环境因子对长江口潮滩沉积物中NH+4的释放影响

以长江口潮滩沉积物湿样进行模拟实验,研究盐度、pH和温度等环境因子对沉积物中NH₄+释放的影响.结果表明,随着盐度和温度的上升,沉积物中NH₄+释放量都显著增加;由于潮滩沉积物缓冲性能较好,pH的影响不太明显.此外,NH₄+的释放与沉积物类型有关,沙性物质含量高的低潮滩沉积物NH₄+的释放量明显低于沙性物质低的高、中潮滩沉积物.      

Critical flow-storm approach to total maximum daily load (TMDL) development: an analytical conceptual model

One of the key challenges in the total maximum daily load (TMDL) development process is how to define the critical condition for a receiving waterbody. The main concern in using a continuous simulation approach is the absence of any guarantee that the most critical condition will be captured during the selected representative hydrologic period, given the scarcity of long-term continuous data. The objectives of this paper are to clearly address the critical condition in the TMDL development process and to compare continuous and event-based approaches in defining critical condition during TMDL development for a waterbody impacted by both point and nonpoint source pollution. A practical, event-based critical flow-storm (CFS) approach was developed to explicitly addresses the critical condition as a combination of a low stream flow and a storm event of a selected magnitude, both having certain frequencies of occurrence. This paper illustrated the CFS concept and provided its theoretical basis using a derived analytical conceptual model. The CFS approach clearly defined a critical condition, obtained reasonable results and could be considered as an alternative method in TMDL development.     

Drainage affects tree growth and C and N dynamics in a minerotrophic peatland

The lowering of the water table resulting from peatland drainage may dramatically alter C and N cycling in peatland ecosystems, which contain one-third of the total terrestrial C. In this study, tree annual ring width and C (delta(13)C) and N (delta(15)N) isotope ratios in soil and plant tissues (tree foliage, growth rings, and understory foliage) in a black spruce-tamarack (Picea mariana-Larix laricina) mixed-wood forest were examined to study the effects of drainage on tree growth and C and N dynamics in a minerotrophic peatland in west-central Alberta, Canada. Drainage increased the delta(15)N of soil NH4+ from a range of +0.6% per hundred to +2.9% per hundred to a range of +4.6% per hundred to +7.0% per hundred most likely through increased nitrification following enhanced mineralization. Plant uptake of 15N-enriched NH4+ in the drained treatment resulted in higher plant delta15N (+0.8% per hundred to +1.8% per hundred in the drained plots and -3.9% per hundred to -5.4% per hundred in the undrained plots), and deposition of litterfall N enriched with 15N increased the delta15N of total soil N in the surface layer in the drained (+2.9% per hundred) as compared with that in the undrained plots (+0.6% per hundred). The effect of drainage on foliar delta(13)C was species-specific, i.e., only tamarack showed a considerably less negative foliar delta(13)C in the drained (-28.1% per hundred) than in the undrained plots (-29.1% per hundred), indicating improved water use efficiency (WUE) by drainage. Tree ring area increments were significantly increased following drainage, and delta(13)C and delta(15)N in tree growth rings of both species showed responses to drainage retrospectively. Tree-ring delta(13)C data suggested that drainage improved WUE of both species, with a greater and more prolonged response in tamarack than in black spruce. Our results indicate that drainage caused the studied minerotrophic peatland to become a more open ecosystem in terms of C and N cycling and loss. The effects of forested peatland drainage or drying on C and N balances deserve further research in order to better understand their roles in future global change.     

Effect of stress corrosion cracking at various strain rates on the electrochemical corrosion behavior of Mg-Zn-In-Sn alloy

This study is aimed to determine the effect of stress corrosion with low strain rates on the electrochemical properties of alloy electrode. Stress corrosion cracking tests of Mg-Zn-In-Sn alloy in 3.5 wt.% sodium chloride solutions at 25℃ were performed. The effects of the electrochemical properties under the stress corrosion with low strain rates were investigated. The microstructures of cross section were observed by optical microscope. The results showed that the ultimate tensile strengths of Mg-Zn-In-Sn alloy increased and the strain decreased as the strain rates increased. Open circuit potentials (OCP) of Mg-Zn-In-Sn alloy electrode possess stability and the loop currents (LC) were improved with the increasing of stress in the elastic zone. The variation of OCP and LC did not change with the increasing of strain-rate. The microstructure of cross section observing revealed the mechanism of OCP and LC changing.     

改造滤岸对城市降雨径流中氮磷去除的中试研究

选择煤渣、锯末、沸石、麦饭石、土壤和马尼拉草构建了城市河岸带改造滤岸中试模型,并对其去除城市降雨径流中氮磷污染物能力进行了研究.结果表明,改造滤岸对表面径流和下渗径流中NH4+-N和TP具有良好的净化效果和较强的去除能力;NH4+-N平均去除率分别为66.5％和83.7％,TP平均去除率分别为42.6％和96.2％,出水水质分别可达国家地表水Ⅳ类和Ⅲ类水标准,模型稳定后对表层径流和下渗径流中TN的去除率可达20％左右;模型对NH4+-N、TN和TP的处理负荷分别为634.1～1114.5 mg-m-2·h-1、102.2 ～594.2mg· m-2·h-1和20.6～ 209.0 mg·m-2· h-1,表面径流大于下渗径流.模型内碳源(锯末)以及其他介质的添加虽然能够提高氮的转化能力,但也会影响模型对TN的去除率;下凹断面和末端断面对氮磷的去除率和去除负荷间存在一定的差异,但随着模型的稳定其差异逐渐降低.模型对氮磷的处理负荷与入水氮磷浓度呈显著正相关,说明模型具有一定的抗冲击能力.     

Linking soil respiration and water table depth in tropical peatlands with remotely sensed changes in water storage from the gravity recovery and climate experiment

Mitigation and Adaptation Strategies for Global Change - Carbon dioxide (CO2) emissions from Southeast Asia peatlands are contributing substantially to global anthropogenic emissions to the...