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ABSTRACT: When present, an epikarst represents the starting point (the first karst compartment) of
11 water flow through a karst system. The air characteristics in a karst, and especially in an
12 epikarst, determine the initial water characteristics, e.g., water aggressiveness, which depends
13 on the partial pressure of CO2 (Pco2) in equilibrium with water. This paper proposes a method
14 to estimate Pco2 in epikarst air using spring water measures as HCO3¯ , temperature, pH and
δ
13C of Total Dissolved Inorganic Carbon (TDIC) and cave air measures as Pco2 and δ
13 15 Cof
CO2. This method accounts for the TDIC variations of δ
13 16 C that are caused by CO2 degassing
17 and calcite precipitation from water. The calculations are based on the influence of pH
variations and carbon loss on δ
13 18 C of TDIC. Measurements are taken at two sites: Lascaux
19 cave and the Cussac cave sites located in Perigord, southwest of France. Four water springs
20 are presented in this case study: two springs from an epikarst compartment, one spring from
21 an unsaturated zone and one spring from a saturated zone. The Pco2 in epikarst air is estimated
22 to be from 4.4% (44 000 ppm) in winter to 10% in summer. These values are higher than the
23 values of air Pco2 measured in the soil (0.27% to 1.60%) or in the caves (0.30% to 3.1%, up to
7.50% in some parts of Lascaux). We show that in epikarst air, Pco2 and δ
13 24 Cco2 are not
25 constant values but vary annually with high Pco2 and depleted values (-22.31‰ VPDB) in the
26 winter and higher Pco2 and more depleted values in the summer (-24.20‰ VPDB).
Geochimica et Cosmochimica Acta 01/2013; · 4.26 Impact Factor
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ABSTRACT: In karstic environments, groundwater is strongly influenced by CO2
partial pressure variations of air present in the infiltration zone of these aquifers. In order to characterize the geochemical changes in groundwater as it moves through the infiltration zone, we monitored various rising springs in the perched
karstic aquifer of Cussac (Dordogne, France), and measured the CO2
partial pressure in air of a nearby cavity (the Cussac Cave) for 24 months. Our method is based on the relationship between the saturation
index with respect to calcite (SIc) and the CO2
partial pressure at atmospheric equilibrium with water.
We distinguished a value for this last parameter when water is at equilibrium with respect to calcite
(SIc = 0) called saturation CO2
partial pressure. The use of this parameter can provide information on flow
conditions and relationships between water, air, and rock. Cussac aquifer is a suitable area to apply these
methods because of its small size, numerous springs, and a cave that provides data for CO2
partial pressure condition inside the massif. Results show that most of the calcium-carbonate mineralization is
acquired in the epikarst followed by a precipitation phase in the upper part of the infiltration zone.
Groundwater reaches the saturated zone with some degree of saturation depending on CO2
partial pressure variations in air inside the massif.
Journal of Hydrology 01/2012; 430:13-24. · 2.66 Impact Factor
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ABSTRACT: Static winching tests were carried out in order to determine the mechanical resistance of Maritime pine to overturning. The tested stands were selected according to podzolic soil conditions: wet Lande, characterised by a shallow ground water table and a hard pan horizon, and dry Lande, with a deeper ground water table and a hard pan absent or broken up. As this soil horizon limits the vertical growth of tree roots, anchorage resistance was investigated with regards to the presence or absence of a hard pan underneath each tree. To determine if mechanical behaviour differed within a stand, trees from inside the stand and edge trees at the border exposed to prevailing winds were also tested. The critical turning moment (TMcrit,total) at the base of the stem was positively related to the variable (H DBH2) (H, total tree height; DBH, tree diameter). Linear regression analyses between TMcrit,total and (H DBH2) showed that the presence of a hard pan had no significant effect on anchorage resistance in uprooted trees. Stem failure occurred for 82% of trees on dry Lande when (H DBH2) < 1m3. Moreover, stem failure type on dry Lande indicated that trees were better anchored. On soil with a hard pan, edge trees were found to be 20% more resistant to overturning than inner trees. Edge trees differed from inner trees in that the soil-root plate was two times larger and also possessed a larger surface area on the windward side.
Trees 06/2004; 18(4):460-466. · 1.68 Impact Factor
