Hydrological modelling and evolution of lakes and playa-lakes in southern Spain constrained by geology, human management and climate change.

The hydrological functioning of wetlands in S Spain is poorly understood. We perform a 22-years hydrological modelling of seven playa-lakes located in a semi-arid region of southern Spain, including dry and wet periods. To do that, we applied a hydrological balance model to reconstruct past lake water levels. In addition, we investigated the hydrochemistry of the water, the basin bathymetry, and the geological setting of the watersheds, acquiring new lithology and active structures data. Once the models were constrained, scenarios considering increases on temperature and human management were implemented, and discussed. The water balance is simplified to precipitation (water input) and basin discharge (evapotranspiration), as the lakes are disconnected from groundwater because of the low-permeability substrate. In addition, unlike in previous studies, we add overflows to the modelling. The results of the model agree with actual lake water monitoring data (R2 > 0.8). We observed that the hydroperiods of some of these lakes vary from permanent lakes to ephemeral, depending strongly on the basin bathymetry. Lakes with steeply margins show longer hydroperiods, whilst it is shorter for low-lying floor playa-lakes. In addition, we observed that steeply lake margins respond to active faults and/or lithological changes. To forecast the effects of climate change on the lake hydroperiods, we applied a 1 °C increase in average temperature in our hydrological modelling. The hydroperiod is significantly reduced for ephemeral playa-lakes, whilst is barely affected in permanent lakes. Moreover, we detected the high sensitivity of ephemeral playa-lakes to the anthropogenic management, including siltation, plant colonization and changes watershed surface.

Online Differential Thermal Isotope Analysis of Hydration Water in Minerals by Cavity Ringdown Laser Spectroscopy.

We have developed a new method for measuring the isotopic composition (δ18O and δD) of different types of bonded water (e.g., molecular water, hydroxyl) contained in hydrated minerals by coupling a thermal gravimeter (TG) and a cavity ringdown laser spectrometer (CRDS). The method involves precisely step-heating a mineral sample, allowing the separation of the different types of waters that are released at different temperatures. Simultaneously, the water vapor evolved from the mineral sample is analyzed for oxygen and hydrogen isotopes by CRDS. Isotopic values for the separate peaks are calculated by integrating the product of the water amounts and its isotopic values, after correcting for background. We provide examples of the application of the differential thermal isotope analysis (DTIA) method to a variety of hydrous minerals and mineraloids including gypsum, clays, and amorphous silica (opal). The isotopic compositions of the total water evolved from a set of natural gypsum samples by DTIA are compared with the results of a conventional offline water extraction method followed by CRDS analysis. The results from both methods are in excellent agreement, and precisions (1σ) for δ18O (±0.12‰) and δD (±0.8‰) of the total gypsum hydration water from the DTIA method are comparable to that obtained by the offline method. A range of analytical challenges and solutions (e.g., spectroscopic interferences produced by VOCs in natural samples, isotopic exchange with structural oxygen, etc.) are discussed. The DTIA method has wide ranging applications for addressing fundamental problems across many disciplines in earth and planetary sciences, including paleoclimatology, sedimentology, volcanology, water exchange between the solid earth and hydrosphere, and water on Mars and other planetary bodies.

In situ Raman characterization of minerals and degradation processes in a variety of cultural and geological heritage sites.

We test the capabilities of in situ Raman spectroscopy for non-destructive analysis of degradation processes in invaluable masterpieces, as well as for the characterization of minerals and prehistoric rock-art in caves. To this end, we have studied the mechanism of decay suffered by the 15th-century limestone sculptures that decorate the retro-choir of Burgos Cathedral (N Spain). In situ Raman probe detected hydrated sulfate and nitrate minerals on the sculptures, which are responsible for the decay of the original limestone. In addition, in situ Raman analyses were performed on unique speleothems in El Soplao Cave (Cantabria, N Spain) and in the Gruta de las Maravillas (Aracena, SW Spain). Unusual cave minerals were detected in El Soplao Cave, such as hydromagnesite (Mg5(CO3)4(OH)2·4H2O), as well as ferromanganese oxides in the black biogenic speleothems recently discovered in this cavern. In the Gruta de las Maravillas, gypsum (CaSO4·2H2O) was identified for the first time, as part of the oldest cave materials, so providing additional evidence of hypogenic mechanisms that occurred in this cave during earlier stages of its formation. Finally, we present preliminary analyses of several cave paintings in the renowned "Polychrome Hall" of Altamira Cave (Cantabria, N. Spain). Hematite (Fe2O3) is the most abundant mineral phase, which provides the characteristic ochre-reddish color to the Altamira bison and deer paintings. Thus, portable Raman spectroscopy is demonstrated to be an analytical technique compatible with preserving our cultural and natural heritage, since the analysis does not require physical contact between the Raman head and the analyzed items.