长江口和浙江近岸海域表层沉积物中颗粒磷的形态分布和影响因素

研究长江口和浙江近岸海域的水团流向、缺氧程度、潮汐作用以及养殖活动对表层沉积物中颗粒磷赋存形式的影响,对东海生态环境的可持续发展有着重要的意义。长江口以北和浙江近岸泥质区各存在一个缺氧中心,杭州湾属于强潮区,而象山港遍布养殖场。2018年8—9月在上述4个海域分别采集表层沉积物,采用SEDEX方法进行了颗粒磷的形态划分和含量测定。研究结果表明：在长江口外北部缺氧区和浙江近岸泥质区的南部缺氧区,由于沉积物-水界面的还原环境可以活化铁结合态磷,使之转变为生物可以直接利用的弱吸附态无机磷,因此表现出沉积物中铁结合态磷的低值和弱吸附态无机磷的高值;前者的缺氧程度高于后者,因此其铁结合态磷的含量相应更低。杭州湾和象山港海域均受潮汐作用影响,两者沉积物中磷的分布比较均匀。象山港表层沉积物中铁结合态磷含量均较低,这可能是因为养殖活动造成的水体缺氧通过潮汐活动扩散到整个港底。象山港废弃养殖场沉积物中的碎屑磷和残余有机磷含量显著低于非养殖区,可能是由于养殖活动累积的生物沉积稀释了陆源输入的碎屑颗粒。     

全新世长江泥沙堆积的时空分布及通量估算

利用长江中下游、河口及口外、浙-闽沿岸陆架6个主要沉积盆地的40个晚第四纪钻孔及其年代学数据和长江口外、陆架的浅地层剖面,计算了全新世不同阶段各沉积盆地的沉积速率,并进行了近7 000年来泥沙堆积通量的估算。研究发现全新世早期距今10 000年至8 000年间长江口下切古河谷是长江泥沙的主要堆积中心,沉积速率可高达15m/ka。随着海平面上升,全新世中期长江中下游也成为长江泥沙的重要沉积盆地,其中江汉盆地的沉积速率可达10m/ka。近2 000年来,口外、陆架的堆积呈明显增加趋势,反映长江中下游盆地和河口可容空间日益减小。根据沉积速率估算,距今7 000年来长江中下游堆积泥沙约13 074×108 t,同期水下三角洲和陆架的泥沙堆积量约为9 470×108 t。研究还发现全新世以来有两个异常低沉积速率时期：距今8000-7 000年期间上述各沉积盆地沉积速率均显著低,未见长江泥沙的沉积中心; 距今4 000-2 000 年期间长江口呈现低沉积速率。 这两次异常的原因推测与海平面、气候波动事件密切相关。     

Distribution and possible sources of organochlorine residues in sediments of a large urban estuary,Port Jackson,Sydney

Sydney Harbour is surrounded by a large capital city of about four million people and its highly urbanised (86%) catchment supports a substantial industrial base and an extensive transport infrastructure. Large commercial and naval ports occupy the waterway and the harbour is an important recreational area. Surficial sediment in Sydney Harbour contains high concentrations of PCBs, HCB, total chlordane, total DDT, aldrin, dieldrin, heptachlor and heptachlor‐epoxide, but low concentrations of lindane. PCBs, total chlordane, and to a lesser extent dieldrin, are most elevated in sediment in creeks on the southern shores of the harbour suggesting sources within older, highly urbanised/industrialised catchments of western‐central Sydney. There are high concentrations of total DDT and HCB in sediments of the upper harbour and Homebush Bay suggesting that chemical industries on the shores of the estuary in this area are sources of these contaminants. Although no sediment quality guidelines apply in Australia, empirically derived biological effects criteria suggest that sediment over extensive areas of Sydney Harbour may have an adverse impact on biota. Especially of concern are sediments containing high concentrations of chlordane and DDT.     

The Eltanin asteroid impact: possible South Pacific palaeomegatsunami footprint and potential implications for the Pliocene–Pleistocene transition

Large asteroid impacts are rare, and those into the deep ocean are rarer still. The Eltanin asteroid impact around 2.51 ± 0.07 Ma occurred at a time of great climatic and geological change associated with the Pliocene–Pleistocene boundary. Numerical models of the event indicate that a megatsunami was generated, although there is debate concerning its magnitude and the region‐wide extent of its influence. We summarise the existing evidence for possible Eltanin megatsunami deposits in Antarctica, Chile and New Zealand, while also examining other potential sites from several locations, mainly around the South Pacific region. In reviewing these data we note that these events were unfolding at the same time as those associated with the Pliocene–Pleistocene boundary and, as such, most of the geological evidence from that time has a climatic interpretation. The potential climatic and geological ramifications of the Eltanin asteroid impact, however, have failed to be considered by most researchers studying this time period. Although we are not advocating that all geological activity at that time is connected with the Eltanin asteroid impact, it raises interesting questions about the role potentially played by such catastrophic events in contributing to or even triggering epochal transitions. Copyright © 2012 John Wiley & Sons, Ltd.     

Towards developing sediment quality assessment guidelines for aquatic systems: An Australian perspective

Sediment at the sediment‐water interface of natural and man‐made waterways forms an integral part of the ecosystem because it is affected by a continuous flux of physical, chemical and biological components between the sediment, interstitial water and the overlying water column. Aquatic sediments contain records of past and present urban and rural runoff, chemical discharges and spills. In recent years sediment quality has received increasing attention following identification of the role of sediment as both a sink for pollutants and as a contaminant source with potential impacts on the quality of receiving waters. Research has indicated that the processes leading to remobilization of contaminated sediments in upstream reaches of a waterway may, through time, exert a significant influence on water quality in the downstream reaches. This, together with the cumulative effects due to contaminant input from point and non‐point source discharges, have dramatic effects on water quality and thus on ecosystem structure and functioning.

The problems associated with elevated concentrations of many hazardous organic and inorganic compounds have resulted in the establishment of aquatic sediment quality criteria and management guidelines in many overseas countries, with the objectives being the reduction and elimination of adverse environmental effects and human health risks associated with contaminated sediments. Whereas more than 70% of the Australian population is clustered around the coastal waterways, little is known about the role of sediments as a repository of environmental pollutants and/or as a source of adverse impacts on water quality and the health of our rivers. The paucity of knowledge on the quality of aquatic sediment highlights the need for the development of coherent guidelines for sediment quality assessment and management of contaminated sites, which are consistent with Australian environmental conditions and land use features.

A comparative evaluation of sediment quality information from eight coastal rivers along the east coast of Australia, presented in this paper, indicates the possibility for establishing a framework for regional sediment quality assessment. This may be achievable by using textural and compositional attributes of bottom sediments in depositional areas to develop databases on the loading and concentration trends of nutrients and contaminants. Regional variability in sediment quality determinants are shown to reflect the influence of catchment hydrology, lithology and land use on nutrient and contaminant concentration trends. Locally, the loading and partitioning behaviour of sediment‐bound contaminants is largely controlled by the nature and the extent of interactions occurring at the sediment‐water interface within individual depositional units.

The concept of ‘Sediment Effect Zone’ is introduced to provide a compartmental approach to the characterization of aquatic sediments and depositional environments in different hydrologic zones. This approach offers a rational basis for follow‐up chemical and biological assessments to establish sediment quality standards and management guidelines. Because of the complex influences of environmental, methodological and statistical factors on defining the sediment variability, the need for implementing proper quality control measures from early stages of design of a sediment quality assessment program is highlighted.     

Biomarkers in sedimentary sulfides of precambrian age

Samples of the Mt Isa formation (Australia, c, 1.5 Ga), and the Shungit formation (U.S.S.R., c. 2.3 Ga) were studied by organic geochemical means. All samples were freed of any low-molecular-weight solvent soluble organic material in order to insure the authenticity of the analysed material. The isolation of biochemical compounds entrapped in sulfides was the major goal of this work.Organic compounds that were entrapped during the early stages of sulfide formation may obviously survive extended periods of time and can be released by a mild hydrogenation of the sulfides. Preliminary investigations of the hydrocarbon fraction indicate n-alkanes, monomethylalkanes, cycloalkanes, and an unknown series of branched alkanes as major constituents. Their distribution patterns show great selectivity with respect to structures and chain lengths of individual compounds. Differences between the hydrogenation reaction product and the sample extract may arise from the release of a different kind of lipid material through dissolution of the sulfides.     

Subfossil and modern diatom plankton and the paleolimnology of Rotsee (Switzerland) since 1850

The diatom biostratigraphy of the topmost sediment meter of Rotsee, Central Switzerland, is characterized by a major change fromCyclotella comensis-dominated toStephanodiscus hantzschii/S. parvus-dominated assemblages. A comparison between old phytoplankton samples, taken between 1910–1930, and subfossil diatom assemblages is used for dating the upper 35 cm of the core. There is evidence that the change in dominant diatoms occurred in 1919/20, thus before the opening of an artificial inlet in 1922, and is due to increasing eutrophication. Furthermore, the sedimentary carbonate content can be used as a good indicator for past phytoplankton productivity in Rotsee.     

Radiometric dating of lake sediments from Signy Island (maritime Antarctic): evidence of recent climatic change

Sediment cores from three lakes (Moss, Sombre and Heywood) in the maritime Antarctic (Signy Island, South Orkney Islands) have been successfully dated radiometrically by²¹⁰Pb and¹³⁷Cs. The core inventories of both fallout radionuclides are an order of magnitude higher than that which can be supported by the direct atmospheric flux at this latitude. The elevated values may be explained by fallout onto the catchment during the winter being delivered directly to the lakes during the annual thaw. Two of the lakes (Sombre and Heywood) show marked increases in sediment accumulation afterc. 1950. This appears to be associated with a documented rise in temperature in the South Orkney Islands, which has caused extensive deglaciation at Signy Island.This is the tenth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P.G. Appleby is guest editing this series.     

Variation among fossil chironomid assemblages in surficial sediments of Bodensee-Untersee (SW-Germany): implications for paleolimnological interpretation

In paleolimnology, subfossil head capsules of chironomids play an important role as ecological indicators of lake history. It is important to determine, therefore, whether fossil assemblages are representative of former biocoenoses. There is evidence that headcapsules washed in from other places can make up a significant percentage of the total. As interpretations are usually drawn from the examination of a single core, it is of special interest to know whether a fossil assemblage of a single site properly reflects limnological conditions of the whole lake. This study examined the taxonomic distribution of subfossil chironomids in the surficial sediments of the Bodensee-Untersee, with the aim of assessing the variability in chironomid assemblages. Apparently, most of the head capsules of the profundal fossil assemblages in the Untersee had been washed in from the littoral zone or from the slope. Although the Bodensee-Untersee is a rather large lake, variability is surprisingly low among all samples. Therefore a correct interpretation from a single core may be possible.