2 results
Origin of aeolian dust emitted from the Tarim Basin based on the ESR signal intensity and crystallinity index of quartz: the recycling system of fine detrital material within the basin
- Yuko Isozaki, Ryuji Tada, Youbin Sun, Hongbo Zheng, Shin Toyoda, Naomi Sugiura, Akinori Karasuda, Hitoshi Hasegawa
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- Journal:
- Geological Magazine / Volume 157 / Issue 5 / May 2020
- Published online by Cambridge University Press:
- 18 May 2020, pp. 707-718
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The Tarim Basin is the major source of aeolian dust in the northern hemisphere. Glacial activity in the mountains, transportation by rivers and homogenization by wind are believed to be responsible for dust production within the basin. However, the major source(s) and homogenization process(es) are not clear. Moreover, provenance studies on fine fractions have never been conducted. Here, we measured electron spin resonance (ESR) signal intensity and the crystallinity index of quartz in fine (< 16 μm) and coarse (> 64 μm) fractions of river sediments, dry lake sediments and mountain loess to examine the process(es) that produce aeolian dust. The result suggests that the coarse fraction of the river sediment was derived from the bedrock in the drainage area. The ESR signal intensity and crystallinity index of the fine fraction of river sediments from the Tian Shan Mountains and mountainous rivers in the westernmost Kunlun and Pamir mountains are also similar to the coarse fraction, suggesting the same sources. However, the ESR signal intensity and crystallinity index of the fine fraction of river sediments from the Kunlun Mountains are different from the coarse fraction and converge towards values close to the average for the fine fraction of river sediments and mountain loess. Convergence of the ESR and crystallinity index values for the fine fraction of river sediments from the Kunlun Mountains can be explained by contamination of the river sediments by aeolian dust. The convergent values resulted from the homogenization of fine detrital material by repeated recycling within the basin.
Adverse effects of ambient ozone on watermelon yield and physiology at a rural site in Eastern Spain
- BENJAMIN S. GIMENO, VICTORIA BERMEJO, RICHARD A. REINERT, YOUBIN ZHENG, JEREMY D. BARNES
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- Journal:
- The New Phytologist / Volume 144 / Issue 2 / November 1999
- Published online by Cambridge University Press:
- 01 November 1999, pp. 245-260
- Print publication:
- November 1999
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The study reported was conducted to establish the impacts of photochemical oxidants (primarily ambient ozone, O3) on the yield of watermelon (Citrullus lanatus) at a site on the east coast of Spain. Fruit yield and quality were monitored in plots established in a commercial watermelon field exposed, in open-top chambers (OTCs), to non-filtered air (NFA; near-ambient levels of ozone) or charcoal-filtered air (decreased levels of photochemical oxidants including O3; CFA), or to ambient air (AA), during the 1988 and 1989 growing seasons. Ambient levels of O3 were found to exceed present UN-ECE (United Nations Economic Commission for Europe; Convention on Long-Range Transboundary Air Pollution) critical level guidelines for the protection of crop yield by approx. twofold in 1988 and by approx. fivefold in 1989. Plants exposed to NFA and AA developed visible O3 injury on the upper surface of sun-exposed older leaves, and fruit yield (annual marketable fruit weight and number) was found to be depressed in OTCs ventilated with NFA in comparison with those receiving CFA. Consistent with inter-annual variations in O3 exposure, greater yield losses were experienced in 1989 (39%) than in 1988 (19%), an effect mediated predominantly by a decline in fruit number rather than average fruit weight. Exposure to ambient levels of ozone also slightly decreased fruit quality (4–8% decline in soluble solids content). Leaf gas exchange measurements made in the field in 1988 revealed effects of O3 on fruit yield and quality to be associated with a decline in the net CO2 assimilation rate per unit leaf area under light saturation (Asat) and stomatal conductance to water vapour (gs), and enhanced rates of dark respiration. A/ci curves (where A is the net CO2 assimilation rate per unit leaf area and ci is the mole fraction of CO2 in the leaf intercellular air space) constructed for plants grown in laboratory-based closed chambers, and exposed to an accumulated O3 exposure similar to that experienced by plants in the field, suggested that the likely cause of the decline in photosynthetic capacity was (1) a decrease in the amount and/or activity of Rubisco and (2) an impaired capacity for regeneration of ribulose 1,5-bisphosphate, which was not mediated through changes in the photochemical efficiency of photosystem II (Fv/Fm, where Fv is variable chlorophyll a fluorescence and Fm is maximum chlorophyll a fluorescence). No shift in the relative stomatal limitation to photosynthesis was observed under the influence of O3, suggesting that the decline in gs induced by the pollutant in both field and laboratory was the result, and not the cause, of the decrease in Asat. Ozone exposure also caused a decrease in C isotope discrimination (approx. 0.5‰), a shift that revealed a departure from predicted theory based on supporting leaf gas exchange measurements. The study demonstrates that ambient levels of photochemical oxidants on the Spanish Mediterranean coast are high enough to adversely influence the yield and physiology of an economically important crop grown in the region, and the magnitude of the effects was greater than would be predicted from exposure–yield-loss relationships for grain and fodder crops in central and northern Europe. Implications for the derivation of UN-ECE ozone standards are discussed, along with the mechanistic basis of the observed yield decreases.