Browsing by Author "Tang, Jianwu"

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    A meta-analysis of 1,119 manipulative experiments on terrestrial carbon-cycling responses to global change
    Song, Jian; Wan, Shiqiang; Piao, Shilong; Knapp, Alan K.; Classen, Aimee T.; Vicca, Sara; Ciais, Philippe; Hovenden, Mark J.; Leuzinger, Sebastian; Beier, Claus; Kardol, Paul; Xia, Jianyang; Liu, Qiang; Ru, Jingyi; Zhou, Zhenxing; Luo, Yiqi; Guo, Dali; Langley, J. Adam; Zscheischler, Jakob; Dukes, Jeffrey S.; Tang, Jianwu; Chen, Jiquan; Hofmockel, Kirsten S.; Kueppers, Lara M.; Rustad, Lindsey E.; Liu, Lingli; Smith, Melinda D.; Templer, Pamela H.; Thomas, R. Quinn; Norby, Richard J.; Phillips, Richard P.; Niu, Shuli; Fatichi, Simone; Wang, Yingping; Shao, Pengshuai; Han, Hongyan; Wang, Dandan; Lei, Lingjie; Wang, Jiali; Li, Xiaona; Zhang, Qian; Li, Xiaoming; Su, Fanglong; Liu, Bin; Yang, Fan; Ma, Gaigai; Li, Guoyong; Liu, Yanchun; Liu, Yinzhan; Yang, Zhongling; Zhang, Kesheng; Miao, Yuan; Hu, Mengjun; Yan, Chuang; Zhang, Ang; Zhong, Mingxing; Hui, Yan; Li, Ying; Zheng, Mengmei (2019-09)
    Direct quantification of terrestrial biosphere responses to global change is crucial for projections of future climate change in Earth system models. Here, we synthesized ecosystem carbon-cycling data from 1,119 experiments performed over the past four decades concerning changes in temperature, precipitation, CO2 and nitrogen across major terrestrial vegetation types of the world. Most experiments manipulated single rather than multiple global change drivers in temperate ecosystems of the USA, Europe and China. The magnitudes of warming and elevated CO2 treatments were consistent with the ranges of future projections, whereas those of precipitation changes and nitrogen inputs often exceeded the projected ranges. Increases in global change drivers consistently accelerated, but decreased precipitation slowed down carbon-cycle processes. Nonlinear (including synergistic and antagonistic) effects among global change drivers were rare. Belowground carbon allocation responded negatively to increased precipitation and nitrogen addition and positively to decreased precipitation and elevated CO2. The sensitivities of carbon variables to multiple global change drivers depended on the background climate and ecosystem condition, suggesting that Earth system models should be evaluated using site-specific conditions for best uses of this large dataset. Together, this synthesis underscores an urgent need to explore the interactions among multiple global change drivers in under-represented regions such as semi-arid ecosystems, forests in the tropics and subtropics, and Arctic tundra when forecasting future terrestrial carbon-climate feedback.
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    Potential contaminants at a dredged spoil placement site, Charles City County, Virginia, as revealed by sequential extraction
    Tang, Jianwu; Whittecar, G. Richard; Johannesson, Karen H.; Daniels, W. Lee (American Institute of Physics, 2004-12-07)
    Backfills of dredged sediments onto a former sand and gravel mine site in Charles City County, VA may have the potential to contaminate local groundwater. To evaluate the mobility of trace elements and to identify the potential contaminants from the dredged sediments, a sequential extraction scheme was used to partition trace elements associated with the sediments from the local aquifer and the dredged sediments into five fractions: exchangeable, acidic, reducible, oxidizable, and residual phases. Sequential extractions indicate that, for most of the trace elements examined, the residual phases account for the largest proportion of the total concentrations, and their total extractable fractions are mainly from reducible and oxidizable phases. Only Cd, Pb, and Zn have an appreciable extractable proportion from the acidic phase in the filled dredged sediments. Our groundwater monitoring data suggest that the dredged sediments are mainly subject to a decrease in pH and a series of oxidation reactions, when exposed to the atmosphere. Because the trace elements released by carbonate dissolution and the oxidation (e.g., organic matter degradation, iron sulfide and, ammonia oxidation) are subsequently immobilized by sorption to iron, manganese, and aluminum oxides, no potential contaminants to local groundwater are expected by addition of the dredged sediments to this site. (C) 2004 American Institute of Physics.