贵州红枫湖汞的生物地球化学循环

上世纪八十年代，科学家们发现在北美和北欧一些远离汞污染源的湖泊中，某些鱼汞含量远远超过了世界卫生组织建议的食用水产品汞含量标准，这一现象引起了人们对水环境系统中汞的生物地球化学循环的极大关注。因此本论文对贵州红枫湖和加拿大安大略省3个小湖中汞的形态与分布特征进行了详细的研究，并对红枫湖整个汞的生物地球化学循环做了较为完整深入的探讨。本论文主要包括以下4方面的研究内容：（1）沉积物甲基汞分析方法的建立；（2）红枫湖水体、沉积物、鱼体中各种汞形态的含量、分布特征以及水体富营养化对其影响的研究；（3）红枫湖汞形态转化、输入输出通量及其质量平衡的估算；（4）红枫湖的对比研究点—加拿大安大略省的Mary、St. George和Philips湖中不同形态汞分布特征的初步研究。通过本论文的研究，得出以下主要结论： 1. 建立了硝酸和硫酸铜溶液浸提，CH2Cl2萃取并结合水相乙基化和GC-CVAFS测定沉积物及土壤中甲基汞的方法。该方法平均回收率为 97.8%，相对标准偏差≤10.2%，方法检出限为0.6pg/g，具有所需试剂少、不用连续萃取、简捷易行、回收率高以及精密度好等特点。 2． 2004年红枫湖湖水总汞浓度在2.5-14 ng/L之间，平均值为6.9 ng/L；溶解态汞浓度范围在1.2-8.0 ng/L之间，平均为3.9 ng/L。不管是红枫湖水体汞浓度的空间分布，还是季节变化都严重受到人为污染源的干扰。湖水汞在颗粒态和溶解态之间的分配，主要受内源有机质以及氧化还原条件的影响。2004年春季后五由于水华现象大量繁殖的藻类，吸附了大量的汞，从而改变了汞在水库中的分配和迁移。这些藻类的生长对水体中溶解气态汞浓度分布也有显著的影响。湖水中活性汞分布特征主要受Hg2+的光致还原过程、Hg2+的甲基化过程以及人为源的输入等过程控制。 3. 红枫湖夏季下层滞水带中，甲基汞含量显著升高，特别是在后五缺氧层，最高值达0.92ng/L。夏季总甲基汞和溶解态甲基汞在水体剖面上的分布表明：在富营养化较严重的后五，水体中升高的甲基汞主要来自水体中汞的甲基化过程；而在富营养化特征不明显的大坝，水体中升高的甲基汞主要来自沉积物甲基汞的释放。红枫湖水体中各种汞形态的分布特征表明，富营养化对汞的迁移转化影响显著，尤其是汞的甲基化过程。水体富营养化为汞的甲基化提供了有利条件，给水生生态环境及人体健康带来了潜在的威胁。 4. 红枫湖沉积物总汞浓度为0.392 ± 0.070 μg/g，高于世界其它背景区汞浓度，也高于处于同一流域的乌江渡水库和东风水库，表明红枫湖受到了一定程度的汞污染。两个采样点总汞无明显的季节变化，但其剖面分布都有在上层富集的趋势。沉积物甲基汞浓度的季节变化和剖面最大峰值分布，主要受氧化还原带的季节性迁移所控制。沉积物甲基汞浓度在春季最高，其余季节则没有明显差异，甲基汞峰值出现在表层0～8cm以内，与红枫湖沉积物中硫酸盐还原菌活动区域一致。 5. 红枫湖总汞在孔隙水中的浓度及在固/液之间的分配系数主要和温度有关，与沉积物中总汞相关性不大，而孔隙水中甲基汞浓度则和沉积物甲基汞浓度存在着极显著的相关性（r=0.70, p<0.001）。沉积物和孔隙水甲基汞浓度除受到固/液分配系数影响外，主要还受到甲基汞产生过程控制。 6. 由于本次研究所采集的鱼类多为红枫湖人工饲养鱼，生长速度快，食物链短，故总汞含量（32ng/g）和甲基汞含量(12ng/g)都远远低于国家食用标准。汞含量在不同鱼种中的分布趋势为：肉食性鱼类>杂食性鱼类>草食性鱼类，这表明鱼体中汞含量主要和鱼的摄食习惯有关。 7． 红枫湖总汞质量平衡模型的估算结果表明，红枫湖水体中汞的总源为30066 g.a-1，总汇为31010g.a-1。水体中总汞最大的源来自于河流输入（82%），而最大的汇是水体颗粒态汞的沉降（78%）。甲基汞质量平衡模型的估算结果表明河流输出是水体甲基汞一个重要的汇，占总汇的45%, 比河流输入占总源的比例高30%，表明水库是下游水体甲基汞的源。 8. 红枫湖汞在水-沉积物界面的迁移通量表明，沉积物是水体中汞和甲基汞一个巨大的汇，而沉积物对上覆水体总汞和甲基汞的贡献却很有限。红枫湖汞在水-气界面的迁移通量表明，大气汞沉降特别是干沉降是红枫湖水体总汞一个重要的污染源，其对红枫湖汞的贡献远大于水体向大气释放的汞，大气沉降每年向红枫湖净贡献汞量为3364 g.a-1。 9. 在对比研究的湖泊中，水体中甲基汞的剖面分布表明，斜温层颗粒态甲基汞的沉降、沉积物甲基汞的释放以及水体汞的甲基化过程都是下层水体高甲基汞的重要来源。在这些湖泊中近代汞的沉积通量为22.1 μg m-2 a-1，远低于红枫湖中汞的沉积通量（714 μg m-2 a-1）。与红枫湖以及一些典型的沉积物甲基汞的垂直剖面分布相比，这些小湖中甲基汞的产生不仅发生在沉积物表层，在较深的沉积物中可能也有汞的甲基化过程，而且这个过程和有机质的含量密切相关。

Influence of dispersive coupling coefficient in microring channel drop filters

Wide transmission dips are observed in the through spectra in microring and racetrack channel drop filters by two-dimensional finite-difference time-domain (FDTD) simulation. The transmission spectra, which reflect the coupling efficiency, are also calculated from the FDTD output as the pulse just travels one circle inside the resonator. The results indicate that the dips are caused by the dispersion of the coupling coefficient between the input waveguide and the resonator. In addition, a near-zero channel drop on resonance and a large channel drop off resonance are observed due to the near zero coupling coefficient and a large coupling coefficient, respectively. If the width of the input waveguide is different from that of the ring resonator, the oscillation of the coupling coefficient can be greatly suppressed.

Modeling the effect of ozone loss on photobleaching of chromophoric dissolved organic matter in the St. Lawrence estuary

Temporal trends in total ozone for the St. Lawrence estuary were estimated from ground-based measurements at the NOAA/CMDL station in Caribou, Maine. Linear regression analysis showed that from 1979 to 1999 total ozone has decreased by about 3.3% per decade on an annual basis and ≤6.2% per decade on a monthly basis relative to unperturbed (pre-CFC) levels. The influence of increased ultraviolet-B (280–320 nm) radiation associated with ozone depletion on water column photochemical processes was evaluated by modeling the photobleaching of chromophoric dissolved organic material (CDOM). Linear regression analysis showed small (<0.5% per decade), but statistically significant upward trends in maximum noontime photobleaching rates. Most notably, positive trends in relative rates for May, June, and July, when maximum absolute rates are expected, were predicted. A global model based on TOMS ozone data revealed increases in photobleaching of ≤3% per decade at high latitudes in the Southern Hemisphere. Radiation amplification factors for increases in photochemically weighted UV (280–400 nm) in response to ozone depletion were estimated at 0.1 and 0.08 for photobleaching of CDOM absorbance at 300 and 350 nm, respectively. Application of the laboratory-based model to conditions that more closely resembled those in situ were variable with both overestimation and underestimation of measured rates. The differences between modeled rates and observed rates under quasi-natural conditions were as large or larger than the predicted increases due to ozone depletion. These comparisons suggest that biological activity and mixing play an important, but as yet ill-defined, role in modifying photochemical processes.

The influence of arrangement of St in MBS on the properties of PVC/MBS blends

Three series of MBS core-shell impact modifiers were prepared by grafting styrene and methyl methacrylate onto PB or SBR seed latex in emulsion polymerization. All the MBS modifiers were designed to have the same total chemical composition, and MMA/Bd/St equals 30/42/28, which is a prerequisite for producing transparent blends with PVC. Under this composition, there were three different ways of arrangement for styrene in MBS, which led to the different structure of MBS modifier. The concentration of MBS in PVC/MBS blends was kept at a constant value of 20 wt.%. The effects of arrangement of St in MBS on the mechanical and optical properties of PVC/MBS blends were studied. The notched Izod impact test results showed that the MBS with a PB homopolymer core grafted with St had a lowest brittle-ductile transition (BDT) temperature and BDT temperature increased with the amount of St copolymerized with Bd in the core of MBS. The transparency of blends also increased with the amount of St copolymerized with Bd in the core. TEM results showed that the arrangement of St in MBS influenced the deformation behavior. Two deformation modes were observed in the blends: cavitation and shear yielding.

Studies on polyepichlorohydrin-based polyurethane/poly(MMA-co-St) IPNs

Interpenetrating polymer networks of polyepichlorohydrin-based polyurethane/poly(MMA-co-St) have been prepared with simultaneous mettled by changing the weight fraction of MMA(W-MMA) in copolymer of MMA with styrene. The IPNs have been studied by DSC, TEM and dynamic mechanical spectroscopy(DMS). The results show that the IPNs have only one T-g, when W-MMA is greater than 0. 6. But when W-MMA IMA is less than 0. 4, the IPNs have two T(g)s, and phase separation is observed on TEM. The phenomenon is explained according to the solubility parameters(delta) and the fraction of hydrogen bond(delta(h)) of P (MMA-co-St). The study reveals that there is a close correlation among the delta, domain size and mechanical properties of PU (PECH)/P(MMA-co-St) IPN.

VTMS与Bz、St���HFP等离子体共聚物的性能研究

采用外部电极电容耦合的RF辉光放电装置,对乙烯基三甲基硅烷(VTMS)与苯(Bz)、苯乙烯(St)以及六氟丙烯(HFP)进行共聚合。通过IR、TG、防潮试验、接触角测试研究了共聚物膜的性能。发现VTMS与Bz、St���共聚物膜具有优良的防潮性。

Isolation and characterization of a novel variant of HMW glutenin subunit gene from the St genome of Pseudoroegneria stipifolia

The x- and y-type high molecular weight (HMW) glutenin subunits are conserved seed storage proteins in wheat and related species. Here we describe investigations on the HMW glutenin subunits from several Pseudoroegneria accessions. The electrophoretic mobilities of the HMW glutenin subunits from Pd. stipifolia, Pd tauri and Pd strigosa were much faster than those of orthologous wheat subunits, indicating that their protein size may be smaller than that of wheat subunits. The coding sequence of the Glu-1St1 subunit (encoded by the Pseudoroegneria stipifolia accession PI325181) was isolated, and found to represent the native open reading frame (ORF) by in vitro expression. The deduced amino acid sequence of Glu-1St1 matched with that determined from the native subunit by mass spectrometric analysis. The domain organization in Glu-1St1 showed high similarity with that of typical HMW glutenin subunits. However, Glu-1St1 exhibited several distinct characteristics. First, the length of its repetitive domain was substantially smaller than that of conventional subunits, which explains its much faster electrophoretic mobility in SDS-PAGE. Second, although the N-terminal domain of Glu-1St1 resembled that of y-type subunit, its C-terminal domain was more similar to that of x-type subunit. Third, the N- and C-terminat domains of Glu-1St1 shared conserved features with those of barley D-hordein, but the repeat motifs and the organization of its repetitive domain were more similar to those of HMW glutenin subunits than to D-hordein. We conclude that Glu-1St1 is a novel variant of HMW glutenin subunits. The analysis of Glu-1St1 may provide new insight into the evolution of HMW glutenin subunits in Triticeae species. (C) 2007 Elsevier Ltd. All rights reserved.

Phylogeography of the Qinghai-Tibetan Plateau endemic Juniperus przewalskii (Cupressaceae) inferred from chloroplast DNA sequence variation

The vegetation of the northeast Qinghai-Tibetan Plateau is dominated by alpine meadow and desert-steppe with sparse forests scattered within it. To obtain a better understanding of the phylogeography of one constituent species of the forests in this region, we examined chloroplast trnT-trnF and trnS-trnG sequence variation within Juniperus przewalskii, a key endemic tree species. Sequence data were obtained from 392 trees in 20 populations covering the entire distribution range of the species. Six cpDNA haplotypes were identified. Significant population subdivision was detected (G(ST) = 0.772, N-ST = 0.834), suggesting low levels of recurrent gene flow among populations and significant phylogeographic structure (N-ST > G(ST), P < 0.05). Eight of the nine disjunct populations surveyed on the high-elevation northeast plateau were fixed for a single haplotype (A), while the remaining, more westerly population, contained the same haplotype at high frequency together with two low frequency haplotypes (C and F). In contrast, most populations that occurred at lower altitudes at the plateau edge were fixed or nearly fixed for one of two haplotypes, A or E. However, two plateau edge populations had haplotype compositions different from the rest. In one, four haplotypes (A, B, D and E) were present at approximately equivalent frequencies, which might reflect a larger refugium in the area of this population during the last glacial period. Phylogenetic analysis indicated that the most widely distributed haplotype A is not ancestral to other haplotypes. The contrasting phylogeographic structures of the haplotype-rich plateau edge area and the almost haplotype-uniform plateau platform region indicate that the plateau platform was recolonized by J. przewalskii during the most recent postglacial period. This is supported by the findings of a nested clade analysis, which inferred that postglacial range expansion from the plateau edge followed by recent fragmentation is largely responsible for the present-day spatial distribution of cpDNA haplotypes within the species.