Dissolved gases as natural tracers in karst hydrogeology; radon推荐.pdf

Dissolved gases as natural tracers in karst hydrogeology; radon and beyond Heinz Surbecka Center of Hydrogeology (CHYN), University of Neuchâtel, Emile-Argand 11, CH- 2007 Neuchâtel, Switzerland Abstract. Gases present in the atmosphere or produced in the soil dissolve in rain- water and then are transported by percolation down to the saturated zone. Of par- ticular interest are gases like radon and CO that have a well delimited place of 2 production and that can be measured continuously in the field. Both are mainly produced in the soil but have different chemical and physical properties. Radon decays with a half live of about 4 days whereas CO reacts with the carbonate on 2 its way down to the saturated zone. Temporal variations of their concentrations in underground rivers or in spring water can thus be used to gain information about fast transport processes in karst systems. Other dissolved gases mainly oxygen and nitrogen may show short peaks of supersaturation due to a clogging of parts of the conduits in the vadose zone during high flow. Still not well known among hydro- geologists, supersaturation that can be easily measured continuously in the field may become a useful tool to study dynamics in karst systems. This lecture has mainly the intention to make you familiar with radon CO and TDGP measure- 2 ments and to show what they can be used for. Its not so much about well estab- lished techniques and contains some unproven claims and open questions. Introduction Gases present in the atmosphere can dissolve in rainwater and thus be transported down to an aquifer. Other gases are produced in the soil and are taken up by perco- lating water. Comparing the concentrations of all these gases in underground rivers a heinz.surbeck@unine.ch 2 Hei