Ammonia volatilization and availability of Cu, Zn induced by applications of urea with and without coating in soils

Ammonia volatilization and the distribution of Cu and Zn were investigated in two types of soil treated with coated and uncoated urea. The rate of ammonia volatilization in two weeks after fertilizing with coated urea was 8% in soil 1 (soil derived from river alluvial deposits in Dongting Lake Plain) and 5.15% in soil 2 (red soil derived from quaternary red clay), about half the rates observed when fertilizing with common urea, implying that the hydrolysis speed of the coated urea was lower than for common urea, and that the coated urea can increase nitrogen use efficacy. As for the availability of Cu and Zn, their concentrations decreased in the first week after fertilization, and then increased, which was contrary to the effect of treatment on soil pH. For example, when the pH was 7.99, there was 0.79 mg/kg exchangeable Cu and 0.85 mg/kg exchangeable Zn in the soil derived from river alluvial deposits in Dongting Lake Plain. However, the concentrations of exchangeable Cu and Zn were generally lower for the common urea treatments than those with the coated urea because the peak pH for the common urea treatment was greater. The concentrations of these elements correlated well with pH in the range 4-8 in second order polynomial fits.     

Nitrogen deposition alters soil chemical properties and bacterial communities in the Inner Mongolia grassland

Nitrogen deposition has dramatically altered biodiversity and ecosystem functioning on the earth; however, its effects on soil bacterial community and the underlying mechanisms of these effects have not been thoroughly examined. Changes in ecosystems caused by nitrogen deposition have traditionally been attributed to increased nitrogen content. In fact, nitrogen deposition not only leads to increased soil total N content, but also changes in the NH₄⁺-N content, NO₃^--N content and pH, as well as changes in the heterogeneity of the four indexes. The soil indexes for these four factors, their heterogeneity and even the plant community might be routes through which nitrogen deposition alters the bacterial community. Here, we describe a 6-year nitrogen addition experiment conducted in a typical steppe ecosystem to investigate the ecological mechanism by which nitrogen deposition alters bacterial abundance, diversity and composition. We found that various characteristics of the bacterial community were explained by different environmental factors. Nitrogen deposition decreased bacterial abundance that is positively related to soil pH value. In addition, nitrogen addition decreased bacterial diversity, which is negatively related to soil total N content and positively related to soil NO₃^--N heterogeneity. Finally, nitrogen addition altered bacterial composition that is significantly related to soil NH₄⁺-N content. Although nitrogen deposition significantly altered plant biomass, diversity and composition, these characteristics of plant community did not have a significant impact on processes of nitrogen deposition that led to alterations in bacterial abundance, diversity and composition. Therefore, more sensitive molecular technologies should be adopted to detect the subtle shifts of microbial community structure induced by the changes of plant community upon nitrogen deposition.     

Degradation of pyrene by immobilized microorganisms in saline-alkaline soil

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) is very difficult in saline-alkaline soil due to the inhibition of microbial growth under saline-alkaline stress. The microorganisms that can most effectively degrade PAHs were screened by introducing microorganisms immobilized on farm byproducts and assessing the validity of the immobilizing technique for PAHs degradation in pyrene-contaminated saline-alkaline soil. Among the microorganisms examined, it was found that Mycobacterium sp. B2 is the best, and can degrade 82.2% and 83.2% of pyrene for free and immobilized cells after 30 days of incubation. The immobilization technique could increase the degradation of pyrene significantly, especially for fungi. The degradation of pyrene by the immobilized microorganisms Mucor sp. F2, fungal consortium MF and co-cultures of MB+MF was increased by 161.7% (P < 0.05), 60.1% (P < 0.05) and 59.6% (P < 0.05) after 30 days, respectively, when compared with free F2, MF and MB+MF. Scanning electron micrographs of the immobilized microstructure proved the positive effects of the immobilized microbial technique on pyrene remediation in saline-alkaline soil, as the interspace of the carrier material structure was relatively large, providing enough space for cell growth. Co-cultures of different bacterial and fungal species showed different abilities to degrade PAHs. The present study suggests that Mycobacterium sp. B2 can be employed for in situ bioremediation of PAHs in saline-alkaline soil, and immobilization of fungi on farm byproducts and nutrients as carriers will enhance fungus PAH-degradation ability in saline-alkaline soil.     

Soil warming effect on net ecosystem exchange of carbon dioxide during the transition from winter carbon source to spring carbon sink in a temperate urban lawn

The significant warming in urban environment caused by the combined effects of global warming and heat island has stimulated widely development of urban vegetations. However, it is less known of the climate feedback of urban lawn in warmed environment. Soil warming effect on net ecosystem exchange (NEE) of carbon dioxide during the transition period from winter to spring was investigated in a temperate urban lawn in Beijing, China. The NEE (negative for uptake) under soil warming treatment (temperature was about 5℃ higher than the ambient treatment as a control) was -0.71 μmol/(m².sec), the ecosytem was a CO₂ sink under soil warming treatment, the lawn ecosystem under the control was a CO₂ source (0.13 μmol/(m².sec)), indicating that the lawn ecosystem would provide a negative feedback to global warming. There was no significant effect of soil warming on nocturnal NEE (i.e., ecosystem respiration), although the soil temperature sensitivity (Q₁₀) of ecosystem respiration under soil warming treatment was 3.86, much lower than that in the control (7.03). The CO₂ uptake was significantly increased by soil warming treatment that was attributed to about 100% increase of α (apparent quantum yield) and A_max (maximum rate of photosynthesis). Our results indicated that the response of photosynthesis in urban lawn is much more sensitive to global warming than respiration in the transition period.     

碳源对工业污染场地土壤中HCHs和DDTs降解的促进作用

我国对有机氯农药的大量需求使得在农药生产、加工和分装等过程中造成了许多城镇中存在有机氯农药污染场地,限制了土地的后续开发利用.本研究选取3种类型的碳源组成有机修复剂A、B、C,添加到受有机氯工业污染场地土壤中进行微生物降解试验,并对比了3种修复剂的效果.试验过程中,反应体系水分含量为50％,添加零价金属调节氧化还原电位,采用好氧/厌氧交替循环方式进行生物降解.实验结果表明:3种修复剂对HCHs和DDTs的降解都有显著促进作用.与DDTs相比,HCHs较易降解.90 d内,添加修复剂(A、B、C)的处理中∑HCH的浓度分别从73.37~85.71 mg·kg^-1降解到了15.88~38.21 mg·kg^-1.与未添加修复剂的对照相比较,∑HCH的降解率提高了19%~52%,90 d内,ΣHCH的降解率最高可达81%.添加修复剂(A、B、C)的处理中ΣDDT的浓度分别从91.68~119.79 mg·kg^-1降解到了45.1~60.7 mg·kg^-1,相对未添加修复剂的对照试验,∑DDT的降解率提高了39%~45%,30 d内∑DDT的降解率最高可达到51%,但30 d后降解效率无明显增加.就不同类型碳源的促进作用来看,C/N最高,而含水率最低的修复剂B的效果最好,而C/N比最低而含水率最高的修复剂A效果最差.     

集约化种植区硝态氮在土壤剖面中的分布与累积特征

采用GPS定位、土钻取样的方法,在北京市大兴区14个乡镇的农田土壤中选取了91个土壤剖面,分别在0～20cm、20～40cm、40～60cm、60～80cm4个不同深度取得土壤样品,并在一次种植期结束后,综合考虑种植类型和土壤质地后选取24个重复取样点.在此基础上,分析了种植类型及土壤质地对硝态氮分布及累积情况的影响.结果表明,研究区土壤中的硝态氮含量有随土壤深度的增加呈降低的趋势.露地菜田和设施菜田最容易出现硝态氮淋洗现象,果园和粮田的总体状况较好,但粮田个别地区有一定的污染风险,细质地土壤具有较强的保水保肥能力.大兴区采育镇及长子营镇地区有较高的硝态氮累积量,为硝态氮淋洗污染危险区,应进行合理施肥,以免在一个种植期结束后造成较深层土壤中硝态氮的累积.研究结果可为大兴区地下水环境保护提供参考.     

基于Kriging插值的路旁土壤重金属含量空间分布 ——以310国道郑州-开封段为例

分别在G310国道郑州-开封段的杏花营路段两侧150m×150m范围内布设7条垂直于公路的采样子断面,从路肩向两侧每隔10m采集1个表土混合样,共采集226个样品（包括2个对照样品）.用ICP-MS测定了土壤重金属（Pb、Cu、Zn、Cd、Cr和Ni）含量,并用Universal Kriging插值法分析路旁土壤重金属空间分布特征.结果表明,路旁土壤重金属呈与道路平行的带状分布,表明6种重金属含量均受公路交通影响,属于公路源重金属.土壤Cr和Cu含量在路基处含量最高,向两侧逐渐下降,呈指数分布;土壤Pb、Zn、Cd和Ni含量在距路基30～50m处出现峰值,呈偏态分布.路旁土壤Pb、Cu、Zn、Cd、Cr和Ni均为交通源重金属.     

广州市“南肺”果园土壤H g和A s的形态分析

采用Tessier连续提取法、BCR连续提取法和Leleyter连续提取法,研究广州"南肺"果园土壤Hg和As的形态分布和生物可给性。结果表明,果园土壤Hg和As形态分布都以残渣态为主;3种方法的土壤生物可给性分析均表明,Hg和As生物可利用态的含量较少;生物不可利用态是主要形态,其次是潜在可利用态。     

城市环境中自然通风研究进展

城市环境中自然通风源于城市热压梯度及城市风压梯度的综合作用。城市环境中自然通风影响着城市"五岛"效应(城市热岛、湿岛、干岛、浑浊岛及雨岛),城市大气的自净能力和城市居民的身体健康,也是研究快速城市化地区广义城市风环境(风场、温度场、湿度场)的参考因子。为了全面理解国内外针对城市环境中自然通风的研究进展,从城市环境中自然通风的监测、模拟及应用三个方面对目前国内外针对城市环境中自然通风的研究现状进行了综述,最后结合环境物联网、无线传感技术等目前在城市环境中自然通风研究的相关技术及应用领域的新进展,对城市环境中自然通风的后续研究热点和关键问题进行了展望,为城市环境中自然通风的相关技术及应用问题的后续研究提供了基础研究素材。     

有机氯农药污染土壤的Fenton氧化修复研究

研究了Fenton氧化对某实际有机氯农药污染场地土壤的修复效果。结果显示:Fenton氧化能够快速有效地降解污染土壤中的六氯和DDTs。当Fe2+浓度为80 mmol/L,Fe2+与H2O2的摩尔浓度比为1∶5,水土比10∶1时,反应6 h,土壤中六氯和总DDT的去除率分别为:96.7%和78.2%。每方土的修复成本估算为951元。