海洋环境汞甲基化/去甲基化研究进展

汞（Hg）是一种在大气中具有较长停留时间并能进行长距离传输的全球性污染物.甲基汞（MeHg）具有毒性强、易富集、可随食物链放大的特点，是引起环境风险的主要汞形态.通过各种来源排放到海洋环境中的无机汞在沉积物和水柱中均可甲基化为MeHg，原位甲基化和去甲基化是控制海洋环境中甲基汞水平的关键过程.虽然目前已有综述总结了环境中汞甲基化/去甲基化，但对海洋生态系统中汞甲基化/去甲基化过程涉及相对较少.本文在总结海洋汞甲基化/去甲基化过程速率、途径和热点区域基础上，详细讨论了海洋光化学、非光化学以及微生物3种汞甲基化/去甲基化途径机制，并对未来研究方向进行了展望.在现有研究基础上，未来应在不同汞甲基化/去甲基化途径贡献估算、实际海洋环境汞甲基化/去甲基化基因/微生物作用验证、环境因素对海洋汞甲基化/去甲基化影响方面开展更深入研究.海洋汞甲基化/去甲基化的研究可为深入理解海洋汞的环境行为与风险和发展有效的汞污染风险防控技术提供科学依据和数据支撑.     

沉积物中汞的甲基化研究进展

汞是环境中存在的一种重要污染物质,其毒性与之化学形态密切相关。环境中的汞主要以无机汞形态存在,然而无机汞可以通过甲基化作用转化为毒性更强的甲基汞,从而给受到暴露的生物及人类带来更高的健康风险。沉积物是汞在水生环境系统中的主要分布相,也是无机汞甲基化过程发生的主要场所。沉积物中汞的甲基化过程受到生物种类、汞的生物可利用性等生物因素及温度、含硫化合物、有机质、氧化还原条件等环境理化性质的影响。本文对汞在沉积物中甲基化过程的作用机制及其影响因素的研究现状及最新进展进行了总结,并对未来更深入的研究进行了展望。     

硫化汞纳米颗粒的微生物摄入及其在汞甲基化中的作用

甲基汞因其独特的食物链富集特性和毒性使汞成为重要的全球污染物.厌氧环境中微生物介导的汞甲基化是甲基汞生成最主要的来源,厌氧环境中不同汞地球化学形态控制着甲基汞的生成过程.硫化汞纳米颗粒是在实际厌氧环境中新近发现的重要颗粒汞形态,对其环境行为还缺乏基本认识.本文基于硫化汞纳米颗粒的环境行为,重点围绕其与微生物的相互作用,讨论并总结了硫化汞纳米颗粒的生成、硫化汞纳米颗粒的微生物摄入、溶解以及硫化汞纳米颗粒对微生物汞甲基化的影响,并进一步对硫化汞纳米颗粒与微生物相互作用的未来研究重点进行了展望.     

硒（Ⅳ）对无机汞生物甲基化影响的初步研究

本文以蓟运河含汞底泥为实验材料,研究了硒(Ⅳ)对无机汞生物甲基化的影响,发现低浓度的硒(Ⅳ)对汞的生物甲基化有促进作用,而较高浓度时则可抑制汞的生物甲基化。当硒量达20ppm后则无机汞不能进行甲基化作用。     

环境中汞微生物转化研究进展

汞(Hg)污染是全球最为关注的环境问题之一.Hg的不同形态之间毒性差异大,其以有机形态存在的甲基汞(MeHg)具有强神经毒性,且能在生物体内富集,具有很强的健康与生态风险.环境中不同形态的Hg可以在生物与非生物作用下进行转化,特别是微生物在一定条件下驱动着Hg的甲基化、去甲基化、还原与氧化,从而影响Hg的移动性和生物有效性.因此,理解微生物参与Hg转化的特征与机制对人体健康和生态环境都有着重要的意义.已有不少研究报道了Hg的微生物转化过程,但缺乏一个系统的总结与归纳.本文综述了关于Hg微生物甲基化、去甲基化、还原和氧化的最新研究进展,重点讨论Hg甲基化微生物类群,分析了微生物对Hg的甲基化和还原机制,以及影响Hg甲基化过程的主要环境因子,并提出未来关于Hg微生物转化的研究方向与重点.     

七株硫酸盐还原菌汞甲基化能力的比较

目前硫酸盐还原菌汞甲基化的研究集中在Desulfovibrio desulfuricans ND132菌株上,由于D.desulfuricans ND132并非商业化提供的菌株,使得国内很多实验室难以获得该菌株开展微生物汞甲基化的相关研究.本文收集了7株商业化的硫酸盐还原菌,通过系统研究探寻其中可用作替代的汞甲基化模式菌株.在实验室培养条件下,通过对甲基化关键基因(hgcA和hgcB)、生长特性、汞的耐受性以及汞甲基化能力的测试,结果发现,Desulfomicrobium escambiense(CGMCC 1.3481)生长较快、具有较好的汞甲基化率(7.5%±0.7%),具备作为汞甲基化模式菌株的潜力.     

金矿区中国林蛙体内DNA甲基化水平

采集金矿附近山区河流水质、沉积物和当地两栖类动物中国林蛙样品,应用高效液相色谱仪测定污染区和对照区林蛙体内各组织器官的胞嘧啶(c)和5-甲基胞嘧啶(5-mc)含量,探讨因金矿开采引起的汞污染以及对林蛙体内组织器官DNA甲基化水平的变化,研究汞胁迫下,两栖类动物体内分子水平的影响。结果表明:金矿开采区河流水质和沉积物已受到甲基汞污染,污染区林蛙体内甲基汞含量远高于对照区;林蛙体内各组织器官中DNA甲基化水平发生不同的变化:污染区林蛙肝脏和皮肤中DNA甲基化水平高于对照区,肌肉和脑干DNA甲基化水平低于对照区;雄性林蛙肝脏和脑干DNA甲基化水平高于雌性,肌肉和皮肤DNA甲基化水平却低于雌性。以上结果说明汞胁迫下,中国林蛙体内组织器官DNA甲基化水平可以发生一定的变化,环境中重金属汞离子进入林蛙体内含量的不同,可以促进或抑制其体内甲基化水平的变化,引起基因毒性作用。     

Research progress on occurrence forms and microbial transformation of mercury北大核心CSCD

汞是一种高毒性且具有持久性的重金属污染物,汞污染的治理与修复在近几十年一直是国内外研究热点.了解微生物对汞赋存形态的转化作用,对汞污染的治理与修复具有重要意义.总结汞的不同赋存形态、毒性及对应的常用分析方法,其中甲基汞(methyl mercury,MeHg)是毒性最强的汞形态之一.环境中汞的化学形态能发生转化,尤其以微生物驱动的汞的甲基化、MeHg的去甲基化和汞的氧化还原最为常见.依据汞转化类型将汞转化相关微生物分为汞甲基化、MeHg去甲基化、汞还原、汞氧化等类群,将对应的汞转化作用机制分为基于hgcAB基因的汞甲基化、基于mer操纵子基因的MeHg去甲基化和Hg2+还原、胞内过氧化氢酶介导的Hg0氧化.微生物汞转化过程不仅受到pH和温度的显著影响,而且还受到汞的赋存形态和游离汞的浓度、微生物种/群结构与功能、矿物种类、中间体和次生产物及其交互作用的影响,基于此,提出正确客观表征汞的微生物转化过程需要综合分析微生物组和矿物组的变化规律及其交互作用的综合效应.针对酸性矿山废水(AMD)极端环境微生物汞转化研究的不足,未来的工作将聚焦结合多组学手段、同步辐射谱学和密度泛函理论(DFT)计算等分析技术研究汞赋存形态的微生物转化过程,分析和阐明汞转化中间体的键合作用方式和转化机制,从而为AMD汞污染的预防、治理和修复提供依据.(图2表2参107)     

三峡库区消落带土壤淹水过程中汞的释放及甲基化特征

为探索三峡库区消落带土壤淹水期汞的环境化学行为,利用模拟试验,设置A(15℃,低溶解氧(DO))、B(30℃,低DO)、C(15℃,高DO)3组处理,在人工气候培养箱中进行消落带土壤淹水过程中汞的释放与甲基化特征研究,淹水试验共进行了40 d.结果表明,淹水初期(0—10 d)土壤汞呈释放趋势,A、B、C等3组处理水体中总汞浓度逐渐增加,而土壤中总汞含量相应降低;随淹水时间的延长(10 d),二者达到平衡.淹水后,A、B、C处理上覆水甲基汞浓度随淹水时间的延长而升高,且分别在第15天、第8天、第15天达到峰值,第30天基本达到平衡;土壤甲基汞含量随淹水时间的延长而增高,并在第30天达到平衡,平衡时土壤及上覆水甲基汞浓度规律均表现为BAC.土壤-上覆水系统温度的适当升高利于土壤汞的释放及甲基化;高溶解氧利于土壤汞的释放,低溶解氧则更利于汞的甲基化.     

稻田水体中汞的非生物甲基化研究

本文采用稻田原位培养的方法,考察了稻田水体汞的非生物甲基化及沼灌对稻田水体汞非生物甲基化的影响.结果表明,开阔水面无机汞甲基化的转化率为3.14%—3.17%,明显高于水稻行间(0.83%—1.95%),光照加速了稻田水体无机汞的甲基化过程.常规稻田水体中甲基汞以生成为主,表现为随着培养时间的延长,水体中甲基汞的含量逐渐增加至0.63 ng·L~(-1).与常规稻田水体相比,沼灌稻田水体先出现甲基汞的峰值,随着体系光量子的累积,甲基汞逐渐光解,其含量逐渐降低.常规稻田水甲基汞的含量与光照呈线性正相关关系(R~2=0.71—0.86),而沼灌稻田水中甲基汞的含量与光照呈抛物线关系(R~2=0.33—0.80).沼灌稻田水体中高分子量的溶解态有机质如腐殖质和富里酸的含量明显高于常规稻田水体,且芳香性物质含量占比较高,使其中无机汞的甲基化过程要更复杂.     

Rapid,recurring, structured survey versus bioblitz for generating biodiversity data and analysis with a multispecies abundance model

A bioblitz inexpensively and quickly generates biodiversity data, but bioblitzes are often conducted with haphazard, unreplicated sampling. Results tend to be taxonomically, geographically, or temporally biased, lack metadata, and consist of lists of observed taxa that do not enable further analyses or correction for imperfect detection. A rapid, recurring, structured survey (RRSS) uses a structured sampling design and temporal and spatial replication to survey randomly selected sites on a conservation property. We participated in a loosely structured bioblitz and a subsequent RRSS at Big Canoe Creek Nature Preserve in Springville (St. Clair County), Alabama (USA) to compare observed richness derived from the 2 survey approaches. The RRSS data structure enabled us to fit models that accounted for imperfect detection to estimate abundances, occupancy probabilities, and habitat associations. The loosely structured bioblitz data could not be used in such models. We present a new integrated multispecies abundance model that we applied to avian RRSS data. Our model extension enables estimation for the community, employs data augmentation to estimate the number of undetected species, and incorporates covariates. The RRSS generated a more comprehensive and less biased list of observed taxonomic richness than the loosely structured bioblitz (e.g., 73 vs. 45 bird species and 104 vs. 63 insect families from the RRSS vs. loosely structured bioblitz, respectively). Models fit to the RRSS data identified seasonal patterns in avian community composition and allowed for estimation of habitat–occupancy relationships for insect taxa. The RRSS protocol has potential for broad transferability as a standardized, quick, and inexpensive way to inventory biodiversity and estimate ecological parameters while providing an outreach opportunity.     

Compliance with and ecosystem function of biodiversity offsets in North American and European freshwaters

Land-use change via human development is a major driver of biodiversity loss. To reduce these impacts, billions of dollars are spent on biodiversity offsets. However, studies evaluating offset project effectiveness that examine components such as the overall compliance and function of projects remain rare. We reviewed 577 offsetting projects in freshwater ecosystems that included the metrics project size, type of aquatic system (e.g., wetland and creek), offsetting measure (e.g., enhancement, restoration, and creation), and an assessment of the projects’ compliance and functional success. Project information was obtained from scientific and government databases and gray literature. Despite considerable investment in offsetting projects, crucial problems persisted. Although compliance and function were related to each other, a high level of compliance did not guarantee a high degree of function. However, large projects relative to area had better function than small projects. Function improved when projects targeted productivity or specific ecosystem features and when multiple complementary management targets were in place. Restorative measures were more likely to achieve targets than creating entirely new ecosystems. Altogether the relationships we found highlight specific ecological processes that may help improve offsetting outcomes.     

A palaeo-hydrogeological model for arsenic contamination in southern and south-east Asia

An argument is presented in which areas of natural arsenic contamination of modern groundwaters throughout Asia have a common origin. Arsenic originally accumulated in oceanic ferro-manganoan sediments of the eastern Palaeo-Tethys. This was further concentrated through oceanic crustal extinction in what later became the south-east Chinese accreted mineralised terrain. Proto-Himalayan uplift of this area created the palaeo-drainage systems of the Ganges – Brahmaputra, Irrawaddy, Mekong, and Red Rivers, with consequent headwater erosion of arsenic-rich sediments. Their downstream deposition as immature and easily redistributed Neogene sandstones, silts, and iron-rich clays has created secondary and tertiary reservoirs of adsorbed and authigenic arsenic, from which the current arsenic-rich groundwaters have evolved. Considering river basins within the above palaeo-hydrogeological framework provides a basis for assessing the risk of arsenic in groundwater basins of south and south-eastern Asia.     

Cost‐effective conservation of an endangered frog under uncertainty

How should managers choose among conservation options when resources are scarce and there is uncertainty regarding the effectiveness of actions? Well‐developed tools exist for prioritizing areas for one‐time and binary actions (e.g., protect vs. not protect), but methods for prioritizing incremental or ongoing actions (such as habitat creation and maintenance) remain uncommon. We devised an approach that combines metapopulation viability and cost‐effectiveness analyses to select among alternative conservation actions while accounting for uncertainty. In our study, cost‐effectiveness is the ratio between the benefit of an action and its economic cost, where benefit is the change in metapopulation viability. We applied the approach to the case of the endangered growling grass frog (Litoria raniformis), which is threatened by urban development. We extended a Bayesian model to predict metapopulation viability under 9 urbanization and management scenarios and incorporated the full probability distribution of possible outcomes for each scenario into the cost‐effectiveness analysis. This allowed us to discern between cost‐effective alternatives that were robust to uncertainty and those with a relatively high risk of failure. We found a relatively high risk of extinction following urbanization if the only action was reservation of core habitat; habitat creation actions performed better than enhancement actions; and cost‐effectiveness ranking changed depending on the consideration of uncertainty. Our results suggest that creation and maintenance of wetlands dedicated to L. raniformis is the only cost‐effective action likely to result in a sufficiently low risk of extinction. To our knowledge we are the first study to use Bayesian metapopulation viability analysis to explicitly incorporate parametric and demographic uncertainty into a cost‐effective evaluation of conservation actions. The approach offers guidance to decision makers aiming to achieve cost‐effective conservation under uncertainty.     

Parasitic wasps orient to green leaf volatiles

Summary Undamaged plants emit low levels of green leaf volatiles (GLVs), while caterpillar-damaged and artificially damaged plants emit relatively higher levels of certain GLVs. Female braconid parasitoids,Microplitis croceipes, oriented to both damaged plants and to individual GLVs in no-choice tests in a wind tunnel, but seldom oriented to undamaged plants. Female ichneumonid parasitoids,Netelia heroica, also oriented to individual GLVs in a wind tunnel. Males of both wasp species failed to orient to the GLVs. These data show that leaf-feeding caterpillars can cause the release of GLVs, and that parasitic wasps can respond to these odors by flying upwind (chemoanemotactic response), which brings the wasps to their caterpillar hosts. This supports the hypothesis that plants communicate with members of the third trophic level,i.e., plants under herbivore attack emit chemical signals that guide natural enemies of herbivores to sites of plant damage. In this interaction, the GLVs serve as tritrophic plant-to-parasitoid synomones. That parasitoids from two different wasp families oriented to GLVs suggests that the response may be widespread among the Hymenoptera.Mention of a commercial or proprietary product does not constitute an endorsement by the U.S. Department of Agriculture     

Potential for Electropositive Metal to Reduce the Interactions of Atlantic Sturgeon with Fishing Gear

Atlantic sturgeon (Acipenser oxyrhynchus) populations have been declared either endangered or threatened under the U.S. Endangered Species Act. Effective measures to repel sturgeon from fishing gear would be beneficial to both fish and fishers because they could reduce both fishery‐associated mortality and the need for seasonal and area closures of specific fisheries. Some chondrostean fishes (e.g., sturgeons and paddlefishes) can detect weak electric field gradients (possibly as low as 5 Μv/cm) due to arrays of electroreceptors (ampullae of Lorenzini) on their snout and gill covers. Weak electric fields, such as those produced by electropositive metals (typically mixtures of the lanthanide elements), could therefore potentially be used as a deterrent. To test this idea, we recorded the behavioral responses of juvenile Atlantic sturgeon (31–43 cm fork length) to electropositive metal (primarily a mixture of the lanthanide elements neodymium and praseodymium) both in the presence and absence of food stimuli. Trials were conducted in an approximately 2.5 m diameter × 0.3 m deep tank, and fish behaviors were recorded with an overhead digital video camera. Video records were subsequently digitized (x, y coordinate system), the distance between the fish and the electropositive metal calculated, and data summarized by compiling frequency distributions with 5‐cm bins. Juvenile sturgeon showed clear avoidance of electropositive metal but only when food was present. On the basis of our results, we conclude that the electropositive metals, or other sources of weak electric fields, may eventually be used to reduce the interactions of Atlantic sturgeon with fishing gear, but further investigation is needed. El Potencial del Metal Electropositivo para Reducir las Interacciones del Esturión Atlántico con Instrumentos de Pesca Bouyoucos, Bushnell & Brill 13–003     

The role of time and species identities in spatial patterns of species richness and conservation

Many conservation actions are justified on the basis of managing biodiversity. Biodiversity, in terms of species richness, is largely the product of rare species. This is problematic because the intensity of sampling needed to characterize communities and patterns of rarity or to justify the use of surrogates has biased sampling in favor of space over time. However, environmental fluctuations interacting with community dynamics lead to temporal variations in where and when species occur, potentially affecting conservation planning by generating uncertainty about results of species distribution modeling (including range determinations), selection of surrogates for biodiversity, and the proportion of biodiversity composed of rare species. To have confidence in the evidence base for conservation actions, one must consider whether temporal replication is necessary to produce broad inferences. Using approximately 20 years of macrofaunal data from tidal flats in 2 harbors, we explored variation in the identity of rare, common, restricted range, and widespread species over time and space. Over time, rare taxa were more likely to increase in abundance or occurrence than to remain rare or disappear and to exhibit temporal patterns in their occurrence. Space–time congruency in ranges (i.e., spatially widespread taxa were also temporally widespread) was observed only where samples were collected across an environmental gradient. Fifteen percent of the taxa in both harbors changed over time from having spatially restricted ranges to having widespread ranges. Our findings suggest that rare species can provide stability against environmental change, because the majority of species were not random transients, but that selection of biodiversity surrogates requires temporal validation. Rarity needs to be considered both spatially and temporally, as species that occur randomly over time are likely to play a different role in ecosystem functioning than those exhibiting temporal structure (e.g., seasonality). Moreover, temporal structure offers the opportunity to place management and conservation activities within windows of maximum opportunity.     

Main nutrient compounds in food bodies of Mexican <Emphasis Type="Italic">Acacia</Emphasis> ant-plants

Summary. Myrmecophytic plants use obligate ant mutualists as a constitutive indirect defence mechanism. These plants often produce cellular food bodies (FBs) to nourish their resident ants. Lipids, proteins, and even highly specialised compounds such as glycogen have been reported from FBs, but detailed chemical analyses of FB composition have so far been presented only for Southeast Asian Macaranga and Central American Piper myrmecophytes. Here we report the chemical composition of FBs of five myrmecophytic Acacia (Fabaceae) species from Mexico using HPLC (carbohydrates and proteins) and GC-MS (lipids). Feeding experiments revealed no hints on any use of external food sources by the inhabiting Pseudomyrmex ants. These ants obviously rely completely on FBs and extrafloral nectar provided by their hosts. The total content of nutrients in Acacia FBs was 15-25% of FB dry mass, being much lower than in Macaranga or Piper FBs. Proteins were dominating (8-14 % dm) in Acacia FBs and thus were present in higher amounts than in Macaranga FBs, yet in lower amounts than in Piper. Lipids contributed 1-9 % of dry mass, showing a lower proportion than in FBs of Macaranga or Piper. Carbohydrates made up 3-11 % dm, reaching in most Acacia species the same range as observed in Macaranga and in Piper FBs. Water content was 18-24 % of FB fresh mass, and structural tissue obviously made up a much higher proportion in Acacia FBs than in Macaranga or Piper FBs. Both characters might represent an adaptation to producing FBs unprotected at the leaf tips under dry conditions. Acacia FBs contain all amino acids and all fatty acids that are considered essential for insects, and their contents of lipids and proteins are higher than in the leaves from which they are ontogenetically derived. This indicates a putatively adaptive enrichment of nutritionally valuable compounds in structures functioning as ant-food.     

Examining the uncertain origin and management role of martens on Prince of Wales Island,Alaska

Conservation biologists are generally united in efforts to curtail the spread of non‐native species globally. However, the colonization history of a species is not always certain, and whether a species is considered non‐native or native depends on the conservation benchmark. Such ambiguities have led to inconsistent management. Within the Tongass National Forest of Alaska, the status of American marten (Martes americana) on the largest, most biologically diverse and deforested island, Prince of Wales (POW), is unclear. Ten martens were released to POW in the early 1930s, and it was generally believed to be the founding event, although this has been questioned. The uncertainty surrounding when and how martens colonized POW complicates management, especially because martens were selected as a design species for the Tongass. To explore the history of martens of POW we reviewed other plausible routes of colonization; genetically and isotopically analyzed putative marten fossils deposited in the late Pleistocene and early Holocene to verify marten occupancy of POW; and used contemporary genetic data from martens on POW and the mainland in coalescent simulations to identify the probable source of the present‐day marten population on POW. We found evidence for multiple routes of colonization by forest‐associated mammals beginning in the Holocene, which were likely used by American martens to naturally colonize POW. Although we cannot rule out human‐assisted movement of martens by Alaskan Natives or fur trappers, we suggest that martens be managed for persistence on POW. More generally, our findings illustrate the difficulty of labeling species as non‐native or native, even when genetic and paleo‐ecological data are available, and support the notion that community resilience or species invasiveness should be prioritized when making management decisions rather than more subjective and less certain conservation benchmarks.