Use of Total Organic Carbon (TOC) as tracer of diffuse infiltration in a dolomitic karstic system: The Nerja Cave (Andalusia, southern Spain)

Abstract

Recent studies in several karstic systems in France have highlighted that Total Organic Carbon (TOC) was a relevant parameter in order to characterise the behaviour of aquifers, to differentiate the water types that participate in karstic flow (fast infiltration, unsaturated zone, saturated zone) and to evaluate their vulnerability. This study on TOC dynamics at the experimental site of the Nerja Cave has been performed to test the potential of this tracer in a particular climatic (Mediterranean climate), lithologic (dolomitic marbles) and hydrodynamic (diffuse flow behaviour) context. TOC evolution, compared to those of classical tracers used in hydrogeology, permits the understanding of the hydrodynamical behaviour of the unsaturated zone of this dolomitic aquifer, whose response to precipitation is slower than that commonly obtained in karstic aquifers of calcareous nature.

Contribution of artificial galleries to the knowledge of karstic system behaviour in addition to natural cavern data

“…Organic matter, used as a tracer of fast circulation in karstic systems, associated with chemical components like Mg 2+ , NO 3 -and �iO 2 -concentrations, enables to understand the hydrogeological functioning of the aquifers (Emblanch, 1997;Emblanch et al, 1998aEmblanch et al, , 1998bBatiot et al, 2002;Batiot et al, 2003). TOC mean annual variation ranged from 0.93 mg/l for the B-point to 2,15 mg/l for the GA�-point, in unsaturated zone, and the mean calculated standard deviations vary from 0.19 for the A-point to 0.63 for the GA�-point.…”

“…This aquifer belongs to the lower Cretaceous and is composed of a 1500 m thick limestone series (Masse, 1968) between Necomanian marls and upper Aptian marls. It is made of an 800 m thick unsaturated zone, which has an important hydrodynamic role in the system (Emblanch et al, 2003) and by a 700 m thick saturated zone. Among a list of 600 natural cavities (Gaubert & Le Falher, 1990, are documented in the studied area, most of them have a quite-vertical development and they have no significant perennial flow.…”

Carbon dioxide concentration in air within the Nerja Cave (Malaga, Andalusia, Spain)

“…in atmospheric CO 2 must be related to the reduction in the plant cover of the immediate surroundings of the cave, as many species lose their leaves as a mechanism of adaptation to the very dry conditions normally encountered during this season (Batiot et al, 2003) and to the reduction in the plants' vital activities.…”

Speleothems

“…Total organic carbon measurements have also been used (Batiot et al, 2003) to trace karstic hydrology, but the UV-fl uorescing fraction (e.g. Baker and Genty, 1999;Baker et al, 1999a) appears to be selectively incorporated in speleothems (McGarry and Baker, 2000).…”