Using atmospheric tracers to reduce uncertainty in groundwater recharge areas

A Monte Carlo-based approach to assess uncertainty in recharge areas shows that incorporation of atmospheric tracer observations (in this case, tritium concentration) and prior information on model parameters leads to more precise predictions of recharge areas. Variance-covariance matrices, from model calibration and calculation of sensitivities, were used to generate parameter sets that account for parameter correlation and uncertainty. Constraining parameter sets to those that met acceptance criteria, which included a standard error criterion, did not appear to bias model results. Although the addition of atmospheric tracer observations and prior information produced similar changes in the extent of predicted recharge areas, prior information had the effect of increasing probabilities within the recharge area to a greater extent than atmospheric tracer observations. Uncertainty in the recharge area propagates into predictions that directly affect water quality, such as land cover in the recharge area associated with a well and the residence time associated with the well. Assessments of well vulnerability that depend on these factors should include an assessment of model parameter uncertainty. A formal simulation of parameter uncertainty can be used to delineate probabilistic recharge areas, and the results can be expressed in ways that can be useful to water-resource managers. Although no one model is the correct model, the results of multiple models can be evaluated in terms of the decision being made and the probability of a given outcome from each model.     

对逆冲断层一些普遍观念的质疑：以美国西部科迪勒拉及中国华北的野外研究？

在过去的２５年里,由于许多原因,作为最常见,分布也最广泛的地质构造形迹之一,逆冲断层成为倍受关注的科学研究主题。文中指出,关于逆总断层及其几何学特征的许多普遍认识,并不像以往文献中所阐述的那样简单,其中之一的“薄皮”冲断构造是受地层控制的,极少有或者没有结晶基底物的卷入。     

Effects of barium and cadmium on the population development of the marine nematode Rhabditis (Pellioditis) marina

Offshore oil and gas drilling often involves the use of fluids containing barium and traces of other heavy metals. These may affect the environment, but information on their toxicity to benthic biota remains scant. Here, we present results of a 10-day bioassay with the marine nematode Rhabditis (Pellioditis) marina at different loads of barium (0-10 ,000 ppm nominal concentrations) and cadmium (0-12 ppm) in the range of concentrations reported from drilling-impacted sediments. Barium did not affect the fitness and population development of R. (P.) marina at concentrations up to 300 ppm, but did cause a decrease in population abundance and an increase in development time from concentrations of 400-2000 ppm onwards. Increased mortality occurred at 4800 ppm Ba. For cadmium, LOEC and EC?? values for total population abundance were 2.95 and 8.82 ppm, respectively. Cd concentrations as low as 2.40 to 2.68 caused a decrease in the abundance of adult nematodes, indicating that assays covering more generations would likely demonstrate yet more pronounced population-level effects. Our results indicate that oil and gas drilling activities may potentially have important implications for the meiobenthos through the toxicity of barium and associated metals like cadmium.     

Sediment characteristics and macrofauna distribution along a human-modified inlet in the Gulf of Oristano (Sardinia, Italy)

We studied the spatial variability and within-year temporal changes in hydrological features, grain size composition and chemical characteristics of sediments, as well as macrofaunal assemblages, along a heavily modified inlet in the Gulf of Oristano (western Sardinia, Italy). The inlet connects the Cabras lagoon to the gulf through a series of convoluted creeks and man-made structures, including a dam and fish barriers built in the last three decades. Sediments were muddy and mainly composed of the "non-sortable" fraction (i.e., <8 microm particle size) in all four areas investigated: Lagoon, Creeks, Channel and Seaward. Along the inlet, however, the ratio between the <8 microm and the 8-64 microm fractions was highest in Creeks and Channel, between the fish barriers and the dam, suggesting impaired hydrodynamics. Consistently, steep gradients in water salinity, temperature and dissolved oxygen concentrations were found in proximity to the fish barriers. The whole inlet was characterized by a major organic enrichment of sediments, with up to an annual mean of 33.6% of organic matter and 11.7% of total organic carbon in Seaward due to the presence of seagrass leaf litter. Acid-volatile sulphide and chromium-reduced sulphur concentrations were highest throughout the year in Seaward and Lagoon, respectively, with a peak in summer. Consistently, the whole inlet supported low structured macrofaunal assemblages dominated by few opportunist species, with a relatively lower diversity in Lagoon throughout the year and the highest abundances in Seaward in summer. We infer that the presence of artificial structures along the inlet, such as fish barriers and the dam, impair the lagoon-gulf hydrodynamics, sediment exchange and animal recruitment and colonization. We suggest that the removal of these structures would favour water renewal in the Cabras lagoon, but would also increase the outflow of organic C-bonding fine particles into the gulf with serious consequences for Posidonia oceanica and Cymodocea nodosa seagrass meadows. We conclude that all possible consequences of such initiatives should be carefully considered before any action is taken.     

The molecular emission-line spectrum of IRC +10216 between 330 and 358 GHz

We have conducted a spectral line survey of IRC +10216 using the Caltech Submillimeter Observatory to an average sensitivity of < or approximately 95 mK. A deconvolution algorithm has been used to derive the continuous single-sideband spectrum from 330.2 to 358.1 GHz. A total of 56 spectral lines were detected of which 54 have been identified with 8 molecules and a total of 18 isotopomers. The observed lines are used to derive column densities and relative abundances for the detected species. Within this frequency range the spectral lines detected contribute the majority of the total flux emitted by IRC +10216. We use the derived column densities and excitation temperatures to simulate the molecular line emission (assuming LTE) at frequencies up to 1000 GHz. The observed and simulated flux from line emission is compared to broadband total flux measurements and to dust emission assuming a power-law variation of the dust emissivity. We conclude that significant corrections for the line flux must be made to broadband flux measurements of IRC +10216 at wavelengths longer than approximately 750 micrometers.     

冰碛物建造型相及天秦运动的讨论

以往对冰碛物的研究 ,只重视其沉积特征及古地理的恢复 ,未讨论其建造型相。笔者通过对其沉积特征、产出构造环境的讨论 ,认为山麓冰碛物是造山期后的产物 ,属于磨拉石建造 ,大陆冰碛物代表寒冷地区风化壳产物 ,可作底砾岩看待 ;冰蚀面可当作沉积间断面或寒冷地区的风化壳。并认为我国新元古代末期罗圈组及其相当层位的冰碛岩属磨拉石建造。由此推断在新元古代末期 -早古生代初期存在一期未被认识的、在地史上具划时代意义的构造运动 ,命名为天秦运动。天秦运动是晋宁运动后的另一期构造运动 ,是新元古代与古生代的分界运动 ,时限在80 0Ma以后 ,70 0～ 5 4 0Ma是主构造期 ,前期以造山为主 ,后期以裂解为主 ,是Rodinia超大陆的裂解、古亚洲洋和古特提斯海形成期 ,扬子地块和塔里木地块先后从澳大利亚板块中裂解出来     

巴布亚新几内亚的波格拉金矿床

导论 Fleming等(1986)对波格拉矿作了综合报道。下述简短报道强调在该矿最近所做的工作,对已报道的资料将不再重述。矿床位置该矿床位于巴布亚新几内亚西部高地的恩甘省,离最近的主要城镇—哈根山北西向约130公里,即在波格拉乡间小镇之西5公里处,为海拔约2500米的厚层苔藓植物森林覆     

燕辽地区中生代构造格局的再讨论

本文中,笔者对燕辽地区的构造形迹进行了重新厘定,并将其划分成不同构造阶段的产物,提出了一些新的认识:燕辽地区范围包括"内蒙地轴"和燕山沉降带,其构造格局主要由燕辽向斜、燕辽复向斜和秦皇岛背形及其配套断裂组成,在这三个区域构造样式之下又发育次一级的褶皱构造及其配套断裂,并且后期构造对前期构造改造、叠加和利用,致使出现复杂的构造格局.海西一印支期形成了燕辽向斜及其配套断裂,"内蒙地轴"是燕辽向斜的北翼.燕辽沉降带是燕辽向斜的南翼.早中侏罗世进一步褶皱成复向斜,"内蒙地轴"南缘断裂是复向斜的轴部纵断裂并充填了上侏罗统作为裂隙充填物.中晚侏罗世开始,以秦皇岛-凌源断裂为轴面褶皱成一个背形.秦皇岛-凌源断裂的存在及其对燕山段和辽西段的影响致使燕山段和辽西段具有不同的地表出露形态.