Geochemistry of eolian dust and its elemental contribution to Lake Qinghai sediment

Located at the midpoint of the Asian &quot;airborne dust corridor&#39;&#39;, Lake Qinghai receives substantial dust annually, which may impact the biogeochemical cycles of the system. In order to determine quantitatively the flux and chemical contributions of dust to Lake Qinghai sediment, dust samples were collected monthly at two sites surrounding the lake from June 2009 to May 2011. The results demonstrate similar chemical compositions of dust samples to the local loess, implying strong representativeness of regional dust. The average dust deposition flux is 265.7 +/- 55.0 g/m(2)/a, constituting 56.6 +/- 11.7% of the modern sediment, approximating to previous estimates (similar to 65%). Contributions of dust-derived elements in the sediment differ substantially, with a minimum of 16.7% for Sr and a maximum of 83.9% for Cu. Among these elements, the contribution of lithophile elements (Na, Al, K, Ti, Mn, Fe and Rb) is close to that of the bulk dust; the contributions of mobile elements (Mg, Ca and Sr) are low, only 16.7% (Sr)-26.1% (Mg), whereas potentially harmful metals (Cu, Zn and Pb) have high contributions (70.3-83.9%). Seasonal variations of elemental inputs indicate that springtime contributions dominate the annual dust fluxes for all elements into the sediment, in agreement with the high dust flux in spring. These observations not only quantify the contribution of dust to the sediment of Lake Qinghai, but also highlight the important role of dust in the accumulation of various elements in the sediment, especially for potentially harmful metals.</p

Mineralogy of the otoliths of naked carp Gymnocypris przewalskii (Kessler) from Lake Qinghai and its Sr/Ca potential implications for migratory pattern

Otoliths are biogenic carbonate minerals whose microstructure and microchemistry have been used for age determination, stock identification, life history and environmental tracing. Using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, we have determined the mineral types and crystalline characteristics of three pairs of otoliths from naked carp Gymnocypris przewalskii, the predominant fish in Lake Qinghai. The results indicate that the mineral of both lapillus and sagitta of the naked carp is aragonite, and that of asteriscus is vaterite. The aragonite of lapillus has prefect crystallization. Given the shape of lapillus and the sensitivity of its aragonite to water chemistry, lapillus was used to analyze temporal Sr/Ca ratios along the maximal growth axis by an electron probe microanalyzer (EPMA). Consistent variations of Sr/Ca ratios with a range of 1.0x10(-3)-5.0x10(-3) on the long and short radii indicate that Sr/Ca ratios of lapillus potentially respond to the chemical compositions of the host waters during the period of the naked carp&#39;s growth and migration. Discontinuous (dark) zones of lapillus were formed during fall and winter when the naked carp grows slowly in Lake Qinghai, resulting in similar low Sr/Ca ratios to lake water, whereas incremental zones with higher Sr/Ca ratios respond to its migratory river waters during spring and summer. Various Sr/Ca ratios of incremental zones suggest that the migratory pattern of the naked carp may be much more flexible, rather than in a single river. Therefore, high-resolution otolith microchemistry of the naked carp can be used to trace its migratory behavior, which is of significance for determining its migratory pattern and life history of this precious species inhabiting the Tibetan Plateau.</p

Spatial and seasonal variability of water-soluble ions in PM2.5 aerosols in 14 major cities in China

We analyzed PM2.5 aerosols from 14 major cities in China for concentrations of water-soluble (WS) major and trace elements (Na, Mg, Ca, K, Fe, Mn, Zn, Rb, Sr, Ba, Pb, S and Cl). The main focus was to examine patterns in spatial distribution and seasonal variability. Using principal component analysis, we identified three general sources for WS-elements in aerosols as anthropogenic, seasalts and fine dust particles originating from soils. The spatial patterns identified show that anthropogenic activity is the most important factor influencing the concentration of heavy metals in aerosols. Concentrations of WS-S, Zn and Pb were correlated with the locations of major industrial zones, and regulated by topography and seasonal weather patterns. We found higher WS-metals concentrations during the winter season, probably related to coal combustion in northern China. Moderate correlations of WS-S, Zn, Pb and Cl suggest that coal combustion releases. The seasonal pattern in WS-Fe concentrations shows the importance of acid precipitation events where coal combustion contributes to additional Fe (II) deposition. The findings of this study support the argument that WS-S in fine particles enhanced the production of hydrogen ions act to reduce the pH values of precipitation. Our interpretation of these spatial and seasonal patterns in WS-major and trace elements in aerosols highlights the need for continued research on trends in acidic deposition in major industrial cities in China.</p

Effects of dry grinding on the structure and granularity of calcite and its polymorphic transformation into aragonite

The structure and granularity of calcite were measured during dry grinding in a ball mill by X-ray diffraction, Fourier transform infrared spectroscopy and laser diffraction, and its morphology was observed by a scanning electron microscope. During the early stage of grinding (0-10. min), the median particle size and X-ray diffraction intensity of the calcite decreased, while the full width at half maximum increased as grinding progressed. During the middle grinding stage (20-300. min), the grain size and crystalline degree of ultrafine calcite particles no longer changed with time; this was attributed to aggregation, which hindered the breakage of particles. During the final grinding stage (360-720. min), a polymorphic transformation of calcite into aragonite took place.</p

Hydrogeochemical processes between surface and groundwaters on thenortheastern Chinese Loess Plateau: Implications for water chemistryand environmental evolutions in semi-arid regions

A large area of the continents is covered by loess that is subject to fast erosion, but detailed research is lacking about processes influencing the hydrogeochemistry in loess-covered regions. This study presents the first &delta;18O and &delta;D, and major ion contents of various waters (rain, rivers, lake, springs and wells) from Daihai Lake catchment on the Chinese Loess Plateau (CLP). In combination with historical hydrological and meteorological data during the past 60 years, we investigate factors affecting water chemistry and lake evolution on the CLP, and thereby provide insight into hydrogeochemical processes under semi-arid climatic conditions. On the northeast CLP, river and groundwaters show elevated TDS (450 and 461 mg/L, respectively), about ~4 times higher than the global river mean value. Their water chemistry is dominantly influenced by carbonate weathering. Lake waters show even higher TDS at 5758 mg/L, ~50 times of the global mean, which is attributed to strong evaporation and associated with precipitation of calcite and dolomite. The order of carbonate (calcite and dolomite) saturation indexes follows lake water N river water N groundwater. Downstream rivers to the west of Daihai Lake are characterized by elevated SO4 2&minus;, indicating high lake levels in the past. Comparison of &delta;18O, &delta;D, TDS and ion contents of river and groundwaters implies that shallow groundwaters are derived from surface runoff via fast infiltration, a hydrological process different from limited infiltration of groundwater on the Tibetan Plateau. Water quality assessment indicates that all river and 79% of well waters belong to moderately hard to hard-fresh waters, suitable for drinking and irrigation of plants with moderate salt tolerance. In contrast, all lake and spring waters and 21% of well waters belong to very bad water quality, and hence are not suitable for irrigation or drinking. Owing to intensified human activities under drying and warming climate, the lake water level of Daihai declined by 4.83 m from 1955 to 2003, and started to accelerate since 1980. As a result, TDS and Cl&minus; increased by 1.8 times and Mg/Ca rose by 156 times from 1953 to 2010. Our data show that environment degradation poses a great threat to human occupation on the CLP. Considering the uniformity of loess, hydrogeochemical processes between surface and groundwaters on the loess regions may represent a widespread status of the CLP.</p

Boron isotopic compositions in growing corals from the South China Sea

In order to determine incorporation of boron species, boron isotopic fractionation, and influence of trace elements on isotopic compositions of boron in corals (delta B-11(coral)), concentrations of Mg, Sr, Na, B and delta B-11(coral) in growing corals from the South China Sea were measured. Relative to seawater, Sr enriched while Mg depleted in corals in the South China Sea. Although the delta B-11(coral) values were different from various species and were not closely correlated with the element concentrations in corals in the South China Sea, Mg(OH)(2) existed in corals can result in high delta B-11(coral). Thus, it is necessary to examine the existence of Mg(OH)(2) and to choose the same species when delta 11B(coral) is used in the (delta B-11-pH proxy. Based on the measured delta B-11 values of corals and coexisting seawater as well as the seawater pH in the South China Sea, a new isotopic fractionation factor a(4-3) between B(OH)(4)(-) and B(OH)(3) was determined to be 0.979. Besides B(OH)(4)(-) into corals, our results showed that B(OH)(3) may also be incorporated into corals with variable proportions. The incorporation of B(OH)(3) into corals may challenge the hypothesis of delta 11B(coral) = delta B-11(4) resulting in increasing uncertainty to the calculated seawater pH values to the delta B-11-pH proxy. We suggested that a best-fit empirical equation between delta B-11 of bio-carbonates and seawater pH needs to be established by the precipitation experiments of inorganic carbonates or culture experiments of corals or foraminifera.</p

Geochemical records in Holocene lake sediments of northern China: Implication for natural and anthropogenic inputs

Daihai Lake is located in a hydrologically closed basin within the transitional zone of the East Asian monsoon, which has experienced significant lake-level fluctuations. The sedimentary sequence of a 12.08 m core was analyzed for mobile (Ca, Mg, and Sr) and immobile elements (Al and Fe) and trace metals (e.g., Co, Ni, Cu, Zn, and Pb) in order to study the changes of natural chemical compositions and the potential influences of the historical mining and use of metals during the Holocene period. Climate changes have a significant influence on the concentrations of mobile elements in the Holocene lake sediment; high concentrations occurred during the times with high lake level, resulting from enhanced catchment weathering due to strong monsoon effects. Different from these mobile elements, the variation of immobile elements and trace metals in Daihai Lake sediment shows clear anthropogenic impact of the mining and use of metals in the last several millenniums. A gradual increase in the concentrations and fluxes of metals from similar to 5000 cal. a B.P. is correlated well with the emergence of Chinese civilization. The concentrations and fluxes of these metals and immobile elements in the sediments increased rapidly between 2100 and 1250 cal. a B.P., indicating the extensive use of metals during the Warring States Period (475-221 B.C.), and the early Han Dynasty (206 B.C.-220 A.D.). Further increase of trace metals, such as Cu, Ni, Co, and Pb, after the Medieval Warm Period (1200-800 a B.P.) likely reflects the increased metal emissions associated with extensive mining and utilization activities. Similar patterns of sedimentary metals between Daihai Lake in northern China and Liangzhi Lake in central China further indicate significant environmental impacts of the mining and utilization of metals in the progress of Chinese civilization in the past several thousand years.</p

A validated analytical procedure for boron isotope analysis in plants by MC-ICP-MS

Boron (B) is an essential micronutrient for plant growth. Lack of valid methods for pretreatment and measurement of delta B-11 in plant restrict applications of it in the biosphere. Dry ashing, one step cation exchange and micro-sublimation were combined to separate and purify boron (B) in plant tissues. The low procedure blank, high B recovery and the accurate delta B-11 values of the plant reference materials demonstrate that this method is suitable and valid for B pretreatment and delta B-11 measurement in plant samples by MC-ICP-MS. Based on this method, the delta B-11 in different plants (Brassica napes, Chenopodium album L, moss, lichen, and Nostoc commune) was analyzed. For Brassica napus, delta B-11 increased gradually from root to leaf, and then decreased to rapeseed. For the same parts, the delta B-11 increased from the lower parts to the higher parts. This variation may be due to the B(OH)(3) transporter of NIP6;1 and the incorporation of B into the cell. The reason for lower delta B-11 values in shell and rapeseed compared to those in leaves presumably is to the preferred transport of borate in the phloem. The largest delta B-11 fractionation between leaf and root in Brassica napus and Chenopodium album L was + 24.2 parts per thousand and + 26.6 parts per thousand, respectively. The large variation and fractionation of delta B-11 within plants indicates that 81113 is a good tracer to study the B translocation mechanisms and metabolism within plants. The delta B-11 in Nostoc commune, lichen, and moss showed variations of -4.1 parts per thousand to + 21.5 parts per thousand, - 9.4 parts per thousand to + 7.3 parts per thousand, and - 18.3 parts per thousand to + 11. 9 parts per thousand, respectively. In the same site, delta B-11 in different plants ranked Nostoc commune > moss > lichen and delta B-11 in mosses growing in different environment ranked soil > tree > rock. Rain and soil available B are the main B sources for these plants. The delta B-11 in Nostoc commune, lichen, and moss may be a useful tracer to study the atmospheric B input. In the future, plants culture experiments under certain environments and studies from molecular level are necessary to decipher the variation of delta B-11 and fractionation mechanisms within plants

Controls on Sr/Ca in benthic foraminifera and implications for seawater Sr/Ca during the late Pleistocene

Changes in the Sr to Ca ratio of sea water have important implications for the interpretation of past climate. It has proven difficult to interpret Sr/Ca of foraminiferal calcite as a measure of seawater Sr/Ca or as reflecting the influence of deep water carbonate ion saturation (Delta[CO32-]) on the incorporation of Sr into benthic foraminiferal carbonate. Here, we address this issue by measurements of paired benthic foraminiferal Sr/Ca and B/Ca (a proxy for deep water A[Delta[CO32-]) for core-tops from the global ocean and three down cores at different settings during the Last Glacial-interglacial cycle. These new data suggest a significant control of deep water Delta[CO32-] on benthic foraminiferal Sr/Ca, and that down-core shell Sr/Ca variations can be largely accounted for by past deep water Delta[CO32-] changes. We conclude that seawater Sr/Ca has likely remained near-constant on glacial-interglacial timescales during the late Pleistocene, in agreement with model results. With due caution, benthic Sr/Ca may be used as an auxiliary proxy for deep water Delta[CO32-] if seawater Sr/Ca is constant.</p

Morphology and ultrastructure of Hippodonta qinghainensis sp nov. (Bacillariophyceae), a new diatom from Lake Qinghai, China

A new medium-sized species of Hippodonta (Bacillariophyceae) is described from Lake Qinghai, China. The morphology and ultrastructure of Hippodonta qinghainensis sp. nov. are described using light and scanning electron microscopy. This new species is compared with similar species of Hippodonta using conventional and geometric morphometric analyses. Hippodonta qinghainensis can be separated from the other species of Hippodonta by a unique combination of characters that include an elliptic-lanceolate to rhombic-lanceolate valve shape, non protracted apices, the absence of fascia, relatively coarse, uniseriate striae and the presence of two rows of lineolae around the valves apices.</p