Chen Xuechu

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Chen
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Xuechu
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  • Article
    Enhanced carbon uptake and reduced methane emissions in a newly restored wetland
    (American Geophysical Union, 2020-01-04) Yang, Hualei ; Tang, Jianwu ; Zhang, Chunsong ; Dai, Yuhang ; Zhou, Cheng ; Xu, Ping ; Perry, Danielle C. ; Chen, Xuechu
    Wetlands play an important role in reducing global warming potential in response to global climate change. Unfortunately, due to the effects of human disturbance and natural erosion, wetlands are facing global extinction. It is essential to implement engineering measures to restore damaged wetlands. However, the carbon sink capacity of restored wetlands is unclear. We examined the seasonal change of greenhouse gas emissions in both restored wetland and natural wetland and then evaluated the carbon sequestration capacity of the restored wetland. We found that (1) the carbon sink capacity of the restored wetland showed clear daily and seasonal change, which was affected by light intensity, air temperature, and vegetation growth, and (2) the annual daytime (8–18 hr) sustained‐flux global warming potential was −11.23 ± 4.34 kg CO2 m−2 y−1, representing a much larger carbon sink than natural wetland (−5.04 ± 3.73 kg CO2 m−2 y−1) from April to December. In addition, the results showed that appropriate tidal flow management may help to reduce CH4 emission in wetland restoration. Thus, we proposed that the restored coastal wetland, via effective engineering measures, reliably acted as a large net carbon sink and has the potential to help mitigate climate change.
  • Preprint
    Enhancement of nitrate removal at the sediment-water interface by carbon addition plus vertical mixing
    ( 2014-12) Chen, Xuechu ; He, Shengbing ; Zhang, Yueping ; Huang, Xiaobo ; Huang, Yingying ; Chen, Danyue ; Huang, Xiaochen ; Tang, Jianwu
    Wetlands and ponds are frequently used to remove nitrate from effluents or runoffs. However, the efficiency of this approach is limited. Based on the assumption that introducing vertical mixing to water column plus carbon addition would benefit the diffusion across the sediment–water interface, we conducted simulation experiments to identify a method for enhancing nitrate removal. The results suggested that the sediment-water interface has a great potential for nitrate removal, and the potential can be activated after several days of acclimation. Adding additional carbon plus mixing significantly increases the nitrate removal capacity, and the removal of total nitrogen (TN) and nitrate-nitrogen (NO3--N) is well fitted to a first-order reaction model. Adding Hydrilla verticillata debris as a carbon source increased nitrate removal, whereas adding Eichhornia crassipe decreased it. Adding ethanol plus mixing greatly improved the removal performance, with the removal rate of NO3--N and TN reaching 15.0-16.5 g m-2 d-1. The feasibility of this enhancement method was further confirmed with a wetland microcosm, and the NO3--N removal rate maintained at 10.0-12.0 g m-2 d-1 at a hydraulic loading rate of 0.5 m d-1.
  • Article
    Evaluation of laser-based spectrometers for greenhouse gas flux measurements in coastal marshes
    (John Wiley & Sons, 2016-04-18) Brannon, Elizabeth Q. ; Moseman-Valtierra, Serena M. ; Rella, Chris W. ; Martin, Rose M. ; Chen, Xuechu ; Tang, Jianwu
    Precise and rapid analyses of greenhouse gases (GHGs) will advance understanding of the net climatic forcing of coastal marsh ecosystems. We examined the ability of a cavity ring down spectroscopy (CRDS) analyzer (Model G2508, Picarro) to measure carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes in real-time from coastal marshes through comparisons with a Shimadzu GC-2014 (GC) in a marsh mesocosm experiment and with a similar laser-based N2O analyzer (Model N2O/CO, Los Gatos Research) in both mesocosm and field experiments. Minimum (analytical) detectable fluxes for all gases were more than one order of magnitude lower for the Picarro than the GC. In mesocosms, the Picarro analyzer detected several CO2, CH4, and N2O fluxes that the GC could not, but larger N2O fluxes (218–409 μmol m−2 h−1) were similar between analyzers. Minimum detectable fluxes for the Picarro were 1 order of magnitude higher than the Los Gatos analyzer for N2O. The Picarro and Los Gatos N2O fluxes (3–132 μmol m−2 h−1) differed in two mesocosm nitrogen addition experiments, but were similar in a mesocosm with larger N2O fluxes (326–491 μmol m−2 h−1). In a field comparison, Picarro and Los Gatos N2O fluxes (13 ± 2 μmol m−2 h−1) differed in plots receiving low nitrogen loads but were similar in plots with higher nitrogen loads and fluxes roughly double in magnitude. Both the Picarro and Los Gatos analyzers offer efficient and precise alternatives to GC-based methods, but the former uniquely enables simultaneous measurements of three major GHGs in coastal marshes.