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Black carbon (BC), ubiquitous in soils, plays an important role in global carbon cycles, the radiative heat balance of the Earth, pollutant fate, emissions of greenhouse gas, soil fertility, soil microbial community, and ecosystem stability. However, information on BC in topsoils of the northeastern Qinghai-Tibet Plateau is limited. Therefore, this study performed field sampling and analyzed contents of total BC and soot BC in topsoils. The results indicated that the contents of total BC in all soil samples ranged from 0.504 to 74.381 g kg−1 with an average value of 5.152 g kg−1, whereas those of soot BC were in the range of 0.400–15.200 g kg−1 with a mean value of 1.719 g kg−1. Contents of BC were significantly correlated with those of total carbon and total organic carbon. Soil types affected the distribution of soil BC. The contents of total BC in the loam soils were larger than those in the clay soils, whereas soot BC was more easily enriched in the clay soils. Total BC was negatively correlated with Ca, and soot BC was negatively correlated with Ti. The contents of soil BC in functional areas, such as agricultural and pastoral areas, industrial areas, and mining areas, were significantly higher than those in other areas, illustrating that anthropogenic activities drastically affected the distribution of soil BC. This study exhibits the fundamental information on soil BC in the northeastern Qinghai-Tibet Plateau to provide important knowledge on global soil carbon sink.

Little attention has been paid to the study of sedimentary records from DaQaidam Salt Lake regarding brine evolution and hydro-climate change. Here we report the results of AMS 14C dating and mineralogical investigation on a sediment profile D4 from the south central of perennial saline water-body. The result revealed that pinnoite deposit in the lakebed was formed in early Holocene, the lake underwent three stages of lake-level and brine evolution in Holocene period, which were determined mainly by precipitation-controlled catchment inflow. The mineralogical records also depicted fluctuations in lake level and hydrochemistry on decadal and centennial scales.

The physicochemical properties of soils might be affected by the addition of biomass black carbon, a special black carbon produced by incomplete combustion of biomass. Therefore, this study performed experiments to explore the effects of yak dung biomass black carbon (YBC) on physicochemical properties of soils in the northeastern Qinghai-Tibet Plateau. Three YBCs (pyrolyzed at 300, 500, and 700 &deg, C) were separately added into four typical soils with three addition amounts (1%, 5%, and 10%). Changes of soil texture, pH, electrical conductivity (EC), cation exchange capacity (CEC), CHN contents, morphologies, functional groups, and mineral constituents of soils were comparatively studied. The results showed that addition of YBCs affected physicochemical properties of soils. Soil pH, EC, CEC, and carbon/nitrogen content were positively related with addition amount of YBCs. YBC particles were unevenly distributed among soil particles and positively related with addition amount. Addition of YBCs did not change texture, functional groups, and mineral constituents of soils. These results indicated that addition of YBC would be beneficial to stability of the soil ecosystem and sustainability of the northeastern Qinghai-Tibet Plateau.

Mineralogy is very important in the study of lake, especially in the study of regional and past global change using lake sediments. In the final analysis, mineralogy could be involved in the study of the in-depth mechanism of lake sediments. In this paper, analysis the minerals by XRD in the sediments of Toson lake in the northeast of Qinghai-Tibet Plateau, the results showed that the main minerals in Toson lake were aragonite, calcite, quartz, halite, albite, muscovite, clinochlore and dolomite. And the main categories were detrital minerals and carbonate minerals with obvious reverse correlation. It suggested that Toson lake was mainly situated carbonate sedimentary stage, and the input of carbonate was lacustrine authigenic carbonate.

The paper focused on heavy metal (Cr, Cu, Pb, Zn, As, Co, Ni and Mn) concentrations from surface sediment in the southeastern Da Qaidam Salt Lake. Based on the pressed powder pellet method and X-ray fluorescence spectrometry analysis, as well as the enrichment factor, geoaccumulation index and potential ecological risk index, the possible sources and pollution level of heavy metals were studied. The results showed that spatial distributions of heavy metal concentration were indicative of nonuniform characteristics in different zones of Da Qaidam Salt Lake, the average enrichment level of heavy metals followed the decreasing order: EF(As) > EF(Mn) > EF(Cu) > EF(Zn) > EF(Pb) > EF(Cr) > EF(Ni) > EF(Co), and arsenic was the main heavy metal contaminant. In a word, the level of heavy metal pollution in the southeastern Da Qaidam Salt Lake was not strong, but anthropogenic emissions would become the main source of heavy metals along with the frequent and strong human activities in the surrounding region.

An integrated analysis has been carried out on core dated by qualitative X-ray fluorescence core scanning combination of quantitative ICP-AES in order to characterize the extent of elements Cd, Cr, Cu, Zn, and Pb in the Lake Toson in the northeastern Tibet Plateau. When combining both the quantitative and qualitative measurements, we observed a significantly positive correlation. Comparing the ratios between element intensities and concentration, we found that the XRF element intensities were related to the amount of water. Using the intensity of Cl as an indicator of water content, the element intensities of Cd, Cr, Cu, Zn, and Pb in the core samples were corrected. The correlation coefficients of each pairs of the two datasets among Cd, Cr, Cu, Zn, and Pb were significantly raised. These data sets with highly correlations were used to produce a transfer function to relate XRF element intensity with element concentration. Calculated element concentrations from the intensities show only minor differences from concentrations obtained by ICP-AES, indicating XRF core scanners are a very useful tool for measuring element concentration in lacustrine sediments.

The pinnoite deposit occurred in the lakebed of Da Qaidam Salt Lake in Qaidam Basin is rare in the world. This study focused on the pinnoite, ulexite and hydroboracite from Da Qaidam Salt Lake, through multi-index methods including mineralogy and geochemistry, aiming to interpret the mechanism of pinnoite and other borate minerals. The results showed that pinnoite as well as ulexite and hydroboracite in lakeside are formed in the lake environment with specific hydrogeochemical conditions (e.g., alkaline brine, hydrochemical types, boron concentration, boron ions, Mg/Ca ratio, dilution and mixing mechanism). The borate formation was controlled by a coupling mechanism, i.e., the inherent geochemical characteristics and the external conditions.

The paper focused on the study of detrital yellow layer from sediment profile D3 of DaQaidam Salt Lake, based on AMS 14C chronologic and mineralogical methods, aimed to discuss the dust storm events recorded by detrital yellow layer of DaQaidam region since Late Glacial period. The results showed that the grain-size distribution curve displayed double kurtosis, the main peak (10 µm in average) reflected the fine-grained fractions into lake by fluviation, and the secondary peak (> 32 µm) reflected the coarse silt fractions into lake by wind effect and fluviation. Finally, the coarse-grained fractions (> 64 µm) from sediment profile D3 probably recorded the dust storm events since Late Glacial period.

Using an X-ray Fluorescence (XRF) core scanner with nondestructive and successive, the chemistry features of lacustrine sediment can be measured directly. This method of XRF core scanner measurements has been widely applied to core sediment analysis but uncertain of the precision and accuracy. Comparison of intensities obtained by XRF core scanning and the concentration measured by conventional X-ray Fluorescence, indicates effects of physical properties varied from different elements on elemental intensities in the lacustrine sediments of a core from Lake Hurleg in the northeastern Tibetan Plateau. Correlation among elements Ti and Sr between the two measurement methods of the XRF and the conventional XRF is high. Using the intensity of Cl as an indicator of water content, the element intensities of Ti and Sr in the core samples is corrected. But the correlation coefficients of Ti and Sr is litter raised. The results show that XRF core scanning is a very useful tool for measuring element concentration in sediments particularly for high intensities elements.

Mg-borates were traditionally thought to be diagenetic products of other primary borate minerals. Here we report results from the study of pinnoite deposit from DaQaidam saline lake, indicating that pinnoite minerals are primary in origin. Within the detecting limit of X-ray powder diffraction analysis (XRD) analysis, no other borate minerals than pinnoite are detected from the Mg-borate deposit. The cemented pinnoite orebody shows the sedimentary structure of light-dark lamination couplets, which signal marked seasonal variations in brine chemistry. The scanning electronic microscopy coupled with an energy dispersive X-ray spectrometer (SEM-EDX) examination reveals that all pinnoite minerals displayed euhedral, giving no indication of diagenetic origin. A marked shift in lithology from clastic sediment to evaporitic deposit reflects a critical change in sedimentation regime associated with abrupt changes in hydroclimatic conditions. The deposition of the pinnoite ore-layer containing abundant hydromagnesite marked the beginning of the evaporite formation and the end of the clastic deposition. This suggests that aridification occurred abruptly and the saline lake was much more alkaline than today in the early-stage of the evaporite deposition. The intensified summer evaporation and seasonal variations in water chemistry brought about a shallow to nearly desiccated paleo-lake with pH exceeding 9.3, Mg/Ca ratio &gt, 39, and boron concentration &gt, 600 mg/L, which favored pinnoite precipitation and the formation of pinnoite deposit in the central DaQaidam saline lake.

Qaidam Basin is a hyperarid inland basin with an area of 121 × 10 3 km 2 located on the northern Tibetan Plateau. Today, one fourth of the basin is covered by playas and hypersaline lakes. Nearly 80% of brine lithium found in China is contained in four salt lakes: Bieletan (BLT), DongTaijinaier (DT), XiTaijinaier (XT) and Yiliping (YLP). In the past decade, great attention was paid to improving the technology for the extraction of lithium from the brine deposits, but studies on origin and mode of formation of the brine deposits remained limited. Our recent investigations found that: (1) ~ 748.8 t of lithium was transported annually into the lower catchment of the four salt lakes via the Hongshui–Nalinggele River (H–N River), the largest river draining into the Qaidam Basin, (2) Li + -rich brines are formed only in salt lakes associated with inflowing rivers with Li + concentrations greater than 0.4 mg/L, and (3) the water Li + concentration is positively correlated with both the inflowing river and the associated subsurface brine, including saline lakes with low lithium concentrations. These findings clearly indicate that long-term input of Li + from the H–N River controls the formation of lithium brine deposits. Here we determine that the source of the lithium is from hydrothermal fields where two active faults converge in the upper reach of the Hongshui River. The hydrothermal fields are associated with a magmatic heat source, as suggested by the high Li + and As 3 + content water from geysers. Based on the assumption of a constant rate of lithium influx, we estimate that the total reserves of lithium were likely formed since the postglacial period. Our data indicate that lithium reserves in each of the four salt lakes depend on the influx of Li + -bearing water from the H–N River. The data also suggest that during the progradation of the alluvial Fan I, the H–N River drained mostly into the BLT salt lake until the Taijinaier River shifted watercourse to the north and began to feed the salt lakes of the DT, XT and YLP, alongside with the Fan II progradation. The inference is consistent with stratigraphic evidence from the sediment cores of the four salt lakes. One of the major findings of our work is the importance of the contrasting hydroclimatic conditions between the high mountains containing ice caps and the terminal salt lakes. The greater than 4000 m of relief in the watershed enables a massive amount of ions, such as K + , to be weathered and transported together with detrital material from the huge, relatively wet alpine regions to the hyperarid terminal basins, where intense evaporation rapidly enriches the lake water, resulting in evaporite deposition and associated K + - and Li + -rich brine deposits.