The formation mechanisms of the mega-dunes and lakes in the hinterland of Badain Jaran Desert,China,is the focus of extensive academic research in the field of geoscience,and an often debated topic is whether atmospheric precipitation on the mega-dune can infiltrate to recharge groundwater.In the present study,the probability distribution functions and the return period analysis of extreme daily precipitation based on long-term precipitation records for the southern margin of Badain Jaran Desert and 2-year observation of hinterland precipitation were used to classify precipitation in the desert region.The data of automatic weather station and eddy covariance system in the desert hinterland were used to analyze evaporation on the mega-dune surface after various rain events.The results showed that the rain events in the desert could be divided into three categories.The first is conventional precipitation(CP),which is below 5 mm,accounting for roughly 90%of all rain events in the desert.The second and third categories are ordinary annual maximum(OAM)and extreme precipitation(EP),in which precipitation is roughly 20 mm and more than 40 mm,respectively.The atmospheric precipitation of CP and OAM evaporated from the megadune surface in 1–3 days and 3–4 weeks,respectively.Following an EP event,the mega-dune evaporation was negatively influenced by the upper dry sand layer,and a lengthy period was required for its complete removal.The accumulative evaporation and accumulative precipitation of all three types of rain events indicated that local atmospheric precipitation had no significant contribution to recharging the groundwater system in the hinterland of Badain Jaran Desert.This research will benefit comprehensive elucidation of the formation mechanism of lakes in the hinterland of Badain Jaran Desert.
Ning MaNaiang WangLiqiang ZhaoZhenyu ZhangChunyu DongShiping Shen
巴丹吉林沙漠腹地及东南部湖泊众多,除分布110个常年积水湖泊外,还存在若干季节性湖泊和干涸湖盆.通过对巴丹吉林沙漠湖泊群的实地考察、湖泊遗迹测量及14C和OSL定年,获得了全新世泛湖期存在的地貌学、沉积学和生物遗迹证据,揭示了巴丹吉林沙漠全新世早、中期湖盆面积扩大、区域气候相对湿润的特点.测年结果表明,巴丹吉林沙漠泛湖期开始于10cal ka BP,此前为泥炭发育期或湖沼期(11~10cal ka BP),大致在8.6~6.6cal ka BP,湖泊群达到全新世最大高湖面,并于晚全新世(约3.5cal ka至今)普遍出现退缩乃至干涸.根据植物钙质根管的形成时代及其所揭示的降水量阈值研究,巴丹吉林沙漠东南部在7.7~5.3cal ka BP期间古降水量可能达到200mm a^(-1).水量平衡计算表明,百年至千年尺度相对暖湿的区域气候条件,特别是南部和东南部深层地下水来水量增多,是巴丹吉林沙漠全新世湖泊群维持和史前文化发展的关键因素.
Lake area information in the Badain Jaran Desert in 1973,1990,2000,and 2010 was obtained by visual interpretation and water index analysis of remote sensing images,based on the spatial and temporal characteristics of lake area changes during 37 years.Results indicated that the number of lakes declined from 94 to 82 and the total surface area was reduced by 3.69 km2during1973–2010.The desert lake area reduced by different degrees in different periods,but this occurred most rapidly during1973–1990.According to the statistics of lake area changes,lake area decreases mainly occurred in the lakes with areas less than0.2 km2,while the areas of lakes greater than 0.9 km2only fluctuated.The changes of lake areas were probably due to changes in the quantity of underground water supplies rather than the effects of local climate change or human factors.
The Badain Jaran Desert is the second-largest area of shifting sands in China. Our first measurements of the energy components and water vapor fluxes on a megadune using eddy covariance technology were taken from April 2012 to April 2013. The results indicate that the longwave and shortwave radiative fluxes exhibited large fluctuations and seasonal dynamics. The total radiative energy loss by longwave and shortwave radiation was greater on the megadune than from other underlying surfaces. The radiation partitioning was different in different seasons. The land-atmosphere interaction was primarily represented by the sensible heat flux. The average sensible heat flux(40.1 W/m2) was much larger than the average latent heat flux(14.5 W/m2). Soil heat flux played an important role in the energy balance. The mean actual evaporation was 0.41 mm/d, and the cumulative actual evaporation was approximately 150 mm/a. The water vapor would transport downwardly and appear as dew condensation water. The amount of precipitation determined the actual evaporation. The actual evaporation was supposed to be equal to the precipitation on the megadune and the precipitation was difficult to recharge the groundwater. Our study can provide a foundation for further research on land-atmosphere interactions in this area.
HU WenfengWANG Nai'angZHAO LiqiangNING KaiZHANG XunheSUN Jie
We present a case study of physical and chemical indicators and isotope characteristics of Lake Nuoertu,one of the largest and deepest lakes of the Badain Jaran Desert.We analyze the concentrations of eight ions,total dissolved solids,and stable isotope composition of the lake and groundwater,as well as radioactive isotope tritium concentration in groundwater.The results show that annual and seasonal variations of the physical and chemical characteristics of Lake Nuoertu water are significantly greater than those of groundwater.The lake is uniformly mixed in the horizontal and vertical directions,and the hydrochemical types of the lake at different depths are consistent for Na–Cl–CO3–(SO4).Stable isotope composition of the lake and groundwater at Nuoertu is distributed along the local evaporation line(EL)slope,which is less than the slope of the global meteoric water line.The comparatively small slope shows the characteristic strong evaporation in the study area.Lake water isotopes are mostly in the upper right corner of the EL,whereas groundwater is mostly in the lower left corner.The main recharge source of Nuoertu lake water is groundwater,in combination with lake water and groundwater level change.The age of tufa springs around Nuoertu is about75–80 a,which shows that the initial recharge source of the lake is a mix between modern and 1952 or older;however,further research is required.
