Models to determine first-order rate coefficients from single-well push-pull tests

Push-pull tests (PPTs) have been successfully employed to quantify various microbially mediated processes in the subsurface. Current models for determining first-order rate coefficients (k) from PPTs assume complete and instantaneous mixing of injected test solution in the portion of the aquifer investigated by the test, i.e., the system is treated like a well-mixed reactor. Here we present two alternative models to estimate k that are based on different mixing assumptions, i.e., plug-flow and variably mixed reactor models. Rate coefficients estimated by the models were compared using a sensitivity analysis and numerical simulations of PPTs. Results indicated that all models yielded reasonably accurate k estimates (errors < 13%), while best accuracy (errors < 1%) was obtained using the variably mixed reactor model. The well-mixed reactor model generally overestimated true (simulation input) k values, whereas true k values were consistently underestimated by the plug-flow reactor model. However, estimates of k obtained with the latter models bracketed true k values in all cases. As the variably mixed reactor model is more difficult to apply, we suggest using the well-mixed and plug-flow reactor models to obtain intervals for k estimates that will encompass true k values with high certainty. In an example application, we used all models to reanalyze a published PPT data set to obtain k estimates for nitrate consumption in a petroleum-contaminated aquifer. Similar results were obtained for all three models (relative differences < 10% between k estimates), indicating that all three models are robust tools for estimating k values from PPT experimental data.     

An experimental investigation of nitrogen gas produced during denitrification

In situ denitrification relies on indigenous microorganisms to reduce nitrate to N(2) gas. However, when initial nitrate concentrations are large, produced gas volumes also can be very large, potentially resulting in reduced water saturation and hydraulic conductivity in the treatment zone. In this study, we investigated the fate of N(2) and other gases produced during denitrification in a laboratory flow cell containing packed sediment. Denitrifying activity was stimulated by additions of nitrate and ethanol. Microbial activity was monitored by measuring nitrate, nitrite, and ethanol concentrations; gas saturations were measured during the experiment using a gamma imaging system. Biomass was measured using phospholipid fatty acid analysis of sediment samples. Bioenergetic calculations calibrated to measured nitrate consumed and biomass produced predicted that 1.2 L N(2) gas/L water should have been produced following the addition of 100 mM nitrate. However, the maximum measured gas saturation was only 23%, indicating substantial gas loss from the sediment pack. Temporal gamma images and visual observations confirm that small gas bubbles formed in the sediment pack coalesced into larger bubbles and migrated upward through gas-filled channels to the sediment pack surface. Although gas saturations increased, there was no significant change in sediment pack hydraulic conductivity. These results suggest that in permeable reactive barriers used for in situ denitrification, gas production will not necessarily lead to unlimited gas accumulation in the pore space and that the effects of gas production on water saturation and hydraulic conductivity may be relatively minor.     

风玫瑰图和风速直方图的制作

通过office办公软件的现有功能,利用WORD（EXCEL）文档快速制作风玫瑰图;风速直方图,解决手工制作精度不高和安装软件的麻烦,提高效率,满足社会各方面的需求。     

约旦南部瓦迪巴希亚地区铀矿化地球物理特征

通过对瓦迪巴希亚（Wadi Bahiya）地区开展地质调查、岩石取样分析以及地面γ能谱测量等综合研究,认为研究区铀矿化主要产于上白垩统—古新统MCM组近地表风化破碎的灰褐色砂土状泥灰岩之中,矿化类型为现代氧化作用成因的钙结岩型,研究区γ能谱测量铀质量分数平面特征表现为异常规模小,晕圈梯度变化大,深部揭露表明,自近地表向深部铀质量分数逐渐降低,岩石取样分析结果与γ能谱测量具有对应性,铀矿化主要位于地表以下0.5～1.5m的范围内。     

Estimate of recharge of a rising water table in semiarid Niger from 3H and 14C modeling

A hydrodynamic survey carried out in semiarid southwest Niger revealed an increase in the unconfined ground water reserves of approximately 10% over the last 50 years due to the clearing of native vegetation. Isotopic samplings (3H, 18O, 2H for water and 14C, 13C for the dissolved inorganic carbon) were performed on about 3500 km2 of this silty aquifer to characterize recharge. Stable isotope analyses confirmed the indirect recharge process that had already been shown by hydrodynamic surveys and suggested the tracers are exclusively of atmospheric origin. An analytical model that takes into account the long-term rise in the water table was used to interpret 3H and 14C contents in ground water. The natural, preclearing median annual renewal rate (i.e., recharge as a fraction of the saturated aquifer volume) lies between 0.04% and 0.06%. For representative characteristics of the aquifer (30 m of saturated thickness, porosity between 10% and 25%), this implies a recharge of between 1 and 5 mm/year, which is much lower than the estimates of 20 to 50 mm/year for recent years, obtained using hydrological and hydrodynamic methods and the same aquifer parameters. Our study, therefore, reveals that land clearing in semiarid Niger increased ground water recharge by about one order of magnitude.     

环大西洋显生宙造山带中的前中生代地体

环大西洋显生宙造山带内前中生代地体已经由IGcP第233项工作组成员收集了一张二叠纪复原再造图上,即一个封闭的大西洋。最初提出在环太平洋造山带应用地体概念需要对环大西洋造山带的概念作某些修改。因而,地体重新定义为这样的一种地区,其内部地质特点具有连续性(包括地层、生物群、构造、变质作用、火成岩、成矿作用、地球物理特点及古地磁记录),它被断层或代表海沟杂岩的混杂岩,或一条隐地缝合线所圈定,穿过这种界限,相邻地体(1)具有用相变不能解释的一些截然不同的地质记录(外来地体);或(2)可以具有类似的地质记录(近源地体),只有根据代表叠生大洋岩石圈的地体边界的存在才能识别它们。地体可以依据年龄和构造背景划分:原地叠瓦状基底/冒地斜、陆隆、大洋岩石圈、大洋岩系、岩浆弧杂岩、弧缘盆地、海沟杂岩、断裂(disruptes)地体(构造混杂岩)、原岩不明的变质岩、源地不明