A new approach to protecting karst landscape resources through continuous monitoring.
Chlorophyll groundwater monitoring in karst landscapes
The protection of karst resources is a fundamental objective for territories entirely covered by these limestone formations.
Many drinking water plants are supplied by karst springs near rivers, lakes or even saltwater. The relationship between the restitution karst and surface water is a key element in the management of drinking water catchments. Depending on the water levels, the circulation of water within the karst can be reversed (the phenomenon of “estavelle” or “inversac”).
Estavelle events represent a major contamination risk: they must be identified and qualified in order to manage the supply of drinking water. The different chemical characteristics of surface water and groundwater can be used to identify estavelle events through hydro-chemical studies. However, surface water and groundwater often have similar characteristics, which require the use of other parameters to differentiate them.
Surface water with high chlorophyll a concentration. Burgundy Canal.
A case study in karstic limestones of Ouche valley, Burgundy (France).
Underground spring. Name: Crucifix.
First project of CPGF with Hyperion probe (in 2018), to highlight mass transfer between surface water and groundwater.
A new approach
In order to characterize mass transfers in karst landscapes, CPGF Horizon has developed, over many years, a new approach based on the study of chlorophyll, as a natural parameter with a characteristic identifier for one of the water bodies (surface water) and almost zero background noise for the other (groundwater). Indeed, algae, which contain chlorophyll-a, live only in surface waters exposed to sunlight. Chlorophyll-a, therefore, represents a natural biological tracer that distinguishes surface water from groundwater.
Continuous monitoring using Valeport Water EnviroLog
Consequently, the continuous monitoring of chlorophyll-a makes it possible to study river-karst mass transfers and the risks of inversac. As part of one of its studies CPGF Horizon, requested Valeport Water to supply a system for the continuous monitoring of chlorophyll-a. Indeed, Valeport Water offers a wide range of fluorimeters in its Hyperion range of optical sensors, including a chlorophyll-a probe with a detection limit of 0.025 μg/L. Combined with its EnviroLog or EnviroLog 4G data logger, Valeport Water’s solution makes it possible to characterise the exchange of chlorophyll-a concentrations in karst compartments.
A case study in Charente near Cognac (France).
A recent CPGF project with the Valeport Water Hyperion Chlorophyll a (in 2021) to highlight mass transfer between surface water and groundwater.
The two sensors make it possible to distinguish between surface water and groundwater, with no mixing observed.
Left: Abstraction of drinking water
Right: Surface water with high Chlorophyll a concentration