Variations in the composition and adsorption behavior of dissolved organic matter at a small, forested watershed

This study investigated the properties and sorption by goethite of bulk (unfractionated) dissolved organic matter (DOM) from surface and shallow groundwaters at McDonalds Branch, a small freshwater fen in the New Jersey Pine Barrens (USA). Water samples were collected in the spring and fall seasons from two surface-water sampling sites, an upstream potential recharge area and a downstream discharge area, as well as from a set of in-stream nested wells in the upstream potential recharge area. Changes in DOM concentration, molecular weight distribution, and molar absorptivity at 280 nm were measured. Surface and shallow (1.6 m below land surface) groundwater samples collected in spring 1997 in the potential recharge zone (actual recharge impeded by an extensive clay lens) were found to be very similar in terms of DOM concentrations and physicochemical properties and is believe to originate from a common source. Samples taken in fall 1997 yielded no surface water because of drought conditions, and the shallow groundwater DOM collected from the recharge well contained significantly less and chemically altered DOM. This change in chemical properties is believed to be caused in part by fractionation resulting from sorption to mineral phases. Batch isotherm experiments show that sorption by goethite of the DOM from both spring surface and shallow groundwaters in the potential recharge area were similar, whereas the fall groundwater possessed a much lower affinity for the sorbent. This study demonstrated that shallow groundwaters collected under different climatic and hydrologic conditions (spring, high flow versus fall, drought conditions) resulted in different physicochemical properties and adsorption affinities.     

水溶性有机质对土壤中镉吸附行为的影响

水溶性有机质 (DOM)是陆地生态系统和水生生态系统中的一种很活跃的组分 .本文以赤红壤、水稻土和褐土作为供试土壤 ,研究了来源于稻秆和底泥的DOM对土壤中Cd吸附行为的影响 .DOM对土壤中Cd的吸附行为具有明显的抑制作用 .这种抑制作用与土壤类型和DOM种类有关 .在 3种供试土壤中 ,无论添加稻秆DOM还是底泥DOM ,都会使Cd的最大吸附容量和吸附率明显降低 ,其下降幅度为17 3%～ 93 9%.在添加同一种DOM的前提下 ,DOM对Cd吸附的抑制作用均为 :赤红壤 >水稻土 >褐土 .如果不添加DOM ,则土壤对Cd的最大吸附容量主要取决于土壤固相的吸附特性 ,添加DOM后土壤对Cd的最大吸附容量则主要取决于液相中的DOM .由此推断 ,传统的看法 ,通过施用有机肥来固定土壤中的Cd并达到治理重金属污染土壤的观点值得商榷 .     

水溶性有机质对土壤吸附菲的影响

研究了来源于稻草腐熟物的外源水溶性有机质(DOM)和土壤本身固有的内源DOM对有机碳含量不同的3种土壤吸附菲的影响.结果表明,不同处理土壤对菲的吸附曲线均为线性,其吸附系数(K_d)与土壤有机碳含量(f_oc)正相关.去除内源DOM后,黄棕壤、红粘田和黑土吸附菲的K_d值增加了7.08%～21.4%,增加量(ΔK_d)和增加幅度与f_oc正相关,表明土壤中存在的内源DOM抑制土壤对菲的吸附.而外源DOM对土壤吸附菲的影响与其浓度密切相关.在供试浓度范围(0～106 mg DOC·L^-1)内,红粘田吸附菲的K_d值随加入外源DOM浓度的提高先增大后减小.外源DOM浓度为28 mg DOC·L^-1时,红粘田吸附菲的K_d值增加了19.5%;而当外源DOM浓度≥52 mg DOC·L^-1时,则明显抑制菲的吸附.内源和外源DOM对土壤吸附菲的影响,主要与DOM和菲在溶液中的结合作用、在土壤中的累积吸附效应等有关.     

Molecular simulations of adsorption and separation of acetylene and methane and their binary mixture on MOF-5, HKUST-1 and MOF-505 metal–organic frameworks

In this work, the adsorption of acetylene and its binary mixture with methane on MOF-5, HKUST-1 and MOF-505 was studied using Grand Canonical Monte Carlo molecular simulations. The preferred adsorption sites of acetylene and methane molecules into metal–organic frameworks (MOFs) were investigated. The simulated adsorption isotherms of acetylene on MOF-5 and MOF-505 agreed well with the experimental ones without any reparameterisation of the potential parameters but for HKUST-1 the interaction parameters of the acetylene and copper ion were reparameterised. Comparisons of the calculated adsorption isotherms of acetylene in the studied MOFs showed that the MOF-5 had the lowest adsorption capacity. Our results revealed that guest molecules were most adsorbed on the entrance windows of the octagon pore of HKUST-1, while the preferred adsorption sites were large pores and on the metal ion cluster of MOF-505 and MOF-5, respectively. Adsorption of binary mixtures of methane and acetylene on MOF-5, HKUST-1 and MOF-505 revealed that acetylene adsorption is higher than that of methane. Finally, the results showed that C₂H₂/CH₄ selectivity values on HKUST-1 are significantly higher than on MOF-505 and MOF-5. The preferred adsorption sites of acetylene and methane in an equimolar binary mixture were calculated and discussed.     

Mechanism of ammonium adsorption from wastewater by modified bentonite and optimization by response surface

Three modified bentonites, dry alkali modification, thermal modification, and acid modification, were prepared and characterized by XRD and FTIR. Batch experiments were performed to evaluate their efficiency as adsorbent for ammonium removal. Multi-variables interaction effects were evaluated by Response Surface Methodology. The results showed that the adsorption efficiency of ammonium by dry alkali modification bentonite was the best in three modified methods; the next was that of thermal modification. The crystalline structure of bentonite was significantly changed with dry alkali modification. Na₂SiO₃ and Na₂AlSi₃O₈(OH) were achieved by bentonite with powder NaOH modification. The increase in the mole ratio of exchangeable cations indicated that the adsorption efficiency of ammonium increased; while the layer spacing of bentonite expanded with the amount of the adsorbed water and hydrated water increased by thermal modification. In multi-variables interaction effects (holding time, calcination temperature, pH, dosage), the most significant factors were calcination temperature and dosage.     

土壤溶解性有机质及其表面反应性的研究进展

溶解性有机质(DOM)是土壤溶液中的一个重要的组成部分,在土壤化学和生物过程中起着十分重要的作用。虽然DOM在天然有机质中所占的比例并不高,但它将土壤中的矿物质、有机质联系在一起,并能调控环境污染物的迁移转化与归宿,因此国内外学者都很重视溶解性有机质对土壤环境中污染物环境行为影响的研究。综述了DOM的分类和分离技术,DOM的结构及其表征方法,DOM的表面反应性以及对有机污染物、重金属在土壤中吸附、迁移的影响等,并提出了有待于进一步研究的一些问题。     

城市绿地年龄对土壤有机碳积累的影响

为了了解城市土壤有机碳积累的空间变化规律,从杭州市采集了48个点的绿地土样,采用化学和生物学分析方法研究了城市绿地土壤有机碳全量、颗粒状有机碳、黑碳、微生物生物量碳含量和代谢熵等随城市绿地年龄的变化。结果表明:与其他陆地生态系统相似,城市环境下人为的强烈干扰一旦停止和成土条件相对稳定后,绿地土壤将向一定方向发展;随着城市绿地年龄(即保持相对稳定的绿地景观的持续时间)的增加,土壤容重下降,有机碳全量和黑碳逐渐积累,并趋向稳定,土壤微生物生物量碳及其占有机总碳的比例逐渐增加,而代谢熵(qCO2)明显降低;表明作为成土因素之一的时间因素在城市绿地土壤演变和性质空间变异上起着重要的作用;随着人为干扰停止及城市绿地景观形成时间的增加,土壤受人为干扰的影响也逐渐减弱。     

基于多光谱遥感影像的表层土壤有机质空间格局反演

利用多光谱LandSat TM遥感影像反演辽宁省阜新镇表层土壤有机质的空间格局,筛选出与土壤有机质分布相关的TM波段,分析并确定表层土壤有机质含量与TM1、TM2、TM3、TM4、TM5、TM6、TM7波段亮度值(digital number,DN)的相关关系,建立了土壤有机质含量的光谱预测模型.结果表明:研究区表层土壤有机质含量与TM4、TM5波段DN值呈极显著的负相关关系(r分别为-0.617和-0.623,P0.001),与TM3、TM5波段DN值之间满足负二次多项式回归关系(R2=0.9134,P0.001);基于TM3、TM5波段DN值的回归模型对研究区表层土壤有机质含量的预测结果可靠(R2=0.9151,P0.001).研究区表层土壤有机质含量10g·kg-1的农田主要分布在山地边缘地带,而平坦地区农田表层土壤有机质含量一般10g·kg-1,部分达到15～20g·kg-1.     

有机污染物在表层土壤中光降解的研究进展

土壤是承载有机污染物的重要介质,而光降解是降解土壤表层有机污染物的一种非常重要的非生物转化途径。研究土壤表层有机物的光降解对认识污染物土壤环境行为有非常重要的意义。20世纪90年代以来对土壤中有机污染物的光降解研究有了大量报道。本文阐述了土壤组成和质地、土壤湿度、土壤pH值和土壤厚度等因素对光解影响的研究现状;介绍了目前研究土壤光降解所采用的研究方法：土壤表层直接光解、土壤悬浮液光解、溶剂萃取与光降解联合处理,及其研究土壤光降解应用的动力模型;对不同农药和其它有机污染物在土壤中的光降解研究进行了综述,并对今后的研究作了展望。     

Application of solid surface fluorescence EEM spectroscopy for tracking organic matter quality of native halophyte and furrow-irrigated soils

Solid surface fluorescence excitation-emission matrix (EEM) is developed a potential method to characterize soil organic matter (SOM). Solid surface EEM spectroscopy with parallel factor analysis (PARAFAC) and hierarchical cluster analysis (HCA) is used to extract fluorescent components, to seek latent factors, and to investigate spatial distribution of SOM. Soil samples were collected from four native halophyte and two furrow-irrigated soil profiles, i.e. Comm. Salicornia europaea (CSE), Comm. Suaeda glauca (CSG), Comm. Kalidium cuspidatum (CKC), Comm. Sophora alopecuroides (CSA), corn fields (CFD), and wheat fields (WFD). SOM contained six fluorescent components: microbial/terrestrial fulvic-like fluorescent components (C1), tryptophan-like/lignin-derived phenol fluorescent components (C2), terrestrial humic-like fluorescent component (C3), lignin oxidative degradation by-products (C4 and C5), and amino acids (C6). The C 4 and C5 were the representative components of SOM within the CSE, CSG, CKC, CSA and CFD soil profiles, while the C2 and C6 were dominated within the WFD soil profile. The C4, C5, C1 and C2 were latent factors, and they could roughly distinguish SOM within the whole saline soil profiles except the CFD. A humification index (H/L) deduced from the fluorescent components, was very suitable to indicate humification levels of SOM. Humification levels of SOM within the halophyte soil profiles decreased with soil depth, but the opposite trends within the furrow-irrigated soil profiles. The H/L was closely correlated with exchangeable sodium percentage (ESP), and humification levels increased with the decreasing ESP. Soil surface EEM may not only indicate organic matter fractions of saline soils, but may be transferred to other types of landscape.     

不同施肥处理对土壤活性有机碳和甲烷排放的影响

通过采集田间试验区连续3a施入有机肥的稻田耕层土壤,分析土壤中微生物量碳(MBC)、水溶性有机碳(DOC)、易氧化有机碳(ROC)和可矿化有机碳(readily mineralizable carbon,RMC)等活性有机碳的含量,稻田甲烷(CH_4)的排放通量,探讨施用有机肥的土壤活性有机碳变化及与CH_4排放的关系。研究结果显示:(1)施有机肥对土壤中的活性有机碳均有一定的促进作用。3a不同施肥处理土壤中DOC、ROC、MBC和RMC的平均含量分别为383.6、2501.2、640.4 mg/kg和291.7 mg/kg。3a施猪粪(猪粪+化肥,PM)、鸡粪(鸡粪+化肥,CM)和稻草(稻草+化肥,RS)的DOC的含量分别比化肥(CF)处理增加5.6%、6.7%和19.3%,ROC的含量分别比CF增加6.6%、8.4%和9.8%;MBC含量分别比CF增加5.1%、14.8%和21.5%,RMC增加6.8%、22.0%和33.9%。不同施肥处理的稻田土壤活性有机碳为分蘖期高于成熟期。(2)施肥处理显著增加稻田CH_4排放,CH_4分蘖期的排放通量是成熟期的143倍,3a PM、CM和RS处理的CH_4排放分别比CF处理增加37.0%(P0.05)、92.7%(P0.05)和99.4%(P0.05)。(3)不同施肥处理的DOC、ROC、MBC和RMC含量与CH_4排放通量均存在显著正相关关系,ROC与CH_4排放的相关系数最高,为0.754(P0.01),且4种有机碳间关系密切。稻田分蘖期土壤中的活性有机碳与稻田CH_4排放呈显著正相关关系。(4)综合分析,在4种有机碳中,土壤中ROC和MBC的含量直接影响CH_4排放。     

土地利用方式对土壤有机质的影响

通过对地带性常绿阔叶林、杉木人工林、农田、竹林等不同土地利用方式下土壤有机质总量、活性有机质及其组分的研究,发现土地利用方式对土壤有机质和活性有机质各组分的影响差异显著,其中阔叶林含量最高,杉木人工林低于阔叶林,竹林和农田最低。这些差别主要是由于凋落物的数量、质量以及各种管理措施不同所致。     

Methane diffusion mechanism in catenated metal–organic frameworks

In this work, molecular dynamics simulations were performed to investigate the gas diffusion mechanism in catenated metal–organic frameworks (MOFs), for which methane was adopted as a probe and two catenated IRMOFs with interwoven structure, IRMOF-11 and IRMOF-13, were considered. This work reveals that the diffusion pathways of methane molecules in catenated MOFs are mainly governed by the strong confinement in catenation regions, leading to a 3D diffusion along the sheets formed by the A-regions (xy-direction) as well as from one A-region to another by crossing a B-region (z-direction). In addition, the present work shows that the effect of catenation on methane diffusivity is very large, much larger than that on hydrogen diffusivity at room temperature, and that both adsorption selectivity and dynamic selectivity of gas mixtures may be enhanced largely in catenated MOFs, indicating that catenation is a good strategy to improve the overall performance of a material as a membrane in separation applications.     

石灰土演替过程中颗粒态有机质和矿物结合态有机质的微生物群落特征

碳酸盐岩经风化作用并在地形、植被、气候、时间及生物等因素的影响下逐渐演替出黑色石灰土、棕色石灰土、黄色石灰土和红色石灰土。【目的】研究不同演替阶段石灰土颗粒态有机质(particulate organic matter, POM)和矿物结合态有机质(mineral-associated organic matter, MAOM)的微生物群落特征,为岩溶土壤有机质稳定机制研究提供理论依据。【方法】以广西弄岗国家级自然保护区的黑色石灰土、棕色石灰土、黄色石灰土和红色石灰土为研究对象,运用湿筛法将土壤有机质(soil organic matter, SOM)分为POM和MAOM,分析其理化性质以及微生物群落特征。【结果】石灰土演替过程中POM和MAOM的有机碳、总氮、交换性钙含量均呈下降趋势,且MAOM的C/N均大于POM,POM的C/P均大于MAOM。细菌α多样性在黑色石灰土POM和MAOM中最高,且四类石灰土MAOM的真菌多样性比POM要高。Acidobacteria、Proteobacteria、Ascomycota均为石灰土演替过程中POM和MAOM的优势菌门。总磷是影响石灰土演替过...     

Mapping soil organic matter in low-relief areas based on land surface diurnal temperature difference and a vegetation index

Accurate estimates of the spatial variability of soil organic matter (SOM) are necessary to properly evaluate soil fertility and soil carbon sequestration potential. In plains and gently undulating terrains, soil spatial variability is not closely related to relief, and thus digital soil mapping (DSM) methods based on soil–landscape relationships often fail in these areas. Therefore, different predictors are needed for DSM in the plains. Time-series remotely sensed data, including thermal imagery and vegetation indices provide possibilities for mapping SOM in such areas. Two low-relief agricultural areas (Peixian County, 28 km × 28 km and Jiangyan County, 38 km × 50 km) in northwest and middle Jiangsu Province, east China, were chosen as case study areas. Land surface diurnal temperature difference (DTD) extracted from moderate resolution imaging spectroradiometer (MODIS) land surface temperature (LST), and soil-adjusted vegetation index (SAVI) at the peak of growing season calculated from Landsat ETM+ image were used as predictors. Regression kriging (RK) with a mixed linear model fitted by residual maximum likelihood (REML) and residuals interpolated by simple kriging (SK) were used to model and map SOM spatial distribution; ordinary kriging (OK) was used as a baseline comparison. The root mean squared error, mean error and mean absolute error calculated from leave-one-out cross-validation were used to assess prediction accuracy. Results showed that the proposed covariates provided added value to the observations. SAVI aggregated to MODIS resolution was able to identify local highs and lows not apparent from the DTD imagery alone. Despite the apparent similarity of the two areas, the spatial structure of residuals from the linear mixed models were quite different; ranges on the order of 3 km in Jiangyan but 16 km in Peixian, and accuracy of best models differed by a factor of two (3.3 g/kg and 6.3 g/kg SOM, respectively). This suggests that time-series remotely sensed data can provide useful auxiliary variable for mapping SOM in low-relief agricultural areas, with three important cautions: (1) image dates must be carefully chosen; (2) vegetation indices should supplement diurnal temperature differences, (3) model structure must be calibrated for each area.     

沈阳市城郊表层土壤有机污染评价

城市土壤是保护城市环境的一个重要生态屏障.随着有机污染物的“致癌、致畸、致突变”特性被人们所认知,土壤有机污染也逐渐受到人们的重视.在我国目前缺乏相关环境质量标准的背景下,尝试采用因子分析评价法,对沈阳城郊表层土壤有机污染物进行识别,并对土壤有机污染程度进行定量评价与分级.结果表明,苯并(a)芘、滴滴涕、六氯苯和六六六对土壤污染负荷的贡献率最高,是主要的有机污染因子;利用因子分析评价法,34个城郊表层土壤采样点的有机污染评价综合评分在O-224.62之间,以较轻度污染和中度污染为主,评价结果及分级与实际情况基本相符.在此基础上,分析了各类有机污染物的污染来源,对防治城市土壤污染,进而保障居民的食品安全和饮水安全具有重要意义.     

表层水体中典型小分子有机氮的光铵化反应

地表水体中溶解性有机氮(DON)向无机氮的光化学转化是氮循环的重要过程之一。本文以自然水体中典型小分子DON(如氨基酸、核苷酸、尿素等)为对象,通过检测不同条件下的光铵化速率,探究小分子DON的结构、光源及水质条件对其光铵化过程的影响。结果表明:模拟自然光下,含有芳香环结构的氨基酸可以发生不同程度光铵化反应,酪氨酸和色氨酸的光铵化速率最大,6 h转化率可达约50%,而尿素和核苷酸则无明显光铵化反应发生;自然光下,酪氨酸和色氨酸在缓冲液中发生明显光铵化反应,而自然水样中组氨酸和苯丙氨酸也可生成NH4+;可见光波段对DON的光铵化几乎没有贡献,说明DON的光铵化速率受光源与水质组分影响。分子结构也影响DON的光铵化反应,如组氨酸分子中的氮可以完全转化为NH4+,而一个色氨酸分子中则仅有一个氮原子可以发生转化。基于密度泛函理论计算发现,氨基酸光铵化速率与其分子轨道能隙值有较好的负相关性。系列实验表明了水体中DON光化学转化的复杂性,应当在氮循环、水质变化和生态环境的评估中得到重视。