Présentations Colloques

Session 5.02: Groundwater and global change
Dumont (orateur)
300 years of urbanization in Paris (France) and its impacts on shallow groundwater - evidences from speleothems and water monitoring

Urbanization is a complex process that can lead to a huge disturbance of both groundwater quantity and quality. Direct recharge can be reduced by impervious surfaces, while other sources of recharges can occur, such as leaks in water supply systems or sewers (Lerner, 2002). Identifying the separate effects of different anthropogenic activities is often impossible because of the multiple sources of disturbance as well as the lack of information on the pre-urbanization period. This study presents the combined use of groundwater monitoring, urban speleothems analysis and historical data for the reconstruction of 300 years of groundwater evolution in the NE part of Paris. On the study site, two independent groundwater aquifers were first drained in the 1100s to supply the City of Paris with water. Artificial underground water supply systems in calcareous geological context has locally lead to the formation of secondary carbonate deposits, that develop on the walls or on the floor. Speleothems sampled in an ancient aqueduct have then recorded groundwater chemistry evolution through their continuous growth over 300 years (Pons-Branchu et al., 2014, 2015). Dating of the speleothems and analyzing heavy metal composition and isotopic imprint show that several processes linked to progressive urbanization steps seem to have been recorded- (I) agricultural activity, (ii) road-building, (iii) influence of wastewater collection system (iv) technological innovation. Today even with the global soil sealing of the watershed, the historical drainage network is still active. Quantitative and qualitative monitoring of this network indicates that rainwater infiltration is still occurring but that the main recharge to groundwater comes from the anthropic water network (sewer, drinking water, &hellip+). From a qualitative point of view sulfate and nitrate concentration in water are still the main indicators of urbanization. As stormwater infiltration is becoming more and more encouraged in many urban areas, developing new methods can help understanding the consequences of such stormwater management policies on groundwater quality and quantity.< p>