Estimating Regional Hydraulic Conductivity Fields—A Comparative Study of Geostatistical Methods

Geostatistical estimations of the hydraulic conductivity field (K) in the Carrizo aquifer, Texas, are performed over three regional domains of increasing extent: 1) the domain corresponding to a three-dimensional groundwater flow model previously built (model domain); 2) the area corresponding to the 10 counties encompassing the model domain (County domain), and; 3) the full extension of the Carrizo aquifer within Texas (Texas domain). Two different approaches are used: 1) an indirect approach where transmissivity (T) is estimated first and K is retrieved through division of the T estimate by the screen length of the wells, and; 2) a direct approach where K data are kriged directly. Due to preferential well screen emplacement, and scarcity of sampling in the deeper portions of the formation (> 1 km), the available data set is biased toward high values of hydraulic conductivities. Kriging combined with linear regression, simple kriging with varying local means, kriging with an external drift, and cokriging allow the incorporation of specific capacity as secondary information. Prediction performances (assessed through cross-validation) differ according to the chosen approach, the considered variable (log-transformed or back-transformed), and the scale of interest. For the indirect approach, kriging of log T with varying local means yields the best estimates for both log-transformed and back-transformed variables in the model domain. For larger regional scales (County and Texas domains), cokriging performs generally better than other kriging procedures when estimating both (log T)^∗ and T^∗. Among procedures using the direct approach, the best prediction performances are obtained using kriging of log K with an external drift. Overall, geostatistical estimation of the hydraulic conductivity field at regional scales is rendered difficult by both preferential well location and preferential emplacement of well screens in the most productive portions of the aquifer. Such bias creates unrealistic hydraulic conductivity values, in particular, in sparsely sampled areas.     

P- and S-wave velocities and densities in silicate and calcite rocks from the Peloritani Mountains, Sicily (Italy): The effect of pressure, temperature and the direction of wave propagation

The Peloritani Mountain Belt (north-eastern Sicily) represents the connection between the Southern Appenninic Range and the Appenninic Maghrebid Chain. The lithotypes outcropping in a 36 km long and approximately 8 km wide area in the eastern part of the Peloritani Mountains are considered to represent most properly the composition of the lower crust. We selected 7 representative samples of silicate rocks (amphibolite, paragneisses, augen gneiss, phyllitic quartzite, pegmatitic rock) and 3 samples of calcite rocks (calc-schist, marbles) for the petrophysical measurements. Measurements were done on sample cubes of dry rocks in a multi-anvil apparatus. Raising of pressure gives rise to velocity increase, but the rate is different in the silicate and calcite rocks and closely related to progressive closure of microcracks. Linear behaviour is approached above about 200 MPa. Increasing temperature at 600 MPa decreases velocities in most silicate and in the calcite rocks with almost linear slopes. Substantial anisotropy of P- and S-wave velocities and shear wave splitting is found in both rock types. The residual anisotropy observed above about 200 MPa is attributed to lattice preferred orientations (LPO) of major minerals. 3D velocity calculations for an amphibolite, a paragneiss and a marble sample based on the LPO of hornblende, biotite and calcite, respectively, confirm the experimental findings of a close relationship between velocity anisotropy, shear wave splitting, shear wave polarization, lattice preferred orientation and the structural frame of the rocks (foliation, lineation). In the silicate rocks, the intrinsic (600 MPa) average P-wave velocities and Poisson's (Vp / Vs) ratios exhibit a tendency for a linear increase with densities, whereas the three calcite rocks cluster at markedly higher P-wave velocities and Poisson's (Vp / Vs) ratios, compared to their densities. In the silicate rocks, there is also a linear trend for an inverse relationship between the SiO₂ content, density and the Poisson's (Vp / Vs) ratio, respectively.     

Transpiration in Quercus suber trees under shallow water table conditions: the role of soil and groundwater

Water is one of the major environmental factors limiting plant growth and survival in the Mediterranean region. Quercus suber L. woodlands occupy vast areas in the Iberian Peninsula, frequently under shallow water table conditions. The relative magnitude of soil and groundwater uptake to supply transpiration is not easy to evaluate under these circumstances. We recently developed a conceptual framework for the functioning of the root system in Q. suber that simulates well tree transpiration, based on two types of root behaviour: shallow connected and deep connected. Although this significantly improved knowledge on the functional traits of Mediterranean Q. suber, the approach has the limitation of requiring root sap flow data, which are seldom available. In this work, we present alternative methodologies to assess if trees are connected to groundwater and to estimate the soil and groundwater contributions to tree transpiration. We provide evidence on the tree unrestricted access to groundwater solely based on meteorological, stem sap flow and leaf water potential data. Using a soil mass balance approach, we estimated the yearly soil and groundwater contributions to tree transpiration: 69.7% and 30.3%, respectively. Groundwater uptake became dominant in the dry summer: 73.2% of tree transpiration. Results reproduce extremely well those derived from root modelling. Because of its simplicity both in formulation and data requirements, our approach is potentially liable to be adapted to other groundwater‐dependent Mediterranean oak sites, where interactions between land use and water resources may be relevant. Copyright © 2013 John Wiley & Sons, Ltd.     

Study on the Historical Distribution of Metals in Aquatic Sediments

In this study, the historical distribution of metals, phosphorous, and sulfur at four different depths in the sediments of different lakes formed in the course of an urban river (in Londrina, Parana State, Brazil) were determined. The transport of metals along the course of the river was observed mainly for Mn, Cr, and Zn. High concentrations of Pb in the Capivara Bay and Cr in the river were attributed to contamination from a battery plant and a tannery, respectively. The concentrations of heavy metals in the deepest layers of the sediments remain high several years after deposition.     

Trace metal concentrations in southern right whale (Eubalaena australis) at Península Valdés, Argentina

The presence of essential (Fe, Mn, Zn, Cu, Ni and Al) and non-essential trace metals (Cd and Pb) was tested in liver (N=26) and kidney (N=42) from dead Southern Right Whale (SRW--Eubalaena australis) calves found beached in Península Valdés, Argentina. Essential metals were detected in all samples, particularly in hepatic tissue; though Ni and Al were accumulated mainly in the kidney. Cd and Pb were not detected in any samples. Sex and length of calves did not influence metal levels found, nor did the geographic location of carcasses. Our findings for essential metals were similar to those reported for mysticetes in other parts of the world. Except for a previous report on one SRW calf, this is the first data on trace metals for this species in Patagonia. This information is vital for SRW management considering increasing human pressures impacting their feeding and breeding grounds.     

Atmospheric noble gas signatures in deep Michigan Basin brines as indicators of a past thermal event

Atmospheric noble gases (e.g., ²²Ne, ³⁶Ar, ⁸⁴Kr, ¹³⁰Xe) in crustal fluids are only sensitive to subsurface physical processes. In particular, depletion of atmospheric noble gases in groundwater due to boiling and steam separation is indicative of the occurrence of a thermal event and can thus be used to trace the thermal history of stable tectonic regions. We present noble gas concentrations of 38 deep brines (~ 0.5–3.6 km) from the Michigan Basin. The atmospheric noble gas component shows a strong depletion pattern with respect to air saturated water. Depletion of lighter gases (²²Ne and ³⁶Ar) is stronger compared to the heavier ones (⁸⁴Kr and ¹³⁰Xe). To understand the mechanisms responsible for this overall atmospheric noble gas depletion, phase interaction models were tested. We show that this atmospheric noble gas depletion pattern is best explained by a model involving subsurface boiling and steam separation, and thus, consistent with the occurrence of a past thermal event of mantle origin as previously indicated by both high ⁴He/heat flux ratios and the presence of primordial mantle He and Ne signatures in the basin. Such a conceptual model is also consistent with the presence of past elevated temperatures in the Michigan Basin (e.g., ~ 80–260 °C) at shallow depths as suggested by previous thermal studies in the basin. We suggest that recent reactivation of the ancient mid-continent rift system underneath the Michigan Basin is likely responsible for the release of both heat and mantle noble gases into the basin via deep-seated faults and fracture zones. Relative enrichment of atmospheric Kr and Xe with respect to Ar is also observed, and is interpreted as reflecting the addition of sedimentary Kr and Xe from associated hydrocarbons, following the hydrothermal event. This study pioneers the use of atmospheric noble gases in subsurface fluids to trace the thermal history of stable tectonic regions.     

The fluoride in the groundwater of Guarani Aquifer System: the origin associated with black shales of Paraná Basin

This work presents petrological and geochemical results of the black shales interval from Permian and Devonian strata of the Paraná Basin, Brazil and its relationships with fluoride of groundwater from Guarani Aquifer System. The Guarani Aquifer, located in South Brazil, Uruguay, Paraguay and Argentine, presents contents of fluoride higher than the Brazilian accepted potability limits. Several hypotheses have been presented for the origin of the fluoride in the groundwater of the Guarani Aquifer. Microcrystalline fluorite was registered in black shales of Ponta Grossa and Irati formations from Paraná Basin. The results shown in this work suggest that fluoride present in groundwater of Guarani Aquifer can be originated in deeper groundwater that circulates in Ponta Grossa and Irati formations. The interaction of the groundwater coming from deeper black shales with the groundwater-bearing Aquifer Guarani System occurs through regional fragile structures (faults and fractures) that constitute excellent hydraulic connectors between the two sedimentary packages. The microcrystalline fluorite registered in Ponta Grossa and Irati Formations can be dissolved promoting fluoride enrichment in groundwater of these black shales and Guarani Aquifer System.     

Effect of fabric anisotropy on compressional-wave propagation in various metamorphic rocks for the range 20–700°C at 2 kbars

In all rocks investigated (peridotite, amphibolite, serpentinite, marble) the observed seismic anisotropy is primarily a consequence of preferred orientation of minerals and of the elastic anisotropy of the constituent minerals of the rocks. Generally the compressional-wave velocity decreases with temperature. The amount of velocity decrease, however, is different in the various rock types and even for different directions in the same anisotropic media. Fabric-induced seismic anisotropy is not drastically reduced with temperature. In the amphibolite, and especially in the serpentinite seismic anisotropy even increases with temperature. It is expected that the preferred orientation of minerals may have an effect on wave propagation even at great depths in the earth's crust and in the upper mantle.     

Effect of high-low quartz transition on compressional and shear wave velocities in rocks under high pressure

The compressional and shear wave velocities in quarzite, granite, and granulite are determined at a fixed confining pressure of 2 kb as a function of temperature up to 720° C. The high-low quartz transition of the constituent quartz minerals is associated with a pronounced decrease in velocity of the compressional waves when approaching the transition and with a significant velocity increase after the transition. In contrast, the effect of the α-β transition on shear wave velocities is small. The drop of V _P is explained by the elastic softening of structure of the constituent quartz minerals near the α-β transition and the opening of grain-boundary cracks, caused by the very high volumetric thermal expansion of the quartz relative to the other component minerals. The velocity increase in the β-field may be attributed to an elastic hardening of the quartz structure. Poisson ratios computed from the velocity data are anomalous for a solid: they become negative within the transition regime. The transition temperature, as indicated by the minimum velocities, is higher in the polycristalline rocks than is expected on grounds of single crystal behavior, and the discrepancy is more marked in granite than in quartzite. The shift of the transition temperature to higher values is explained by internal stresses that arise from the anisotropy of the thermal expansion and compressibility of individual grains and the differences in thermal expansion and compressibility between different component minerals. The role of the α-β quartz transition as a possible cause of low-velocity layers is discussed.