Dissolution Rate of Fluor-Apatite Crystals Inserted in Acid Soils of a Forested Catchment (Vosges Mountains, NE France)

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In the Strengbach catchment (Vosges Mountain, NE France), the Ca and Mg nutrition of spruce and beech stands is very poor. Water and mineral fluxes through beech and spruce stands have been monitored at these sites since 1987. Ca supply is limited because its amount in the granite bedrock (CaO = 0.15-0.30 wt.%), in the bulk soil (CaO = 0.01-0.30 wt.%) and on the cation exchange capacity (CaO = 0.01-0.3 creole kg -1) is very low. Total and exchangeable Ca in the fine earth (< 2mm) of the layer soil (0-120 cm) is respectively about 8.4-9.6 t.ha -1 and 130-140 kg ha l . The rate of calcium release by weathering of soil primary minerals has been computed from detailed quantitative mineralogical data and mineral fluxes monitored at these two sites using steady state soil chemistry model PROFILE (Sverdrup and Warfvinge; 1993). Obtained values were extremely low (0.1-1.2 kg ha i yr l ) (Fichter et al., 1998a). Ca-bearing minerals in soils are albite and apatite. Although, apatite is the trace mineral in soil, Ca is principally located in this mineral because Ca content in albite is very low (CAO:0.45-0.53 wt.%) (Fichter et al., 1998b). Only few data of fluorapatite dissolution rate of fluor-apatite were published. In the aim to determinate the dissolution rate of fluor-apatite in these soils, the mineral test technique was used.