Michel Bakalowicz

Comptes Rendus Géoscience

C. R. Geoscience 335 (2003) 423–424PerspectiveNatural organic carbon in groundwaterMichel BakalowiczHydrosciences, CNRS, université Montpellier-2, cc MSE, 34095 Montpellier cedex 5, Francee[2]rstasat-anicateron;asd-ndpro-foron).ntiedchiss-a-deers.in-varhandndin-pei-eo-rstrgeDer.atmeiskarstflower,theCaninlyticnicstthesheated.ntntalnlyBatiot, Emblanch and Blavoux [3] present somof the main results from Batiot’s PhD dissertationconcerning the information on flow conditions in kaaquifers provided by the total organic carbon (TOC)a natural tracer. Investigations of natural organic mter in groundwater are scarce and very recent. Orgmatter is, however, abundant in surface and soil wand plays a geochemical part in complex formatimoreover, it has an obvious micro-biochemical roleprimary nutrient. Studies of organic carbon in grounwater are essentially related to organic pollution atheir purpose is to assess self-remediation or topose remediation solutions.The two most commonly measured parametersorganic matter in water are the Total Organic Carb(TOC) and the Dissolved Organic Carbon (DOCBatiot [2] showed that there is generally no significadifference between TOC and DOC in the studcarbonate aquifers.The TOC content in soil water may rea300 mg l−1, whereas it rarely exceeds 100 mgl−1 inriver water. According to [7], TOC in groundwaterlower than 1 mgl−1: the long residence time is asumed to favour the oxidation into CO2 by the bacter-ial activity in the aquifers. Most of the rare investigtions of natural organic carbon in groundwater, maduring the last decade, are related to karst aquifKarst aquifers are particularly well suited to suchvestigations, because their recharge occurs underious conditions: diffuse and slow infiltration througfissures and matrix, dispersed but concentratedfast infiltration in fractures, highly concentrated aE-mail address: baka@msem.univ-montp2.fr(M. Bakalowicz).1631-0713/03/$ – see front matter 2003 Académie des sciences. Preserved.doi:10.1016/S1631-0713(03)00085-3-rapid recharge through swallow holes and directlyjected into the phreatic conduit network [1]. Each tyof infiltration is characterised by its own flow condtions and residence time, and consequently by its gchemical characteristics. Therefore, the TOC in kaaquifers may indicate the travel time of the rechawater.As previously shown by Emblanch in his Phdissertation [4], TOC is an interesting natural tracFollowing his footsteps, Batiot [2] demonstrated thTOC is an excellent tracer of the residence tiand flow conditions in karst systems. Her workeasily generalised, because she explored severalsystems, characterised by different recharge andconditions, in various temperate climates. Moreovshe monitored the aquifers in order to describetime variation, so that the wide range of natural TOvariations in karst groundwater is now known and cbe compared to well-known inorganic tracers.TOC is relatively abundant below the soil andrapid infiltration water (up to 10 mg l−1). Its transportby infiltration and in the phreatic zone occurs mainin rapid flow conditions. During storage in the phreazone, the groundwater progressively looses orgaso that the TOC is oxidised into CO2 and its contenmay fall to values lower than 0.5 mg l−1.In a previous approach, James [5] exploredpossibility of CO2 production inside karst aquiferby organic oxidation; she then tried to prove texistence of an internal production of CO2 favouringthe development of karst in carbonate formationdepth. However, her results could not be generalisThe question is now: is TOC a useful and efficietool in (karst) hydrogeology?Inorganic natural tracers as well as environmeisotopes are now well researched and commoublished by Éditions scientifiques et médicales Elsevier SAS. All rights424 M. Bakalowicz / C. R. Geoscience 335 (2003) 423–424hehem.berofhearemeideanasor-aly-re-gl-hodor-lf-anitund-es.olo-ionséralxpéri-ine,deto--eo-car-diter-taineVau-nicInt.ars-rsitéffused for defining groundwater flow conditions. Taquifer functioning is analysed by deciphering ttracer variations at the outlet of a karst systeThis analysis requires the use of a large numof independent tracers typical of the input andthe different compartments or flow pathways. Tgeochemical characteristics of karst groundwaterhighly variable in time and space. Because sotracers [6] may originate either at the surface or insthe aquifer, like magnesium, or be changed by humactivities, like chloride, other natural tracers suchTOC should be looked for.Recent progress particularly in analytical perfmances makes possible easy and rapid low-level anses of organic carbon content in groundwater. Moover, Batiot [2] explored the possibility of studyinthe nature of TOC in water by spectrofluorimetry. Athough it requires some improvements, the metis presently very attractive and may give new infmation about karst aquifer functioning and its sepurification capacity. Organic carbon should also beinteresting natural tracer in alluvial aquifers, wherecan be used to quantify the exchange between growater and river.References[1] M. Bakalowicz, La zone d’infiltration des aquifères karstiquMéthodes d’étude. Structure et fonctionnement, Hydrogégie 4 (1995) 3–21.[2] C. Batiot, Étude expérimentale du cycle du carbone en régkarstiques. Apport du carbone organique et du carbone minà la connaissance hydrogéologique des systèmes. Site emental de Vaucluse, Jura, Larzac, Région nord-montpelliéraNerja (Espagne), thèse, université d’Avignon et des PaysVaucluse, 2002.[3] C. Batiot, C. Emblanch, B. Blavoux, Carbone organiquetal (COT) et magnésium (Mg2+) : deux traceurs complémentaires du temps de séjour dans l’aquifère karstique, C. R. Gscience 335 (2003) 205–214.[4] C. Emblanch, Les équilibres chimiques et isotopiques dubone dans les aquifères karstiques : étude en région méranéenne de montagne sur le bassin expérimental de la Fonde Vaucluse, thèse, université d’Avignon et des Pays decluse, 1997.[5] J. James, The relationship between the availability of orgacarbon and cavern development in the phreatic zone, in: 8thCongr. Speleol., Bowling Green, USA, 1981, pp. 237–240.[6] V. Plagnes, Structure et fonctionnement des aquifères ktiques. Caractérisation par la chimie des eaux, thèse, univeMontpellier-2, 1997.[7] E. Thurman, Organic Chemistry of Natural Waters, NijhoJunk, Dordrecht, 1985.

Natural organic carbon in groundwater

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Natural organic carbon in groundwater

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