Dynamic processes in Venice region outlined by environmental isotopes

Research 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

In 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

Origin and effects of nitrogen pollution in groundwater traced by δ15N–NO3 AND δ18O–NO3: the case of Abidjan (Ivory Coast)

Groundwater 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

Coincident Application of a Mass Balance of Radium and a Hydrodynamic Model for the Seasonal Quantification of Groundwater Flux into the Venice Lagoon, Italy

A mass balance of the naturally occurring short-lived radium isotopes (223,224Ra) in the Venice Lagoon was conducted by an integrated approach combining the directly estimated individual Ra contributions and hydrodynamic model results. Hydrodynamic data allows for the calculation of the Ra mass balance in sub-sections of the Venice Lagoon (boxes), which are characterized by physically homogeneous properties, instead of investigating the entire lagoon. Utilizing this method, both the seasonal and the spatial variability of the submarine groundwater discharge in the Venice Lagoon have been estimated. Between 14–83 × 109 L d− 1 of water were calculated to flow across the sediment–sea interface, corresponding to 5–28 times the mean annual river input. The submarine groundwater discharge estimates were correlated with the residence time calculation to better understand spatial and seasonal variation

Tracing nitrification and denitrification processes in a periodically flooded shallow sandy aquifer

The 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

Salinidad del recurso hídrico subterráneo del Altiplano Central

Salinity of the groundwater on the central altiplano Present hydrological balance of the aquifer on the central Bolivian Altiplano (6 000 km2) shows an input of 50 106 m3 by the Rio Desaguadero and by infiltration of rainfall runoff close to the piedmonts. The losses are due to evaporation and flow to the Salars. Close to the piedmont, groundwater is fresh and depleted in heavy isotopes like the rain of humid season (<0,5 mS cm-1 ; δ180<-14‰). Close to the recharge zone by the Desaguadero, groundwater has similar characteristics to the mean values of the Rio (2 mS cm-1 y δ18O ≈ -10‰). Downstream, a more saline zone 3-6 mS cm-1) presents an isotopic signal of evaporated water and an age of around 3 500 B.P. (14C and hydraulic model). It could be bound to the Taúca lake, prior to 8000 years, or to a more recent paleolake.Salinité de la ressource en eau souterraine de l'altiplano central Le bilan hydrologique actuel de l'aquifère de 1'Altiplano central bolivien (6 000 km2) montre une alimentation annuelle de 50 106 m3 par le rio Desaguadero et par infiltration près des piedmonts. Les sorties sont l'évaporation et l'écoulement vers les salars. Près des piedmonts, l'eau souterraine est douce (<0,5 mS cm-1) et pauvre en isotopes lourds comme la pluie de la saison humide (δ180<-14‰). Près de la zone de recharge par le Desaguadero, l'eau souterraine a des caractéristiques proches de la moyenne de celles du rio (2 mS cm-1 y δ18O ≈ -10‰). Plus à l'aval, une zone plus salée (3-6 mS cm-1) présente un signal isotopique d'eau évaporée et un âge (14C et modèle hydraulique) d'environ 3 500 B.P. Elle pourrait être liée au lac Taúca, antérieur à 8 000 ans, ou à un paléolac plus récent.El balance hidrológico actual del acuífero del Altiplano central boliviano (6000 km2) muestra una alimentación anual de 50 106 m3 por el río Desaguadero y por infiltración cerca de los montes. Las pérdidas son por evaporación y por flujo hacia los salares. Cerca de los montes, el agua subterránea es dulce (<0,5 mS cm-1) y empobrecida, como la lluvia del verano, en isótopos pesados (δ180<-14‰). En el área de influencia del Desaguadero, el agua subterránea tiene características salinas y isotópicas similares a las del río (2 mS cm-1 y δ18O ≈ -10‰). Aguas abajo, una zona salina (3-6 mS cm-1) tiene una señal isotópica de agua evaporada y una edad (14C y modelo hidráulico) de aproximadamente 3500 años. Podría ser relacionada al lago Taúca, anterior a 8000 años, o a un paleolago más reciente.Coudrain-Ribstein Anne, Pratx Bruno, Quintanilla Jorge, Zuppi Gian Maria, Cahuaya David. Salinidad del recurso hídrico subterráneo del Altiplano Central. In: Bulletin de l'Institut Français d'Études Andines, tome 24, N°3, 1995. Eaux, glaciers & changements climatiques dans les Andes tropicales. pp. 483-493