Atmospheric mercury pollution due to losses of terrestrial carbon pools?

Plants accumulate significant amounts of atmospheric mercury (Hg) in aboveground biomass, likely sequestering over 1,000 Mg of atmospheric Hg every year. This large mercury uptake could be strong enough to affect tropospheric Hg levels and might be partially responsible for seasonal variations in atmospheric Hg observed at Mace Head, Ireland. The fluctuations of Hg concentrations coincide temporally with the annual oscillation of carbon dioxide (CO₂) in the Northern Hemisphere, which is a result of seasonal growth of vegetation. Therefore, declining Hg concentrations in spring and summer may be attributed in part to plant uptake of atmospheric Hg. Further, the increase of Hg concentrations during non-active vegetation periods might partially be due to plant-derived Hg emitting back to the atmosphere during carbon mineralization. The implications of these propositions are that past and future changes in biomass productivity and organic carbon pools may have had—and may continue to have—significant effects on atmospheric Hg levels. Specifically, large losses in soil and biomass carbon pools in the last 150 years could have contributed significantly to observed increases in atmospheric Hg pollution. The roles of vegetation and terrestrial carbon pools should receive detailed consideration on how they might attenuate or exacerbate atmospheric Hg pollution.     

Mercury inputs and outputs at a small lake in northern Minnesota

Storages and cycling of total mercury (Hg_T), methylmercury (MeHg), and Hg⁰ are described for Spring Lake, a small bog lake in the Marcell Experimental Forest in north-central Minnesota. We quantified photoredox transformations, MeHg photolysis, burial to the sediments, and internal and external loadings of Hg_T and MeHg. Atmospheric deposition was the main input of Hg_T; MeHg was supplied by a combination of atmospheric, near-shore wetland, and biotic (methylation) sources. Hg_T outputs were dominated by burial (67%), and Hg⁰ evasion accounted for 26% of Hg_T outputs. The watershed of Spring Lake is small (3.7× lake surface area), and accordingly, bog and upland runoff were minor contributors to both Hg_T and MeHg inputs. Wet deposition was ∼9% of total MeHg input, and other external inputs (runoff, sediment porewater) provided only an additional 7%, indicating that internal production of MeHg was occurring in the lake. Photolysis of MeHg, measured in the field and laboratory, removed ∼3× the lake mass of MeHg (20 mg) annually, and was the dominant sink for MeHg. Residence times of MeHg and Hg_T in the lake were 48 and 61 days, respectively, during the open-water season, compared with only 8 days for the residence time of MeHg on settling particles (seston). Photoreduction of Hg²⁺ to Hg⁰ was greater than the reverse reaction (Hg⁰ photooxidation), and the residence time of Hg⁰ in the photic zone was short (hours). Data from this study show active cycling of all the measured species of mercury (Hg_T, MeHg, and Hg⁰) and the importance of MeHg photolysis and photo-redox processes.     

Effects of snow cover on the timing and success of reproduction in high-Arctic pink-footed geese <Emphasis Type="Italic">Anser brachyrhynchus</Emphasis>

During four breeding seasons, 2003–2006, we studied the relationship between snow cover and nesting performance in pink-footed geese (Anser brachyrhynchus) in a key breeding site on Svalbard. Snow cover in late May, i.e., at the time of egg laying of geese, was derived from MODIS satellite images. Snow cover had a profound cascading effect on reproductive output via the number of nesting pairs and timing of nesting, which affected nest success, while there was only a tendency for a negative effect on clutch size. Hence, we estimated a five-fold difference in the number of young produced (to post-hatching) between years with little snow and years with high snow cover. The results from the study area correlated with whole-population productivity estimates recorded in autumn. Thus, snow cover derived from MODIS satellite images appears to provide a useful indicator of the breeding conditions in the Arctic.     

日本海太平洋褶柔鱼生物学特征的年际变化

根据2010~2013年连续4个年度在日本海进行鱿钓生产采集的样本,利用SSPS软件统计拟合生长和Logistic曲线的方法,分析了太平样褶柔鱼(Todarodes pacificus)的胴长、体重、性别、性成熟度和摄食强度等生物学特征,以及日本海太平洋褶柔鱼群体结构和组成的年际变化。太平洋褶柔鱼总样本数量为388尾,其中雌、雄个体的平均胴长分别为231 mm和230 mm,优势胴长组为220~250 mm。各年度样本的雄雌性比均接近1︰1,总性比为0.89。胴长和体质量关系呈幂函数变化。Logistic曲线拟合个体初次性成熟胴长,其中雌性为216.04 mm,雄性为216.71 mm。样本以性成熟个体为主,成熟率(Ⅲ、Ⅳ和Ⅴ期)高达78.35%。摄食强度主要分布在Ⅰ、Ⅱ、Ⅲ等级,从胃含物组成的出现频率来看,以鱼类最高且主要是沙丁鱼类和灯笼鱼类,频率达70%以上;头足类次之,甲壳类较少。日本海太平洋褶柔鱼各年度的群落结构稍有差异,推测其生长发育与海洋环境因子有关,如温度、海流、盐度、饵料丰度等不同变化造成。     

Multimode selective detection of mercury by chiroptical fluorescent sensors based on methionine/cysteine

Two multimode Hg(II) sensors, L‐MethBQA and L‐CysBQA, were obtained by fusing methionine or S‐methyl cysteine, into a bis‐quinolyl amine‐based chiral podand scaffold. Quinolyl groups serve as the fluorophore and possess nitrogen lone pairs capable of chelating metal ions. On exposure to Hg²⁺ or Zn²⁺, these sensors show signal enhancement in fluorescence. However, Cu²⁺ quenches their fluorescence in 30:70 acetontrile/water. L‐CysBQA complexes with Hg²⁺, producing an exciton‐coupled circular dichroism spectrum with the opposite sign to the one that is produced by Cu²⁺ or Zn²⁺ complexation. L‐CysBQA binds Hg²⁺ more strongly than Zn²⁺ and is shown to differentiate Hg²⁺ from other metal ions, such as Zn²⁺, Cu²⁺, Ni²⁺, and Pb²⁺, exceptionally well. The synergistic use of relatively soft sulfur, quinoline‐based chiral ligands and chiroptically enhanced fluorescence detection results in high sensitivity and selectivity for Hg²⁺. Chirality, 2011. © 2011 Wiley‐Liss, Inc.     

Total mercury in stranded marine mammals from the Oregon and southern Washington coasts

Muscle samples from 105 marine mammals stranded along the Oregon and Washington coasts (2002–2009) were tested for levels of total mercury (THg) by Cold Vapor Atomic Fluorescence Spectrometry. The THg present is in the form of the highly toxic methylmercury. After normalizing tissue to 75% water weight, Steller sea lions and northern elephant seals exhibited the highest mean concentrations of THg followed by harbor seals, harbor porpoises, and California sea lions, 0.34 ± 0.278, 0.34 ± 0.485, 0.21 ± 0.216, 0.17 ± 0.169, and 0.15 ± 0.126 mg/kg normalized wet weight (ww), respectively. The mean normalized values demonstrate limited muscle methylmercury accumulation in these species in the Pacific Northwest. However, actual ww concentrations in some of the stranded carcasses may pose a risk to scavengers. Normalizing muscle mercury concentrations eliminated the variability from desiccation, and allowed for a clearer indication of the amount of mercury the animal accumulated before stranding.     

Crystal structure and substrate-binding mode of cellulase 12A from Thermotoga maritima

Cellulases have been used in many applications to treat various carbohydrate-containing materials. Thermotoga maritima cellulase 12A (TmCel12A) belongs to the GH12 family of glycoside hydrolases. It is a β-1,4-endoglucanase that degrades cellulose molecules into smaller fragments, facilitating further utilization of the carbohydrate. Because of its hyperthermophilic nature, the enzyme is especially suitable for industrial applications. Here the crystal structure of TmCel12A was determined by using an active-site mutant E134C and its mercury-containing derivatives. It adopts a β-jellyroll protein fold typical of the GH12-family enzymes, with two curved β-sheets A and B and a central active-site cleft. Structural comparison with other GH12 enzymes shows significant differences, as found in two longer and highly twisted β-strands B8 and B9 and several loops. A unique Loop A3-B3 that contains Arg60 and Tyr61 stabilizes the substrate by hydrogen bonding and stacking, as observed in the complex crystals with cellotetraose and cellobiose. The high-resolution structures allow clear elucidation of the network of interactions between the enzyme and its substrate. The sugar residues bound to the enzyme appear to be more ordered in the -2 and -1 subsites than in the +1, +2 and -3 subsites. In the E134C crystals the bound -1 sugar at the cleavage site consistently show the α-anomeric configuration, implicating an intermediate-like structure.     

长白山北坡森林土壤汞的含量和形态分布

分别于2009年4月和9月对长白山北坡的土壤样品进行了采集,研究北方森林地区不同海拔土壤样品中的总汞和甲基汞的分布情况.长白山土壤THg和MeHg含量分别为0.08～0.73 mg·kg-1和0.05～0.56 μg·kg-1,库存量分别为97 kg·km-2和128 g·km-2,高于吉林省背景值,MeHg的最高含量...