3:30 - 4:00 PM
Mr. Zhang Xiaolang Department of Earth Sciences, HKU
The Badain Jaran desert (BJD) covers an area of 49,000 km2 making it the second largest desert of China. The desert has the tallest stationary dunes in our planet. Despite hyper arid conditions, a remarkable feature of BJD is the existence of nearly 70 permanent lakes that lies in the inter-dune depressions. These mysterious lakes are believed to be fed by groundwater. Due to scarce meteorological and hydrogeological data in the desert, various hypotheses have been proposed on the recharge sources of lake water and groundwater.
The groundwater recharge rate is of significance for lake water balance. Sumujanran Lake, the second large lake in BJD, is chosen to analyze lake-aquifer relations and lacustrine groundwater discharge rate. These desert lakes were thought to be fresh when the climate was much wetter than today. The linear relation of radium and barium coupled with mass balance equations can be employed to calculate the time for a fresh lake growing into a brine lake. Behaviors of the boron isotope in groundwater are also examined to shed light on lacustrine groundwater flow path. Area variations of total 38 permanent lakes are used to investigate fractal behaviors and speculate possible water origin. These groundwater-fed lakes are sensitive to climate change. It was found there were a high lake level period about 30,000 years ago. A simulation model is set up to explore how climate change influences regional groundwater flow.