Effects of Grazing on Ecosystem CO2 Exchange in a MeadowGrassland on the Tibetan Plateau During the Growing Season

Effects of human activity on ecosystem carbon fluxes (e.g., net ecosystem exchange (NEE), ecosystem respiration (R eco), and gross ecosystem exchange (GEE)) are crucial for projecting future uptake of CO2 in terrestrial ecosystems. However, how ecosystem that carbon fluxes respond to grazing exclusion is still under debate. In this study, a field experiment was conducted to study the effects of grazing exclusion on R eco, NEE, and GEE with three treatments (free-range grazing (FG) and grazing exclusion for 3 and 5&nbsp;years (GE3 and GE5, respectively)) in a meadow grassland on the Tibetan Plateau. Our results show that grazing exclusion significantly increased NEE by 47.37 and 15.84&nbsp;%, and R eco by 33.14 and 4.29&nbsp;% under GE3 and GE5 plots, respectively, although carbon sinks occurred in all plots during the growing season, with values of 192.11, 283.12, and 222.54&nbsp;g&nbsp;C&nbsp;m&minus;2 for FG, GE3, and GE5, respectively. Interestingly, grazing exclusion increased temperature sensitivity (Q 10) of R eco with larger increases at the beginning and end of growing season (i.e., May and October, respectively). Soil temperature and soil moisture were key factors on controlling the diurnal and seasonal variations of R eco, NEE, and GEE, with soil temperature having a stronger influence. Therefore, the combined effects of grazing and temperature suggest that grazing should be taken into consideration in assessing global warming effects on grassland ecosystem CO2 exchange.</p

Chemical composition of rainwater at Lijiangon the Southeast Tibetan Plateau: influences from variousair mass sources

Daily rainwater samples collected at Lijiang in 2009 were analyzed for pH, electrical conductivity, major ion (SO42&minus;, Cl&minus;, NO3&minus;, Na+, Ca2+, Mg2+, and NH4+) concentrations, and &delta;18O. The rainwater was alkaline with the volume-weighted mean pH of 6.34 (range: 5.71 to 7.11). Ion concentrations and &delta;18O during the pre-monsoon period were higher than in the monsoon. Air mass trajectories indicated that water vapor from South Asia was polluted with biomass burning emissions during the pre-monsoon. Precipitation during the monsoon was mainly transported by flow from the Bay of Bengal, and it showed high sea salt ion concentrations. Some precipitation brought by southwest monsoon originated from Burma; it was characterized by low &delta;18O and low sea salt, indicating that the water vapor from the region was mainly recycled monsoon precipitation. Water vapor from South China contained large quantities of SO42&minus;, NO3&minus;, and NH4+. Throughout the study, Ca2+ was the main neutralizing agent. Positive matrix factorization analysis indicated that crustal dust sources contributed the following percentages of the ions Ca2+ 85 %, Mg2+ 75 %, K+ 61 %, NO3&minus; 32 % and SO42&minus; 21 %. Anthropogenic sources accounted for 79 %, 68 %, and 76 % of the SO42&minus;, NO3&minus; and NH4+, respectively; and approximately 93 %, 99 %, and 37 % of the Cl&minus;, Na+, and K+ were from a sea salt source.</p

Chemical characterization of aerosol collected at Mt. Yulong in wintertime on the southeastern Tibetan Plateau

In order to evaluate the chemical composition of aerosol on the southeastern Tibetan Plateau, aerosol samples were acquired at Mt. Yulong during January to February, 2010. Eighteen elements (Al, Si, P, S, Ca, Ti, K, Cr, Mn, Fe, Ni, Zn, As, Br, Ba, Pb, Sb and Cu) and major water-soluble ions (SO42-, NO3-, Cl-, Na+, NH4+, K+, Mg2+, and Ca2+) were detected. The results show that Ca, Fe, Al, Si, S, K and Ti are major elements which mainly originate from crustal material, while SO42- and Ca2+ are the dominant anion and cation in the samples, respectively. Results of ion analysis indicate that our samples are alkaline and that the main compounds present are CaCO3, (NH4)(2)SO4, and CaSO4. The enrichment factors (EFs) determined for As, Br, Ca, Cu, S. Pb and Zn are greater than 10; in particular, EFs for As and Br are above 100. However, the high EF for As could be caused by crustal sources because the high level of As enrichment can be found commonly on the Tibetan Plateau. Analyses including Scanning Electron Microscope (SEM) observations, EF determinations, backward trajectories and correlation coefficients reveal that Al, Fe, Ca, Ti, Mn, Fe, K and Mg2+ mainly originate from crustal sources: Pb, Br, Cu, Ni, Zn and Sb come mainly from traffic-related emissions: and biomass burning influences Cl-, Br, S and P.</p

Elemental compositions of PM2.5 and TSP in Lijiang, southeastern edge of Tibetan Plateau during pre-monsoon period

PM2.5 and total suspended particulate (TSP) samples were collected at Lijiang, southeastern Tibetan Plateau, China. Sixteen elements (Al, Si, S, K, Ca, Cr, Mn, Ti, Fe, Ni, Zn, As, Br, Sb, Pb and Cu) were analyzed to investigate their elemental compositions during the pre-monsoon period. The results showed that Ca was the most abundant element in both PM2.5 and TSP samples. The enrichment factors (EFs) of Si, Ti, Ca, Fe, K and Mn were all below 10 for both PM2.5 and TSP, and these elements also had lower PM2.5/TSP ratios (0.32-0.34), suggesting that they were mainly derived from crustal sources. Elements Cu, Zn, S, Br and Sb showed strong enrichment in PM2.5 and TSP samples, with their PM2.5/TSP ratios ranging from 0.66 to 0.97, indicating that they were enriched in the fine fractions and influenced by anthropogenic sources. Analysis of the wind field at 500 hPa and calculations of back trajectories indicated that Al, Si, Ca, Ti, Cr, Mn and Fe can be influenced by transport from northwestern China during the dust-storm season, and that S, K, Ni, Br and Pb reached high concentrations during westerly transport from south Asia. Combined with the principle component analysis and correlation analysis, elements of PM2.5 samples were mainly from crustal sources, biomass burning emissions and regional traffic-related sources.</p

Airborne particulate organic markers at the summit (2060 m,a.s.l.) of Mt. Hua in central China during winter: Implications for biofuel and coal combustion

Sugars, n-alkanes and PAHs in PM10 and size-segregated samples collected from the summit (2060 m, altitude) of Mt. Hua in Guanzhong Plain, central China during the winter of 2009 were characterized using a GC/MS technique. Concentrations of sugars, n-alkanes and PAHs in PM10 are 107&plusmn;52, 121&plusmn;63, 7.3&plusmn;3.4 ng m&minus;3, respectively. Levoglucosan and fossil fuel derived n-alkanes are more abundant in the air masses transported from southern China than in those from northern China with no spatial difference found for PAHs, suggesting that emissions from biomass burning and vehicle exhausts are more significant in southern part of the country. Dehydrated sugars, fossil fuel derived n-alkanes and PAHs presented a unimode size distribution, peaking at the size of 0.7&ndash;1.1 &mu;m, whereas non-dehydrated sugars and plant wax derived n-alkanes showed a bimodal pattern, peaking at 0.7&ndash;2.1 and 5.8&ndash;9.0 &mu;m, respectively. Principal component analysis showed that biofuel combustion plus plant emission is the most important source in Mt. Hua, being different from the cases in Chinese urban areas where fossil fuel combustion is the major source. By comparison with previous mountain and lowland observations and aircraft measurements we found that wintertime PAHs in China are still characterized by coal burning emissions especially in the inland regions, although in the country increasing rate of SO2 emission from coal combustion has decreased and emissions of vehicle exhaust has sharply increased.</p

Soil-derived sulfate in atmospheric dust particles at Taklimakan desert

Dust-associated sulfate is believed to be a key species which can alter the physical and chemical properties of dust particles in the atmosphere. Its occurrence in the particles has usually been considered to be the consequence of particles&#39; aging in the air although it is present in some crustal minerals. Our observation at the north and south edge of Taklimakan desert, one of the largest dust sources in the Northern Hemisphere, during a dust episode in April 2008 revealed that sulfate in atmospheric dust samples most likely originated directly from surface soil. Its TSP, PM10 and PM2.5 content was proportional to samples&#39; mass and comprised steadily about 4% in the differently sized samples, the ratio of elemental sulfur to iron was approximately constant 0.3, and no demonstrable influence of pollutants from fossil fuel combustion and biomass burning was detected. These results suggest that sulfate could be substantially derived from surface soil at the desert area and the lack of awareness of this origin may impede accurate results in any investigation of atmospheric sulfur chemistry associated with Taklimakan dust and its subsequent local, regional and global effects on the atmosphere.</p

Background-like nitrate in desert air

The atmospheric nitrogen cycle is a key process driving the earth&#39;s environmental evolution. Current model studies require knowledge of NOx soil emissions from various land types, but desert emissions remain unquantified or are not addressed with high confidence. Our measurements at two observatories in Taklimakan desert during a dust episode showed an approximately stable and dust-independent nitrate in the air. Its concentration estimated from PM2.5, PM10 and TSP samples under non-dust, floating dust and dust storm conditions was 3.81&plusmn;1.24&mu;gm-3, 2.95&plusmn;0.69&mu;gm-3, 4.99&plusmn;1.71&mu;gm-3, respectively, despite the more-than-one-order difference of dust loading. This concentration was much larger than that in remote marine and tropical forest air. Comprehensive investigation revealed a similar presence of nitrate in other desert air. The nitrate was hypothesized to be the consequence of the conversion of NOx released from desert soils. These results indicate a background-like nitrate and active reactions of nitrogen compounds in desert air.</p

Carbonaceous and Ionic Components of Atmospheric Fine Particles in Beijing and Their Impact on Atmospheric Visibility

Ground-based observation of fine particulate matter (PM2.5) in Beijing was carried out continuously in 2006. The carbonaceous and ionic components, as well as their distribution characteristics and seasonal variation, were obtained. The annual mean mass concentration of PM2.5 was 176.6 +/- 100.3 mu g/m(3). Long-range transport dust and local dust raised by strong wind during the spring made a considerable contribution to PM2.5 mass concentration. There was significant seasonal variation in carbonaceous and water-soluble ionic components associated with diverse emission sources, varying meteorological conditions during different seasons, and different mechanisms of formation for secondary aerosol ions. Comparing studies under different synoptic conditions suggested that PM2.5 pollution was mainly caused by transportation of particulates from remote sources, whereas hazy synoptic conditions are caused by local pollution. PM2.5 and visibility were negatively correlated, and the relationship between the concentrations of NH4+, SO42-, and NO3- with PM2.5 concentration during winter can be described using power function fitting.</p

Validation and application of a thermal-optical reflectance (TOR) method for measuring black carbon in loess sediments

In an effort to assess the potential contamination and determine the environmental risks associated with heavy metals, the surface sediments in Liaodong Bay, northeast China, were systematically sampled and analyzed for the concentrations of Cu, Pb, Zn, Cr, Ni, As, and Hg. The metal enrichment factor (EF) and geoaccumulation index (I (geo)) were calculated to assess the anthropogenic contamination in the region. Results showed that heavy metal concentrations in the sediments generally met the criteria of China Marine Sediment Quality (GB18668-2002); however, both EF and I (geo) values suggested the elevation of Pb concentration in the region. Based on the effect-range classification (TEL-PEL SQGs), Cu, Pb, Ni, and As were likely to pose environment risks, and the toxic units decreased in the order: Ni &gt; Pb &gt; Cr &gt; Zn &gt; As &gt; Cu &gt; Hg. The spatial distribution of ecotoxicological index (mean-ERM-quotient) suggested that most of the surface sediments were &quot;low-medium&quot; priority zone. Multivariate analysis indicated that the sources of Cr, Ni, Zn, Cu, and Hg resulted primarily from parent rocks, and Pb or As were mainly attributed to anthropogenic sources. The results of this study would provide a useful aid for sustainable marine management in the region.</p

Characterization, mixing state, and evolution of urban single particles inXi'an (China) during wintertime haze days

A Single Particle Aerosol Mass Spectrometer (SPAMS) was deployed in the urban area of Xi&#39;an to investigate size-resolved chemical composition and mixing state of single particles during the heavy haze episode occurred from January 13 to January 27 in 2013. Nine major single particle types were resolved with ART-2a algorithm including biomass burning (BB), Potassium-Secondary (KSec), elemental and organic Carbon (ECOC), sodium-potassium-rich ECOC (NaKECOC), sodium-potassium-rich-secondary (NaKSec), EC, OC, and Dust. Daily PM2.5 mass concentration was 213&nbsp;&plusmn;&nbsp;122&nbsp;&mu;g&nbsp;m&minus;&nbsp;3. ~&nbsp;96% of the ambient particles were carbonaceous and internally mixed with secondary species such as sulfate and nitrate. The major particle types were from combustion sources, including coal burning, biomass burning, and vehicle exhaust. Mixing state analysis suggests gas-to-particle conversion was an important mechanism forming organic species during the winter haze episode. The relative abundances of the aged particle types, such as KSec and NaKSec increased with the elevated RH when RH&nbsp;&lt;&nbsp;80%. The fraction of aged particles in terms of number concentration was prominent during high levels of PM2.5 under stagnant air conditions. This study gained new knowledge on atmospheric aerosol formation and evolution in urban environment heavy winter haze condition.</p