Glacial sediment causing regional-scale elevated arsenic in drinking water

In the upper Midwest, USA, elevated arsenic concentrations in public drinking water systems are associated with the lateral extent of northwest provenance late Wisconsin-aged drift. Twelve percent of public water systems located within the footprint of this drift (212 of 1764) exceed 10 microg/L arsenic, which is the U.S. EPA's drinking water standard. Outside of the footprint, only 2.4% of public water systems (52 of 2182) exceed 10 microg/L arsenic. Both glacial drift aquifers and shallow bedrock aquifers overlain by northwest provenance late Wisconsin-aged sediment are affected by arsenic contamination. Evidence suggests that the distinct physical characteristics of northwest provenance late Wisconsin-aged drift--its fine-grained matrix and entrained organic carbon that fosters biological activity--cause the geochemical conditions necessary to mobilize arsenic via reductive mechanisms such as reductive desorption and reductive dissolution of metal oxides. This study highlights an important and often unrecognized phenomenon: high-arsenic sediment is not necessary to cause arsenic-impacted ground water--when "impacted" is now defined as >10 microg/L. This analysis also demonstrates the scientific and economic value of using existing large but imperfect statewide data sets to observe and characterize regional-scale environmental problems.     

Changes in the marine environment of Port Kembla Harbour, NSW, Australia, 1975-1995: a review

Data on water quality, sediment quality and aquatic organisms in Port Kembla Harbour from the 1970s to the 1990s are reviewed. In the 1970s, the marine environment of Port Kembla Harbour was in poor condition as a result of pollution from heavy industries. Elevated concentrations of pollutants were found in water, sediment and fish in the harbour; aquatic biodiversity was limited and many fish kills were reported. With the implementation of pollution reduction programs (required by legislation changes) by the industries surrounding the harbour since the 1970s, pollution in the harbour has been reduced dramatically, and the quality of the marine environment of the harbour has noticeably improved. Large reductions in the concentrations of certain toxic wastes and heavy metals in water have occurred. Marine life has returned to the whole harbour (parts were described in 1977 as abiotic). Contaminants in fish have decreased. Despite this achievement, however, there is still considerable room for improvement in the quality of the marine environment of the harbour.     

Assessing herbicide concentrations in the saturated and unsaturated zone of a Chalk aquifer in southern England

The behavior of the herbicides isoproturon (IPU) and chlortoluron (CTU) in ground water and shallow unsaturated zone sediments were evaluated at a site situated on the Chalk in southern England. Concentrations of IPU in ground water samples varied from < 0.05 to 0.23 microgram/L over a five-year period of monitoring, and were found to correlate with application of the pesticide. Concentrations of pesticides in ground water samples collected during periods of rising water table were significantly higher than pumped samples and suggest that rapidly infiltrating recharge water contains higher herbicide concentrations than the native ground water. Significant variations in herbicide concentrations were observed over a three-month period in ground water samples collected by an automated system, with concentrations of IPU ranging from 0.1 to 0.5 microgram/L, and concentrations of a recent application of CTU ranging from 0.2 to 0.8 microgram/L. Different extraction methods were used to assess pore water concentrations of herbicides in the unsaturated zone, and samples were analyzed by standard HPLC analysis and immunoassay (ELISA) methods. These data indicated highly variable concentrations of herbicide ranging from 4 to 200 g/ha for HPLC and 0.01 to 0.04 g/ha for ELISA, but indicate a general pattern of decreasing concentrations with depth. The results of this study indicate that transport of IPU and CTU through the unsaturated zone to shallow ground water occurs and that this transport increases immediately following herbicide application. Measured concentrations of herbicides are generally lower than specified by the European Union Drinking Water Directive, but are observed to spike above this limit. These results imply that, while delivery of pesticides to ground water can occur as a result of normal agricultural practices, the impact on potable supplies is likely to be negligible due to the potential for degradation during the relatively long travel time through the unsaturated zone and high degree of dilution that occurs within the aquifer. As a result of the wide variation in concentrations detected by different techniques, it is suggested that for future site investigations more than one sampling strategy be employed to characterize the occurrence of pesticide residues and elucidate the transport mechanisms.     

Reconciling Spectroscopic Electron Temperature Measurements in the Solar Corona with In Situ Charge State Observations

We present new results on the recently discovered 69 ms X-ray pulsar AXS J161730-505505, the sixth youngest example of a rotation-powered pulsar. We have undertaken a comprehensive X-ray-observing campaign of AXS J161730-505505 with the ASCA, BeppoSAX, and RXTE observatories and follow its long-term spin-down history between 1989 and 1999 using these observations and archival Ginga and ASCA data sets. The spin-down is not simply described by a linear function as originally thought, but instead we find evidence of a giant glitch (DeltaP&solm0;P greater, similar10-6) between 1993 August and 1997 September, perhaps the largest yet observed from a young pulsar. The glitch is well described by steps in P and P&d2; accompanied by a persistent P&d3; similar to those seen in the Vela pulsar. The pulse profile of AXS J161730-505505 presents a single asymmetric peak that is maintained over all observation epochs. The energy spectrum is also steady over time, characterized by a highly absorbed power law with a photon index Gamma=1.4+/-0.2, consistent with that found for other young rotation powered pulsars.     

松辽盆地北部石炭—二叠系油气远景

松辽盆地基底内部石炭—二叠系生烃潜力一直是人们关注的焦点。松深地震剖面和钻井资料显示:松辽盆地北部基底及其周边地区石炭—二叠系分布广、厚度大,主要分布于西部断陷区、中央断隆区和东南断隆区,林甸地区厚度达7 km;三肇地区及肇东地区厚度达到6 km,东北隆起区厚度达5 km。基底石炭—二叠系有机质类型一般为Ⅱ2—Ⅲ型,总有机碳含量高,热演化程度不均一。通过TTI-Ro法恢复了松辽盆地北部基底石炭—二叠系上覆地层沉积之前的热演化程度,有机质成熟度有明显变化,盆地东部有利于二次生烃。另外,松辽盆地石炭—二叠系具有二次生烃的热演化条件。石炭—二叠系油气远景主要受石炭—二叠系发育情况、二次埋藏前及二次埋藏过程中的热演化程度控制,松辽盆地北部石炭—二叠系存在3个有利的油气远景区:西部断陷区的林甸地区、东北隆起区的绥化断陷区、东南断陷区徐家围子断陷区。     

层形态的概念及地质意义

层形态是作者在开发“大陆伸展盆地构造沉积模拟系统”过程中提出的一个新概念，层形态是指能够反映盆地构造沉积演化过程的沉积地层的几何形态，大陆伸展盆地的构造沉积学模拟结果表明，在不同伸展速率下形成的盆地具有不同的层形态，瞬时伸展盆地的层形态为板状，快速持续伸展盆地表现为尖楔形层形态，在这两种端元情况下存在着一系列过渡类型，通过在地震剖面和地质剖面上分析盆地的层形态和其随时间的变化，有助于对盆地构造沉积