Groundwater discharge quantification in marine, and desert environments using radium quartet, radon-222 and stable isotopes

Abstract

Groundwater discharge is an important component of global water cycle. Along with groundwater discharge, large amount of chemicals are transported and loaded into surface waters. This thesis investigates groundwater discharge in both terrestrial and marine environments using isotopic approaches. Radium quartet and radon-222 (222Rn), highly concentrated in groundwater and conservatively behaving during the transport, are proved to be effective tracers in quantifying groundwater discharge in various environments. Stable isotopes (δ 18O and δ 2H), significantly fractionated during evaporation, are useful and applicable in studying the water balance in arid waters.

Groundwater discharge is an important component of global water cycle. Along with groundwater discharge, large amount of chemicals are transported and loaded into surface waters. This thesis investigates groundwater discharge in both terrestrial and marine environments using isotopic approaches. Radium quartet and radon-222 (222Rn), highly concentrated in groundwater and conservatively behaving during the transport, are proved to be effective tracers in quantifying groundwater discharge in various environments. Stable isotopes (δ 18O and δ 2H), significantly fractionated during evaporation, are useful and applicable in studying the water balance in arid waters.

Desert lakes, lacking of surface runoff, are mostly supplied by groundwater discharge. These lakes play a vital role in maintaining desert water balance, creating unique landscapes, supporting distinctive ecosystems. In this thesis, radium quartet, 222Rn, δ 18O and δ 2H are used to estimate groundwater discharge into the Badain Jaran Desert (BJD) lakes and to reveal these lake evolutions. Most of the desert lakes are flow through lakes, reflecting groundwater discharge is larger than lake surface evaporation and explaining their existence in the extremely arid environment. The salinazation time of the desert lakes is estimated to start about 4000 yrs B.P.

Radium and radon disequilibrium in the fractured aquifer system is used to estimate the hydrogeological parameters such as water residence time, effective surface area and mean aperture, based on long time monitoring of radium and radon activities in the spring water. Adsorption exerts a dominant effect in controlling radium quartet transport in fracture aquifer system.