Relocation effects of dredged marine sediments on mercury geochemistry: Venice lagoon,Italy     

Seunghee Han  Joris Gieskes  Anna Obraztsova  Dimitri D. Deheyn  Bradley M. Tebo 《Estuarine, Coastal and Shelf Science》2011

Understanding the biogeochemical process of Hg is critical in the overall evaluation of the ecological impacts resulting from the reuse of Hg-contaminated dredged sediment. Sediment banks (V1 and V2) were constructed with freshly dredged sediments from a navigational channel in Venice Lagoon, Italy, with the goal of clarifying potential differences in the biogeochemistry of Hg between the reused dredged sediments and those from surrounding sites (SS1 and S2). Toward this purpose, Hg and monomethylmercury (MMHg) concentrations, and Hg methylation rates (MMRs) in the surface 2.5 cm sediments were monitored, along with ammonium, iron, sulfate and sulfide concentrations in the pore waters of banks and surrounding sites from November 2005 to February 2007. Pore water analyses indicate that the bank sediments are characterized by lower levels of sulfate and iron, and by higher levels of ammonium and sulfide compared to the surrounding sediments. With respect to Hg speciation, the fractions of MMHg in total Hg (%MMHg/Hg) and the MMRs were significantly lower in the bank V1 compared to those in the reference site SS1, whereas the %MMHg/Hg and the MMRs were similar between V2 and S2. A negative correlation is found between the logarithm of the particle-water partition coefficient of Hg and the MMR, indicating that the reduced MMRs in V1 are caused by the limited concentrations of dissolved Hg. Organic matter appears to play a key role in the control of MMR via the control of Hg solubility.  相似文献   

青海湖盆地史前狩猎采集人群的石料利用策略研究     

申旭科  王建  姚娟婷  夏欢  王倩倩  任晓燕  Olaf Joris  张东菊 《第四纪研究》2020,(2):525-537

史前人类向青藏高原扩散的过程和适应高海拔缺氧环境的机制是多学科关注的热点科学问题.青海湖盆地是青藏高原旧石器-中石器时代遗址分布最为丰富的区域,对这些遗址出土的石制品原料的分析有助于深入理解青藏高原史前狩猎采集人群的石料开发策略、人群迁徙和交流联系.青海湖盆地151遗址出土的928件石制品的石料研究分析显示,处于末次冰消期的下文化层的石制品以近源的石英和石英岩为主要原料,而处于全新世早中期的上文化层在同类型近源石料仍占主体地位的情况下,开始出现较高比例和多样化的优质硅质石料,并且主要用于生产细石器.野外调查和查阅地质资料均未发现青海湖盆地内有151遗址中出现的同类型优质硅质石料产出,推测其来自远距离搬运.青海湖盆地内其他8个末次冰消期至全新世中期遗址的3269件石制品石料分析结果显示,与151遗址同类型的远源优质硅质石料在全新世早期开始在盆地内的遗址中出现.这一结果表明青海湖盆地末次冰消期古人类活动强度和范围有限,全新世早中期古人类受到全新世大暖期气候变好和周边地区农业人群兴起挤压活动空间的双重影响,在高原上的活动范围和强度大大增加,伴随着开始有意识地开发优质石料,较频繁地进行远距离迁移和人群交流.远源优质硅质石料的产地可能位于北祁连山区和青藏高原上的陆相火山岩区,需要未来更深入的研究揭示.该研究为深入理解青藏高原古人类的高海拔环境适应策略和移动模式提供了重要材料,为理解史前人类向高原扩散的机制提供了重要信息.  相似文献   

The impact of land use change and check‐dams on catchment sediment yield     

Carolina Boix‐Fayos  Joris de Vente  María Martínez‐Mena  Gonzalo G. Barberá  Víctor Castillo 《水文研究》2008,22(25):4922-4935

Extensive land use changes have occurred in many areas of SE Spain as a result of reforestation and the abandonment of agricultural activities. Parallel to this the Spanish Administration spends large funds on hydrological control works to reduce erosion and sediment transport. However, it remains untested how these large land use changes affect the erosion processes at the catchment scale and if the hydrological control works efficiently reduce sediment export. A combination of field work, mapping and modelling was used to test the influence of land use scenarios with and without sediment control structures (check‐dams) on sediment yield at the catchment scale. The study catchment is located in SE Spain and suffered important land use changes, increasing the forest cover 3‐fold and decreasing the agricultural land 2·5‐fold from 1956 to 1997. In addition 58 check‐dams were constructed in the catchment in the 1970s accompanying reforestation works. The erosion model WATEM‐SEDEM was applied using six land use scenarios: land use in 1956, 1981 and 1997, each with and without check‐dams. Calibration of the model provided a model efficiency of 0·84 for absolute sediment yield. Model application showed that in a scenario without check dams, the land use changes between 1956 and 1997 caused a progressive decrease in sediment yield of 54%. In a scenario without land use changes but with check‐dams, about 77% of the sediment yield was retained behind the dams. Check‐dams can be efficient sediment control measures, but with a short‐lived effect. They have important side‐effects, such as inducing channel erosion downstream. While also having side‐effects, land use changes can have important long‐term effects on sediment yield. The application of either land use changes (i.e. reforestation) or check‐dams to control sediment yield depends on the objective of the management and the specific environmental conditions of each area. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Sulfide and iron control on mercury speciation in anoxic estuarine sediment slurries   总被引：2，自引：0，他引：2  

Seunghee Han  Anna Obraztsova  Patrizia Pretto  Dimitri D. Deheyn  Joris Gieskes  Bradley M. Tebo   《Marine Chemistry》2008,111(3-4):214-220

In order to understand the role of sulfate and Fe(III) reduction processes in the net production of monomethylmercury (MMHg), we amended anoxic sediment slurries collected from the Venice Lagoon, Italy, with inorganic Hg and either potential electron acceptors or metabolic byproducts of sulfate and Fe(III) reduction processes, gradually changing their concentrations. Addition of sulfide (final concentration: 0.2–6.3 mM) resulted in an exponential decrease in the sulfate reduction rate and MMHg concentration with increasing concentrations of sulfide. Based on this result, we argue that the concentration of dissolved sulfide is a critical factor controlling the sulfate reduction rate, and in turn, the net MMHg production at steady state. Addition of either Fe(II) (added concentration: 0–6.1 mM) or Fe(III) (added concentration: 0–3.5 mM) resulted in similar trends in the MMHg concentration, an increase with low levels of Fe additions and a subsequent decrease with high levels of Fe additions. The limited availability of dissolved Hg, associated with sulfide removal by precipitation of FeS, appears to inhibit the net MMHg production in high levels of Fe additions. There was a noticeable reduction in the net MMHg production in Fe(III)-amended slurries as compared to Fe(II)-amended ones, which could be caused by a decrease in the sulfate reduction rate. This agrees with the results of Hg methylation assays using the enrichment cultures of anaerobic bacteria: whereas the enrichment cultures of sulfate reducers showed significant production of MMHg (4.6% of amended Hg), those of Fe(III), Mn(IV), and nitrate reducers showed no production of MMHg. It appears that enhanced Fe(III)-reduction activities suppress the formation of MMHg in high sulfate estuarine sediments.  相似文献   

Simulating stochastically excited oscillations: The mode lifetime of ξ Hya     

Dennis Stello  Hans Kjeldsen  Timothy R. Bedding  Joris De Ridder  Conny Aerts  Fabien Carrier  SØren Frandsen 《Solar physics》2004,220(2):207-228

The discovery of solar-like oscillations in the giant star ξ Hya (G7 III) was reported by Frandsen et al. (2002). Their frequency analysis was very limited due to alias problems in the data set (caused by single-site observations). The extent to which the aliasing affected their analysis was unclear due to the unknown damping time of the stellar oscillation modes. In this paper we describe a simulator created to generate time series of stochastically excited oscillations, which takes as input an arbitrary window function and includes both white and non-white noise. We also outline a new method to compare a large number of simulated time series with an observed time series to determine the damping time, amplitude, and limited information on the degree of the stochastically excited modes. For ξ Hya we find the most likely amplitude to be ∼ 2 m s⁻¹, in good agreement with theory (Houdek and Gough, 2002), and the most likely damping time to be ∼ 2 days, which is much shorter than the theoretical value of 15–20 days calculated by Houdek and Gough (2002).  相似文献   

A consistent geochemical modelling approach for the leaching and reactive transport of major and trace elements in MSWI bottom ash     

Joris J. Dijkstra  Johannes C.L. Meeussen  Hans A. Van der Sloot  Rob N.J. Comans 《Applied Geochemistry》2008

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Halide systematics in interstitial waters of ocean drilling sediment cores     

Joris M. Gieskes  Chris Mahn 《Applied Geochemistry》2007

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Stellar dynamics in young clusters: the formation of massive runaways and very massive runaway mergers     

Dany Vanbeveren  Houria Belkus  Joris Van Bever  Nicki Mennekens 《Astrophysics and Space Science》2009,324(2-4):271-276

In the present paper we combine an N-body code that simulates the dynamics of young dense stellar systems with a massive star evolution handler that accounts in a realistic way for the effects of stellar wind mass loss. We discuss two topics.

1. The formation and the evolution of very massive stars (with masses >120 M_⊙) is followed in detail. These very massive stars are formed in the cluster core as a consequence of the successive (physical) collisions of the 10–20 most massive stars in the cluster (this process is known as ‘runaway merging’). The further evolution is governed by stellar wind mass loss during core hydrogen and core helium burning (the WR phase of very massive stars). Our simulations reveal that, as a consequence of runaway merging in clusters with solar and supersolar values, massive black holes can be formed, but with a maximum mass ≈70 M_⊙. In low-metallicity clusters, however, it cannot be excluded that the runaway-merging process is responsible for pair-instability supernovae or for the formation of intermediate-mass black holes with a mass of several 100 M_⊙.
2. Massive runaways can be formed via the supernova explosion of one of the components in a binary system (the Blaauw scenario), or via dynamical interaction of a single star and a binary or between two binaries in a star cluster. We explore the possibility that the most massive runaways (e.g. ζ Pup, λ Cep, BD+43°3654) are the product of the collision and merger of two or three massive stars.

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The pattern speed of the bar in NGC 4596     

Joris Gerssen  Konrad Kuijken  Michael R. Merrifield 《Monthly notices of the Royal Astronomical Society》1999,306(4):926-930

The pattern speed is a defining parameter of any barred galaxy. A large number of model-dependent techniques have therefore been developed to derive the pattern speed. However, the only model-independent technique for measuring this quantity – the Tremaine–Weinberg method – has hitherto been applied to just one case, the SB0 galaxy NGC 936. In this paper, we apply the technique to a second system, the SBa galaxy NGC 4596. The resulting estimate for the pattern speed is Ω_p=52±13 km s⁻¹ kpc⁻¹. This result is corroborated by a spectrum obtained along the major axis of the bar in this system. The corotation radius associated with this pattern speed lies just beyond the end of the bar indicating a fast bar. Combining the bar major-axis spectra with data obtained from a Hubble Space Telescope WFPC2 image, we also find strong evidence for a nuclear disc.  相似文献   

Sediment cascades and the entangled relationship between human impact and natural dynamics at the pre-pottery Neolithic site of Göbekli Tepe,Anatolia     

Moritz Nykamp  Fabian Becker  Ricarda Braun  Nadja Pöllath  Daniel Knitter  Joris Peters  Brigitta Schütt 《地球表面变化过程与地形》2021,46(2):430-442

This study presents a meta-analysis of radiocarbon ages for the environs of Göbekli Tepe – one of the oldest monumental structures worldwide – using cumulative probability functions to diachronically assess phases of geomorphodynamic activity as controlled by natural or anthropogenic drivers. We employ sediment cascades as a heuristic framework to study the complex responses of the geomorphological system to various triggers at local to supra-regional scales. Possible triggers include climatic variability as documented by supra-regional hydroclimatic proxy data, regional demographic trends, and local to regional socioeconomic developments such as the emergence of sedentism or the introduction and dispersal of livestock herding. Our results show that phases of intensified geomorphodynamic activity occurred between ca. 7.4–7.0 and 5.8–3.3 ka BP. These phases roughly coincide with phases of population growth in southern Turkey and climatic variations in Turkey and the Levant. The phase between ca. 5.8–3.3 ka BP also corresponds to the time when organized agriculture and the seeder plough were introduced. Also, the identified phases are in agreement with the general trend of varying geomorphodynamic activity in the Eastern Mediterranean as driven by human impact and climatic change. However, neither the Younger Dryas–Holocene transition nor the development of herding during the Pre-Pottery Neolithic left a clear signature. We demonstrate how the different depositional environments in the studied landscape compartments vary with respect to their spatiotemporal coverage and discuss challenges when trying to understand processes that once shaped landscapes of past societies. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献