Environmental impacts of groundwater overdraft: selected case studies in the southwestern United States

The southwestern United States—this papers study region—is home to large urban centers and features a thriving agro-industrial economic sector. This region is also one of the driest in North America, with highly variable seasonal and inter-annual precipitation regimes and frequent droughts. The combination of a large demand for usable water and semi-arid climate has led to groundwater overdraft in many important aquifers of the region. Groundwater overdraft develops when long-term groundwater extraction exceeds aquifer recharge, producing declining trends in aquifer storage and hydraulic head. In conjunction with overdraft, declines in surface-water levels and streamflow, reduction or elimination of vegetation, land subsidence, and seawater intrusion are well documented in many aquifers of the southwestern United States. This work reviews case studies of groundwater overdraft in this region, focusing on its causes, consequences, and remedial methods applied to counter it.     

Single and double ITCZ in an aqua-planet model with constant sea surface temperature and solar angle

It has been known for more than a decade that an aqua-planet model with a globally- and temporally-uniform sea surface temperature and solar isolation angle can generate intertropical convergence zones (ITCZ). Employing such a model, previous studies have shown that one of several means can be used to change between a single ITCZ over the equator and a double ITCZ straddling the equator. These means include switching to a different cumulus parametrization scheme, making changes within the cumulus parametrization scheme, and changing other aspects of the model such as horizontal resolution. Here, an interpretation of these findings is offered. In an aqua-planet model with globally and temporally uniform sea surface temperature and solar isolation angle, the latitudinal location of an ITCZ is the latitude where a balance exists between two types of attraction, both resulting from the Earths rotation. The first attraction pulls the ITCZ towards the equator and is not sensitive to changes in model design. It is directly related to the Coriolis parameter, which provides stability to the atmosphere. The second ssattraction pulls the ITCZ poleward and is sensitive to changes in model design. It is related to the convective circulation, modified by the Coriolis force. A balance between the two types of attraction is reached either at the equator or more than 10° north and south of the equator, depending on the shape and magnitude of the attractions. A balance at the equator yields a single ITCZ over the equator, whereas a balance north and south of the equator yields a double ITCZ straddling the equator.     

Zn-Pb mineralisation in the Silvermines district,Ireland: a product of burial diagenesis

Carbonate-sulphide cement stratigraphic relationships in the host rock and ore have been used to constrain the age of mineralisation at the Silvermines zinc-lead-barium deposit. The base-metal sulphides post-date planar dolomite and replace stylolites. Furthermore, the pre-mineralisation planar dolomites also replace stylolites. These and other diagenetic observations indicate that the base-metal sulphides formed at burial depths greater than 800 m, but probably predate the Variscan deformation (since pressure shadows overgrow base metal sulphides). This indicates that the sulphides are of epigenetic origin, constraining the age of mineralisation to between the late Chadian (347 Ma) and the late Westphalian (307 Ma). However, the most likely age for mineralisation, (based on widespread macro-stylolite development) is Asbian (339 Ma) or younger. No evidence of synsedimentary sulphides (in the form of hydrothermal chimneys, vent faunas, or sulphides intergrown with marine cements) was observed at Silvermines. Mineralised breccias (black matrix breccias), late-stage internal sediments, and dissolution zones within the carbonate cements all appear to be produced by hydrothermal karsting that occurred during the mineralisation process. Fluid inclusion homogenisation temperatures for ore-stage calcites (up to 300 °C) approach the peak temperature estimates derived from regional maturation parameters (270 to 310 °C from conodont alteration indices and vitrinite reflectance). This suggests that homogenisation temperatures represent maximum heating temperatures (probably during Variscan time) rather than mineralisation temperatures.Editorial handling: J. Mengue     

Atomistic simulation of the structure and segregation to the (0001) and surfaces of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The segregation of ten isovalent impurities (Al³⁺ Cr³⁺, Eu³⁺, Gd³⁺, Ho³⁺, La³⁺, Lu³⁺, Nd³⁺, Tb³⁺, Y³⁺) to the and the (0001) surfaces of haematite (-Fe₂O₃) have been studied using atomistic simulation where the forces between the atoms are modelled using the Born model of solids. Segregation is found to be energetically favoured in virtually every case. The results for the surface show that the most favourable impurity surface concentration is 33.33%. The (0001) surface has two possible terminations, one terminated by iron atoms and the other by oxygen. No minimum is calculated for the Fe termination of the (0001) surface at low temperatures, but when the effect of raising the temperature is considered, an energy minimum is found, also at 33.33% impurity coverage. In contrast, the O terminated (0001) surface has a minimum in the segregation energy for between 16.67 and 33.33% depending on the cation being considered.     

Le phytoplancton du lac de Neuchâtel

Résumé L'analyse du phytoplancton récolté de 1959 à 1962 montre qu'à son tour le lac de Neuchatel a atteint un degré de pollution favorisant l'implantation et l'expansion d'espèces indésirables. Le r?le que jouent actuellementAphanizomenon flos-aquae, Oscillatoria rubescens, O. prolifica, Tabellaria fenestrata, entre autres, ainsi que lesChlorophycées, a rapidement modifié la physionomie de la biocénose. L'inventaire des algues planctoniques dressé parFuhrmann en 1897/1898 fournit d'autre part un élément de comparaison mettant en évidence l'évolution survenue dans ce bassin subjurassien au cours de 65 années. Travail réalisé avec l'appui du Fonds national suisse de la Recherche.     

Influence des perturbations thermiques de l'atmosphère sur la qualité des images solaires

Résumé Le Pic du Midi de Bigorre étant pris comme site expérimental, l'influence sur la qualité des images solaires de deux types de perturbations thermiques de l'atmosphère est examinée, celles-ci étant dues respectivement au sol local et à la convection au sein de l'écoulement incident. Une méthode pyrhéliométrique permettant la détection de la convection en ciel clair est exposée.

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A parameter characterizing the quality of photospheric images has been defined through a three class distribution; it has been estimated over various samples taken during 230 hours of observing time at the Pic du Midi Observatory.Its occurrence is compared to that of two types of atmospheric thermal disturbances, one being created by the local ground and the other brought along by the incident flow and due mainly to convection.The time-derivation of the temperature, which is, under some conditions, well related to the nearby thermal field, may be taken as a characteristic atmospheric parameter, and it is shown that the best quality for solar images occurs only - and then with a fairly good frequency - when its value is slightly positive.A method is described which aims at the detection of convection in the clear atmosphere; as the upward motions are bringing aerosols from the lower layers, a less transparent volume is ascending during the first part of the day and then, its top may intercept the optical axis of the telescope. The diurnal variation of the atmospheric transparency, as observed with a pyrheliometer, shows clearly this occurrence, which may be quite different from one day to another.

     

The urban boundary-layer field campaign in marseille (ubl/clu-escompte): set-up and first results

The UBL/CLU (urban boundary layer/couche limite urbaine) observation and modelling campaign is a side-project of the regional photochemistry campaign ESCOMPTE. UBL/CLU focuses on the dynamics and thermodynamics of the urban boundary layer of Marseille, on the Mediterranean coast of France. The objective of UBL/CLU is to document the four-dimensional structure of the urban boundary layer and its relation to the heat and moisture exchanges between the urban canopy and the atmosphere during periods of low wind conditions, from June 4 to July 16, 2001. The project took advantage of the comprehensive observational set-up of the ESCOMPTE campaign over the Berre–Marseille area, especially the ground-based remote sensing, airborne measurements, and the intensive documentation of the regional meteorology. Additional instrumentation was installed as part of UBL/CLU. Analysis objectives focus on (i) validation of several energy balance computational schemes such as LUMPS, TEB and SM2-U, (ii) ground truth and urban canopy signatures suitable for the estimation of urban albedos and aerodynamic surface temperatures from satellite data, (iii) high resolution mapping of urban land cover, land-use and aerodynamic parameters used in UBL models, and (iv) testing the ability of high resolution atmospheric models to simulate the structure of the UBL during land and sea breezes, and the related transport and diffusion of pollutants over different districts of the city. This paper presents initial results from such analyses and details of the overall experimental set-up.     

Phreatic Surface in Island Aquifers with Regular Geometry and Time-Independent Recharge and Pumping

The equation of groundwater flow in marine island aquifers in which there is time-independent, spatially-variable recharge and pumping is solved in closed form for rectangular, circular, and elliptical island geometries. The solution of the groundwater flow equation is expressed in terms of the elevation of the phreatic surface within the flow domain. The depth of the seawater-freshwater interface below mean sea level follows from the Dupuit–Ghyben–Herzberg relation. The method of solution presented in this work relies on expanding the hydraulic head and forcing function (recharge and groundwater extraction) as Fourier series that transforms the two-dimensional Poisson-type flow equations into second-order ordinary differential equations solvable using classical theory. The important case of constant recharge (without groundwater extraction) leads to solutions in which the hydraulic head is expressible as the product of a flow factor equal to the squared root of the ratio of recharge over hydraulic conductivity times a geometric factor involving island shape parameters and flow boundary conditions. Estimability conditions for the hydraulic conductivity are derived for the cases of constant recharge and spatially variable recharge with pumping.     

The role of the NNW structural trend in the recent geodynamic evolution of north-eastern sicily and its volcanic implications in the etnean area

The seismic and eruptive events occurring in Eastern Sicily between 1978 and 1981 are analyzed with reference to the existence neoctectonic structures beginning with the Gulf of Patti earthquake (1978, Lower Tyrrhenian Basin). From this analysis, the geodynamic consistency of the movements developing along the NNW and NE trends becomes apparent. In particular, the relation between these two trends enables the authors to verify their previously elaborated deformation model for the Etnean area and to emphasize its coherence with the regional geodynamic context. Finally, the close connection is shown between the Etnean area and the NNW-SSE wrench zone breaking the Southern Calabro-Peloritan Arc.