Transformación de los ecosistemas áridos para su uso agrícola en Baja California Sur, México. Un análisis desde la historia ambiental.

En este artículo se estudia la dedicación histórica de los ecosistemas áridos de Baja California Sur a diferentes tipos de agricultura. En esa aislada y árida región del noroeste mexicano, la agricultura, desconocida para sus habitantes indígenas, fue introducida por los jesuitas en el siglo XVIII a través de algunas familias que se establecieron en los ranchos asociados a las misiones. Basándose en el conocimiento indígena del medio ambiente y adaptando la cultura de regadío del Mediterráneo y de Oriente Medio, los rancheros aprovecharon integralmente los recursos naturales e hicieron un uso sustentable del agua y el suelo de los oasis donde se establecieron. Esto permitió la conservación de los frágiles ecosistemas locales y la construcción de un paisaje cultural original. El estilo de vida ranchero prevaleció hasta mediados del siglo XX y constituye el fundamento de la identidad regional. Desde finales del siglo XIX, la perforación de pozos permitió la extensión y diversificación de la agricultura. Pero el mayor impacto ecológico ocasionado por la sobreexplotación del agua y el suelo ocurrió entre 1950 y 1990. El deterioro ambiental de los ecosistemas áridos bajacalifornianos y sus consecuencias socioeconómicas demostraron que la región no era apta para la producción a gran escala de granos ni de plantas industriales exigentes en agua y causantes del agotamiento de suelos. Empleando el enfoque de la historia ambiental es posible identificar los principios que pueden permitir el desarrollo sustentable de la agricultura en la región, inspirándose en la relación de los rancheros con el ambiente.In this article we study how the arid ecosystems of lower southern California were opened to different kinds of agriculture. In this isolated and arid region modern forms of agriculture were unknown to the indigenous inhabitants and were only introduced in the 18th century by Jesuit missionaries and their accompanying ranchers. Based on indigenous knowledge of the local environment and on the adaptation of Mediterranean and Middle Eastern oases culture, the ranch society and economy developed efficient strategies that allowed them to enjoy the sustainable use of water, soil and other natural resources of the oases where they had established themselves, thereby maintaining these fragile ecosystems and building an original cultural landscape. From the last decades of the 19th century, however, the perforation of wells permitted the extension and diversification of agriculture. The greatest ecological disturbances were due to overuse of land and water between 1950 and 1990. The deterioration of the ecosystems and its dire socioeconomic consequences showed that the region was in no way suitable for large scale production of grain; while the high volume of water required by industrial plants caused soil exhaustion. Using an environmental historical approach, based on the ranchero relationship with the environment, one may identify the means and circumstances whereby agriculture in the region could have experienced sustainable development

Respuesta hidrológica al cambio climático en regiones áridas: caso de estudio en los Comondú, Baja California Sur, México

Background. Currently, climate change is one of the most relevant phenomena within the scientific environment; this change has been recorded as an increase in temperatures on a global scale. For the central zone of Baja California Sur (BCS), Mexico, climate models also indicate an increase in the frequency of extreme precipitation. The study area covers two towns (San José and San Miguel de Comondú) whose urban and rural areas are located in a ravine of approximately 16 km in length and up to 800 m in width. Goals. To carry out a historical, statistical analysis of the climatic variability and model the response of the Comondú stream to extreme precipitation events. Methods. Climatic variability was analyzed with databases from the Comondú weather station, operated by the National Meteorological Service (SMN). In addition, the runoff pattern in the Comondú stream was ascertained in the event of extreme precipitation events, similar to or close to events with a return time of 1000 years, using hydrological and hydraulic models of HEC-1 and HEC-RAS software. Results. In the case of Los Comondú, BCS, there is a clear upward trend in the 24-hour extreme precipitation data, which implies that the danger of flooding in populated areas and crops increases considerably. The occurrence of a 1000-year event would affect about 86,864 m2 of the urban area of both towns and 201,570 m2 of the area under cultivation. Conclusions. The results of our modeling indicate an increase in area, depth, and speed of the stream, increasing the risk of flooding in the lower areas of Los Comondú, BCS. Based on our modelings results, measures should be promoted to safeguard the population and the economy of Los Comondú.Antecedentes. En la actualidad, el cambio climático es uno de los fenómenos con mayor relevancia dentro del medio científico; dicho proceso se ha registrado como un incremento de las temperaturas a escala global. Para la zona central de Baja California Sur (BCS), México, los modelos climáticos indican, además, un aumento en la frecuencia de precipitaciones extremas. El área de estudio abarca dos poblaciones (San José y San Miguel de Comondú) cuyas zonas urbanas y rurales se encuentran ubicadas en una cañada de aproximadamente 16 km de longitud y hasta 800 m de ancho. Objetivos. Realizar un análisis estadístico histórico de la variabilidad climática y modelar la respuesta del arroyo Comondú ante eventos extremos de precipitación. Métodos. Se analizó la variabilidad climática de acuerdo con las bases de datos de la estación climatológica de Comondú, operada por el Servicio Meteorológico Nacional (SMN). También se determinó el patrón de los escurrimientos en el arroyo Comondú durante episodios de precipitación extrema, similares o cercanos a eventos con tiempo de retorno de 1000 años por medio de los modelos hidrológicos e hidráulicos de los software HEC-1 y HEC-RAS. Resultados. Para el caso de los Comondú, se observa una clara tendencia a la alza en los datos de precipitación extrema de 24 horas, lo cual implica que el peligro de inundaciones en la zonas pobladas y de cultivos aumenta considerablemente. La ocurrencia de un evento de 1000 años afectaría cerca de 86,864 m2 en la zona urbana de ambos poblados y 201,570 m2 en la zona de cultivo. Conclusiones. Los resultados de la modelación indican un incremento en área, profundidad y velocidad de la corriente, lo que aumenta el riesgo de inundación en las zonas bajas de los Comondú. Con base en los resultados de la modelación, se pueden promover medidas que permitan salvaguardar a la población y la economía de este lugar

Disponibilidad y uso del agua en el oasis de los Comondú, Baja California Sur: retos y oportunidades para el desarrollo rural

el desarrollo en las zonas áridas está estrechamente re - lacionado con la disponibilidad y calidad del recurso agua tanto para uso humano como productivo. Este artículo se refiere a su estado actual, disponibilidad y uso en San Mi - guel y San José de Comondú, dos comunidades-oasis de Baja California Sur, México, en el contexto de una política pública que promueve su crecimiento con base en la ex - plotación de su potencial turístico. Con esto se pretende ofrecer un marco de referencia para comprender la cultu - ra ambiental y de manejo hídrico en esas poblaciones, así como ofrecer opciones para un mejor uso de este recurso en una zona vulnerable, que es representativa de localida - des sudcalifornianas aisladas, pero en vías de integración a los procesos económicos y de urbanización que se viven en la entidad

Future of Coastal Lagoons in Arid Zones under Climate Change and Anthropogenic Pressure. A Case Study from San Jose Lagoon, Mexico

In arid and semiarid zones, groundwater plays a key role in the ecology and availability of freshwater. Coastal lagoons in arid zones have great importance as a refuge for species of flora and fauna, as a source of freshwater, and for recreational purposes for local communities and tourism. In addition, as environments under natural stress, they are suffering pressure from anthropogenic activities and climate change, especially in zones with intense touristic development as in the case of the Baja California Peninsula in northwest Mexico. In this paper, we analyze the future of a coastal lagoon impacted by climate change and anthropogenic pressures. We constructed a groundwater MODFLOW-SWI2 model to predict changes in freshwater–saltwater inputs and correlated them with the geospatial analysis of the distribution and evolution of the water body and surrounding vegetation. The methodology was applied to the San Jose lagoon, one of the most important wetlands in the Baja California peninsula, which had been affected by anthropogenic activities and endangered by climate change. According to our water balance, the deficit of the San Jose aquifer will increase by 2040 as a result of climate change. The water table north of the lagoon will drop, affecting the amount of freshwater inflow. This reduction, together with an increase of evapotranspiration and the sea-level rise, will favor an increase of mineralization, reducing the surface water and groundwater quality and in consequence affecting the vegetation cover. Without proper management and adequate measures to mitigate these impacts, the lagoon may disappear as a freshwater ecosystem. Results of this research indicate that the use of a groundwater flow model, together with a geospatial analysis provide effective tools to predict scenarios for the future of coastal lagoons, and serve as a basis for land planning, nature conservation, and sustainable management of these ecosystems

Caracterización del peligro por inundaciones en el oasis La Purísima, Baja California Sur, México

En el estado de Baja California Sur existen solo cuatro oasis con extensiones mayores a 2.0 km 2 ; La Purísima (2.25 km 2 ) representa el tercero en extensión. En el pasado el oasis fue frecuentemente afectado por inundaciones resultantes de los eventos extremos de precipitación, que generaron graves daños en la cuenca. Se realizó un diagnóstico del oasis La Purísima, con respecto a posibles inundaciones como consecuencia de lluvias extremas, lo cual incluye el análisis estadístico de la precipitación para la elaboración de un modelo hidrológico e hidráulico, con el fin de calcular el caudal máximo, el volumen y la frecuencia de crecidas en los cursos del arroyo Cadegomo bajo diferentes escenarios de lluvias extremas. Finalmente se elaboró un mapa de peligro por inundación según los escenarios elaborados Se efectuó un análisis de la ocurrencia de inundaciones en el pasado y sus efectos en el oasis por medio de evidencias históricas de inundación de la zona, para verificar su posible aplicación en la calibración de los modelos. Los caudales resultantes de los eventos de precipitación extremos generan un incremento importante de los niveles en el drenaje de la cuenca. La respuesta del arroyo es un incremento en el área de inundación de hasta 14% respecto al tiempo de retorno de 20 años. Un evento de 1 000 años generaría un incremento en el área de inundación de 67% y bajas, afectando las zonas de la región urbana, así como todos los lotes de cultiv

Hydrogeochemical Characterization as a Tool to Recognize “Masked Geothermal Waters” in Bahía Concepción, Mexico

Geo-thermalism has been widely recognized on the Baja California Peninsula, especially during the last decade. The current research, carried out on Bahia Concepcion, evidences the existence of geothermal springs, which get recharged mainly by groundwater and seawater. The groundwater can be characterized as Na+-Cl− and Na+-HCO3− type, with a pH value close to neutrality. The slightly more acidic thermal sites presented temperatures between 32 °C and 59 °C at the surface. Based on the relationships of the Cl− and Br−, as well as the B/Cl−, and Br−/Cl− ratios, seawater was recognized as the main source of salinity. The spatial distribution is explained directly through marine intrusion, or via sprays and aerosols within the rainwater. Seawater ratios in thermal springs varied from 62% to 83%, corresponding mainly to shallow inflow, but seawater inputs into the deep thermal reservoir were also recognized. Temperatures in the geothermal deep reservoir were inferred from 114 to 209 °C, calculated through the SiO2 and Na+-K+ geothermometers. In addition to previously reported thermal sites at Bahía Concepción, and based on their elevated temperatures, two new sites were identified. Another five springs do not fulfill the commonly used definition, based on differential temperature, but show the typical hydrogeochemical signature of thermal water. A new approach to identify this low-temperature geothermal-influenced spring water by its hydrogeochemical composition is presented, for which the term “Masked Geothermal Waters” (MGW) is introduced. Our findings increase the area of the geothermal anomaly and, therefore, the potential of geothermal resources. The approach proposed in this research will also be useful to identify more MGW in other coastal areas

Arsenic Concentration in the Surface Water of a Former Mining Area: The La Junta Creek, Baja California Sur, Mexico

The mining activity in the San Antonio-El Triunfo district, located in a mountainous region at 60 km southeast of La Paz, occured for more than 250 years and left behind severe contamination of soils and riverbed sediments which led to elevated concentrations of arsenic and other trace elements in the surface- and groundwater of the region. Although the main mining activity ended around 1911, contamination is still beeing distributed, especially from left behind tailings and mine waste piles. The contamination levels in the groundwater have been reported in several studies, but there is little information available on the surface water quality, and especially the temporal variation. In this study, we analyzed the surface water of the La Junta creek, in the southern part of the San Antonio-El Triunfo mining district. The working hypothesis was that by means of a spatial analysis of surface water and shallow groundwater, in combination with the temporal observation of the concentrations in runoff water, the effects of different sources of arsenic (natural geogene anomalies, due to historic mining activity, and hydrothermal related impact) in the La Junta creek can be recognized. This present study revealed that historic mining activity caused a mojor impact of arsenic but less contamination was observed than in the northern part of the district and elevated arsenic concentrations in stream water generally occurred during times of low streamflow

Hydrochemical Indicator Analysis of Seawater Intrusion into Coastal Aquifers of Semiarid Areas

Saltwater intrusion into groundwater systems is a problem worldwide and is induced mainly by human activities, such as groundwater overexploitation and climate change. The coastal Los Planes aquifer in the southern part of the Baja California Peninsula (Mexico) is affected by seawater intrusion due to more than 40 years of groundwater overexploitation. A dataset of 55 samples was compiled, including 18 samples from our campaigns between 2014 and 2016. Several methods exist to define the impact of seawater in a coastal aquifer, such as the “seawater fraction”, the “Chloro-Alkaline Indices”, the “Hydrochemical Facies Evolution Diagram”, and the “Saltwater Mixing Index”. These methods provide reasonable results for most of the coastal zone of the Los Planes aquifer. A slight increase in mineralization was observed from 2014 to 2016 compared with the situation in 2003. However, in its northwestern part, samples from hydrothermal wells were not recognized by these methods. Here, the aquifer is affected mainly by thermal water with elevated mineralization, introduced through the El Sargento fault, a main fault, which cuts through the study area in the north–south direction. By considering known hydrothermal manifestations in the interpretation, samples could be classified as a combination of four end-members: fresh groundwater, seawater, and the composition of two types of thermal water. One thermal endmember with very low mineralization coincides with the thermal water described from the Los Cabos Block, where meteoric water represents the source (found in the Sierra la Laguna). The second endmember is comparable to coastal thermal manifestations where seawater represents the main source. Therefore, the higher mineralization in the northwestern zone is the result of the mobilization of thermal groundwater and direct mixing with seawater, which is introduced locally at the coast due to overextraction. This finding is important for future management strategies of the aquifer