Major ion geochemistry of shallow groundwater in the Qinghai Lake catchment, NE Qinghai-Tibet Plateau

Conventional hydrochemical techniques and statistical analyses were applied to better understand the solute geochemistry and the hydrochemical process of shallow groundwater in the Qinghai Lake catchment. Shallow groundwater in the Qinghai Lake catchment is slightly alkaline, and is characterized by a high ion concentrations and low water temperature. The total dissolved solids (TDS) in most of the samples are &lt; 1,000 mg/L, i.e. fresh water and depend mainly on the concentration of SO4 (2-), Cl- and Na+. Groundwater table is influenced directly by the residents&#39; groundwater consumption. Most of the groundwaters in the Qinghai Lake catchment belong to the Ca2+(Na+) -HCO3 (-) type, while the Qinghai Lake, part of the Buha (BHR) and the Lake Side (LS) samples belong to the Na+-Cl- type. The groundwater is oversaturated with respect to aragonite, calcite and dolomite, but not to magnesite and gypsum. Solutes are mainly derived from strong evaporite dissolution in Daotang, BHR and LS samples and from strong carbonate weathering in Hargai and Shaliu samples. Carbonate weathering is stronger than evaporite dissolution with weak silicate weathering in the Qinghai Lake catchment. Carbonate weathering, ion exchange reaction and precipitation are the major hydrogeochemical processes responsible for the solutes in the groundwater in the Qinghai Lake catchment. Most of the shallow groundwaters are suitable for drinking. More attention should be paid to the potential pollution of nitrate, chloride and sulfide in shallow groundwater in the future.</p

Solute geochemistry and its sources of the groundwaters in the Qinghai Lake catchment, NW China

Major ion compositions were analyzed in 65 groundwater samples to decipher water quality, solute geochemistry and sources of groundwater within the Qinghai Lake catchment, NE Tibetan Plateau. Ground-waters were slightly alkaline with pH varying from 7.2 to 8.7. The total dissolved solids (TDS) varied over two orders of magnitude from fresh (88%) to brackish (12%) with a mean value of 672 mg/L, higher than river waters within the Qinghai Lake catchment and river waters draining the Himalayas and the southeastern Tibetan Plateau. Most of the samples, approximately 80%, were the Ca2+-Mg2+-HCO3- type and suitable for drinking and irrigation. Some of the Lakeside, the Buha and the Qinghai Lake water were the Na+-Cl- type and not suitable for drinking and irrigation. Water quality of Hargai and Shaliu samples was better than the others. Rock weathering, ion exchange and precipitation are the major geochemical processes responsible for the solutes in the groundwater within the Qinghai Lake catchment. Anthropogenic input to the groundwater is minor. The forward models on the input of groundwaters from various sources showed that the contributions were 40.1% for carbonate weathering, 29.0% for evaporite dissolution, 16.8% for atmospheric input and 14.1% for silicate weathering of the total dissolved cations for the whole catchment. Evaporite dissolution was dominating in the Lakeside, the Buha and the Daotang samples, contributing 15.3-45.9%, 20.4-61.1% and 21.3-63.9% of the total dissolved cations. respectively. Carbonate weathering was dominated in the Shaliu and the Hargai samples, contributing 23.9-71.7% and 31.8-95.4% of the total dissolved cations, respectively. The result also demonstrated that carbonate weathering had higher contribution to the groundwaters than silicate weathering.</p

Geochemistry and solute sources of surface waters of the Tarim River Basin in the extreme arid region, NW Tibetan Plateau

Major ion concentrations of river, lake and snow waters were measured to better understand the water quality, hydrochemical processes and solute sources of surface waters within the Tarim River Basin in the extreme arid region. Surface waters are slightly alkaline and are characterized by high total dissolved solids (TDS). TDS values varies over two orders of magnitude from fresh (76%) to brackish (24%) with a mean value of 1000 mg/L, higher than the global river average and river waters draining the Himalayas and the southeastern Tibetan Plateau. Most of the samples were Ca(2+)-(Mg(2+))-HCO(3)(-) type and suited for drinking and irrigation. Water quality of Aksu River (AK), Hotan River (HT) and Northern Rivers (NR) is better than the others. Rock weathering, ion exchange and precipitation are the major hydrogeochemical processes responsible for the solutes in rivers waters. Anthropogenic input to the water chemistry is minor and human activities accelerate increase of river TDS. The quantitative solute sources are first calculated using a forward model in this area. The results show that evaporite dissolution, carbonate weathering, atmospheric input, and silicate weathering contributed 58.3%, 25.7%, 8.7%, and 8.2% of the total dissolved cations for the whole basin. Evaporite dissolution dominated in Lake Waters (LW), HT, Yarkant River (YK), Tarim River (TR), and Southern Rivers (SR), contributing 73.5%, 53.4%, 56.7%, 77%, and 74.2% of the total dissolved cations, respectively. Carbonate weathering dominated in AK and NR, contributing 48% and 44.4% of the total dissolved cations, respectively. The TDS flux of HT, TR, AK, YK was 66.0, 118.6, 134.9, and 170.4 t/km(2)/yr, respectively, higher than most of the rivers in the world. Knowledge of our research can promote effective management of water resources in this desert environment and add new data to global river database.</p

Otolith microchemistry of modern versus well-dated ancient naked carpGymnocypris przewalskii: Implication for water evolution of Lake Qinghai

There is ongoing debate over how the water level and composition of the water in Lake Qinghai changed in the past and might change in future. This study of the microchemistry of otoliths from ancient naked carp explores the chemistry of a relict lake isolated from Lake Qinghai during the Little Ice Age (LIA). A close correlation between the ages measured on fish bone and otoliths by AMS-14C, and by optically stimulated luminescence on overlying sediments, confirms a high water level in Lake Qinghai before 680–300 years ago. The contrasting compositions of the ancient otoliths relative to modern otoliths and waters indicate that the relict lake became enriched in 18O, Mg, Li, B and to a lesser extent Ba, but depleted in 13C, owing to strong evaporation, authigenic carbonates precipitation, (micro-)organism activity, and less fresh water input after it was isolated. If there were long-term fresh water input, however, a reverse trend might occur. The most important observation is that, because the waters have been supersaturated with respect to carbonates, authigenic carbonate precipitation would result in low but consistent Sr/Ca ratios in the lakes, as recorded by both the ancient and modern otoliths. The geochemical records of ancient versus modern biogenic carbonates provide insights into the long-term hydroclimatic evolution processes of an inland water body

The significant role of inorganic matters in preservation and stability of soil organic carbon in the Baoji and Luochuan loess/paleosol profiles, Central China

The preservation and stability mechanisms of soil organic carbon (SOC) are the important factors to evaluate the capacity of soil carbon pool and the potential of sustainable utilization. To understand the preservation time and mechanisms of SOC under burial conditions, in the present study, the distributions of total organic carbon (TOC) and stable organic carbon (StOC), and their correlations with the contents of clays and clay minerals and different forms of iron oxides were investigated in the Baoji and Luochuan loess-paleosol profiles. Four facts were observed as the followings. (1) The labile SOC almost was decomposed and the mostly stable SOC was preserved in the loess and paleosol after 375 kyr since their formation. StOC could be preserved at least 762 kyr in both loess and paleosol under burial condition. (2) The TOC was positively correlated with clay contents, with correlation coefficients of 0.72 (Baoji) and 0.63 (Luochuan). (3) The TOC, StOC, mineral-protected organic carbon (MOC), and recalcitrant organic carbon (ROC) were positively correlated with kaolinite, with correlation coefficients of 0.93, 0.72, 0.52, 0.81 (Baoji) and 0.78, 0.58, 0.50, 0.49 (Luochuan), respectively, both with neither illite nor vermiculite. (4) The TOC was highly correlated with complex iron (Fe-p) with correlation coefficients of 0.90 (Baoji) and 0.82 (Luochuan), so with amorphous oxides of iron (Fe-o) as well. Among them, Fe-o mainly affected by sorption and Fe-p by complexation on SOC preservation, whereas kaolinite had both chemical and physical effects. The values of coefficients further highlight that the contributions of inorganic matters to the fixation of organic carbon were ranked to an order of kaolinite &gt; Fe-p &gt; Fe-o.</p

A study of elevated pollution layer over the North China Plain using aircraft measurements

An elevated pollution layer (EPL) at altitude &sim;1700 m was observed over the North China Plain (NCP) in November 2016. The vertical profiles of aerosol loadings, chemical compositions and meteorological parameters were in-situ measured at both ground and aircraft platforms. The EPLs were observed simultaneously over Beijing and Baoding city (&sim;150 km distance between) with similar aerosol concentration and size distribution, indicating the impact of the EPL at regional scale. The synoptic and remote sensing analysis suggest the pollutants in the EPL may result from regional transport from the polluted southwest, and then elevated by the influence of anticyclone circulation and surrounding terrain. The descent air mass next day may lead to EPL entrainment and contribute to increased aerosol concentration at lower level. The non-refractory compositions measured by aerosol mass spectrometer showed more significant fraction of nitrate and secondary organics in the EPL compared to the other layers. The pollutants in the EPL was then mixed into the developed planetary boundary layer (PBL), leading to uniform distribution of aerosol composition. Such atmospheric stratification at high level and its subsequent impact on the lower level needs to be considered for the future radiative forcing study over this region.</p

Connectivity of earthquake-triggered landslideswith the fluvial network: Implicationsfor landslide sediment transport afterthe 2008 Wenchuan earthquake

Evaluating the influence of earthquakes on erosion, landscape evolution, and sediment-related hazards requires understanding fluvial transport of material liberated in earthquake-triggered landslides. The location of landslides relative to river channels is expected to play an important role in postearthquake sediment dynamics. In this study, we assess the position of landslides triggered by the Mw 7.9 Wenchuan earthquake, aiming to understand the relationship between landslides and the fluvial network of the steep Longmen Shan mountain range. Combining a landslide inventory map and geomorphic analysis, we quantify landslide-channel connectivity in terms of the number of landslides, landslide area, and landslide volume estimated from scaling relationships. We observe a strong spatial variability in landslide-channel connectivity, with volumetric connectivity (&xi;) ranging from ~20% to ~90% for different catchments. This variability is linked to topographic effects that set local channel densities, seismic effects (including seismogenic faulting) that regulate landslide size, and substrate effects that may influence both channelization and landslide size. Altogether, we estimate that the volume of landslides connected to channels comprises 43 + 9/ 7% of the total coseismic landslide volume. Following the Wenchuan earthquake, fine-grained (&lt;~0.25 mm) suspended sediment yield across the Longmen Shan catchments is positively correlated to catchment-wide landslide density, but this correlation is statistically indistinguishable whether or not connectivity is considered. The weaker-than-expected influence of connectivity on suspended sediment yield may be related to mobilization of fine-grained landslide material that resides in hillslope domains, i.e., not directly connected to river channels. In contrast, transport of the coarser fraction (which makes up &gt;90% of the total landslide volume) may be more significantly affected by landslide locations.</p

Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii (Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China

Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-C-14 ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-C-14 dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction (XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn&#39;t change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca ((70.12 +/- 18.50)x10(-5)) and delta O-18 ((1.76 +/- 1.03)parts per thousand) of ancient lapilli are significantly higher than those of modern lapilli (average Mg/Ca=(3.11 +/- 0.41)x10(-5) and delta O-18=(-4.82 +/- 0.96)parts per thousand). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and delta O-18 ratios than modem Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today&#39;s Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km(2) during the Ming Dynasty, approximately similar to 5% larger than it is today.</p

Unveiling the morphology of buried In(Ga)As nanostructures by selective wet chemical etching: From quantum dots to quantum rings

The three-dimensional morphology of In(Ga)As nanostructures embedded in a GaAs matrix is investigated by combining atomic force microscopy and removal of the GaAs cap layer by selective wet etching. This method is used to investigate how the morphology of In(Ga)As quantum dots changes upon GaAs capping and subsequent in situ etching with AsBr3. A wave function calculation based on the experimentally determined morphologies suggests that quantum dots transform into quantum rings during in situ etching. (c) 2007 American Institute of Physics