Soluble salt sources in medieval porous limestone sculptures: A multi-isotope (N, O, S) approach

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• 作者：W. Kloppmann ; O. Roll ; E. Proust ; A.T. Montech
• 关键词：Stone degradation ; Sulphate ; Nitrate ; Capillary rise ; Cultural heritage ; Isotope fingerprinting
• 刊名：Science of the Total Environment
• 出版年：1 February, 2014
• 年：2014
• 卷：470-471
• 期：Complete
• 页码：559-566
• 全文大小：1148 K

文摘

The sources and mechanisms of soluble salt uptake by porous limestone and the associated degradation patterns were investigated for the life-sized 15th century 鈥渆ntombment of Christ鈥?sculpture group located in Pont-脿-Mousson, France, using a multi-isotope approach on sulphates (未³⁴S and 未¹⁸O) and nitrates (未¹⁵N and 未¹⁸O). The sculpture group, near the border of the Moselle River, is within the potential reach of capillary rise from the alluvial aquifer. Chemical analyses show a vertical zonation of soluble salts with a predominance of sulphates in the lower parts of the statues where crumbling and blistering prevail, and higher concentrations of nitrates and chloride in the high parts affected by powdering and efflorescence. Isotope fingerprints of sulphates suggest a triple origin: (1) the lower parts are dominated by capillary rise of dissolved sulphate from the Moselle water with characteristic Keuper evaporite signatures that progressively decreases with height; (2) in the higher parts affected by powdering the impact of atmospheric sulphur becomes detectable; and (3) locally, plaster reparations impact the neighbouring limestone through dissolution and re-precipitation of gypsum. Nitrogen and oxygen isotopes suggest an organic origin of nitrates in all samples. N isotope signatures are compatible with those measured in the alluvial aquifer of the Moselle River further downstream. This indicates contamination by sewage or organic fertilisers. Significant isotopic contrasts are observed between the different degradation features depending on the height and suggest historical changes of nitrate sources.