喀斯特森林群落退化对浅层岩溶地下水化学的影响

对贵州中部喀斯特地区植被调查及径流和岩溶水样分析,探讨喀斯特森林群落退化过程中浅层岩溶地下水化学组成的变化。结果表明:喀斯特森林生态系统降雨中离子浓度大小的排序为SO2 -4 > K+ 、Ca2 + 、HCO-3 >Na + 、Mg2 + 、Cl - > NO-3 、NH+4 > PO3 -4 ,而径流中离子浓度的大小排序为HCO-3 > SO2 -4 Ca2 + > Mg2 + 、Cl - > K+ 、Na + 、NO-3 > NH+4 > PO3 -4 ;岩溶地下水离子组成与径流总体相似,但岩溶地下中HCO-3 、Ca2 + 和Mg2 + 的含量及电导率明显增加高于地表径流。随着喀斯特森林群落从阔叶林群落向灌木林群落、灌草群落方向演替,其岩溶地下水中HCO-3 和Ca2 + 比例明显减少,而SO2 -4 比例明显增加。岩溶地下水的HCO-3 、Ca2 + 含量与森林覆盖率之间存在显著的正相关,而K+ 、NH+4 含量与森林覆盖率之间则存在显著的负相关。HCO-3 含量是影响岩溶地下水电导率的最重要因子,其次是Ca2 + ,再次是K+ 、Mg2 + ;岩溶地下水电导率可以作为评价喀斯特森林群落退化对生态环境影响的数量指标。

喀斯特石漠化过程中植被演替及其对径流水化学的影响

通过对贵州中部喀斯特地区进行植被调查以及土壤和径流样品的分析,探讨石漠化过程中植被演替及其对径流水化学组成的影响。结果表明:喀斯特石漠化后,土壤出现粘质化,有机质含量急剧下降,土壤毛管孔隙度下降,干旱季节表层和次表层土壤的含水量明显减少,改变了生态系统的水分运动规律。喀斯特地表径流中离子浓度的大小排序为HCO -3 > SO2 -4 > Ca2 + >Mg2 + > K+ 、NO-3 、Cl - > Na + > NH+4 > PO3 -4 ,地表径流水化学类型以HCO32Ca 型为主;随着石漠化程度的增加,地表径流中PO3 -4 输出量明显增加,其次是Ca2 + 、NO-3 ,这部分养分的流失造成土壤养分水平下降,同时影响受纳水体的环境质量。地下径流离子组成与地表径流总体相似,但HCO-3 、Ca2 + 、Mg2 + 的含量高于地表径流,而K+ 、NH+4 的含量低于地表径流;石漠化发生后,地下径流中HCO-3 、Mg2 + 浓度明显减少,岩溶作用减弱,而NH+4 、NO-3 浓度明显增加,对地下水质产生一定的影响。

稳定氮同位素在环境污染示踪中的应用进展

自然界的氮循环已被严重扰乱,失衡的氮循环过程中产生的一些氮氧化物和氮氢化物(如N2O、NO-3 、NO -2 、N H3 、NH +4 等) 是全球温室效应、水体富营养化和酸雨危害的主要贡献者。稳定氮同位素作为一种有效的示踪手段,在研究氮循环特别是污染氮源的识别方面有重要意义。本文在简要总结氮的同位素分馏效应的基础上,重点论述和分析了稳定氮同位素在植被O土壤O地下水系统和大气系统中的氮源识别,并结合研究现状探讨了研究前景。

贵州百花湖分层晚期有机质降解过程与溶解N2O循环

百花湖是一个具有季节性分层的富营养小型湖泊,在秋季湖水倒转期经常发生水质恶化事件,碳氮循环出现异常。文章研究特选择在秋初,湖泊分层开始消失时,测定了湖水中不同深度的N2O ,CH4 ,CO2 ,有机和无机碳同位素以及其他化学参数变化。结果发现:采样时百花湖在约6m和16m 深度附近出现了两个温度不连续层(SDL和PDL) ,并影响到有机颗粒的沉降和分解。相对而言,有较多的有机质在这两个层内发生降解,但降解的途径有所不同,上部主要是有氧降解,下部则主要是无氧降解过程。N2O 的产生和消耗与有机质的降解过程完全对应:PDL 层以上,ΔN2O 与AOU 的线性关系反映了N2O 主要形成于硝化作用;PDL 层以下反硝化作用导致N2O 严重不饱和;PDL 内位于硝化作用和反硝化作用过渡带的N2O 峰,显然是硝化与反硝化联合作用的结果。PDL 层内较大的CH4 浓度变化梯度,说明嗜甲烷细菌可能通过氧化NH+4 贡献了部分N2O。百花湖秋、冬季表层湖水N2O 都是过饱和的,都是大气N2O 的源,依据分子扩散模型计算湖泊N2O 的释放通量在12～14μmol/ m·day 之间,秋、冬季没有明显的差别。秋季底层湖水的反硝化作用是湖泊N2O 的汇,其消耗通量与表层的释放通量基本相当。

大气降水化学的统计学分析——以浙江省金华市为例

运用相关分析、因子分析和聚类分析等统计学方法, 对2004—2005年间浙江省金华市的大气降水化学组成和分布特征进行了分析. 结果表明, SO2 -4 , NH +4 , Ca2 + , NO -3 和H+是降水的主要离子, 降水的pH值、电导率及离子组分均呈明显的正偏态分布, 降水样品以低离子含量的样本为主. 降水中水溶性离子主要分为4类, SO2 -4 , NH+4 , NO -3 , Ca2 +和F- 主要来自人为活动的贡献, K+和Mg2 +主要来自土壤、沙尘等地壳来源, Na+和Cl- 属于典型的海盐性成分, H+则反映了各种离子中和作用对降水酸度的综合影响.

Novel hydrogen-bonded three-dimensional networks encapsulating one-dimensional covalent chains: [M(4,4 '-bipy)(H2O)4](4-abs)2 center dot nH(2)O (4,4 '-bipy=4,4 '-Bipyridine; 4-abs=4-aminobenzenesulfonate) (M=Co, n=1; M=Mn, n=2)

Two novel compounds, [Co(4,4'-bipy)(H2O)(4)](4-abS)(2).H2O (1) and [Mn(4,4'-bipy)(H2O)(4)](4-abs)(2).2H(2)O (2) (4,4'-bipy = 4,4'-bipyridine; 4-abs = 4-aminobenzenesulfonate), have been synthesized in aqueous solution and characterized by single-crystal X-ray diffraction, elemental analyses, UV-vis and IR spectra, and TG analysis. X-ray structural analysis revealed that 1 and 2 both possess unusual hydrogen-bonded three-dimensional (3-D) networks encapsulating one-dimensional (1-D) covalently bonded infinite [M(4,4'-bipy)(H2O)(4)](2+) (M = Co, Mn) chains. The 4-abs anions in 1 form 1-D zigzag chains through hydrogen bonds. These chains are further extended through crystallization water molecules into 3-D hydrogen-bonded networks with 1-D channels, in which the [Co(4,4'-bipy)(H2O)(4)](2+) linear covalently bonded chains are located. Crystal data for 1: C22H30CoN4O11S2, monoclinic P2(1), a = 11.380(2) Angstrom, b = 8.0274(16) Angstrom, c = 15.670(3) Angstrom, alpha = gamma = 90degrees, beta = 92.82(3)degrees, Z = 2. Compound 2 contains interesting two-dimensional (2-D) honeycomb-like networks formed by 4-abs anions and lattice water molecules via hydrogen bonding, which are extended through other crystallization water molecules into three dimensions with 1-D hexagonal channels. The [Mn(4,4'-bipy)(H2O)(4)](2+) linear covalent chains exist in these channels. Crystal data for 2: C22H32WN4O12S2, monoclinic P2(1)/c, a = 15.0833(14) Angstrom, b = 8.2887(4) Angstrom, c = 23.2228(15) Angstrom, alpha = gamma = 90degrees, beta = 95.186(3)degrees, Z = 4.

Preparation And Optical Properties Of Cdte/Cdo Center Dot Nh(2)O Core/Shell Nano-Composites In Aqueous Solution

The deposition of CdO center dot nH(2)O On CdTe nanoparticles was studied in an aqueous phase. The CdTe nanocrystals (NCs) were prepared in aqueous solution through the reaction between Cd2+ and NaHTe in the presence of thioglycolic acid as a stabilizer. The molar ratio of the Cd2+ to Te2- in the precursory solution played an important role in the photoluminescence of the ultimate CdTe NCs. The strongest photoluminescence was obtained under 4.0 of [Cd2+]/[Te2-] at pH similar to 8.2. With the optimum dosage of Cd(II) hydrous oxide deposited on the CdTe NCs, the photoluminescence was enhanced greatly. The photoluminescence of these nanocomposites was kept constant in the pH range of 8.0-10.0, but dramatically decreased with an obvious blue-shifted peak while the pH was below 8.0. In addition, the photochemical oxidation of CdTe NCs with cadmium hydrous oxide deposition was markedly inhibited.

Preparation and optical properties of CdTe/CdO center dot nH(2)O core/shell nano-composites in aqueous solution

The deposition of CdO center dot nH(2)O On CdTe nanoparticles was studied in an aqueous phase. The CdTe nanocrystals (NCs) were prepared in aqueous solution through the reaction between Cd2+ and NaHTe in the presence of thioglycolic acid as a stabilizer. The molar ratio of the Cd2+ to Te2- in the precursory solution played an important role in the photoluminescence of the ultimate CdTe NCs. The strongest photoluminescence was obtained under 4.0 of [Cd2+]/[Te2-] at pH similar to 8.2. With the optimum dosage of Cd(II) hydrous oxide deposited on the CdTe NCs, the photoluminescence was enhanced greatly. The photoluminescence of these nanocomposites was kept constant in the pH range of 8.0-10.0, but dramatically decreased with an obvious blue-shifted peak while the pH was below 8.0. In addition, the photochemical oxidation of CdTe NCs with cadmium hydrous oxide deposition was markedly inhibited.

Taxonomic re-evaluation of Aphanizomenon flos-aquae NH-5 based on morphology and 16S rRNA gene sequences

The taxonomy of Aphanizomenon flos-aquae strain NH-5, a producer of cyanotoxins, was re-evaluated by comparison with six other Aphanizomenon strains using morphological characteristics and 16S rRNA gene sequences. Strain NH-5 was concluded to be improperly identified as Aph. flos-aquae based upon (1) lack of bundle formation in the trichomes, (2) location of akinetes next to heterocytes, (3) lower similarities (less than 97.5%) in the 16S rRNA gene sequences relative to Aph. flos-aquae strains, and (4) comparison within a phylogenetic tree constructed from 16S rRNA gene sequences. The Aphanizomenon strains investigated in this study are classified to four morphological groups as described by the classical taxonomy of Komarek & Kovacik (1989). This classification was supported from the phylogenetic results of 16S rRNA gene sequences. This study also discusses the generic boundaries between Aphanizomenon and Anabaena.

Poly[[diaqua-mu-4,4 '-bipyridine-dinitratodi-mu-L-tyrosinato-dicopper(II)]: a chiral two-dimensional coordination polymer

The title compound, [Cu-2(C9H10NO3)(2)(NO3)(2)(C10H8N2)-(H2O)(2)](n), contains Cu-II atoms and L-tyrosinate (L-tyr) and 4,4'-bipyridine (4,4'-bipy) ligands in a 2:2:1 ratio. Each Cu atom is coordinated by one amino N atom and two carboxylate O atoms from two L-tyr ligands, one N atom from a 4,4'-bipy ligand, a monodentate nitrate ion and a water molecule in an elongated octahedral geometry. Adjacent Cu atoms are bridged by the bidentate carboxylate groups into a chain. These chains are further linked by the bridging 4,4'-bipy ligands, forming an undulated chiral two-dimensional sheet. O-H center dot center dot center dot O and N-H center dot center dot center dot O hydrogen bonds connect the sheets in the [100] direction. This study offers useful information for the engineering of chiral coordination polymers with amino acids and 4,4'-bipy ligands by considering the ratios of the metal ion and organic components.

catena-Poly[diammonium [diaquabis(pyridine-2,4-dicarboxylato-kappa N-2,O-2)cuprate(II)] [[diaquacopper(II)]-mu-pyridine-2,4-dicarboxylato-kappa N-3,O-2:O-2 '-[tetraaquacadmium(II)]-mu-pyridine-2,4-dicarboxylato-kappa O-3(2):N,O-2 '] hexahydrate]

The title mixed-metal complex, {(NH4)(2)[Cu(C7H3NO4)(2)(H2O)(2)][CdCu(C7H3NO4)(2)(H2O)(6)]center dot 6H(2)O}(n), contains one octahedrally coordinated Cd-II center and two octahedrally coordinated Cu-II centers, each lying on an inversion center. The two Cu-II atoms are each coordinated by two O atoms and two N atoms from two 2,4-pydc (2,4-H(2)pydc = pyridine-2,4-dicarboxylic acid) ligands in the equatorial plane and two water molecules at the axial sites, thus producing two crystallographically independent [Cu(2,4-pydc)(2)(H2O)(2)](2-) metalloligands. One metalloligand exists as a discrete anion and the other connects the Cd(H2O)(4) units, forming a neutral chain.

Supramolecular isomerism in zinc hydroxide coordination polymers with pyridine-2,4-dicarboxylic acid: Two polymorphs with centrosymmetric two-dimensional and acentric three-dimensional coordination networks

Reactions of Zn(BF4)(2) and pyridine-2,4-dicarboxylic acid (2,4-pydcH(2)) in the presence of 1,2-bis( 4-pyridyl) ethylene or 1,3-bis(4-pyridyl) propane under hydro(solvo) thermal conditions yielded two polymorphic metal-organic coordination polymers formulated as Zn-2(OH)(2)(2,4-pydc) (1 and 2). Polymorph 1 features a two-dimensional (2-D) layer-like structure that is constructed by 2,4-pydc ligands bridging between the Zn-OH-Zn double-chain units. Each single Zn-OH-Zn chain is composed of mu(2)-OH groups connecting trigonal bipyramidal and tetrahedral Zn centers. Polymorph 2 is a 3-D coordination polymer containing 2-D Zn-OH-Zn sheets that consist of mu(2)- and mu(3)-OH groups and trigonal bipyramidal Zn centers. The sheets are pillared by 2,4-pydc ligands to form an acentric structural architecture. 1 and 2 are rare examples that the two polymorphs exhibit a centrosymmetric 2-D coordination network and an acentric 3-D coordination network, respectively. The different structures lead to differences in photoluminescent properties and thermal stabilities for 1 and 2.

catena-Poly[[[di-mu-acetato-kappa O-4 : O '-bis[(acetato-kappa O-2,O ')manganese(II)]]-di-mu-4,4 '-bipyridine-kappa N-4 : N '] monohydrate

The title compound, {[Mn-2(CH3CO2)(4)(C10H8N2)(2)](H2O)-H-.}(n), is a one-dimensional coordination polymer with a ladder-like structure. Two Mn-II atoms, each coordinated by a chelating acetate ligand, are bridged by two bidentate acetate ligands to form a centrosymmetric [Mn-2(CH3CO2)(4)] unit. Two 4,4'-bipyridine ligands link the [Mn-2(CH3CO2)(4)] units through Mn-N bonds to generate a molecular ladder. The water O atom lies on a crystallographic twofold rotation axis.

Synthesis, crystal structure, and thermal property of a novel supramolecular assembly: (NH42810424)(CHNO) O-[H(V)O(]2H)4(10)28(2), constructed from decavanadate and caffeine

A novel 3D supramolecular assembly constructed from decavanadate and caffeine building blocks, (NH4)(2)(C8H10N4O2)(4)[H4V10O28].2H(2)O (1), has been synthesized in aqueous solution and characterized by elemental analysis, IR, H-1 NMR, V-51 NMR, TG-DTA, and single crystal X-Ray diffraction. The compound 1 crystallizes in monoclinic system, space group P2(1)/n, a = 15.801(1) Angstrom, b = 12.914(1) Angstrom, c = 15.913(2) Angstrom, beta = 113.55degrees, V = 2976.4 (5) Angstrom(3), Z = 2, R = 0.0498 with 6818 reflections. Water molecules, ammonium ions, and caffeine act as "cement" linking the polyanions into 1D chain along the c-axis by hydrogen bonding. In compound 1, extensive hydrogen-bond contacts and strong pi-pi interactions lead to an ordered 3D supramolecular framework. TG-DTA curves indicate that the weight loss of the complex can be divided into three stages.

Poly[di-mu(3)-chloro-mu(2)-trans-1,2-di-4-pyridylethylene-dicopper(I)]: a two-dimensional organic-inorganic hybrid constructed from linear CuCl clusters and bridging ligands

The structure of the title compound, [Cu2Cl2(C12H10N2)](n), contains infinite CuCl staircase-like chains, which lie about inversion centres. The trans-1,2-di-4-pyrid-ylethyl-ene mol-ecules also lie about inversion centres and connect the CuCl chains through Cu-N coordination bonds into a two-dimensional organic-inorganic hybrid network. The planar sheets are stacked along the c axis and associated through weak C-H center dot center dot center dot Cl inter-actions. The results show a reliable structural motif with controllable separation of the CuCl chains by variation of the length of the ligand.