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Groundwater recharge in an arid grassland as indicated by soil chloride profile and multiple tracers
Previous studies have shown that shallow groundwater in arid regions is often not in equilibrium with near‐surface boundary conditions due to human activities and climate change. This is especially the case where the unsaturated zone is thick and recharge rate is limited. Under this nonequilibrium condition, the unsaturated zone solute profile plays an important role in estimating recent diffuse recharge in arid environments. This paper combines evaluation of the thick unsaturated zone with the saturated zone to investigate the groundwater recharge of a grassland in the arid western Ordos Basin, NW China, using the soil chloride profiles and multiple tracers (2H, 18O, 13C, 14C, and water chemistry) of groundwater. Whereas conventional water balance and Darcy flux measurements usually involve large errors in recharge estimations for arid areas, chloride mass balance has been widely and generally successfully used. The results show that the present diffuse recharge beneath the grassland is 0.11–0.32 mm/year, based on the chloride mass balance of seven soil profiles. The chloride accumulation age is approximately 2,500 years at a depth of 13 m in the unsaturated zone. The average Cl content in soil moisture in the upper 13 m of the unsaturated zone ranges from 2,842 to 7,856 mg/L, whereas the shallow groundwater Cl content ranges from 95 to 351 mg/L. The corrected 14C age of shallow groundwater ranges from 4,327 to 29,708 years. Stable isotopes show that the shallow groundwater is unrelated to modern precipitation. The shallow groundwater was recharged during the cold and wet phases of the Late Pleistocene and Holocene humid phase based on palaeoclimate, and consequently, the groundwater resources are nonrenewable. Due to the limited recharge rate and thick unsaturated zone, the present shallow groundwater has not been in hydraulic equilibrium with near‐surface boundary conditions in the past 2,500 years. 相似文献
76.
定位精度是评价雷电定位网络的重要指标之一,定位算法直接影响雷电探测结果的精度。雷电监测系统探测数据误差不可避免,传统定位算法不具备抗误差干扰能力,迭代计算易发散,定位结果精度不高。为了满足实际应用需求,提出一种新的雷电定位算法DG-LLA(DBSCAN and grid-search lighting location algorithm),在定位计算中引入DBSCAN(density-based spatial clustering of applications with noise)方法与网格搜索方法。通过仿真与国家雷电监测网实际定位结果对比分析定位算法性能。结果表明:到达时间差(time difference of arrival,TDOA)法和Taylor级数展开法定位误差较大,仿真区域的均方根误差分别为982 m和668 m;定位中引入DBSCAN方法后,均方根误差明显减小为406 m,引入DBSCAN方法和网格搜索方法后,均方根误差减小为349 m;在相同回击数据条件下,算法DG-LLA与国家雷电监测网相比定位数量更多,回击数据的利用率从43.4%提升到51.5%,新增定位结果周围雷达回波特征较强,定位精度更高。 相似文献
77.
This paper aims to compare the geochemical characteristics of loess-paleosol sequences in the upper reaches of the Hanjiang and Weihe river valleyswhich are located in the semi-humid temperate zone and humid subtropical zonerespectively. The Mituosi(MTS) profile in the upper reaches of the Hanjiang River valley and the Yaohecun(YHC) profile in the Weihe River valley were selected for this comparative research. The stratigraphic characteristicscompositionchemical weathering intensityleaching rates of Ca and Namobility of major elementsand transport features of Na and Fe were analyzed with respect to depth and compared between the two profiles. This study reached the following conclusions.(1) The composition of the loess-paleosol sequences in two regions are quite similar to the average composition of the upper continental crust(UCC)indicating that the loess in the two regions came from multiple sources and was mixed well. Thereforethe loess in the two regions is considered aeolian loess.(2) Compared with the loess-paleosol sequence in the Weihe River valleythe loess-paleosol sequence in the upper reaches of the Hanjiang River valley features a darker color; a higher chemical index of alteration(CIA) value; higher leaching rates of Na and Ca; higher migration ratio(relative to K) of AlSiMgand Na; and lower migration ratio of Fe and Ca. This evidence indicates that the loess-paleosol sequence in the humid subtropical environment experienced stronger chemical weathering intensity than the loess-paleosol sequence in the semi-humid temperate zone.(3) Both the YHC profile and MTS profile record a period of climate deterioration at 6000–5000 a BP. The period punctuated the mid-Holocene Climatic Optimum(8500–3100 a BP) in the study area. 相似文献
78.
工业区位因素变化与工业地理学研究的新动向 总被引:3,自引:0,他引:3
工业生产在国家和地区社会经济发展中的作用表现为阶段性变化,并在工业区位因素和工业空间特征的变化上表现出来。80年代以来,这种变化突出表现为技术因素和社会文化因素对工业生产和工业区位的影响日盆增强以及工业生产组织的国际合作的扩展,这种变化导致了工业地理学研究方法和研究领域的革新拓展。 相似文献
79.
The annual life cycle of the brown seaweed Undaria pinnatifi da(Harvey)Suringer comprises a macroscopic diploid sporophyte stage and a microscopic haploid gametophyte stage.In 2011,an unusual zoospore-derived monoecious gametophyte isolate(designated as line 10-5-3)of U.pinnatifi da was observed.To understand this phenomenon,a comprehensive screening of eighty-two previously identifi ed male gametophyte cultures,isolated from three randomly selected cultivars(lines 10,7,and 5)was performed.Thirty-six of the isolates developed both antheridia and oogonia on the same fi lamentous fragment in a standard gametogenesis test(SGT: 18°C,60 μmol photons/(m 2·s)).Selfi ng of the monoecious gametophyte or crossing it with a normal male gametophyte both gave rise to morphologically normal sporophytic offspring.However,crossing resulted in a much higher fertilization rate(89.7%).The hybrid and selfed sporophytic offspring were grown to maturity in fl ow tanks at an ambient temperature of 10–18°C over a period of 69 days.Active zoospores were released from both types of mature sporophylls.The majority of these developed into male gametophytes,while 15%–20% developed into the observed monoecious structures on the same fi lament.Using PCR amplifi cation it was found that all the monoecious gametophyte isolates and the sporophytic offspring resulting from the selfi ng and crossing lacked the femalelinked microsatellite sequence(a part of the locus Up-AC-2A8,GenBank accession No.AY738602.1),indicating their male nature.U.pinnatifi da is an invasive species in some regions and the implications of the above fi ndings for this species in nature are briefl y discussed. 相似文献
80.
通过9煤层、11煤层、12-1煤 层中 工程对 FE9'断层的 揭露 ,并结合 巷探 、钻探 等手段 ,对 FE9'断层 的空 间 展布有了新 的认 识。对 周边 12-2煤层 的规划 开发、断层样 式的 认识乃 至井 田应力 场分 布的研 究提 供了依 据。 相似文献