José Miguel Andreu

Variations in seepage water geochemistry induced by natural and anthropogenic microclimatic changes: Implications for speleothem growth conditions

During an annual cycle the affect of microclimatic changes (of natural and anthropogenic origin) on the geochemical characteristics of seepage water and mineral precipitation rates was analyzed for two karstic caves which contrast in environmental stability and energy exchange with exterior. On the one hand, Castañar cave (Caceres, Spain) is an extremely controlled show cave with limited visitation showing a minimum exchange rate of energy with the external atmosphere and, secondly, Canelobre cave (Alicante, Spain), is a widely visited cave where the anthropogenic impact generates rapid and high-energy environmental changes. Mineral saturation state of seepage water of both caves is controlled by microclimatic variations, such as: 1) natural underground air renewal through the porous system of the upper soil and the network of host-rock fissures, or elso through the cave entrance, 2) cumulative disruptions in the pCO2 levels of cave air due to the presence of visitors, and 3) forced ventilation of the subterranean atmosphere due to the uncontrolled opening of cave entrances. The obtained results reinforce the significance of the microclimatic fluctuations on short time scales in the dynamics of the subterranean karst systems, in terms of rates of mineral precipitation and growth of speleothems, as well as their key role for cave conservation.

Definition of Microclimatic Conditions in a Karst Cavity: Rull Cave (Alicante, Spain)

Rull Cave (Alicante, SE Spain) is a shallow karstic cavity located in metre-thick beds of Miocene limestone conglomerate and overlain by soil with little profile development. A microenvironmental monitoring system was installed in order to record the exchange between the cave and the external atmosphere. Data were collected every 15 min over a period of 14 months (from 22/11/2012 to 13/01/2014). Both radon and CO2 concentration values changed over the course of the annual cycle and were strongly controlled by the difference in air temperature between the exterior and the cave atmosphere. Wavelet transform was applied to the data to determine the influence of visitors on the environmental parameters controlling the cave’s microclimate.

Mineral-Forming Processes at Canelobre Cave (Alicante, SE Spain)

Canelobre cave presents a remarkable collection of speleothems, such as stalactites, coralloids, stalagmites, flowstones, draperies, columns, helictites, gours, spars, crusts and flowers. Most of them are calcitic in composition, although sulphate speleothems have been found in some lower chambers in the cave. Gypsum speleothems appear as white uniform crusts or as flowers (antholites). The younger speleothems recognized in the cave corresponds to soda-straw stalactites, helictites and some active stalagmites. Vadose speleothems clearly prevail the phreatic ones, which are represented mainly by calcite spar deposits. Different mechanisms of speleothem formation can be recognized in the cave: dripping or flowing water, seepage, capillarity, etc. The parameters that control the speleothem deposition are the characteristics of karstic waters and the cave microclimate.

Overexploitation and water quality in the Crevillente aquifer (Alicante, SE Spain)

The Crevillente aquifer is a karstic aquifer, situated in Alicante province in the SE of Spain. The aquifer basically comprises a series of Jurassic limestones and dolomites, belonging to the Betic Cordillera. Intense exploitation of the aquifer started in the early 1960s. Exploitation was initially concentrated in two sectors of the Sierra de Crevillente and, years later, extended to a third sector. As a consequence of abstractions that were much greater than recharge into the system, a continual drop in the water level persisted for several decades. These abstractions have occasionally caused local dewatering over depths of more than 300 m. From a hydrogeological point of view, the aquifer dewatering in one of the sectors was accompanied by increased mineralization and a fall in quality of the groundwater, and several boreholes had to be abandoned. In recent years, the degree to which the aquifer is overexploited has fallen considerably, and it appears to have entered a new hydrodynamic stage. New hydrogeochemical characterisations have been carried out, which indicate that the aquifer water is relatively strongly mineralised due, fundamentally, to the dissolution of evaporite rocks. On the other hand, deterioration in water quality as a consequence of the degree of overabstraction can also be confirmed.

Validating the KAGIS black-box GIS-based model in a Mediterranean karst aquifer: Case of study of Mela aquifer (SE Spain)

This research was funded by the Spanish Ministry of Science and Innovation, Projects CGL2013‐48802‐C3‐3‐R and CGL2015‐69773‐C2‐1‐P; and by the University of Alicante, Projects GRE15‐19 and GRE17‐12.