Carbonate deposits from historical aqueducts in urban area: an archive for human impact on water management and quality

We have developed a methodology for constructing diachronic views of the chemical state of water that infiltrates soils and forms perched aquifers in the north and south of Paris (France). These waters have been drained for centuries and distributed by historic underground aqueducts. The CaCO3 layers deposited by these waters in the aqueducts have been studied. The first challenge is to construct chronologies of these deposits, using uranium-thorium or 14C chronometers and/or lamina counting. Past water quality has been reconstructed using trace elements measured along the growth axis of CaCO3 deposits, combined with isotope analysis (lead, sulfur and strontium) and, in some cases, carbon isotopes. With this methodology, we demonstrate that in Paris, over the last 300 years, the transformation of land use is the most important factor affecting water quality, not only through the presence or absence of building industries, but also through the use of certain materials for construction or embankment.  We use this methodology for the study of ancient aqueducts in archaeological sites to discuss water provenance and quality.