Contributions of Pesticide use to Urban Background Concentrations of Arsenic in Denver,Colorado, U.S.A.

Soil investigations near a former smelter have revealed that historic use of arsenical pesticides has contributed significantly to anthropogenic background concentrations of arsenic on certain residential properties in Denver, Colorado, U.S.A. Remedial investigation data, based on samples collected in relatively undisturbed locations, had previously indicated that the "upper limit" of background arsenic concentrations was 28 mg/kg in the site vicinity. This value compares reasonably well with more regional data, which indicate increasing arsenic concentrations moving from rural to urban land use. Soil sampling during cleanup, however, revealed the presence of arsenic concentrations of a few hundred to more than 1000 mg/kg on a large number of residential lawns due to historic applications of a crabgrass killer, which was missed by the earlier investigation samples because of the sampling bias toward undisturbed land. Data from over 20,000 soil samples now show that several different populations comprise urban background levels of arsenic and that these populations may be stratified by land use and have spatial patterns that should be considered during any background study. A variety of forensic techniques, including spatial analysis, arsenic speciation, and calculation of metals ratios were necessary to separate the smelter impacts from pesticide impacts.     

Validation of regression models for nitrate concentrations in the upper groundwater in sandy soils

For Dutch sandy regions, linear regression models have been developed that predict nitrate concentrations in the upper groundwater on the basis of residual nitrate contents in the soil in autumn. The objective of our study was to validate these regression models for one particular sandy region dominated by dairy farming. No data from this area were used for calibrating the regression models. The model was validated by additional probability sampling. This sample was used to estimate errors in 1) the predicted areal fractions where the EU standard of 50 mg l⁻¹ is exceeded for farms with low N surpluses (ALT) and farms with higher N surpluses (REF); 2) predicted cumulative frequency distributions of nitrate concentration for both groups of farms.Both the errors in the predicted areal fractions as well as the errors in the predicted cumulative frequency distributions indicate that the regression models are invalid for the sandy soils of this study area.     

Geochemical Associations of Sellafield-Derived Radionuclides in Saltmarsh Deposits of the Solway Firth

This paper describes a study of the geochemical associations of Sellafield waste radionuclides in saltmarsh sediments from south-west s]Scotland. The contaminant radionuclides are transported to this environment in association with particulate material and ¹³⁷Cs was found to be predominantly (80-98%) non-extractable. In the case of ^239+240Pu there was a redistribution from the oxalate extractable oxide fraction to the pyrophosphate extractable organic fraction as a consequence of on-shore transfer of contaminated sediment. The relatively aggressive nature of the chemical extractants required to remove the radionuclides from the sediments suggests that they were in a form which was unlikely to result in their being released into the aquatic environment or taken up by plants. Plutonium had a greater potential mobility or bioavailability than Cs. Values of K^D for the desorption of ¹³⁷Cs from the sediment by freshwater, groundwater and seawater were all approximately 10⁵ L kg^-1, confirming its immobility in this environment. The desorption K_D values for stable ¹³³Cs were all approximately 10⁶ L kg^-1, so the stable Cs did not have a significant influence on the radiocaesium in this sediment.     

Mixing regime shapes the community assembly process, microbial interaction and proliferation of cyanobacterial species Planktothrix in a stratified lake

Lake mixing influences aquatic chemical properties and microbial community composition,and thus, we hypothesized that it would alter microbial community assembly and interaction. To clarify this issue, we explored the community assembly processes and cooccurrence networks in four seasons at two depths(epilimnion and hypolimnion) in a mesotrophic and stratified lake(Chenghai Lake), which formed stratification in the summer and turnover in the winter. During the stratification period, the epilimni...     

地下水与优势结构面对库岸滑坡形成的联合效应——以龙羊峡近坝库岸滑坡为例

为了深入研究近坝库岸滑坡的形成机理,首先分析了区域地下水的溶蚀作用和动水压力作用,又运用综合评分法确定出了对滑坡形成有利的优势结构面,发现区域滑坡滑带的形成是地下水与优势结构面长期联合作用的结果。以龙羊峡滑坡为例,揭示了半成岩湖相地层中滑坡滑带独特的三段式结构特征,验证了地下水与优势结构面的联合效应对近坝库岸滑坡形成的控制作用。     

流动镀Ni-P合金镀层工艺的研究

电沉积Ni-P合金镀层由于其优异的性能而在多个领域得到了广泛的应用;流动镀电沉积由于可以较快地提高电沉积速度而受到极大的关注;建立了镀液平行式流过电极表面的流动镀装置,采用该流动镀装置,通过改变电流密度、流速、电极间距等不同的工艺条件,研究了流动镀条件下,电流密度、流速、极间距对电沉积Ni-P合金镀层中P含量和表面形貌的影响规律,并初步探讨了流动镀条件下各工艺条件对电沉积过程的影响机理.     

Medium-scale experiments on vented hydrogen deflagration

A series of medium-scale experiments on vented hydrogen deflagration was carried out at the KIT test side in a chamber of 1 × 1 × 1 m³ size with different vent areas. The experimental program was divided in three series: (1) uniform hydrogen–air mixtures; (2) stratified hydrogen–air mixtures within the enclosure; (3) a layer deflagration of uniform mixture. Different uniform hydrogen–air mixtures from 7 to 18% hydrogen were tested with variable vent areas 0.01–1.0 m². One test was done for rich mixture with 50% H₂. To vary a gradient of concentration, all the experiments with a stratified hydrogen–air mixtures had about 4%H₂ at the bottom and 10 to 25% H₂ at the top of the enclosure. Measurement system consisted of a set of pressure sensors and thermocouples inside and outside the enclosure. Four cameras combined with a schlieren system (BOS) for visual observation of combustion process through transparent sidewalls were used. Four experiments were selected as benchmark experiments to compare them with four times larger scale FM Global tests (Bauwens et al., 2011) and to provide experimental data for further CFD modelling. The nature of external explosion leading to the multiple pressure peak structure was investigated in details. Current work addresses knowledge gaps regarding indoor hydrogen accumulations and vented deflagrations. The experiments carried out within this work attend to contribute the data for improved criteria for hydrogen–air mixture and enclosure parameters to avoid unacceptable explosion overpressure. Based on theoretical analysis and current experimental data a further vent sizing technology for hydrogen deflagrations in confined spaces should be developed, taking into account the peculiarities of hydrogen–air mixture deflagrations in presence of obstacles, concentration gradients of hydrogen–air mixtures, dimensions of a layer of flammable cloud, vent inertia, etc.     

Experimental investigation of fast flame propagation in stratified hydrogen–air mixtures in semi-confined flat layers

This paper presents results of an experimental investigation on fast flame propagation and the deflagration-to-detonation transition (DDT) and following detonation propagation in a semi-confined flat layer filled with stratified hydrogen–air mixtures. The experiments were performed in a transparent, rectangular channel open from below. The combustion channel has a width of 0.3 m and a length of 2.5 m. The effective layer thickness in the channel was varied by using different linear hydrogen concentration gradients. The method to create quasi-linear hydrogen concentration gradients that differ in the range and slope is also presented. The ignited mixtures were accelerated quickly to sonic flame speed in the first obstructed part of the channel. The interaction of the fast flame propagation with different obstacle set-ups was studied in the second part of the channel. The experimental results show an initiation of DDT by one additional metal grid in the obstructed semi-confined flat layer. Detonation propagation and failed detonation propagation were observed in obstructed and unobstructed parts of the channel.     

Marine lakes of karst islands in Ha Long Bay (Vietnam)

Ha Long Bay in North Vietnam is characterized by karst towers and bigger islands totalling more than 3000 isles. Karst processes carved hundreds of caves out of the limestone and contributed to the formation of many enclosed and semi-enclosed saltwater lakes. Here, we report the results of a general survey of several lakes and the first data on the Hang Du I lake, a small basin devoid of any apparent communication with the surrounding sea. Hang Du I is characterized by the presence of Rhizostomeae, genus Mastigias, suggesting strong similarities with the famous lakes described from the archipelago of Palau. Among the benthic organisms sponges are the most important group. Temperature and abundance of the monsoon rains are the main factors influencing remarkable seasonal variations in physical-chemical parameters and the community structure of the lake. A thermal crisis with water temperatures up to 36 °C was recorded in September 2003. In this period, usually abundant medusae and sea anemones totally disappeared. Sponge populations showed fast growth rates in winter and spring and a partial degeneration to face the harsh conditions of the summer season. When isolated from the surrounding marine environment, the saltwater lakes share the condition of oceanic islands, representing spots of habitats surrounded by a completely different environment. The Ha Long Bay marine lakes are not easy to access, being surrounded by tropical forest, but local people usually exploit them for both fishery and oyster harvesting. There is an urgent need to develop measures of protection for these endangered and unique environments, natural laboratories that facilitate the study of evolution of marine organisms, where biodiversity has been until now totally unexplored.     

Droplet size spectra and deposits of two aerially sprayed Bacillus thuringiensis formulations on artificial samplers and live foliage

Abstract

Two commercial formulations of Bacillus thuringiensis var. kurstaki (BTK), Foray^® 48B and Thuricide^® 48LV, were applied aerially over nine spray blocks in a hardwood forest in West Virginia in 1991. Droplet spectra and spray mass deposits were determined using water‐sensitive paper strips (WSPS), glass micro‐fiber filters (GMFFs), glass plates and castor oil. Mass deposits of BTK were also assessed on natural foliage by two bioassay methods, i.e., feeding of homogenized foliage containing a starch‐sucrose solution and force‐feeding bioassay of foliar extracts containing re‐dissolved protein precipitate. Deposits on canopy foliage and ground samplers were also assessed by total protein assay and enzyme‐linked immunosorbent assay (ELISA). Droplet spectra on the WSPS were different from those on castor oil. Droplets on horizontal ground WSPS were larger than those on vertical ground WSPS. WSPS placed at canopy level collected more droplets than those at ground level. The total protein deposits (ng/cm²) were consistently higher on all blocks than the delta‐endotoxin protein deposits. Spray mass recovery on the ground samplers were low, and ranged from 2.9 to 8.0% of the applied rates.