Characteristics and influence factors of NO2 exchange flux between the atmosphere and P. nigra

Nitrogen dioxide(NO_2)is an important substance in atmospheric photochemical processes and can also be absorbed by plants.N02 fluxes between the atmosphere and P.nigrc seedlings were investigated by a double dynamic chambers method in Beijing from June 15to September 3,2017.The range of N02 exchange fluxes between P.nigra seedlings and the atmosphere was from-14.6 to 0.8 nmol/(m~2.sec)(the positive data represent N02 emissior from trees,while the negative values indicate absorption).Under ambient concentrations the mean NO_2 flux during the fast-growing stage(Jun.15-Aug.4)was-3.0 nmol/(m2·sec)greater than the flux of-1.5 nmol/(m2-sec)during the later growth stage(Aug.8-Sept.3)The daily exchange fluxes of NO_2 obviously fluctuated.The fluxes were largest in the morning and decreased gradually over time.Additionally,the N02 fluxes were larger undei high light intensities than under low light intensities during the whole growth period.The effects of temperature on N02 fluxes were different under two growth periods.The NO_2exchange fluxes were larger in a range of temperatures close to 44℃in the fast-growing stage,whereas there were no evident differences in N02 exchange fluxes under widel differing temperatures in the later growth stage.Under polluted conditions,the uptake ability of N02 was weakened.Additionally,the compensation point of N02 was 5.6 ppb ir the fast-growing stage,whereas it was 1.4 ppb in the later growth stage.The depositior velocities of NO_2 were between 0.3 and 2.4 mm/sec.     

Effect of drainage on CO2, CH4, and N2O fluxes from aquaculture ponds during winter in a subtropical estuary of China

Aquaculture ponds are dominant features of the landscape in the coastal zone of China.Generally,aquaculture ponds are drained during the non-culture period in winter.However,the effects of such drainage on the production and flux of greenhouse gases(GHGs)from aquaculture ponds are largely unknown.In the present study,field-based research was performed to compare the GHG fluxes between one drained pond(DP,with a water depth of 0.05 m)and one undrained pond(UDP,with a water depth of 1.16 m)during one winter in the Min River estuary of southeast China.Over the entire study period,the mean CO_2flux in the DP was(0.75±0.12)mmol/(m~2·hr),which was significantly higher than that in the UDP of(-0.49±0.09)mmol/(m~2·hr)(p0.01).This indicates that drainage drastically transforms aquaculture ponds from a net sink to a net source of CO_2in winter.Mean CH_4and N_2O emissions were significantly higher in the DP compared to those in the UDP(CH_4=(0.66±0.31)vs.(0.07±0.06)mmol/(m~2·hr)and N_2O=(19.54±2.08)vs.(0.01±0.04)μmol/(m~2·hr))(p0.01),suggesting that drainage would also significantly enhance CH_4and N_2O emissions.Changes in environmental variables(including sediment temperature,p H,salinity,redox status,and water depth)contributed significantly to the enhanced GHG emissions following pond drainage.Furthermore,analysis of the sustained-flux global warming and cooling potentials indicated that the combined global warming potentials of the GHG fluxes were significantly higher in the DP than in the UDP(p0.01),with values of739.18 and 26.46 mg CO_2-eq/(m~2·hr),respectively.Our findings suggested that drainage of aquaculture ponds can increase the emissions of potent GHGs from the coastal zone of China to the atmosphere during winter,further aggravating the problem of global warming.     

Production and emission of phosphine gas from wetland ecosystems

Phosphine is a part of an atmospheric link of phosphorus cycle on earth, which could be an important pathway for phosphorus transport in environment.Wetland ecosystems are important locations for global biogeochemical phosphorus cycle.In this study, production and emission fluxes of free phosphine from four wetlands types in southern China were observed in different seasons.The results showed that the concentration of phosphine liberated from wetlands was at pg/m3-ng/m3 level.The emission concentrations of different wetlands followed the sequence:paddy field(51.83 ± 3.06) ng/m3 marsh(46.54 ± 20.55) ng/m3 lake(37.05 ± 22.74) ng/m3 coastal wetland(1.71 ± 0.73) ng/m3, the positive phosphine emission flux occurred in rice paddy field(6.67 ± 5.18) ng/(m2·hr) and marsh(6.23 ± 26.9) ng/(m2·hr), while a negative phosphine flux of(-13.11 ± 35.04) ng/(m2·hr) was observed on the water-air interface of Lake Taihu, suggesting that paddy field and marsh may be important sources for phosphine gas in atmosphere, while lake may be a sink of atmospheric phosphine gas during the sampling period.Atmospheric phosphine levels and emission flux from Yancheng marsh and rice paddy field varied in different seasons and vegetational zones.Both diffusion resistance in aqueous phase and temperature were dominating factors for the production and transportation of phosphine to atmosphere.     

The influence of environmental factors on the carbon dioxide flux across the water–air interface of reservoirs in south-eastern Poland

Studies concerning the emission of carbon dioxide(CO_2) were carried out in 2009–2012 for six reservoirs located in four provinces of south-eastern Poland. The CO_2 flux across the water–air interface was measured using the "static chamber" method. The measured fluxes of CO_2(FCO_2) ranged from-30.64 to 183.78 mmol/m~2/day, and the average values varied in the range from-3.52 to 82.11 mmol/m2/day. In most of the cases, emission of CO_2 to the atmosphere was observed. The obtained values of CO_2 fluxes were comparable to values typical for other temperate reservoirs. Analysis of the influence of selected environmental factors on the FCO_2 showed that it depends on parameters characterizing both the sediments and surface water. The CO_2 flux at the water–air interface was positively correlated with parameters of bottom sediments such as porosity, content of organic carbon and total nitrogen; and negatively with p H value and δ~(13)C of organic carbon. In the case of the parameters characterizing surface water, positive dependences on the concentrations of nitrate and total nitrogen, and negative relationships with water temperature and chlorophyll a concentrations, were found.     

Fabrication and performance of PET mesh enhanced cellulose acetate membranes for forward osmosis

Polyethylene terephthalate mesh(PET) enhanced cellulose acetate membranes were fabricated via a phase inversion process. The membrane fabrication parameters that may affect the membrane performance were systematically evaluated including the concentration and temperature of the casting polymer solution and the temperature and time of the evaporation, coagulation and annealing processes. The water permeability and reverse salt flux were measured in forward osmosis(FO) mode for determination of the optimal membrane fabrication conditions. The optimal FO membrane shows a typical asymmetric sandwich structure with a mean thickness of about 148.2 μm. The performance of the optimal FO membrane was tested using 0.2 mol/L Na Cl as the feed solution and 1.5 mol/L glucose as the draw solution. The membrane displayed a water flux of 3.47 L/(m2·hr) and salt rejection of95.48% in FO mode. While in pressure retarded osmosis(PRO) mode, the water flux was4.74 L/(m2·hr) and salt rejection 96.03%. The high ratio of water flux in FO mode to that in PRO mode indicates that the fabricated membrane has a lower degree of internal concentration polarization than comparable membranes.     

Mercury transportation in soil via using gypsum from flue gas desulfurization unit in coal-fired power plant

The mercury flux in soils was investigated, which were amended by gypsums from flue gas desulphurization (FGD) units of coal- fired power plants. Studies have been carried out in confined greenhouses using FGD gypsum treated soils. Major research focus is uptakes of mercury by plants, and emission of mercury into the atmosphere under varying application rates of FGD gypsum, simulating rainfall irrigations, soils, and plants types. Higher FGD gypsum application rates generally led to higher mercury concentrations in the soils, the increased mercury emissions into the atmosphere, and the increased mercury contents in plants (especially in roots and leaves). Soil properties and plant species can play important roles in mercury transports. Some plants, such as tall fescue, were able to prevent mercury from atmospheric emission and infiltration in the soil. Mercury concentration in the stem of plants was found to be increased and then leveled off upon increasing FGD gypsum application. However, mercury in roots and leaves was generally increased upon increasing FGD gypsum application rates. Some mercury was likely absorbed by leaves of plants from emitted mercury in the atmosphere.     

Greenhouse gas emissions from oilfield-produced water in Shengli Oilfield, Eastern China

Greenhouse gas(GHG) emissions from oil and gas systems are an important component of the GHG emission inventory. To assess the carbon emissions from oilfield-produced water under atmospheric conditions correctly, in situ detection and simulation experiments were developed to study the natural release of GHG into the atmosphere in the Shengli Oilfield,the second largest oilfield in China. The results showed that methane(CH4) and carbon dioxide(CO2) were the primary gases released naturally from the oilfield-produced water.The atmospheric temperature and release time played important roles in determining the CH4 and CO2emissions under atmospheric conditions. Higher temperatures enhanced the carbon emissions. The emissions of both CH4 and CO2from oilfield-produced water were highest at 27°C and lowest at 3°C. The bulk of CH4 and CO2was released from the oilfield-produced water during the first release period, 0–2 hr, for each temperature, with a maximum average emission rate of 0.415 g CH4/(m3·hr) and 3.934 g CO2/(m3·hr), respectively. Then the carbon emissions at other time periods gradually decreased with the extension of time. The higher solubility of CO2 in water than CH4 results in a higher emission rate of CH4 than CO2over the same release duration. The simulation proved that oilfield-produced water is one of the potential emission sources that should be given great attention in oil and gas systems.     

Fluoride removal from brackish groundwater by direct contact membrane distillation

The direct contact membrane distillation applied for fluoride removal from brackish groundwater was investigated.The self-prepared polyvinylidene fluoride membrane exhibited high rejection of inorganic salt solutes.The maximum permeate flux 35.6 kg/(m2 ·hr) was obtained with the feed solution at 80°C and the cold distillate water at 20°C.The feed concentration had no significant impact on the permeate flux and the rejection in fluoride.The precipitation of CaCO3 would clog the hollow fiber inlets and foul the membrane surface with increasing concentration factor when natural groundwater was used directly as the feed,which resulted in a rapid decline in the module efficiency.This phenomenon was diminished by acidification of the feed.The experimental results showed that the permeate flux and the quality of obtained distillate kept stable before concentration factor reached 5.0 with the acidified groundwater as feed.The membrane module efficiency began to decline gradually when the feed continued to be concentrated,which can be mainly attributed to the formation of CaF2 deposits on the membrane surface.In addition,a 300 hr continuous fluoride removal experiment of acidified groundwater was carried out with concentration factor at 4.0,the permeate flux kept stable and the permeate fluoride was not detected.     

Effect of cerium on photosynthetic characteristics of soybean seedling exposed to supplementary ultraviolet-B radiation

Effects of cerium （Ce^3＋） on photosynthetic characteristics were investigated by hydroponics under laboratory conditions when soybean seedlings were exposed to two levels of supplementary UV-B radiation. UV-B radiation badly inhibited the photosynthesis in soybean seedling, leading to a reduction in net photosynthetic rate （Pn）, Hill reaction activity, light saturated photosynthetic rate （Ps） and apparent quanta yield （AQY）, as well as the CO2 and light saturated photosynthetic rate （Pro） and carboxulation efficiency （CE）. On the contrary, Ce obviously promoted the photosynthesis of plants by increasing Hill reaction activity, accelerating electron transport and photophosphorylation, and enhancing carboxylation efficiency. For Ce＋UV-B treatments, the values of photosynthetic parameters were still lower than those of the control, but obviously higher than those of UV-B treatment. The results indicated that Ce alleviated the inhibition of UV-B radiation on the photosynthesis in soybean seedling to a certain extent. In correlating of Pn with Hill activity, AQY and CE, we found that the changes of photosynthetic rate were mainly influenced by the regulating effect of Ce on Hill activity and AQY at low level （0.15 W/m^2） of UV-B radiation, but were dominated by the regulating effect of Ce on CE at high level （0.45 W/m^2）. Thus, Ce could regulate many aspects in photosynthesis of soybean seedling under UV-B stress. The regulating mechanism was close related with the dosage of UV-B radiation.     

Mechanism and kinetics study on the ozonolysis reaction of 2,3,7,8-TCDD in the atmosphere

The ozonolysis of 2,3,7,8-tetra-chlorodibenzo-p-dioxin(2,3,7,8-TCDD) is an efcient degradation way in the atmosphere. The ozonolysis process and possible reactions path of Criegee Intermediates with NO and H2 O are introduced in detail at the method of MPWB1K/6-31+G(d,p)//MPWB1K/6-311+G(3df,2p) level. In ozonolysis, H2O is an important source of OH radical formation and initiated the subsequent degradation reaction. The Rice-Ramsperger-Kassel-Marcus(RRKM) theory was applied to calculate rate constants with the temperature ranging from 200 to 600 K. The rate constant of reaction between 2,3,7,8-TCDD and O3 is 4.80 × 10 20cm3/(mole·sec) at 298 K and 760 Torr. The atmospheric lifetime of the reaction species was estimated according to rate constants, which is helpful for the atmospheric model study on the degradation and risk assessment of dioxin.     

三峡水库主要支流沉积物的磷吸附/释放特性

以三峡水库主要支流寸滩、小江、大宁和香溪表层沉积物为对象,通过连续提取法分析4种沉积物磷的赋存形态,模拟研究了pH和温度对不同沉积物磷吸附/释放的影响.结果表明,寸滩、小江、大宁和香溪表层沉积物磷赋存形态均以无机磷为主(占总磷含量的59.29%～78.82%),其中钙结合态磷(Ca-P)含量大于铁/铝结合态磷(Fe/Al-P).上覆水pH值对沉积物磷释放有明显的影响,中性条件下磷释放量最低,酸性条件下由于占优势的Ca-P大量溶解导致磷释放量大于碱性条件,因此,水体酸化易增加三峡主要支流(寸滩、小江、大宁和香溪)的磷释放风险.pH值变化亦明显影响沉积物对于磷的吸附,pH在6～8范围内,4种沉积物对于磷的吸附量保持在较高的水平,吸附量从大到小的顺序为:小江大宁寸滩香溪.偏酸性条件(pH6)下过多的H 与固体表面竞争溶解态活性磷(SRP);偏碱性条件(pH>8)下大量的OH->与SRP竞争沉积物表面的吸附位,故这-pH值范围内(pH<6或pH>8)磷的吸附量明显减少.磷在4种沉积物上的吸附为吸热过程,不同温度下(278K、293K、303K)沉积物对P的吸附均符合修正后的Langmuir模型,标准吸附热为18.92～46.63 kJ·mol-1其中,磷从水体分配到大宁河沉积物中的标准吸附热最大.     

改性枸杞枝作为反硝化脱氮碳源的研究

为提高枸杞枝作为反硝化碳源的效能,采用甲醇（体积占比分别为0、20%、50%、100%）-水-NaOH （0.01 g·mL^-1）体系（分别简称为0组、20%组、50%组、100%组）对枸杞枝进行改性处理,研究原枸杞枝的静态释碳、改性前后枸杞枝的静态反硝化特性、表面形态和脱氮动力学.结果表明,原枸杞枝释碳过程同时符合二级动力学方程和Ritger-Peppas方程;第I阶段（1~3 d）为碳源快速释放期,第II阶段（4~21 d）为碳源稳定释放期;改性后枸杞枝纤维素和半纤维素含量占比增加了8.7%~35.2%;不同甲醇-水-NaOH体系改性枸杞枝平均反硝化速率依次为20%组>50%组>0组>100%组>对照组,20%甲醇-水-NaOH组反硝化速率最高（0.76 mg·g^-1·d^-1）,表明20%甲醇-水-NaOH （0.01 g·mL^-1）是枸杞枝改性的最佳条件;改性后的枸杞枝表面结构粗糙、不规则且有大量的孔洞产生,适合脱氮微生物附着生长,其反硝化脱氮过程符合Monod动力学方程（R²=0.96）.     

汉江襄阳段主要入江支流沉积物营养盐和重金属风险特征研究

采集汉江襄阳段主要入江支流沉积物柱状样,分析沉积物常规理化指标、上覆水和孔隙水中营养盐含量、以及表层沉积物重金属含量,采用一维孔隙水扩散模型(Fick定律)计算营养盐扩散通量,评估沉积物营养盐释放风险,并评价表层沉积物重金属生态风险.结果表明:所有采样点氨氮及磷酸盐均从沉积物向上覆水释放,表明水质存在内源营养盐(氨氮和磷酸盐)释放风险.氨氮、磷酸盐扩散通量范围分别为42.431~81.369 mg·m-2·d-1、0.745~1.437 mg·m-2·d-1,均以航空路样点最大.表层沉积物重金属污染指数SPI值为6.1,总体表现为中度风险;其中小清河样点SPI值为11.8,达到高风险.小清河Cu、Pb和Zn平均含量分别为131.17 mg·kg-1、57.97 mg·kg-1和398.59 mg·kg-1,均超过相应的SEL值(最高效应阈值).富集系数研究表明汉江支流表层沉积物中Cd富集现象严重,平均富集系数高达4.57.汉江襄阳段入江支流沉积物存在内源营养盐释放风险,中度重金属生态风险,且Cd累积风险突出.因水文调控减少汉江干流流量进而导致河流稀释自净能力减弱,从而对汉江水质安全构成较大威胁.     

接种微生物菌剂对枸杞枝条基质化发酵品质的影响

为探讨接种微生物对枸杞枝条基质化发酵品质的影响,采用随机区组设计,以干燥鸡粪和尿素为氮源,进行了接种外源微生物对枸杞枝条基质化发酵性能参数的影响试验.结果表明:接种粗纤维复合益菌、锯末专用复合菌和纤维素类复合酶堆体升温速度快,高温持续时间较长(高于55℃,分别达到9、5和5 d);至发酵80 d时,堆体总有机碳分别下降了8.46%、7.43%、8.06%,C/N值分别降低7.48、6.99、6.23,全氮分别为17.1、17.2、16.2 g·kg-1,全磷分别为5.1、5.2、5.0 g·kg-1,全钾分别为16.5、16.3、16.4 g·kg-1,均显著高于其他处理,且3种菌剂间无显著差异,容重分别增加了1.10%、0.91%、1.20%,总孔隙度分别增加了9.78%、10.45%、10.51%,持水孔隙度分别增加了6.21%、5.36%、8.80%,瓜菜种子发芽指数(GI)均高于85%,腐熟后的各项理化指标基本达到栽培基质的要求.综合基质的发酵温度、腐熟周期和基质保护作物根系生长及固定植株的功能对基质各项理化性质的要求,接种粗纤维复合益菌、锯末专用复合菌和纤维素类复合酶更适合枸杞枝条基质化处理.     

襄阳入江中小河流表层沉积物重金属污染特征及其潜在的生态风险评价

入江中小河流重金属污染状况对中小河流自身及其汇入的大江大河生态系统的健康发展均具有重要意义.通过采集襄阳入江6条河流的表层沉积物和上覆水,分析沉积物粒径、有机质、总氮、总磷及6种重金属含量.同时,采用沉积物质量基准系数和潜在生态危害指数法对重金属污染进行评价,并通过相关分析和冗余分析方法对沉积物中重金属来源进行解析.结果表明,襄阳入江中小河流水体中的重金属均处于较低水平,优于《地表水环境质量标准》(GB3838—2002)Ⅱ类水标准.表层沉积物中Hg、Cd、Cr、Pb、Zn和Cu的平均含量分别为0.23、1.75、48.4、135.8、173.2和44.7 mg·kg~(-1),除Cr外,其他5种重金属含量远超湖北省土壤元素背景值.6种重金属元素的平均含量均处于临界效应浓度和可能效应浓度之间,为中等污染水平.襄阳入江中小河流表层沉积物重金属的综合潜在生态风险指数(RI)的平均值为461.2,整体处于高风险水平,其中,小清河处于很高生态风险水平,其他河流处于高生态风险水平.冗余分析表明,随着沉积物OM、TN和TP含量的增加、粒径的降低,表层沉积物中的各重金属含量相应增加;Hg、Cd、Pb和Zn的富集系数大于1.5,表明在一定程度上受到了人为活动的影响;Hg、Cd和Pb的污染源可能来自于汽车及其相关产业,Cu和Zn的污染源可能来自于农业生产和养殖业.     

平原区二维复杂河流水质模拟计算

研究了湘江航运大源渡枢纽工程对湘江衡阳市区段水质影响的二维的数值计算方法，研究河段具有河道弯曲、分汊、江心有洲的复杂特点，应用有限单元法与单元网络划分的有关理论，在河流速度场资料的情况下，建立了利用河道水下地形图进行河不质数值计算的方法，并计算出了研究河段水质的浓度场分布，应用所建立的方法，可以进行各种复杂地形条件和不同水位情况下平原区线水河流水质的数值计算。     

环境与人口、经济和科技发展的协同探析

本文从环境与人口、经济和科技之间的相依关系出发,探讨了诸因素相互关联的内在协同机理,简析了IPAT模型的建构与应用.嗣后,利用IPAT模型解析了中国近15年来人口、经济和科技发展对环境影响的贡献差异;指出经济规模的迅速扩展和落后技术支持下的传统生产方式是加剧环境恶化的元凶,且技术转型期的负面影响也是不可忽视的重要因素;进而提出了中国未来环境与人口、经济和科技协同演化的对策措施.     

环境与人口、经济和科技发展的协同探析

本文从环境与人口、经济和科技之间的相依关系出发，探讨了诸因素相互关联的内在协同机理，简析了IPAT模型的建构与应用。嗣后，利用IPAT模型解析了中国近15年来人口、经济和科技发展对环境影响的贡献差异；指出经济规模的迅速扩展和落后技术支持下的传统生产方式是加剧环境恶化的元凶，且技术转型期的负面影响也是不可忽视的重要因素；进而提出了中国未来环境与人口、经济和科技协同演化的对策措施。