1,720,981 research outputs found
Dynamic processes in Venice region outlined by environmental isotopes
No full textResearch carried out in the last 40 years has shown the scientific importance of groundwater circulation both in the Northern Adriatic sea bed and within the uppermost sedimentary layers of the Venice lagoon and of the Venice plain. Hydrodynamic processes are strictly controlled by a well-cemented sedimentary horizon lying under and around Venice (‘caranto’), which plays the role of regional aquitard. This layer was attributed to the subaerial cementation of the Flandrian (8–10 ka Before Present) sedimentary surface. The caranto is generalised as a
continuum horizon, being an easy explanation for several environmental, hydrogeological and geotechnical problems, e.g., a base layer for landfills, a confining layer for deep aquifers and the best substratum for locating the oak wooden pile-dwelling needed to support the largest buildings. The preservation of the isotope signal within the deep aquifers and aquiclude system records the changes in surface and groundwater characteristics and suggests the present and past recharge regimes. In this region, the heavily perturbed hydrodynamic conditions do not allow for the use of isotopic signals to derive a correct reconstruction of the present recharge. The perturbations induced by the intensive anthropogenic activity force to follow climate evolution when researching deep groundwater and pore waters. In addition, the presence of carbonatic rocks inside terrigeneous sediments affects the reconstruction of the past. Results indicate that carbonatic rocks are created by seepage, through the sediments, of gaseous carbon compounds from decaying organic layers. The gas interactions with the intra-sedimentary saline and fresh waters produce CO2, inducing the sediments’ cementation
Fonctionnement d’une retenue hydroélectrique française: approche isotopique/Functioning of a French hydroelectric reservoir. Isotopic approach
No full textIn order to better understand the hydric behaviour of the Bort-les-Orgues reservoir, physico-chemical studies, as well as isotopic studies were carried out in 1996 and 1997. The physical results show that the lake is monomictic, with thermic stratification from June to September-October. The high values of pH in the surface water during summer reveal an active development of biological production starting in June. Isotopic values of O-18 show evaporation at the water-atmosphere interface. The C-13 Of the dissolved total inorganic carbon is governed both by atmospheric exchange and biologic activity. Information about the internal dynamics of the reservoir such as a water current, an upstream water column renewal (by 'piston effect'), and a downstream sediment resuspension can thus be obtained
Hydrogeology as a climate recorder: Sahara–Sahel (North Africa) and the Po Plain (Northern Italy)
No full textInformation on palaeoclimate is encoded in groundwater in a variety of measurable "tracers". A great variety of geochemical and isotopic methods has been developed and tested with the aim of defining the different moments and aspects of the water cycle, providing a fundamental information on the recharge and groundwater flow conditions. Furthermore, environmental tracers allow us to reconstruct past environmental changes.
Particular emphasis is put on Western Africa and on the Po valley. In fact, two features are common to these regions: the movement of air masses crossing them and the geological characteristics. From the global perspective, Sahel, North Africa, Mediterranean Basin and Central Europe reveal a relative simple pattern of spatial and temporal composition of precipitation. The displacement of the Intertropical Convergence Zone (ITCZ) and the Azores anticyclone control the climatological regime and, consequently, the isotopic composition of rainfall. Moreover, both regions are characterised by big aquifers in the form of multilayer systems several hundred metres thick in large sedimentary basins. The aquifers are generally formed by sandstones (Sahara) or sands (Po valley) and are interbedded with argillaceous layers and outcrop only in fairly limited areas, constituting the recharge zones. The groundwater movement in confined aquifers is always lower than 1 in year respecting the conditions of steady-state flow regime and hydraulic continuity, necessary for the "hydro-archives".
The comparison between the Sahara-Sahel and southern Alps allows to define the principal periods of aquifer replenishment associated with the displacement of the Intertropical Convergence Zone (ITCZ) and the Azores anticyclone.
Continental isotope archives provide a means of extending the knowledge on the magnitude and the causes of environmental and climate changes. Nevertheless, for a quantitative interpretation of the isotope records preserved in continental archives, it is necessary to know the response of the isotopic composition of precipitation to long-term fluctuations in key climatic parameters over a given area. Further, the transfer functions relating the climate-induced changes of the isotopic composition of precipitation to the isotope record preserved in the given archive should be established. It appears, thus, that stable isotopes can, presently only be used as an indirect proxy dating method for palaeowaters
Origin and effects of nitrogen pollution in groundwater traced by δ15N NO3 and δ18O NO3: the case of Abidjan (Ivory Coast).
No full textGroundwater resources of area of Abidjan are heavily impacted by nitrate pollution. A survey on 13 wells providing drinking water to the city was conducted in 2005, considering stable isotopes of the water molecule and of dissolved compounds (13C
and 15N), and major and trace elements. Nitrogen isotopes allow defi nition of the origin of nitrate contamination, mainly from urban sewage, and the processes controlling its distribution. This information, coupled to hydrogeology and groundwater geochemistry highlights major changes in groundwater quality. Nitrate content is associated with increased acidity of poorly buffered solutions in a geochemically open system and
therefore, is not affected by denitrifi cation. Dissolved inorganic carbon confirms an input from organic matter decomposition, related to both pollution and diagenesis. This geochemical evolution is observed in both Quaternary and Continental Terminal aquifers, and is independent of depth. Comparison with previous hydrochemical data suggests a rapid decline in groundwater quality
Tracing nitrification and denitrification processes in a periodically flooded shallow sandy aquifer (Lomellina, northern Italy)
No full textTracing nitrification and denitrification processes in a periodically flooded shallow sandy aquifer
No full textThe study defi nes the transfer mechanisms of nutrients and heavy metals from soil to groundwater operating in periodically water saturated soils. The study site is located in Lomellina (Po plain, Northern Italy), which is intensively cultivated with rice. Soils are dominantly constituted by sands, with acidic pH and low organic carbon content. The region generally displays low nitrate contamination in shallow groundwater, despite the intensive land use, while Fe and Mn often exceed drinking water limits. Monitoring performed through a yearly cycle closely followed the water table fluctuations in response to periodical flooding and drying of cultivated fields. pH, conductivity and Eh were measured in the field. Water samples were analysed for major ions, trace elements, nutrients and stable isotopes of dissolved inorganic nitrate (DIN). Results evidence the seasonal migration of nutrients, the redox and associated metal cycling, and allow defining nitrifi ation and denitrification processes
Use of stable isotopes to identify origin, transport and removal of dissolved nitrates in groundwater
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