Recovery of meiofauna communities following mudflat disturbance by trampling associated with crab-tiling

The provision of artificial shelters for the collection of crabs, known as crab-tiling, and the subsequent harvesting of the soft "peeler" crabs for angling bait, are associated with trampling disturbance of intertidal mudflats in the United Kingdom. Recovery of meiofauna communities following crab-tiling activity was investigated on an intertidal mudflat in SW England. Harvesting of experimental plots was reproduced six times over a 2-week period. Meiofauna was collected at low tides 12h, 36 h and 144 h after treatment. Meiofaunal and nematode abundance, and nematode species number, was significantly greater in controls compared to crab-tile stations at 12h. At 36 h and 144 h there were no significant differences between treatments, indicating recovery had occurred in 12-36 h. Multivariate analysis showed nematode assemblage composition from control plots to be significantly different from crab-tile plots at 12h. No significant differences were observed between sediment physical parameters with treatment. Results suggest that the predominant effect of disturbance may be vibration-induced burial, which causes nematodes to bury deeper into the sediment, beyond the depth sampled, and explains the rapid recovery.     

陕西黄土高原晚更新世环境变化

岐山剖面孢粉分析表明,黄土高原东南部晚更新世植被与气候变化可分为７个阶段和１３个小阶段。其中末次冰期的３个冷干阶段和２个温湿阶段被分别命名为秦家寨,岐山,坡头冰阶和尚家坡,杨家湾间冰阶。冰阶的植被以温带森林草原为主,间冰阶的植被以落叶阔叶林为主。     

Movement of water infiltrated from a recharge basin to wells

Local surface water and stormflow were infiltrated intermittently from a 40-ha basin between September 2003 and September 2007 to determine the feasibility of recharging alluvial aquifers pumped for public supply, near Stockton, California. Infiltration of water produced a pressure response that propagated through unconsolidated alluvial-fan deposits to 125 m below land surface (bls) in 5 d and through deeper, more consolidated alluvial deposits to 194 m bls in 25 d, resulting in increased water levels in nearby monitoring wells. The top of the saturated zone near the basin fluctuates seasonally from depths of about 15 to 20 m. Since the start of recharge, water infiltrated from the basin has reached depths as great as 165 m bls. On the basis of sulfur hexafluoride tracer test data, basin water moved downward through the saturated alluvial deposits until reaching more permeable zones about 110 m bls. Once reaching these permeable zones, water moved rapidly to nearby pumping wells at rates as high as 13 m/d. Flow to wells through highly permeable material was confirmed on the basis of flowmeter logging, and simulated numerically using a two-dimensional radial groundwater flow model. Arsenic concentrations increased slightly as a result of recharge from 2 to 6 μg/L immediately below the basin. Although few water-quality issues were identified during sample collection, high groundwater velocities and short travel times to nearby wells may have implications for groundwater management at this and at other sites in heterogeneous alluvial aquifers.     

Developing a Radiative Shock Experiment Relevant to Astrophysics

We assume that internal shocks of gamma-ray bursts (GRBs) consist of multiple sub-jets with a collimation half-angle of about several times gamma-1i, where gammai is the Lorentz factor of each sub-jet. If by chance a sub-jet is first emitted off-axis from the line of sight, the observed peak energy can be in the X-ray region. Next, if by chance a subsequent sub-jet is emitted along the line of sight, then the peak energy will be in the gamma-ray region and the gamma ray may arrive after the X-ray precursor from the former sub-jet depending on parameters. This model predicts a new class of GRBs with extremely weak and short gamma-ray emission but X-ray precursors and/or postcursors as well as an afterglow.     

A strategy for detecting derelict fishing gear at sea

Derelict fishing gear (DFG) is a highly persistent form of marine pollution known to cause environmental and economic damage. At-sea detection of DFG would support pelagic removal of this gear to prevent and minimize impacts on marine environments and species. In 2008, experts in marine debris, oceanography, remote sensing, and marine policy outlined a strategy to develop the capability to detect and ultimately remove DFG from the open ocean. The strategy includes three interrelated components: understanding the characteristics of the targeted DFG, indirectly detecting DFG by modeling likely locations, and directly detecting pelagic DFG using remote sensing. Together, these components aim to refine the search area, increase the likelihood of detection, and decrease mitigation response time, thereby providing guidance for removal operations. Here, we present this at-sea detection strategy, relate it to relevant extant research and technology, and identify gaps that currently prevent successful at-sea detection and removal of DFG.     

Hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA) in riverine and estuarine sediments of the Pearl River Delta in southern China, with emphasis on spatial variability in diastereoisomer- and enantiomer-specific distribution of HBCD

Hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA) were measured in surface sediments in the Pearl River Delta, southern China. The concentrations ranged from 0.06 to 304 ng/g dry weight for TBBPA and from 0.03 to 31.6 ng/g for total HBCD. The correlations between the TBBPA and HBCD concentrations were significant in rivers (Dongjiang, Zhujiang, Beijiang, and Dayanhe Rivers) with local input sources but not significant in the Xijiang River and Pearl River Estuary without local sources. HBCD was dominated by γ-HBCD (averaged 52.5-75.0%), whereas α-HBCD contributions were relatively high in sediments from the urban areas. The enantiomeric fractions of γ-HBCD in the sediments (averaged from 0.431 ± 0.035 to 0.479 ± 0.010) differed significantly from that in HBCD technical product except for samples from the e-waste area (Dayanhe River, 0.488 ± 0.091). This suggests that enantioselective biotransformation of HBCD occurs in the aquatic environment in this region.     

Inter-annual variability of wet season freshwater plume extent into the Great Barrier Reef lagoon based on satellite coastal ocean colour observations

Riverine freshwater plumes are the major transport mechanism for nutrients, sediments and pollutants into the Great Barrier Reef (GBR) lagoon and connect the land with the receiving coastal and marine waters. Knowledge of the variability of the freshwater extent into the GBR lagoon is relevant for marine park management to develop strategies for improving ecosystem health and risk assessments. In this study, freshwater extent has been estimated for the entire GBR lagoon area from daily satellite observations of the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2002 and 2010. To enable a reliable mapping of freshwater plumes we applied a physics-based coastal ocean colour algorithm, that simultaneously retrieves chlorophyll-a, non-algal particulate matter and coloured dissolved organic matter (CDOM), from which we used CDOM as a surrogate for salinity (S) for mapping the freshwater extent.     

西安灞河流域现代岩溶作用与CO2吸收量

本文探讨了灞河流域岩溶特征、CO²估算方法和CO²吸收量。观测资料表明,灞河流 域河水中ｐＨ值在冬春季高,夏秋季低,而ＨＣＯ３含量通常与ｐＨ相反。河水和黄土地下水中 ｐＨ值、ＨＣＯ３等化学成分含量与北方南部石灰岩区岩溶水基本相同,表明该区现代岩溶作用 明显,黄土地层也在不断吸收CO²,并对全球碳循环有重要影响。雨水富含CO²,其中约有 ８２％的CO²被岩溶过程吸收,１８％左右的随河水流失。根据一个流域CO²输入量和输出量,可 以计算岩溶过程中 CO²吸收量。计算表明,灞河流域现代岩溶过程中每年吸收的 CO²约为５６３２．８ｔ。     

MTBE and gasoline hydrocarbons in ground water of the United States

The occurrence of methyl tert-butyl ether (MTBE) and gasoline hydrocarbons was examined in three types of studies of ground water conducted by the U.S. Geological Survey: major aquifer surveys, urban land-use studies, and agricultural land-use studies. The detection frequency of MTBE was dependent on the study type, with the highest detection frequency in urban land-use studies. Only 13 ground water samples from all study types, or 0.3%, had concentrations of MTBE that exceeded the lower limit of the U.S. EPA's Drinking-Water Advisory. The detection frequency of MTBE was highest in monitoring wells located in urban areas and in public supply wells. The detection frequency of any gasoline hydrocarbon also was dependent on study type and generally was less than the detection frequency of MTBE. The probability of detecting MTBE in ground water was strongly associated with population density, use of MTBE in gasoline, and recharge. Ground water in areas with high population density, in areas where MTBE is used as a gasoline oxygenate, and in areas with high recharge rates had a greater probability of MTBE occurrence. Also, ground water from public supply wells and shallow ground water underlying urban land-use areas had a greater probability of MTBE occurrence compared to ground water from domestic wells and ground water underlying rural land-use areas. The probability of detecting MTBE in ground water was weakly associated with the density of leaking underground storage tanks, soil permeability, and aquifer consolidation, and only concentrations of MTBE >0.5 microg/L were associated with dissolved oxygen.