Jingtai Han

Geochemical characteristics and fluxes of organic carbon in a human-disturbed mountainous river (the Luodingjiang River) of the Zhujiang (Pearl River), China.

This study aims to investigate the state of the riverine organic carbon in the Luodingjiang River under human impacts, such as reforestation, construction of reservoirs and in-stream damming. Seasonal and spatial characteristics of total suspended sediment (TSS), dissolved organic carbon (DOC) and particulate organic carbon (POC), as well as C/N ratios and the stable carbon isotopic signatures of POC (delta(13)C(POC)) were examined based on a one-year study (2005) in the basin-wide scale. More frequent sampling was conducted in the outlet of the river basin at Guanliang hydrological station. DOC and POC concentrations showed flush effects with increasing water discharge and sediment load in the basin-wide scale. Atomic C/N ratio of POC had a positive relationship with TSS in the outlet of the basin, indicating the reduced aquatic sources and enhanced terrestrial sources during the high flood season. However, the similar relationship was not observed in the basin-wide scale mainly due to the spatial distributions of soil organic carbon and TSS. delta(13)C(POC) showed obvious seasonal variations with enriched values in the period with high TSS concentration, reflecting the increased contribution from C(4) plants with enhanced soil erosion. The specific flux of the total organic carbon (2.30 t km(-)(2) year(-1)) was smaller than the global average level. The ratio of DOC to POC was 1.17, which is higher than most rivers under Asian monsoon climate regime. The organic carbon flux was estimated to decline with decreasing sediment load as a result of reforestation, reservoir construction and in-stream damming, which demonstrates the impacts of human disturbances on the global carbon cycle.

Major ion chemistry and dissolved inorganic carbon cycling in a human-disturbed mountainous river (the Luodingjiang River) of the Zhujiang (Pearl River), China.

Major ion chemistry and dissolved inorganic carbon system (DIC, mainly HCO3(-) and gaseous CO2) in the Luodingjiang River, a mountainous tributary of the Zhujiang (Pearl River), China, were examined based on a seasonal and spatial sampling scheme in 2005. The diverse distribution of lithology and anthropogenic impacts in the river basin provided the basic idea to assess the effects of lithology vs. human activities on water chemistry and carbon biogeochemistry in river systems. Major ions showed great spatial variations, with higher concentrations of total dissolved solids (TDS) and DIC in the regions with carbonate rocks and clastic sedimentary rocks, while lower in the regions with metamorphic sandstones and schists as well as granites. pCO2 at all sampling sites was oversaturated in June, ranging with a factor from 1.6 to 18.8 of the atmospheric concentration, reflecting the enhanced contribution from baseflow and interflow influx as well as in situ oxidation of organic matter. However, in April and December, undersaturated pCO2 was found in some shallow, clean rivers in the upstream regions. delta13C of DIC has a narrow range from -9.07 to -13.59 per thousand, which was more depleted in the regions with metamorphic rocks and granites than in the carbonate regions. Seasonally, it was slightly more depleted in the dry season (December) than in the wet season (June). The results suggested that lithological variability had a dominant control on spatial variations of water chemistry and carbon geochemistry in river systems. Besides, anthropogenic activities, such as agricultural and urban activities and in-stream damming, as well as river physical properties, such as water depth and transparency, also indicated their impacts. The seasonal variations likely reflected the changes of hydrological regime, as well as metabolic processes in the river.

Solar wind‐magnetosphere energy coupling function fitting: Results from a global MHD simulation

Quantitatively estimating the energy input from the solar wind into the magnetosphere on a global scale is still an observational challenge. We perform three- dimensional magnetohydrodynamic (MHD) simulations to derive the energy coupling function. Based on 240 numerical test runs, the energy coupling function is given by E-in = 3.78 x 10(7)n(sw)(0.24)V(sw)(1.47)B(T)(0.86) [sin(2.70)(theta/2) + 0.25]. We study the correlations between the energy coupling function and a wide variety of magnetospheric activity, such as the indices of Dst, Kp, ap, AE, AU, AL, the polar cap index, and the hemispheric auroral power. The results indicate that this energy coupling function gives better correlations than the epsilon function. This result is also applied to a storm event under northward interplanetary magnetic field conditions. About 13% of the solar wind kinetic energy is transferred into the magnetosphere and about 35% of the input energy is dissipated in the ionosphere, consistent with previous studies.

Pliocene-pleistocene climatic change recorded in fluviolacustrine sediments in central China

Abstract A 250-m-thick section located in the Guanzhong basin, central China, consisting of a loess-paleosol sequence in the upper part and fluviolacustrine sequence in the lower, was selected for this study which involves documenting the climate transition around the global glacial initiation about 2.5 Ma, and focuses on the climatic information recorded in the fluviolacustrine sediments. Paleomagnetic study indicates that the entire Shijiawan section developed during the past 3.08 Ma and the fluviolacustrine sequence spans the time-interval of 3.08-1.9 Ma. Sedimentary analysis shows that alluvial facies dominates the so-called fluviolacustrine sequence with strong cyclicity. Pollen study combined with stable carbon-isotope analysis of organic matter displays profound changes of the paleovegetation in response to climate forcing. During the period of 3.0–2.7 Ma, persistent steppe vegetation and elephant fossil fauna suggest long-lasting dry and warm climate conditions with little change. From 2.7 to 2.5 Ma, sparse steppe flora manifests a striking climatic deterioration. The first thick loess-like layer in the fluviolacustrine sequence consistent with the commencement of the loess deposition in the Loess Plateau marks a rapid and great intensification of the Siberian cold-high pressure regime at 2.6 Ma. Afterwards, the regional vegetation fluctuated between dry steppe and forest-grasslands, in agreement with loess-paleosol alternations, corresponding to the climatic oscillations between cold-dry and warm-wet. Such secular climate variation patterns demonstrate the predominant influence of global glacial and interglacial forcing on the regional climate system of the East Asian monsoon. The late Pliocene climate, warm and dry, is distinct from the harmony of temperature with precipitation (i.e. cold with dry, and warm with wet) which is fully exhibited throughout the past 2.6 Ma. Thus the time of the first global glaciation must have involved a rapid reorganization of the regional climate regime and the onset of the modern East Asian monsoon.

Chemical weathering inferred from riverine water chemistry in the lower Xijiang basin, South China

Seasonal sampling was conducted on 13 sites involving the lower stem of the Xijiang river and its three tributaries to determine the spatial patterns of the riverine water chemistry and to quantify the chemical weathering rates of carbonate and silicate of the bedrock. Results indicate that the major ions in the Xijiang river system are dominated by Ca(2+) and HCO(3)(-) with a higher concentration of total dissolved solids, characteristic of the drainages developed on typical carbonate regions. Obvious spatial variations of major ion concentrations are found at various spatial scales, which are dominantly controlled by the lithology particularly carbonate distribution in the region. The four selected rivers show similar seasonal variations in major ions, with lower concentrations during the rainy season. Runoff is the first important factor for controlling the weathering rate in the basin, although increasing temperature and duration of water-rock interaction could make positive contributions to the enhancement of chemical weathering. The chemical weathering rates range from 52.6 to 73.7 t/km(2)/yr within the lower Xijiang basin and carbonate weathering is over one order of magnitude higher than that of silicates. CO(2) consumption rate by rock weathering is 2.0 x 10(11) mol/yr, of which more than 60% is contributed by carbonate weathering. The flux of CO(2) released to the atmosphere-ocean system by sulfuric acid-induced carbonate weathering is 1.1 x 10(5) mol/km(2)/yr, comparable with the CO(2) flux consumed by silicate weathering.

CO2 outgassing from the Yellow River network and its implications for riverine carbon cycle

CO2 outgassing across water-air interface is an important, but poorly quantified, component of riverine carbon cycle, largely because the data needed for flux calculations are spatially and temporally sparse. Based on compiled data sets measured throughout the Yellow River watershed and chamber measurements on the main stem, this study investigates CO2 evasion and assesses its implications for riverine carbon cycle. Fluxes of CO2 evasion present significant spatial and seasonal variations. High effluxes are estimated in regions with intense rock weathering or severe soil erosion that mobilizes organic carbon into the river network. By integrating seasonal changes of water surface area and gas transfer velocity (k), the CO2 efflux is estimated at 7.9 ± 1.2 Tg C yr−1 with a mean k of 42.1 ± 16.9 cm h−1. Unlike in lake and estuarine environments where wind is the main generator of turbulence, k is more correlated with flow velocity changes. CO2 evasion in the Yellow River network constitutes an important pathway in its riverine carbon cycling. Analyzing the watershed-scale carbon budget indicates that 35% of the carbon exported into the Yellow River network from land is degassed during fluvial transport. The CO2 efflux is comparable to the carbon burial rate, while both larger than the fluvial export to the ocean. Comparing CO2 evasion with ecosystem productivity in the Yellow River watershed shows that its ecosystem carbon sink has previously been overestimated by >50%. Present efflux estimates are associated with uncertainty, and future work is needed to mechanistically understand CO2 evasion from the highly turbid waters.

Assessment of the palaeoclimate during 3.0–2.6 Ma registered by transition of Red Clay to loess–palaeosol sequence in central North China

Abstract A continuously accumulated section (the Yanyu section) of Red Clay and loess–palaeosol sequence from the southernmost Chinese Loess Plateau was selected for this study of palaeoclimate of the late Pliocene to early Pleistocene period. Termination of the Red Clay accumulation and onset of loess deposition was coincident with the beginning of extensive Northern Hemisphere glaciation at 2.6 Ma. Field observations and compositional analyses suggest an aeolian origin for the Red Clay, much like the processes experienced by the loess–palaeosol sequence. Pedogenic analysis indicates that the late Pliocene Red Clay first experienced complete decalcification and illuviation (mechanical translocation of clays) in all horizons, including the present carbonate precipitation zones, but other chemical alterations have been rather weak and even weaker than experienced by the overlying loess-derived palaeosols. In great contrast to the Pleistocene climate characterised by frequent and large-amplitude fluctuations between cold–dry and warm–wet, a relatively steady warm–dry climate condition is implied for the late Pliocene. Dustfall rate assessment indicates a much lower accumulation rate during the late Pliocene than in the early Pleistocene, in agreement with a notable systematic coarsening from the Red Clay to the overlying loess and palaeosols. Together, these features suggest that the dust transport agent, the northwesterly winds, were weaker over the late Pliocene. The transition from Red Clay to loess possibly marked a significant and rapid shift in the climatic system in east Asia.

Arsenic removal from water by iron-sulphide minerals

In bench-scaled experiments, iron-sulphide minerals, pyrite and pyrrhotite are used as adsorbents for arsenic removal from As-spiked water of As5+ and As3+ species. The adsorption rate, efficiency, As-adsorption stability and the associated pH conditions have been examined. Observations indicate that these iron-sulphide minerals are very efficient to adsorb arsenic from water for both As5+ and As3+ species. Similar to other studies, As3+-adsorption shows a slower rate than As3+. The stability of the adsorbed arsenic seems closety retated to the pH values of the solution. A lower pH levet commonly less than 4.0 is required to protect the adsorbed arsenic from serious oxidation and backward retease. Fining of the mineral powders and shaking of the solution during adsorption enhance the adsorption efficiency and adsorption rate. For practical use of the method presented in this study, the waste produced should be managed with great care to keep it from redistribution over water system. A further study of the protection for the waste from oxidation on real water systems will greatly enhance the application of the strong ability of arsenic adsorption by these minerals, which is observed from this study.

Sequential extractions and isotope analysis for discriminating the chemical forms and origins of Pb in sediment from Liaodong Bay, China.

Sequential extraction integrated with isotope analysis was carried out on a sediment core from Liaodong Bay, northeast China, for characterizing Pb in various extraction phases and its possible sources. Results show that in all extracted fractions Pb concentrations increased abruptly in the top part of the sediments that deposited after 1980, but remained lower and rather constant before 1980. Consistent with the variation pattern of Pb concentration, the 206Pb/207Pb ratio displays a dramatic decrease around 1980. These findings strongly suggest serious Pb pollution since then. The Pb concentration and the isotopic ratios of 206Pb/207Pb and 208Pb/207Pb in the residual fraction show rather small changes through the entire core, and are similar to those of uncontaminated Chinese loess, possibly representing the characteristics of the regional geogenic background. The isotopic ratios of the sediments before 1980 varied in different extracted fractions with a linear pattern, from the residual at the highest toward the average signature of automobile exhausts and Pb-Zn deposits, implying a prominent two-end member mixing style of the Pb origin; one is the regional geologic background and the other is anthropogenic sources. The difference in isotopic ratios between the extractions might be indicative of varied proportions of the two sources. For sediments after 1980, however, the isotope ratios in nonresidual fractions are all relatively low and show little differentiation, which may suggest that polluted Pb dominates all the extracted fractions for the top part of the core.

Environmental changes during Frasnian-Famennian transition in south China: A multiproxy approach

National Natural Science Foundation[40672118]; National Key Project for basic research[G2000077708]