Comparison of three procedures (single,sequential and kinetic extractions) for mobility assessment of Cu,Pb and Zn in harbour sediments

The mobility of Cu, Pb and Zn in harbour sediments was investigated using single, sequential and kinetic extraction techniques. Each type of extraction provides different information on the mobility of these elements in the environment. The single HCl extraction assesses general mobility, the sequential extraction assesses geochemical partitioning and kinetic extraction allows quickly and slowly mobilized elements to be identified. Kinetic extraction also allows the influence of extraction duration to be assessed. The results presented in this paper highlight the complementary information provided by different types of mobility studies. The lack of correlation between element mobility and total metal concentration emphasises the inadequacy of using total metal concentrations in risk assessment.     

Toward a climate mobilities research agenda: Intersectionality,immobility, and policy responses

Mobility is a key livelihood and risk management strategy, including in the context of climate change. The COVID-19 pandemic has reinforced long standing concerns that migrant populations remain largely overlooked in economic development, adaptation to climate change, and spatial planning. We synthesize evidence across multiple studies that confirms the overwhelming preponderance of in-country and short distance rather than international migration in climate change hotspots in Asia and Africa. The emerging findings highlight the critical importance of addressing immobility and the intersecting social determinants that influence who can move and who cannot in development policy. This evidence suggests a more focused climate mobilities research agenda that includes understanding multiple drivers of mobility and multi-directional movement; intersecting social factors that determine mobility for some and immobility for others; and the implications for mobility and immobility under climate change and the COVID-19 recovery.     

Speciation and mobility of heavy metals in mud in coastal reclamation areas in Shenzhen,China

Coastal reclamation has been carried out along the coastal areas near Shenzhen, China in a large scale since 1980s by dumping fill materials over the marine mud at the sea bottom. Usually the area to be reclaimed is drained first and some of the mud is air-dried for a few weeks before it is buried by fill. After reclamation, the terrestrial groundwater, which is relatively acidic and with high dissolved oxygen, gradually displaces the seawater, which is alkaline with high salinity. The changes in the burial conditions of mud and the properties of the pore water in the mud may induce the release of some heavy metals into the mud. Field survey confirms that the pH and salinity of the groundwater in the reclamation site are much lower than the seawater. Chemical analyses of mud and groundwater samples collected from the reclamation sites reclaimed in different years indicate that most of the heavy metals in the mud decrease gradually with time, but the heavy metals in the groundwater are increased. The release of heavy metals into pore water due to reactivation of heavy metals in the mud is of environmental concern. To understand why some of the heavy metals can be released from the mud more easily than others, a sequential extraction method was used to study the operationally determined chemical forms of five heavy metals (Cu, Ni, Pb, Zn, and Cd) in the mud samples. Heavy metals can be presented in five chemical forms: exchangeable, carbonate, Fe–Mn oxide, organic, and residual. Ni and Pb were mainly associated with the Fe–Mn oxide fraction and carbonate fraction; Zn was mainly associated with organic fraction and Fe–Mn oxide fraction, while Cu and Cd were associated with organic fraction and carbonate fraction, respectively. If the residual fraction can be considered as an inert phase of the metal that cannot be mobilized, it is the other four forms of heavy metal that cause the noticeable changes in the concentration of heavy metals in the mud. On the basis of the speciation of heavy metals, the mobility of metals have the following order: Pb (36.63%) > Cu (31.11%) > Zn (20.49%) > Ni (18.37%) > Cd (13.46%). The measured metal mobility fits reasonably well with the degree of concentration reduction of the metals with time of burial observed in the reclamation site.     

盐湖形成过程中银的迁移形式及富集条件

本文研究了盐湖形成过程中银的迁移形式及富集条件．在热液中银主要以Ａｇ（ＨＳ）￣－＿２·Ａｇ（ＮＨ３）·ＡｇＣｌ络合物形式迁移；在表生条件下银主要以Ａｇ（Ｓ２Ｏ３）络合物形式迁移．它们在盐湖中被演化为ＡｇＣｌ络合物，由于湖水大量蒸发、盐类大量结晶析出，导致盐湖卤水中银的富集．     

Heavy metal distribution in karst soils from Croatia and Slovakia

With the use of the optimised three-step BCR sequential-extraction procedure it was possible to assess the mobility of selected elements in soil profiles from Croatian and Slovakian karst terrains. The soils in the Croatian karst were enriched in Cr, Ni, V, Mn, Cu, Cd and Mo, while soils from the Slovak Karst had high Pb and Zn concentrations. It was determined that the elements were most readily mobilised from the topsoil and the degree of mobility decreased with depth. Cr and Ni were mainly bound to the residual fraction, and Pb in the oxidisable fraction. Cu mobility was high in samples treated with agrochemicals throughout the soil profile.     

Évaluation de la mobilité des métaux dans les sédiments fluviaux du bassin de la Vire (Normandie,France) par extractions simples ou séquentielles

This work compares the quantities of labile metals removed from the Vire River (Normandy) sediments by a sequential extraction procedure to those liberated by single leaches (Mg(NO₃)₂, HCl and EDTA). Compared to the other extractions, Mg(NO₃)₂ underestimated the mobility results. The sequential procedure was the most aggressive, except for Ca and Pb. The hypothetic correlation between quantities of an element removed by single leaches and its fractionation in the sediment according to the sequential procedure was not satisfying. Finally, it should be underlined that enrichments of Cd, Pb and Zn were noticed in the Vire sediments. To cite this article: L. Leleyter, F. Baraud, C. R. Geoscience 337 (2005).     

Contributions respectives des courants et de la houle dans la mobilité sédimentaire d'une plate-forme interne estuarienne. Exemple : le seuil interinsulaire,au large du pertuis d'Antioche,France

This paper investigates the relative influence of waves, wind-induced current and tidal current on the sediment mobility of a macro-tidal environment belonging to the inner shelf seaward of the ‘pertuis Charentais’ (France). This study, mainly based on three-week hydrodynamic in-situ measurements, shows that, for a water depth of 23 m, the swell (rather than wind waves) orbital velocity is large enough to initiate the motion of medium sands that are then transported by currents. Estimations show that medium sand of 0.2 mm is transported during 92% of the measurements, whereas coarse sand and gravel move sporadically, during storm, synchronously with spring tides. Further more, bedload fluxes appear strongly larger when waves are taken into account (370 times larger for 0.2-mm sands). To cite this article: D. Idier et al., C. R. Geoscience 338 (2006).     

Internal architecture and mobility of tidal sand ridges in the East China Sea

On the basis of bathymetric and seismic data and data from piston cores collected by the Chinese–French marine geology and geophysics investigation of 1996, we discuss the internal architecture and mobility of tidal sand ridges in the East China Sea (ECS). We characterized the sand ridges on the middle to outer shelf of the ECS as tide-dominated sand ridges with southwest dipping beds, indicating that the regional net sediment transport is toward the southwest. As the sand ridges gradually migrate toward the southwest, new sand ridges are continually replacing old ones, and several generations of sand ridges have developed in the study area.     

新冠肺炎疫情精准防控的时空间行为地理学研究框架

面向新冠肺炎疫情精准防控的重大需求,时空间行为地理学可以发挥其独特的学科价值。以时间地理学、行为主义地理学、移动性地理学等时空间行为的地理学经典理论为基础,以时空路径表达、活动的复杂情境分析、风险感知地图分析为核心方法,以时空间行为风险评估、居民时空间行为规划与引导、心理情绪引导与智慧社区治理为重点应用方向,尝试搭建疫情精准防控的时空间行为地理学研究框架。未来时空间行为研究应该立足人本导向、流动性导向和应用导向,突出时空间行为地理学在城市规划、城市管理、居民服务等方面的应用价值。