Impact of Bacterial Activity on Sr and Ca Isotopic Compositions (87Sr/86Sr and δ44/40Ca) in Soil Solutions (the StrengbachCZO)

This study deals with soil solutions originating from the spruce parcel of the Strengbach catchment (Vosges mountains, Northeastern France). Samples were collected during winter, spring and summer 2010. Their chemical and isotopic (87Sr/86Sr and δ44/40Ca)compositions allowed to identify micro-organism activity and bio-weathering of apatite in the soil solutions from uppermost (0-10 cm depth) soil horizons. Indeed, in presence of bacteria, any Ca isotopic fractionation due to vegetation uptake is ruled out and δ44/40Ca values reflect the signature of apatite. Thus, bacteria facilitate the Ca uptake from soil. This study highlights the potential of Ca isotopes to identify bacteria activity in soils.