92 research outputs found
Evidence of hydrological control of Sr behavior in stream water (Strengbach catchment, Vosges mountains, France)
No full textStrontium and particularly 87Sr/86Sr ratios in stream water have often been used to calculate weathering rates in catchments. Nevertheless, in the literature, discharge variation effects on the geochemical behavior of Sr are often omitted or considered as negligible. A regular survey of both Sr concentrations and Sr isotope ratios of the Strengbach stream water draining a granite (Vosges mountains, France) has been performed during one year. The results indicate that during low water flow periods, waters contain lower Sr concentrations and less radiogenic Sr isotope ratios (Sr=11.6 ppb and 87Sr/86Sr=0.7246 as an average, respectively) than during high water flow periods (Sr= 13 ppb and 87Sr/86Sr=0.7252 as an average, respectively). This is contrary to expected dilution processes by meteoric waters which have comparatively lower Sr isotopic ratios and lower Sr concentrations. Furthermore, 87Sr/86Sr ratios in stream water behave in 3 different ways depending on moisture and on hydrological conditions prevailing in the catchment. During low water flow periods (discharge < 9 l/s), a positive linear relationship exists between Sr isotope ratio and discharge, indicating the influence of radiogenic waters draining the saturated area during storm events. During high water flow conditions, rising discharges are characterized by significantly less radiogenic waters than the recession stages of discharge. This suggests a large contribution of radiogenic waters draining the deep layers of the hillslopes during the recession stages, particularly those from the more radiogenic north-facing slopes. These results allow one to confirm the negligible instantaneous incidence of rainwater on stream water chemistry during flood events, as well as the existence in the catchment of distinct contributive areas and reservoirs. The influence of these areas or reservoirs on the fluctuations of Sr concentrations and on Sr isotopic variations in stream water depends on both moisture and hydrological conditions. Hence, on a same bedrock type, 87Sr/86Sr ratios in surface waters can be related to flow rate. Consequently, discharge variations must be considered as a pre-requisite when using Sr isotopes for calculating weathering rates in catchments, particularly to define the range of variations of the end-members
Le cycle de l'eau en moyenne montagne tempérée : apport des bassins versants de recherche vosgiens (Ringelbach, Strengbach, Fecht)
No full textThe research catchments studied since 1975 by the C.E.R.E.G. in the Vosges mountains have permitted to precise the spatial and temporal variability of the main components of the water cycle and the controlling parameters in a temperate middle mountain environment. The main results concern the precipitations, the evapotranspiration, the soil water properties and the streamflow. A synthesis of the information available is in progress, using spatiaily semi-distributed and physically-based models. The interdisciplinary, systemic, dynamic approach used makes the results and models transposable to other catchments, environments and scales.Les bassins versants de recherche vosgiens étudiés depuis 1975 par le C.E.R.E.G. ont permis de préciser la variabilité spatio-temporelle des composantes du cycle de l'eau et des paramètres qui les contrôlent en moyenne montagne tempérée. Les principaux résultats concernent les précipitations, l'évapotranspiration, les propriétés hydriques des sols et les écoulements. Une synthèse de ces informations sous forme de modèles spatialisés et à bases physiques est en cours. L'approche interdisciplinaire, systémique et dynamique utilisée rend ces résultats et modèles transposables à d'autres bassins, d'autres milieux et d'autres échelles.Ambroise Bruno, Auzet Anne-Véronique, Humbert Joël, Najjar Georges, Mercier Jean-Luc, Paul P., Viville Daniel. Le cycle de l'eau en moyenne montagne tempérée : apport des bassins versants de recherche vosgiens (Ringelbach, Strengbach, Fecht). In: Annales de Géographie, t. 104, n°581-582, 1995. pp. 64-87
Hydrological behaviour of the granitic Strengbach catchment (Vosges massif, Eastern France) during a flood event
No full textA field campaign combining monitoring devices and determination of isotopes and chemical elements has been performed during a summer thunderstorm in the small granitic Strengbach catchment (Vosges, France). The collected ground data were used in a hydrological modelling exercise including two conceptual rainfallrunoff models (GR4, TOPMODEL). The predominant role in flood generation of pre-event water coming from the superficial layers of the water saturated area has been shown and a conceptual scheme has been proposed derived from the field observations. The two tested modelling structures and assumptions are not able to take into account fully the complexity of the physical processes involved in flood generation
Modelling weathering processes at the catchment scale: The WITCH numerical model
No full textA numerical model of chemical weathering in soil horizons and underlying bedrock (WITCH) has been coupled to a numerical model of water and carbon cycles in forest ecosystems (ASPECTS) to simulate the concentration of major species within the soil horizons and the stream of the Strengbach granitic watershed, located in the Vosges Mountains (France). For the first time, simulations of solute concentrations in soil layers and in the catchment river have been performed on a seasonal basis. The model is able to reproduce the concentrations of most major species within the soil horizons, as well as catching the first-order seasonal fluctuations of aqueous calcium, magnesium and silica concentrations. However, the WITCH model underestimates concentrations of Mg2+ and silica at the spring of the catchment stream, and significantly underestimates Ca2+ concentration. The deficit in calculated calcium can be compensated for by dissolution of trace apatite disseminated in the bedrock. However, the resulting increased Ca2+ release yields important smectite precipitation in the deepest model layer (in contact with the bedrock) and subsequent removal of large amount of silica and magnesium from solution. In contrast, the model accurately accounts for the concentrations of major species (Ca, Mg and silica) measured in the catchment stream when precipitation of clay minerals is not allowed. The model underestimation of Mg2+ and H4SiO4 concentrations when precipitation of well crystallized smectites is allowed strongly suggests that precipitation of well crystallized clay minerals is overestimated and that more soluble poorly crystallized and amorphous materials may be forming. In agreement with observations on other watersheds draining granitic rocks, this study indicates that highly soluble trace calcic phases control the aqueous calcium budget in the Strengbach watershed
d13C pattern of dissolved inorganic carbon in a small granitic catchment: the Strengbach case study (Vosges mountains, France)
No full textThe transfers and origins of dissolved inorganic carbon DIC. were studied for a year in a soil–spring–stream system in
the Strengbach catchment, Vosges mountains, France. This 80 ha experimental research basin is located on the eastern side
of the mountains, at an altitude ranging from 883 to 1146 m.a.s.l. and is mainly covered by spruce 80%.. Brown acid and
podzolic soils developed on a granitic basement, and, as a result, the DIC originates solely from CO2 generated by oxidation
of soil organic matter. The d13CDIC. in catchment waters is highly variable, from about y22‰ in the springs and
piezometers to about y12‰ in the stream at the outlet of the catchment. In the springs, pronounced seasonal variations of
d13C exist, with the DIC in isotopic equilibrium with the soil CO that has estimated d13DIC 2 C of about y24‰ in winter and
y20‰ in summer. These seasonal variations reflect an isotopic fractionation that seems only induced by molecular
diffusion of soil CO2 in summer. In stream water, seasonal variations are small and the relatively heavy DIC y12‰ on
average. is a result of isotopic equilibration of the aqueous CO2 with atmospheric CO2
Hydrograph separation using isotopic, chemical and hydrological approaches (Strengbach catchment, France)
No full textThe streamflow components were determined in a small catchment located in Eastern France for a 40 mm rain event using isotopic and chemical tracing with particular focus on the spatial and temporal variations of catchment sources.
Precipitation, soil solution, springwater and streamwaters were sampled and analysed for stable water isotopes (18O and 2H), major chemical parameters (SO4, NO3, Cl2, Na1, K1, Ca21, Mg21, NH4, H1, H4SiO4, alkalinity and conductivity), dissolved organic carbon (DOC) and trace elements (Al, Rb, Sr, Ba, Pb and U). 18O, Si, DOC, Ba and U were finally selected to assess the different contributing sources using mass balance equations and end-member mixing diagrams.
Isotopic hydrograph separation shows that the pre-event water only contributes to 2% at the beginning of the stormflow to 13% at the main peak flow. DOC associated to Si and U to Ba allow to identify the different contributing areas (upper layers of the saturated areas, deep layers of the hillslope and rainwater). The streamflow (70%) originates from the deep layers of the hillslope, the remaining being supplied by the small saturated areas.
The combination of chemical (both trace and major elements) and isotopic tracers allows to identify the origin of water
pathways. During the first stage of the storm event, a significant part of the runoff (30±39%) comes from the small extended saturated areas located down part of the basin (overland runoff then groundwater ridging). During the second stage, the contribution of waters from the deep layers of the hillslope in the upper subcatchment becomes more significant. The final state is characterised by a balanced contribution between aquifers located in moraine and downslopes.
Indeed, this study demonstrates the interest of combining a variety of hydrometric data, geochemical and isotopic tracers to identify the components of the streamwater in such conditions
The impact of vegetation on fractionation of rare earth elements(REE) during water–rock interaction
No full textPrevious studies on waters of a streamlet in the Vosges mountains (eastern France) have shown that Sr and rare earth elements (REE) principally originate from apatite dissolution during weathering. However, stream water REE patterns normalized to apatite are still depleted in light REE (LREE, La–Sm) pointing to the presence of an additional LREE depleting process. Speciation calculations indicate that complexation cannot explain this additional LREE depletion. In contrast, vegetation samples are strongly enriched in LREE compared to water and their Sr and Nd isotopic compositions are comparable with those of apatite and waters. Thus, the preferential LREE uptake by the plants at the root–water–soil (apatite) interface might lead to an additional LREE depletion of the waters in the forested catchment. Mass balance calculations indicate that the yearly LREE uptake by vegetation is comparable with the LREE export by the streamlet and, therefore, might be an important factor controlling the LREE depletion in river waters
Isotope hydrological study of mean transit time in the granitic Strengbach catchment (Vosges massif, France): application of the FlowPC model with modified input function
No full textHYDROLOGICAL PROCESSESInternational audienceMeasurements of 18O concentrations in precipitation, soil solution, spring and runoff are used to determine water transit time in the small granitic Strengbach catchment (0Ð8 km2; 883–1146 m above sea level) located in the Vosges Mountains of northeastern France. Water transit times were calculated by applying the exponential, exponential piston and dispersion models of the FlowPC program to isotopic input (rainfall) and output (spring and stream water) data sets during the period 1989–95. The input function of the model was modified compared with the former version of the model and estimated by a deterministic approach based on a simplified hydrological balance. The fit between observed and calculated output data showed marked improvements compared with results obtained using the initial version of the model. An exponential piston version of the model applied to spring water indicates a 38Ð5 month mean transit time, which suggests that the volume in the aquifer, expressed in water depth, is 2Ð4 m. A considerable thickness (>45 m) of fractured bedrock may be involved for such a volume of water to be stored in the aquifer
Isotope hydrological study of mean transit time in the granitic Strengbach catchment (Vosges massif, France): application of the FlowPC model with modified input function
No full textHYDROLOGICAL PROCESSESInternational audienceMeasurements of 18O concentrations in precipitation, soil solution, spring and runoff are used to determine water transit time in the small granitic Strengbach catchment (0Ð8 km2; 883–1146 m above sea level) located in the Vosges Mountains of northeastern France. Water transit times were calculated by applying the exponential, exponential piston and dispersion models of the FlowPC program to isotopic input (rainfall) and output (spring and stream water) data sets during the period 1989–95. The input function of the model was modified compared with the former version of the model and estimated by a deterministic approach based on a simplified hydrological balance. The fit between observed and calculated output data showed marked improvements compared with results obtained using the initial version of the model. An exponential piston version of the model applied to spring water indicates a 38Ð5 month mean transit time, which suggests that the volume in the aquifer, expressed in water depth, is 2Ð4 m. A considerable thickness (>45 m) of fractured bedrock may be involved for such a volume of water to be stored in the aquifer
Mid-term trends in acid precipitation, streamwater chemistry and element budgets in the strengbach catchment (Vosges Mountains, France)
No full textIn the Vosges Mountains (NE of France), integrated plot-catchment studies have been carried out since 1985 in the Strengbach basin to study the influence of acid atmospheric inputs on surface water quality and element budgets. In this paper, available mid-term time series (1985–1991) have been considered to detect obvious trends, if any, in surface water chemistry and element budgets. Air quality data showed a slight decline for SO2, whereas NO2 slightly increased over the period, but these trends are not very significant. This is in agreement with increased N concentration (mainly as NH 4 + ) and with the stability of SO 4 2– in open field precipitation. Because of a significant decrease in rainfall amount over the period, only inputs of NH 4 + increased significantly whereas H+ and SO 4 2+ inputs declined. In spring and streamwaters, pH and dissolved Si concentration increased mainly as a result of a reduced flow. Na+, K+, Cl– and HCO-3~– concentrations remained stable whereas Ca2+, Mg2+ and SO 4 2+ concentrations declined significantly. Only NO 3 – concentration increased significantly in springwaters. The catchment budgets revealed significant losses of base cations, Si and SO 4 2– . These losses decreased over the period. Nitrogen was retained in the ecosystem. However, a longer record is needed to determine whether or not changes in surface water chemistry have resulted from short-term flow reductions or long-term changes in input-output ion budgets. This is specially true with N because the decline in SO 4 2– output was accompanied by N accumulation
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