The effect of oxidation and acidification on the speciation of heavy metals in sulfide-rich freshwater sediments using a sequential extraction procedure

The speciation of metals in a contaminated, anoxic, sulfide-rich, freshwater sediment was determined experimentally, using a sequential extraction procedure based on the method of Tessier et al. Taking into account the advantages and disadvantages of sequential extractions, the applied methodology allowed the investigation of the influence of aeration and acidification on the distribution of various metals in the sediment. Aeration caused Zn and Cd to be released from sulfides. Carbonates were partly dissolved by the oxidation process, causing mobilisation of Ca. Fe became less mobile owing to a stronger binding to organic matter. The speciation of K, Al, Ni, Pb and Mn and to a lesser extent of Cu was not affected by aeration. As a result of acidification of the aerated sediment, Ca, Mn, Ni, Zn and Cd became more mobile owing to the dissolution of carbonates.     

Dissolution kinetics of heavy metals in Dutch carbonate- and sulfide-rich freshwater sediments

In two sulfide-rich freshwater sediments from the Biesbosch and Kromme Rijn River in the Netherlands differing in carbonate content and acid volatile sulfide (AVS) content, metal and sulfide dissolution kinetics were studied at different acid concentrations by varying both the procedure of acid addition and the extraction time. The establishment of equilibrium was monitored by measuring the pH in time, which reached a near constant value. The equilibrium pH was reached quickly when large amounts of acid were added and slowly when small amounts of acid were added. This observation was confirmed by the yield of extracted metals after either a 45-min or 24-h extraction over a pH range from 0 to 5. The pH factor seemed to be of more influence than time for the dissolution of metals. The amount of extracted metals was highly dependent on the metal itself due to its physico-chemical behavior. Although the sediments studied varied in carbonate content, acid volatile sulfide (AVS), and total metal content, the extracted fraction of metals compared with their total content in the sediment was similar for most metals. Finally, the AVS content as well as the ratio of simultaneously extracted metals (SEM; sum of Cd, Cu, Ni, Pb, and Zn) to AVS decreased with increasing pH. Because the SEM to AVS ratio may be used to set environmental quality criteria for the sediment compartment, this observation is of significance.     

盐池湾国家级自然保护区景观格局演变分析

景观格局演化是土地利用/覆盖变化和景观破碎化在时空上的直接表现,其时空演变过程和影响因素分析,对了解区域生态环境变化、维持生态系统平衡及可持续发展具有重要意义。该文基于1996、2006和2017年3期遥感影像,结合景观格局分析方法,对盐池湾国家级自然保护区近20年景观格局时空演变及影响因素进行分析。结果表明:1996-2017年盐池湾国家级自然保护区沼泽草地、沼泽地、冰川及永久积雪和沙地面积增幅分别为42.05%、63.24%、259.03%和87.62%,天然牧草地、河流水面和裸岩石砾地面积降幅分别为20.15%、24.33%和22.39%;斑块密度、最大斑块指数减小,斑块形状趋于简单,连通性增强,景观的破碎化程度降低;降水与冰川及永久积雪和裸岩石砾地呈显著相关(P<0.05),气温与各土地覆被类型之间关系不显著(P>0.05)。在自然和人为活动共同作用下,盐池湾国家级自然保护区的景观格局向连通性高、破碎化程度降低的方向演变。     

Simultaneous extraction of bromide, chloride, fluoride and sulfate from soils, waste- and building materials

The simultaneous extraction of bromide, chloride, fluoride and sulfate was studied in soils, waste- and building materials. Acid, neutral and alkaline extractants were used; 0.01 mol l(-1) H(3)PO(4), milliQ-water and 0.01 mol l(-1) NaOH, respectively. The extracts were analysed by ion chromatography and ion selective electrode. Extracted concentrations were compared with the amount obtained by an alkaline smelt, as an approximation of the total extractable content. The results indicate that there is a significant difference in extraction behaviour between waste- and building materials and soils. Bromide and chloride were in general completely extracted from the former solid materials, but less than 10% and 50%, respectively, from soils. Fluoride is strongly bound in all investigated samples; less than 10% of the total content was extracted with any of the three extractants. The fraction of extracted sulfate varied between 4 and 87% of the total content, and was in general larger in waste- and building materials than in soils. Differences in extracted concentration between the 3 extractants occurred mainly for fluoride and sulfate. Extracted bromide was similar with all three extractants and extracted chloride showed differences for the various soil samples only. Increasing the NaOH concentration up to 1 mol l(-1) resulted mainly in an increase of extracted amount of fluoride and for soils also in extracted amounts of bromide and sulfate. Although, the results show that the composition of the solid material strongly influences the final pH of the extract and the extracted amount of investigated anions, application of Milli-Q water as an extractant might be a very fruitful option within the development of the Dutch Building Materials Decree.