Understanding the processes in a historically relevant thermal and mineral spring water by using mixing and inverse geochemical models.

The thermal mineral water of Peñón de los Baños spa (Mexico City) has been used for over 500 years starting in pre-Hispanic times and is famous for the treatment of various pathologies. It has a temperature of 45 °C, which is rich in HCO3-, and its main trace elements are B, Li and Fe, which confers healing effects. Concerns about the sustainability of this important spa have motivated this study to understand the thermal system, possible hydraulic and hydrochemical changes over time and its implications. Stable water isotope data indicate that the thermal water sources originate from local precipitation at Sierra de las Cruces with a recharge elevation of approximately 2770 m above sea level. The recharged water percolates through volcanic and carbonate rock formations and ascends via fault structure conduits, where it eventually is extracted 25 km downstream in Peñon de los Baños. During the gravity-driven deep circulation of up to 4.9 km, the groundwater is heated up to 136-160 °C. A comparison of past and current water levels and water chemical analyses indicates a water table drop and few variations in the chemical composition, confirming the presence of anthropic impact on water quality. Due to the heavy groundwater extractions in Mexico City, the spring water flow has ceased, and water must be pumped now from a 203-m deep well. In addition, the concentration of bicarbonate, sodium and chloride has been reduced by half since the onset of groundwater development. The therapeutic effects of this thermal mineral water are at risk due to the alteration of the chemical signature. However, new and different therapeutical uses may prevent a future deterioration or closure of this historically important thermal spa. It is crucial to establish a monitoring program of the thermal mineral water and reducing or minimizing nearby urban extractions which tap the regional flow component to preserve the properties of the thermal water.

Anthropogenic influence on the sediment chemistry and diatom assemblages of Balamtetik Lake, Chiapas, Mexico.

Balamtetik is the receiving body of the Rio Grande de Comitán and is located just at the outskirts of the Montebello National Park, Chiapas, México. Multi-elemental, infrared spectra, 137Cs, 210Pb, and diatom analyses in a 75-cm sediment core were used to reconstruct the recent disturbance history of the lake. The sequence chronology, based mostly on 137Cs profiles, allowed to infer high sedimentation rates in Balamtetik (~ 7 mm/year) and a nearly cyclic series of disturbance events that can be related to anthropogenic causes such as deforestation and increased development of agriculture and urban areas at local and regional scale. These disturbance events show high local and regional erosion (high Ca, TIC, and Ti), soil organic matter (IR spectra), eutrophication (high P and diatoms), and anoxic bottom water conditions (low Mn) and can be dated to the early 1950s, the late 1950s, and from the 1980s until the 2000s. The entrance of wastewaters is related with an increase in salinity inferred by the diatom record and the organic matter type. The first two disturbance events are related to changes in land use during the agrarian reform that started during the 1940s; the last event is related with the increase in local population and the introduction of intensive agriculture. This last phase of disturbance corresponds with the reports of fish mortality events around 2003; however, high lake turbidity and anoxic bottom waters seem to have been established since the 1980s. The record from Lake Balamtetik also shows that during the intermediate periods, there was a recovery of the lake and its catchment; however, the future trends might be different, as the increase in the speed of organic matter and nutrients arrival to the lake reduces its resilience.

Complex groundwater flow systems as traveling agent models.

Analyzing field data from pumping tests, we show that as with many other natural phenomena, groundwater flow exhibits complex dynamics described by 1/f power spectrum. This result is theoretically studied within an agent perspective. Using a traveling agent model, we prove that this statistical behavior emerges when the medium is complex. Some heuristic reasoning is provided to justify both spatial and dynamic complexity, as the result of the superposition of an infinite number of stochastic processes. Even more, we show that this implies that non-Kolmogorovian probability is needed for its study, and provide a set of new partial differential equations for groundwater flow.