Changes to cadmium associations in canal sediments on drying and oxidation

The mainly 19th Century canal system in the UK, largely managed by British Waterways, has been increasingly brought back into operation over the last few decades, and is now widely used for both leisure, and, increasingly, transport. Both initial and routine dredging of the canal sediment is carried out and these sediments are generally disposed of to land. Because many of the canals were connected with primary industries, their sediments can locally be significantly contaminated with heavy metals, and the behaviour of these metals under differing redox conditions, when introduced into a new environment （i.e., on land） is of importance for environmental risk-assessment purposes. Canal sediments are often rich in sulfidic mineral phases, and we have attempted to quantify the influence of these sulfidic phases on the release and retention of metals in dredged canal sediments, using a combination of traditional chemical techniques （e.g. sequential extraction） and X-ray absorption spectroscopy （XAS）. Sediment samples have been collected from urban fresh-water canals, one in the British Midlands and one in Northern France. It appears from XAS that Cd is largely associated with oxygen in air-dried sediment, and with sulphur in vacuum-dried sediment.     

Influence of humic acid on bioavailability of heavy metals in sediments

The mimetic ocean environment and chemical method were used to research the bioavailability effect of humic acid on five heavy metals in sediment, including Cd, Cu, Zn, Pb and Ni. The sediment was separated into four containers with artificial seawater, and each of them had different concentrations of humic acid. The values of concentrations covered the whole range found in natural sediment （0.1%-10%）. According to the 48 hours LC50 of clam and distribution coefficient, metals were added in artificial seawater, and their speciation was determined at first and then after two days＇ incubation. It was found the bioavailability of heavy metals was reduced in the presence of humic acid. The obvious negative effect on Zn was observed, but the influence on Cd was not remarkable. In addition, the contents of Pb and Ni increased obviously in organic phase, and they are correlative with the concentrations of humic acid.     

Threshold velocity for wind erosion: the effects of porous fences

Porous fence is a kind of artificial windbreak that has many practical applications. The threshold wind velocities at different distances downwind from porous fences were measured and the corresponding characteristics of particle movement observed to assess their shelter effect. It is found that the fence’s porosity is the key factor that determines the resulting shelter effect. The area near a fence can be typically classified into five regions, each with a different mode of particle movement. Dense fences, and especially solid fences, favor the accumulation of sand upwind of the fences. Fences with porosities of 0.3–0.4 produce the maximum threshold wind velocity; those with porosities of 0.3–0.6 (depending on the fence height) provide the maximum effective shelter distance. It is confirmed that the fence porosities of 0.3–0.4 that have been proposed for practical application in previous research are the most effective for abating wind erosion.     

科尔沁沙地土地利用与耕作方式对土壤风蚀的影响

土壤风蚀造成的直接生态后果是土地资源的退化。在春播前两次沙尘暴事件中,对科尔沁沙地几种具有代表性的土地类型的土壤风蚀量及土壤特性进行了野外测定、分析,结果表明:(1)在同一沙尘暴天气下,由于土地利用和耕作方式的不同,土壤风蚀量存在着差异,新垦农地和翻耕农地的风蚀量显著高于未垦草地、免耕农地和麻黄地;免耕农地则与未垦草地的风蚀量相差不大,风蚀危害较轻;麻黄地几乎不受风蚀侵害。新垦农地、翻耕农地、免耕农地、未垦草地、麻黄地两次观测的土壤风蚀量平均值依次为24.59、15.60、2.26、1.46和0.22 g/h.cm2。(2)基于土壤特性计算的土壤退化指数结果表明,新垦农地和翻耕农地发生了较为严重的退化。     

Short-term beach–dune sand budgets on the north sea coast of France: Sand supply from shoreface to dunes, and the role of wind and fetch

Three experimental plots, covering the transition from the upper beach to the dune, on the North Sea coast of France were monitored at various intervals over a period of 18–24 months via high resolution terrain surveys in order to determine inter-site sand budget variability, as well as patterns and processes involved in sand exchanges between the upper beach and dune. The wind regime consists of a fairly balanced mix of moderate (80% of winds are below 8 m/s) onshore, offshore and shore-parallel winds. Sustained dune accretion over several years depends on the periodic local onshore welding of shoreface tidal banks that have developed in the storm- and tide-dominated setting of the southern North Sea. The only site where this has occurred in the recent past is Calais, where bank welding has created a wide accreting upper beach sand flat. At this site, significant sand supply from the subtidal sand bank reservoir to the upper beach flat occurred only once over the 18-month survey following a major storm. The bulk of the sand deposited over this large flat is not directly integrated into the adjacent embryo dunes by onshore winds but is progressively reworked in situ into developing dunes or transported alongshore by the balanced wind regime, thus resulting in alongshore stretching of the embryo dune system. The Leffrinckoucke site near Belgium shows moderate beach–dune mobility and accretion, while the Wissant site exhibits significant upper beach bedform mobility controlled by strong longshore currents that result in large beach budget fluctuations with little net budget change, to the detriment of the adjacent dunes. Accretion at these two sites, which are representative of the rest of the North Sea coast of France, is presently constrained by the absence of a shore-attached sand bank supply reservoir, while upper beach–dune sand exchanges are further limited by the narrow wave-affected upper beach, the intertidal morphology of bars and troughs which segments the aeolian fetch, and the moderate wind energy conditions. The balanced wind regime limits net sand mobilisation in favour of either the beach or the dune, and may explain the relatively narrow longshore morphology of the dune ridges bounding this coast.     

Lake-Level Fluctuations and Small-Scale Vegetation Patterns During the Late Glacial in The Netherlands

Late glacial changes in the vegetation were studied in and around a former lake on the southeastern side of a coversand ridge near Milheeze (southern Netherlands). Analyses of microfossils and macroremains and AMS ¹⁴C dating were performed on four sediment cores along a transect from sand ridge to the lake centre. Small-scale vegetation patterns and lake-level fluctuations were reconstructed in detail based on the information provided by the transect. For the first time in The Netherlands, cores along a transect within one lake were used to reconstruct the amplitude of late glacial lake-level fluctuations. Near Milheeze, a small and shallow lake was formed during the Bølling. The large increase in the water level during the Bølling and early Allerød, and the transition to more eutrophic conditions at the start of the Allerød, were probably related to the disappearance of permafrost. During the Allerød, open birch and pine woodlands developed in the area. In the lake, organic deposits accumulated, and the lake size and depth fluctuated. At the start of the Younger Dryas, higher lake water levels were recorded and woodlands became more open as a result of both a drop in the temperature and an increase in the effective precipitation. During the late Younger Dryas the lake water level dropped as the climate became drier and temperatures slightly increased. Accumulation of organic deposits in the lake ceased at the end of the Younger Dryas, which was caused by a drop in the water level in combination with the hydroseral succession process within the lake itself. The climatic signal reflected in the late glacial flora and lake-level fluctuations agree well with other published data from The Netherlands.     

Biological and Geochemical Record of Anthropogenic Impacts in Recent Sediments from Lake Pupuke, Auckland City, New Zealand

Frozen sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high resolution decadal to annual scale record of changing lake paleoenvironments and geochemistry that reflects changing landuse and hydrology in the catchment over the past c. 190 years. A reliable chronology is available from AMS ¹⁴C and ²¹⁰Pb dating of the sediments, with the timing of the older part of the record supported by the first appearance of pollen of introduced Pinus and Plantago lanceolata associated with European settlement of Auckland in the early 1840s. Diatom stratigraphy, sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions commensurate with European development of the Lake Pupuke catchment, in particular enhanced algal productivity controlled by the influx of nutrients after c. 1920 AD. Attempts to prevent nuisance algal blooms in 1933, 1934 and 1939 using CuSO₄ addition produced Cu spikes in the sediment that allowed confirmation of the accuracy of the ²¹⁰Pb chronology. Hence, the elemental and isotopic composition of the Lake Pupuke sediments reflect the timing of significant anthropogenic activities, rather than climatic variations, that have occurred within the watershed over the past c. 190 years. The comparison of records of land use change in the catchment with the multi-proxy record of changes in the sediments usually allowed unambiguous identification of the signatures of change and their causes.     

Vertical distribution and water solubility of phosphorus and heavy metals in sediments of the St. Lucie Estuary, South Florida, USA

Accumulation and distribution of heavy metals and phosphorus in sediments impact water quality. There has been an increasing concern regarding fish health in the St. Lucie Estuary, which is related to increased inputs of nutrients and metals in recent decades. To investigate vertical changes of contaminants (P, Cd, Cr, Co, Cu, Ni, Pb, Zn, and Mn) in sediments of the St. Lucie Estuary in South Florida, 117 layer samples from six of the 210 to 420 cm depth cores were analyzed for their total and water-soluble P and heavy metals, clay, total Fe, Al, K, Ca, Mg, Na, and pH. Principal component analysis (PCA) was used in two sets of analytical data (total and water-soluble contaminant concentrations) to document changes of contaminants in each core of sediments. The PCA of total contaminants and minerals resulted in two factors (principal components). The first and second factors accounted for 61.7 and 17.2 % of the total variation in all variables, and contrast indicators associated with contaminants of P, Cd, Co, Cr, Ni, Pb, Zn, and Mn and accumulation of Fe and Al oxides, respectively. The first factor could be used for overall assessment of P and heavy metal contamination, and was higher in the upper 45–90 cm than the lower depths of each core. The concentrations of P and heavy metals in the surface layers of sediments significantly increased, as compared with those in the sediments deeper than 45–90 cm. The PCA of water-soluble contaminants developed two factors. The second factor (Cu–P) was higher in the upper than the lower depths of the sediment, whereas the highest score of the first factor (Cd–Co–Cr–Ni–Pb–Zn–Mn) occurred below 100 cm. The water-soluble Cu and P concentrations were mainly dependent on their total concentrations in the sediments, whereas the water-soluble Cd, Co, Cr, Ni, Pb, Zn, and Mn concentrations were mainly controlled by pH.     

地震属性分析中水平切片的应用

利用地震数据体中含有的丰富地质信息,可以有效地进行储层预测。层拉平水平切片地层学解释方法是先将地震剖面目的层段做层拉平处理,然后对切片顺地层层面追踪,勾绘出各种地层现象,并以地层学的观点加以解释。该方法在吉林探区扶新南部地区的应用中,对于识别河道的展布趋势取得了较好的效果,而且发现了多期叠置的扇型沉积体。另外,还可指导反演数据体的解释,做到对岩性体从定性到定量的描述。