In Northern Baja California, environmental conservation may not be fully accomplished in the absence of a clear understanding of key factors controlling and protecting biodiversity. Groundwater is an environmental agent triggering the presence of a wide range of arid ecosystems; therefore, any sustainable development in the region has to maintain a balance between environmental, social and economical benefits. The present study has placed a great emphasis on the understanding and distribution of groundwater flow systems, and their environmental interactions in the protected area of the Valle de Los Círios, using physical-chemical and isotope methods. Results show the presence of three groundwater groups portraying contrasting flow systems conditions. Analyzed samples have been classified as fresh-brackish, and thermal alkaline groundwater as suggested by pH, temperature and TDS. The Br/Cl ratio in most samples was close to the ocean molar value (1.5x10 -3 ) indicating the importance of marine aerosol fraction in the recharged waters; however, Mg/Cl,Na/Cl,Ca/Cl,SO 4 / Cl and Cl/HCO 3 +Cl ratios were significantly different to those of seawater mixing conditions. Dominant ions (Na,Ca and Cl), chemical age proxies (Li), and δ 18 O suggest waters with long residence time, with the possibility of been recharge during the late glacial period. Thermal ground water shows low minor and trace element content and exhibits the dominance of Na-plagioclase hydrolysis; their low levels of Sr and Ba suggest negligible contact with calcareous rocks and their estimated temperature at depth (80to100°C) and TDS suggest groundwater has travelled through fractured media. This introduction study suggests that desertic species in Valle de Los Cirios are highly sustained by groundwater of local and intermediate flows.

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Groundwater flow systems have been differentiated in the metropolitan zone of Mexico City based on their chemical composition and stable isotope contents. The existing hydrogeological framework for the region provided a reference for such differentiation. Local flows (Flow-system I) represent the youngest and shallowest groundwater flow identified in boreholes on the hills. Intermediate flows (Flow-system II) in boreholes on the plain represent a mixture of inflows travelling horizontally, and vertically upwards (Flow-system IV) and downwards (overlaying aquitard leakage) to extraction boreholes. Flow-system III identified in boreholes on the plain is an intermediate flow system which extends deeper than Flowsystem II. Flow-system IV, which is classified as a regional system, is related to a former thermal spring site. Groundwater travelling times, and their regional distribution and the thickness of related rock formations suggest extensive inflow supporting Flow-system IV. Future climate condition evolution (i.e. drought) will only have a limited impact on Flow-system IV as compared to Flowsystem I which have relatively rapid and short flow paths.The identification of the hierarchy of the flow systems is of paramount importance in achieving adequate groundwater management in any region where the aquifer units are several thousand metres thick.

<p>Groundwater flow understanding is a must in any study related to sustainable water management and in preventing or controlling negative environmental responses due to changes in the groundwater regime. Indeed, further developing of methods, terminology, concepts, teaching and research may benefit from considering relevant collective scientific knowledge base. Disregarding psychological and social constraints, several perceptions have been found to prevent reaching to desirable groundwater flow understanding to backup adequate decision making, among them the following three may be stated. Firstly, not all hydrological methodology provides with adequate reference to arrive at the desired groundwater flow understanding. There is a groundwater evaluation method that is usually applied in developed countries based on long periods of daily hydrological data to achieve a reliable water-balance which, however, fails to provide with related processes as groundwater quality changes, soil subsidence, ecosystem functioning, transboundary flow conditions, among others. Disregarding the lack of obtaining reliable and adequate data in time and space in developing countries, the water-balance is the recommended methodology to be applied to seek an understanding of the relation of groundwater with other components of the environment. Secondly, concepts as aquifer (water + rock) provide a further challenge to achieve a groundwater flow understanding due to the quasi-static view it provides for groundwater management. An aquifer is often strongly related to the water-balance concept where natural vertical components of flow are usually neglected. Here, inconsistent terms as overexploitation, scarcity, transmissivity, among others unnecessarily emerge. Thirdly, further education and research is under strong constrains to reach desirable teaching and research to enhance science on Water Security. Existing capacity building in groundwater in top-ranking universities (UK, Canada) has been disappearing or, is under threat, not only directly on groundwater flow systems, but as research in hydrogeology as a subject. Other universities have a latent (France, Spain) capacity building in groundwater flow systems; in many, there is an absence on the topic. It is to note that several universities (Hungary, China) are growing a sound groundwater flow systems capacity building. There are universities (Mexico) where research on groundwater flow systems is carried out by interested hydrogeologists who wait to have institutional support that might even reach government organizations. Groundwater management related government offices required to enhance the acknowledgement of the importance of groundwater remembering that more than 80% of the water supply in many countries is obtained from that source. It should be remembered that groundwater intake of the ecosystem is almost fully related to this source, which needs to be fully understood to achieve a reliable ecological yield.</p><p> </p>

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