation of numerous sinkholes or hundidos (locally known as abras), formed by the alterations of soil structure due to water loss from the main water bodies. Sinkholes in the study area can be small (only a few square centimeters), or large (six or more square meters), depending on their age and how each one is formed. Some doubts remain about the effects of the overexploitation of water in the Cuatrociénegas Valley and also in the surrounding valleys on the instability of the Churince System, but sinkholes are continuously opening, and water levels are quickly decreasing. We registered the formation of sinkholes—their size, depth, water level, and the colonizing pattern of the plants that occupy them. We also recorded the population dynamics and growth form of Samolus ebracteatus var. coahuilensis—one of the main colonizing species. We concluded that sinkholes are constantly appearing and that their physical and biological characteristics are very dynamic. Additionally, these sinkholes are indicators of environmental disturbance and their formation should be used as an early warning system of hydrological changes in this region in which ecosystem integrity is being affected. We suggest that Samolus ebracteatus var. coahuilensis is an indicator of humid microhabitats. Changes in its distribution and in its population dynamics indicate changes in superficial underground water caused by the alteration of the hydrologic system.