Effects of macroalgal blooms on carbon and nitrogen biogeochemical cycling in photoautotrophic sediments: an experimental mesocosm

The effects of floating macroalgae (250 g DW m⁻²) on photoautotrophic microbenthos were studied in a flow-through mesocosm with a parallel mesocosm without macroalgae serving as Control. Vertical microprofiles of O₂ at the sediment-water interface showed a immediate and complete suppression of photosynthetic activity of microphytobenthos (MPB) under the macroalgal canopy, resulting in a shift of benthic metabolism from autotrophic to heterotrophic. MPB abundance and chlorophyll a content decreased and a change from a diatom-dominated to cyanobacteria-dominated community was observed. Inorganic nitrogen nutrients´ concentrations increased in the porewater as a result of the inhibition of MPB nutrient demand, leading to an increase in net ammonification and anaerobic consumption rates. No organic matter transfer from macroalgae to the sediment was detected, resulting in a net consumption of the carbon and nitrogen stored in the sediment. In consequence, sediment was progressively impoverished in nitrogen, reducing sediment nutrient regeneration.     

Early evaluation of coastal nutrient over-enrichment: new procedures and indicators

Recent studies have provided compelling evidence for an accelerated anthropogenic impact on coastal systems, resulting in intense inputs of materials and nutrients from the continent. This has led scientists and policymakers to encourage the implementation of monitoring programmes, which have resulted in the multiplicity of datasets. However surprisingly, only a few attempts have been made to couple observations with statistical and mathematical tools to detect, as soon as the data become available perturbations in coastal systems. Here, we propose new mathematical procedures to evaluate the state of a system, based on the building of relative reference state and indicators of nutrient over-enrichment. The techniques were tested in some French coastal systems using data from the programme SOMLIT. Applied to this dataset, the multivariate procedures rapidly identified and evaluated anthropogenic nutrient anomalies from the continent on three sites (Wimereux, Roscoff and Villefranche-sur-Mer) from 1997 onwards.     

三维衰减模型在地震动和地震灾害评估中应用的实例

用于表征估计地震动的衰减关系经常忽略地球高度可变的三维速度和衰减结构的细节。日益增多的可用衰减模型可用于使预期地震动更为精确。首先,我进行了一些测试以察看像地壳衰减、上地幔衰减和地壳厚度等几个参数变化的影响。然后,使用最近中东地区地壳和上地幔的衰减模型的结果提供一个具体例子。发现相同事件不同方向记录的1Hz谱加速度变化了30％～40％。因为区域整体变化性预计会更高,这种影响太显著了,在地震动估计和地震灾害评估中不能忽视。这就有可能要计算在广泛使用的一维衰减关系中没有考虑的较小尺度的一些振幅变化。     

塔拉哈西首都圈36英尺Hobas主管道爆裂的修复

2008年8月,继Tropical Storm Fay之后,城市圈一段36英尺主管道又发生了三处破裂。这段主管道使用的是Hobas管,位于城市圈巷道下面。巷道属于佛罗里达州的运输部（FDOT）,是塔拉哈西最繁忙的路段。管道破裂采用非开挖修复以加快施工进度,减少对巷道的干扰,并最大限度修复管道。由于Hobas管以前没有破裂过,为了减小对FDOT的干扰,先采用一个试点对管道破裂修复可行性进行了验证。结果在90分钟内完成了280英尺,平均每分钟3英尺,施工过程没有造成干扰。从试点获得的经验在剩余管道设计和维修过程中得到了应用。     

暗星云DC 337.7—4.0的CO成图观测

使用4米毫米波望远镜和中澳合作研制的高分辨率声光频谱仪完成了暗星云DC337.7—4.0的CO分子J=1-0谱线的成图观测。数据处理包含有消干扰步骤。获得云的平均辐射温度为7.3K,平均视向速度3.7km/s,平均谱线半宽1.1km/s。观测结果没显示出云中有恒星形成活动的迹象。     

An experimental approach to investigate mercury species transformations under redox oscillations in coastal sediments

This work describes a laboratory experiment designed to unravel mercury species reactivity in superficial coastal sediments oscillating between oxic and anoxic conditions. The experimental set-up has been applied to a sediment slurry from the Arcachon Bay (France) to follow the evolution of both naturally occurring (i.e. endogenous) and isotopically enriched added mercury species (i.e. exogenous, 1??IHg and 2?1MMHg) at environmental levels. The transformation and partition between the different phases (aqueous, solid and gaseous) of the endogenous and exogenous mercury species (inorganic Hg (IHg), monomethyl Hg (MMHg), elemental Hg (Hg?) and dimethyl Hg (DMHg)) have been investigated by isotopic speciation methods throughout the experiment. The results demonstrate that the experimental approach is able to promote sediment redox oscillations and to simultaneously follow the biogeochemical fate of naturally occurring or added mercury species. Experimentally driven redox transition events were found to significantly enhance the aqueous Hg species concentrations, while the MMHg burden is not greatly affected. Indeed, during the anoxic-oxic transition, while aqueous endogenous IHg and MMHg exhibited a two-fold increase, aqueous exogenous IHg and MMHg increased 7 and 4 times, respectively. Transient increases of the net IHg methylation were recorded during the redox transitions with the largest increase of the MMHg contents (factor 1.8) observed during the oxic-anoxic transition. High resolution in situ redox experiments have not been performed up to now, therefore the developed experimental set-up provides novel insights in both the influence of redox conditions on Hg methylation/demethylation and adsorption/desorption processes and kinetics in superficial sediments.     

Colloidal complexed silver and silver nanoparticles in extrapallial fluid of Mytilus edulis

Metal transport in mollusk extrapallial fluid (EPF) that acts as a "bridge" between soft tissues and shell has surprisingly received little attention until now. Using ultrafiltration and radiotracer techniques we determined silver concentrations and speciation in the EPF of the blue mussel Mytilus edulis after short-term uptake and depuration laboratory experiments. Radiolabelled silver ((11?m)Ag) was used in dissolved or nanoparticulate phases (AgNPs < 40 nm), with a similar low Ag concentration (total radioactive and cold Ag ~0.7 μg/L) in a way that mussels could uptake radiotracers only from seawater. Our results indicated that silver nanoparticles were transported to the EPF of blue mussels at a level similar to the Ag ionic form. Bulk activity of radiolabelled silver in the EPF represented only up to 7% of the bulk activity measured in the whole mussels. The EPF extracted from mussels exposed to both treatments exhibited an Ag colloidal complexed form based on EPF ultrafiltration through a 3 kDa filter. This original study brings new insights to internal circulation of nanoparticles in living organisms and contributes to the international effort in studying the potential impacts of engineered nanomaterials on marine bivalves which play an essential role in coastal ecosystems, and are important contributors to human food supply from the sea.     

The non-native seaweed Asparagopsis armata supports a diverse crustacean assemblage

This is the first study describing the crustacean fauna associated to Asparagopsis armata, a non-native, red seaweed widely distributed along western Mediterranean coasts. First found in Australia and New Zealand, it was introduced naturally through the Strait of Gibraltar and rapidly spread out. A one-year spatio-temporal study (Feb 08-Feb 09) was carried out in the Strait of Gibraltar to characterize the spatio-temporal patterns of the associated crustacean fauna. Maximum biomass of A. armata was measured during April-June, whereas the maximum crustacean abundances were registered from June-October. In total 41 crustacean species were identified. The caprellid Caprella penantis, traditionally associated to non-polluted areas, was more abundant on Tarifa Island (higher values of dissolved oxygen and pH) than in Algeciras (lower oxygen and pH). The gammarid Podocerus variegatus was dominant in Algeciras Bay while Hyale schmidti and Apherusa mediterranea were the most abundant on Tarifa Island. Among isopods, Synisoma nadejda was only found on Tarifa Island. When compared with literature of native algae of the intertidal and shallow sublittoral, the species richness of associated crustaceans was similar in A. armata and the natives. Very little is known about the influence of this algae on altering marine communities, so complete faunistic studies dealing with other groups such as polychaetes or molluscs are necessary to properly address biogeographical, ecological and management programmes dealing with this non-native species.     

滨海湿地水和物质的运移

滨海湿地系统的消长和稳定取决于两种过程的物质平衡:①是河流携带沉积物的加积使盐沼和湿地向上和向海方向进积;②是海平面上升和沼泽地区的压实沉降以及海洋通过潮沟系统对湿地的侵蚀作用不断地产生着可容纳空间.二者的互动构成了滨海湿地复杂的演化历史.重点阐述了三角洲河流泥沙输运、洪水运移、潮汐作用、潮沟系统发育等对湿地的影响.     

Verification of mid-ocean ballast water exchange using naturally occurring coastal tracers

We examined methods for verifying whether or not ships have performed mid-ocean ballast water exchange (BWE) on four commercial vessels operating in the Pacific and Atlantic Oceans. During BWE, a ship replaces the coastal water in its ballast tanks with water drawn from the open ocean, which is considered to harbor fewer organisms capable of establishing in coastal environments. We measured concentrations of several naturally occurring chemical tracers (salinity, six trace elements, colored dissolved organic matter fluorescence and radium isotopes) along ocean transects and in ballast tanks subjected to varying degrees of BWE (0-99%). Many coastal tracers showed significant concentration changes due to BWE, and our ability to detect differences between exchanged and unexchanged ballast tanks was greatest under multivariate analysis. An expanded dataset, which includes additional geographic regions, is now needed to test the generality of our results.