Review: Advances in the methodology and application of tracing in karst aquifers

Ralf Benischke

doi:10.1007/s10040-020-02278-9

Abstract

Tracer methods have been widely used in many fields of environmental and natural sciences, and also in human health sciences. In particular, tracers are used in the study of karst hydrogeology, typically focusing on phenomena such as sinkholes, sinking rivers and large karst springs. It is known that tracers have been used since antiquity. The aim of tracer tests has been to investigate underground flow paths, transport processes and water–rock interactions, and to get an insight into the functioning of a karst aquifer. In karst hydrogeology, tracer methods are the most important investigation tools beside conventional hydrological methods. In early times, tracer methods were applied only to investigate underground flow-paths. Later they were also used to elucidate transport processes associated with water flow, and today they are often the basis, together with detailed hydrological information, of groundwater protection investigations and aquifer modelling. Many substances (spores, microspheres, bacteriophages, salt tracers, fluorescent dyes, radioactive substances) have been investigated for their properties and potential usage in environmental investigations, in particular the often unknown and inaccessible underground systems of karst areas. A great number of analytical techniques is available. This includes instrumentation for laboratory applications and direct online, on-site or in-situ field measurements. Modern instruments have a high capability for data acquisition, storage and transmission in short intervals, as a basis for quantitative evaluation and modelling. This enables research on the hydrological and hydrochemical dynamics of aquifers and their response to different natural or anthropogenic impacts.

Highlights

Tracer techniques are well known in hydrogeology as specialized methods to investigate flow-paths, flow and transport processes, and water–rock interactions, as well as to solve practical problems in environmental sciences in general
The results showed in many cases a radially divergent flow in the karst aquifer
Tracer methods are standard hydrogeologic methods and have been used for many decades to investigate karst aquifers. Their importance can be seen on the increasing number of papers published in the various scientific journals (Divine and McDonnell 2005)

Summary

Introduction

Tracer techniques are well known in hydrogeology as specialized methods to investigate flow-paths, flow and transport processes, and water–rock interactions, as well as to solve practical problems in environmental sciences in general. In a multi-tracer long-distance test (over 1 km) in an alpine karst area in Austria, the four tracers uranine (18.1 g), sulphorhodamine G (15.3 g), deuterium (7,619 g) and sodium bromide (3,842 g) could be compared directly for their transport properties and relative conservative behaviour under predominant conduit flow conditions (Leis and Benischke 2004). For the commonly used inorganic salt tracers and fluorescent dyes, Behrens et al (2001) provided an overview, some of the toxicological information is only based on the experience of experts or literature, and less on specific new tests at the time of publication. Long mean residence times inferred from isotope investigations do not allow one to conclude that a contamination risk does not exist Tracer tests in such cases can give a positive response, as the labelled water volume represents only a short-term component of the entire runoff. Sometimes they are used in addition to water samples to cover concentration levels which are near or below the detection limit of the dye tracer in water samples, but a tracer test with only charcoal bags cannot be recommended

Background of tracer

Evaluation and interpretation

Concluding remarks