Impact of carbo-gaseous saline waters registered by soils

The impact of carbo-gazeous saline spring waters, rich in Ca, Fe, As and P and chemically stable through time, on the chemistry (major and trace eleme nts) and mineralogy of soils developed from anatexite is presented. The soi ls developed beyond the influence of the spring are typical of a granite pe dogenesis on a granitic bedrock with Ca loss, Si, Al and K conservation. Th e soils influenced by the springs are enriched in Ca and Fe, respectively, precipitated as carbonates and oxides. In such soils, the presence of two C a-enrichment peaks may be explained by the occurrence of two distinct preci pitation mechanisms for the carbonates: (1) related to degassing of the car bo-gaseous waters upon emergence at the surface, and (2) in the water-unsat urated zone, related to capillary rise and evaporation processes. The preci pitation of iron oxides is related to a change in the redox potential of th e mineral. waters, following their emergence at the surface. The simultaneous association of As + P with Fe, as evidenced by principal c omponents analysis and in the patterns in concentrations vs. depth observed in soils, can be explained by adsorption and/or coprecipitation of As and P during iron-oxide formation, while The As and P enrichments and the carbo nate formation are independent. The extent of the spring influence was studied: the soil enrichments in Ca and, particularly, Fe sharply decrease with increasing distance from the sp ring on a metric scale. (C) 2001 Elsevier Science B.V. All rights reserved.