Search

Two large sandy seas in northern China, the Taklamakan and Badanjilin deserts, were investigated for geochemical variations of soluble salts in aeolian sands. The aim was to explore factors influencing the composition and distribution of soluble salts in aeolian sands and their environmental implications. The total concentrations of soluble salt in the aeolian sands range between 0.14 and 1.32‰, with pH ranging between 8.4 and 9.6, indicating a primary degree of salt accumulation and alkaline soil conditions in these regions. Sodium chloride and bicarbonate are the major salts. High inter-regional homogenization and small local differences in the chemical compositions and distributional patterns of salt occur in the two deserts. The spatial variations in salt content correlate with regional climatic parameters, such as precipitation and temperature. This suggests that the regional air temperature and moisture conditions of climate have a significant influence on the soluble salts in aeolian sands. The domination of sedimentation of soluble salts in aeolian sands deposited via atmospheric processes, which is heavily associated with dry deposition, is discussed. Case studies from the two deserts suggest that variations in salt content in sedimentary sequences, interlaid by aeolian and lacustrine sediments, should be interpreted with care if the aim is to reveal palaeo-environmental changes. To a certain extent, the two deserts, as inferred from the carbon-bearing salts and the alkalinity of the sandy soils, appear to have potential to provide a significant contribution to the global carbon cycle. [ABSTRACT FROM AUTHOR]

Owing to the limited natural distributions and special medicine-industrial values of Viola philippica , it's urgently needed to explore its population-level differences for promoting the resource utilization efficiencies of this plant. The hypothesis of this study was that different populations of V. philippica plants would have broad-scale differences and interactions of leaf-accumulated metabolites and leaf-colonized bacteria. Hence, two populations (vi-p and vi-j) of this plant were typically collected in China for analyzing multiomics. At first, vi-p and vi-j leaf metabolomes (LMs) were presented with 1,003 metabolites; in contrast of vi-p-LMs, 445 differently accumulated metabolites (DAMs) were identified in vi-j-LMs, with the only up-regulated lipids, vitamin and ketone compounds, the only down-regulated aldehyde compounds, the most up-regulated flavonoids, and the most down-regulated phenylpropanoid compounds. In comparative of vi-p leaf transcriptomes (LTs), 4,645 differently expressed genes (DEGs) were identified in vi-j-LTs, which were typically involved in a series of extracellular defenses and secondary metabolic pathways; the DEGs were frequently co-enriched with DAMs in three biosynthesis pathways of phenylpropanoid, flavonoid, and α-linolenic acid. Furthermore, these DAMs were also found to have the significant correlations with some different types or/and abundances of leaf-assembled bacteria (DTAB) between vi-p and vi-j leaf-assembled bacterial communities (LABCs). Taken together, this study reveals the broad-scale patterns of regulating vi-p and vi-j leaf DAMs with DEGs and DTAB, suggesting that it's essential of keeping plant-population and -habitat diversities for harvesting population-level DAMs in V. philippica. • The plant-level functional metabolites were integrally uncovered in V. philippica. • Two plant populations were identified with differently accumulated metabolites (DAMs). • The typical DAMs were co-enriched with differently expressed genes (DEGs). • These DAMs were also correlated with different types or/and abundances bacteria (DTAB). [ABSTRACT FROM AUTHOR]

Abstract: Sedimentary sequences occurring in desert dunes reflect changes in desert systems, and as such may contain signals useful for recognizing spatial and temporal changes of deserts and their response to regional or even global climate fluctuations. Geomorphological and palaeoenvironmental studies within the dune fields of the Asian middle-latitudes have provided some solid evidence for interpreting the history of these sand seas. Using the Hunshandake (Otindag) Sandy Land, a sandy area covered primarily by stabilized dunes and located in the semi-arid zone of eastern Inner Mongolia, China (Fig. 1), as an example, we studied the initiation and variation in the dune landscape in the eastern portion of the desert belt in northern China. On the basis of physical and biochemical indicators in the sediments and OSL chronology, we herein argue that this dune system in the middle latitudes of eastern Asia is much younger than previously assumed and that it has responded sensitively to climate change during the late Quaternary. Geological evidence from the Sandy Land suggests that most of the current dunes are of late Pleistocene or even Holocene age. Palaeosols intercalated in the aeolian sequences and their OSL chronology show that the climate of the Hunshandake was much wetter than today between 9.6 ka and 3 ka. This resulted in stabilization of the dunes in the eastern and central portions of the Sandy Land. Epochs of reworking or stabilization of the dunes are broadly consistent with the fluctuations in northern hemisphere solar radiation although with an obvious time lag. Because the increase rate of annual precipitation was not sufficient to fully stabilize the dunes in more arid part of the region, some active dunes persisted even during this long-lasting wetter epoch. We conclude that periods of Holocene dune stabilization due to palaeosol formation varied along the climate gradients across the various sandy lands of northern China, and in general it began earlier and lasted longer in the east than in the west. The general nature of the sandy lands and their counterparts in the western portion of the desert belt during the LGM and mid-Holocene climate optimum is discussed in comparison with their current states. [Copyright &y& Elsevier]

Summary: Rivers draining the sedimentary platform of northern Xinjiang (the center of Asian continent) are characterized by low discharge under a temperate and arid climate. The influence of rock mineralogy, climate, relief and human activity on natural water composition and export as a result of weathering is a major scientific concern both at the local and the global scale. While comprehensive work on the controlling mechanism of chemical weathering has been less carried out in the sedimentary platform of northern Xinjiang. Thus, the effects of climate and rock weathering on the inorganic hydrogeochemical processes are not well quantified at this climatic extreme. To remedy this lack a comprehensive survey has been carried out of the geochemistry of the large, pristine rivers in northern Xinjiang, the Erlqis, Yili, Wulungu, Jingou and numerous lesser streams which has not experienced the pervasive effects of glaciation and subsequent anthropogenic impacts. The scale of the terrain sampled, in terms of area, is comparable to that of the Huanghe and includes a diverse range of geologic and climatic environments. In this paper the chemical fluxes from the stable sedimentary basin of the northern Xinjiang platform will be presented and compared to published results from analogous terrains in the monsoon basins of China and world. Overall, the fluvial geochemistry of northern Xinjiang in westerly climate is similar to that of the Chinese rivers (Huanghe and Yangtze) in the East-Asian monsoon Climate, both in property–property relationships and concentration magnitudes. The range in the chemical signatures of the various tributaries is large; this reflects that lithology exerts the dominant influence in determining the weathering yield from the sedimentary terrains rather than the weathering environment. The effect of different rock weathering ranges from rivers dominated by aluminosilicate weathering, mainly of granites, sandstones and shales, to those bearing the signatures of dissolution of carbonates and evaporites and of continental playa deposits. Carbonates are the general predominant lithology undergoing dissolution particularly within the lesser arid areas. The pCO2 in the study rivers is out of equilibrium with respect to atmospheric pCO2, about up to ∼20 times supersaturated relative to the atmosphere but not to such an extent as the Amazon in the floodplain. A roughly positive relationship is observed between solute concentrations and the drought index (DI) for natural waters in the region, indicating a coupled mountain-basin climate has a direct effect. The relative contributions of end-member solute sources to the total dissolved cations from each watershed have been quantitatively estimated using dissolved load balance models, showing the results as evaporite dissolution>carbonate weathering>silicate weathering>atmospheric input for the whole catchment. The areal total dissolved fluxes range from 0.05 to 2.53×106 mol/km2/yr, 0.02–2.09×106 mol/km2/yr and 0.01–1.04×106 mol/km2/yr in the Yili, Zhungarer and Erlqis, respectively, comparable to those of Chinese and Siberia rivers draining sedimentary platforms, even though they are in drastically different climatic regimes. In general, the fluxes from rivers in sedimentary basins are comparable to those from orogenic zones, but are much higher than in the shield regions. The CO2 consumption by aluminosilicate weathering (0.2–284×103 mol/km2/yr) is much smaller than in active orogenic belts (19–1750×103 mol/km2/yr in similar latitudes and 143–1000×103 mol/km2/yr in the tropical basins), but comparable to those of the Chinese (7–106×103 mol/km2/yr) and Siberia (16–112×103 mol/km2/yr) rivers. [Copyright &y& Elsevier]

Abstract: This paper reviews our current understanding of Quaternary climate and landscape changes in the desert areas of northern China, a key portion of the middle-latitude drylands on Earth. Combining earlier studies with our recent research and experience, we offer a comprehensive picture of the state of Chinese deserts during the Quaternary and, in the interest of enhancing future research, identify knowledge gaps and areas of uncertainty. Lacustrine deposits found over an area ranging from China’s western Taklamakan Desert to the eastern Hunshandake Sandy Lands suggest that extensive lakes occurred in China’s deserts during the Pleistocene. Analysis of digital elevation models from SRTM (Shuttle Radar Topography Mission) data supports this interpretation and shows the significant extent of these former lakes. New estimates of mean annual evaporation of ca. 1000 mm from lake surfaces and ca. 100 mm from land surfaces, confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone, especially during intervals when the mean annual rainfall is more than 100 mm. Rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of China are very sensitive ephemeral systems, and not long-lasting as previously thought. Available chronologies suggest that there were large lakes in the western Taklamakan Desert and the Chadamu Basin during MIS (Marine Isotope Stage) 3, at ∼30 ka, probably related to a period of strong influence of northern hemispheric westerly winds. Channels and elevation models revealed by SRTM data and remains of lacustrine sediments also indicate that there was a large lake in the Hunshandake Sandy Lands in the eastern portion of the desert belt during the Quaternary. There is significant evidence that during the middle Holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern China. Lacustrine records from the Badain Jaran Desert in western Inner Mongolia suggest that it was generally dry before 10 cal ka, becoming wetter from 10 to 4 cal ka, and dry again afterwards. Study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt, suggests that there was a period of wet and warm climate in this region during the mid-Holocene Optimum, at a minimum between 6 ka and 4 ka, but possibly lasting longer. Recent observations dealing with the generation and transport of dust from Central Asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed. These results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in Chinese deserts are somehow similar to that having occurred in the Sahara Desert of North Africa. Deserts in northern China were also important focal regions for Neolithic cultures during intervals when environmental conditions supported a denser vegetative cover. There is evidence that some areas of woody vegetation to the west of Badain Jaran Desert were deforested by humans by ca. 4000 yr B P, although it is still debatable whether humans have had a significant impact in other areas at that time. Opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long-term, field-based, investigations. [Copyright &y& Elsevier]

Abstract: In the arid region of northern Xinjiang, one of the least-studied areas in China, three watersheds, namely those of the Yili, Zhungarer and Erlqis, have become the focus of attention due to rapidly increasing human population and water demands. The hydrogeochemistry of natural water from the three watersheds was investigated. The ionic chemistry of natural waters from these watersheds changes considerably on a regional scale. The waters are neutral to alkaline in nature and most of them are soft-fresh waters. The total dissolved solid (TDS) varies over two orders of magnitude with a mean value of 580mg/L, about 1.2 times and 4.6 times those of the Huanghe (Yellow River) and the world spatial median, respectively, but only 40% and 0.8% of those of the Tarim and the western Alashan watersheds, respectively. Much of the solutes and physicochemical parameters in these waters are under the highest desirable limits of the World Health Organization (WHO) for drinking purpose and a plot of sodium adsorption ratio versus EC shows that most waters are of good water quality for irrigation. Water–rock interaction and saturation index (SI) for selected minerals are evaluated. The SI of these natural waters is out of equilibrium (undersaturated) with respect to major carbonates (calcite and dolomite) and evaporites (gypsum and halite). The high concentrations of alkali earth metals, alkalinity and the high (Ca+Mg)/(Na+K) and Na/Cl ratios indicate that the release of major solutes in these waters is controlled largely by dissolution processes of carbonate and partly by silicate weathering, while, cation exchange reactions, soil–salt leaching and evaporation processes also play an important role. The effects of local pollution are minimal in the montane and piedmont areas of these watersheds but are significant in the oases and central areas of the drainage basins. [Copyright &y& Elsevier]