Use of Chlorophyll-a Monitoring to Determine Karst–River Relationships: A Case Study in the Karstic Limestones of Ouche Valley, Burgundy (France)

Abstract

The study of groundwater–river relationships is a challenge for water supply management. In order to provide an indicator for Inversac (Estavelle) events in a karstic aquifer, the water and sanitation department of Dijon Metropole tested a chlorophyll-a probe in addition to pressure and temperature probes. The field tests were performed in karstic Bathonian limestones near a canal, where eutrophication occurs in summer. The study site, called Crucifix site, was chosen based on tracer tests showing a probable infiltration of surface water. The Crucifix site gave the opportunity to study simultaneously a karst system in a natural spring alimented by a karstic conduit, and in a nearby well used for drinking water supply. The survey was performed during one week, with a pumping test lasting 24 h at the beginning of the survey. The results indicated that temperature and water level monitoring were not able to detect unambiguously inflow of surface water. In contrast, the chlorophyll-a probe allowed to detect reliably surface water inflow, because chlorophyll-a is naturally absent in groundwater. This form of monitoring is therefore a promising tool for water supply management and its implementation should be generalized for karstic springs influenced by surface water.