Change of groundwater manifestations and characteristics of associated ecosystems in the Mexican semi-arid region

Abstract

Background. The city of San Miguel de Allende, Guanajuato, was founded in the semi-arid of Mexico in which historically there were numerous springs in the lower part of the La Laja Upper Basin. Its history has led to an excessive extraction of water from the aquifer to meet different needs at the time. Goals. Understand the evolution of the manifestations of groundwater in the Area of Hydrological Influence of the city of San Miguel de Allende (AIHCSMA, in spanish) and in particular the permanence of some springs that allow to identify pro- posals of management towards the conservation of the vegetation and the biodiversity, to recover the water operation in different scales of time. Methods.It was madea delimitation of the area of influence was elabo- rated with hydrological bases (AIH), hydrogeological, history, mapping and characterization of the ecosystems associated to these manifestations. Results. The hydrogeological environment is composed of volcanic rocks in the upper parts of the sub-basin, as well as by poorly consolidated sediments and alluvial fans in the middle and lower parts. 23 springs and three swamps were located and characterized; currently two springs and one swamp have completely dried and two marshes have diminished their historical flow. In the AIH there are 504 wells, of which 61 hm3/year are extracted. The main water pathways are fractured rocks and the granular medium. Conclusions. The location of the springs and swamps is related to geological contact zones between different tectonic structures, they present diverse characteristics that indicate local flows and one of intermediate type; the decrease or loss of flow is associated with the opening of nearby wells. Management proposals are proposed towards the conservation of ve- getation and biodiversity in the sub-basin to recover water performance at different time scales.