Development of a scalable model for predicting arsenic transport coupled with oxidation and adsorption reactions

Understanding the fundamentals of arsenic adsorption and oxidation reactions is critical for predicting its transport dynamics in groundwater systems. We completed batch experiments to study the interactions of arsenic with a common MnO2(s) mineral, pyrolusite. The reaction kinetics and adsorption isotherm developed from the batch experiments were integrated into a scalable reactive transport model to facilitate column-scale transport predictions. We then completed a set of column experiments to test the predictive capability of the reactive transport model. Our batch results indicated that the commonly used pseudo-first order kinetics for As(III) oxidation reaction neglects the scaling effects with respect to the MnO2(s) concentration. A second order kinetic equation that explicitly includes MnO2(s) concentration dependence is a more appropriate kinetic model to describe arsenic oxidation by MnO2(s) minerals. The arsenic adsorption reaction follows the Langmuir isotherm with the adsorption capacity of 0.053micromol of As(V)/g of MnO2(s) at the tested conditions. The knowledge gained from the batch experiments was used to develop a conceptual model for describing arsenic reactive transport at a column scale. The proposed conceptual model was integrated within a reactive transport code that accurately predicted the breakthrough profiles observed in multiple column experiments. The kinetic and adsorption process details obtained from the batch experiments were valuable data for scaling to predict the column-scale reactive transport of arsenic in MnO2(s)-containing sand columns.     

应用Models-3/CMAQ研究长三角区域大气污染及输送

选用美国国家环保局第3代空气质量模式（Models-3，／CMAQ），配合中尺度气象模式（MM5）进行研究，模拟了2001年1、7月份长江三角洲区域冬夏季典型天气条件下大气层二次污染物臭氧及颗粒物的浓度分布及输送状况。采用2001年冬．夏季各10d的小时监测数据对模式验证。结果表明，Models-3／CMAQ对O3、PM10的模拟相关系数分别为0．77和052；一致性指数分别达到081和0．99。模型对于O3略微低估，标准偏差为-31％，而对于PM10则有所高估，标准偏差为46％。对长三角7月份O3浓度及1月份PM10的模拟结果显示，7月份长三角区域16个主要城市O3日均浓度集中在0．043～0．086mg／m^3之间，其中，泰州、扬州．湖州、镇江O3月日均浓度相对较高，均超过0．064mg／m3o模拟时段内O3最高小时浓度达0．276mg／m^3。1月份整个模拟区域PM10月日均浓度为O056mg／m^3，其中，南京市PM10日均浓度最高，达0．080mg／m^3模拟时段内PM10最高小时浓度达0.432mg／m^3研究表明，长三角地区存在明显的污染物输送现象，大气污染已经从局地污染转化为区域污染。     

长江三角洲地区大气O3和PM10的区域污染特征模拟

以TRACE-P污染源资料及上海市地方排放清单为基础,采用Models-3/CMAQ环境空气质量模型和中尺度气象模式MM5,模拟研究了2001-01和2001-07长三角近地面二次污染物O3及PM 10的浓度分布及输送状况,并以上海市国控点2001年冬、夏季各10 d的小时监测数据对模型进行了验证.验证结果显示,Models-3/CMAQ对O3和PM10的模拟结果与监测值的相关系数分别为0.77和0.52;一致性指数分别达到0.81和0.99.模型对O3小时最高浓度的估算偏低27%,标准偏差为-3.1%;对PM10小时平均浓度的估算偏低10%,标准偏差为46%.模型已具备再现和模拟长三角大气污染输送过程的能力,且误差落在可接受的范围之内.模拟结果显示,2001-07长三角区域16个主要城市中,有14个城市O3小时最大浓度超过国家二级标准,高浓度O3可覆盖苏南和浙北广大区域.2001-01泰州、扬州、南京、镇江、常州等城市受本地排放源和北部大气污染输送的影响显著,大气PM10日均浓度超过PM10国家二级标准.长三角地区环境空气质量与污染类型受大气污染传输与化学转化的影响十分明显.夏季太阳辐射较强时,南部城市排放的污染物常以二次污染物的形式影响下风向城市;太阳辐射较弱的情况下,则以一次污染物输送为主的形式影响周边地区.冬季长三角区域颗粒物污染总体水平较高,这与我国北方地区排放的颗粒物在西北风作用下向长三角输送造成的影响密切相关.长三角地区的大气污染已逐渐从局地转为区域问题.     

Microbes do not follow the elevational diversity patterns of plants and animals

The elevational gradient in plant and animal diversity is one of the most widely documented patterns in ecology and, although no consensus explanation exists, many hypotheses have been proposed over the past century to explain these patterns. Historically, research on elevational diversity gradients has focused almost exclusively on plant and animal taxa. As a result, we do not know whether microbes exhibit elevational gradients in diversity that parallel those observed for macroscopic taxa. This represents a key knowledge gap in ecology, especially given the ubiquity, abundance, and functional importance of microbes. Here we show that, across a montane elevational gradient in eastern Peru, bacteria living in three distinct habitats (organic soil, mineral soil, and leaf surfaces) exhibit no significant elevational gradient in diversity (r2<0.17, P>0.1 in all cases), in direct contrast to the significant diversity changes observed for plant and animal taxa across the same montane gradient (r2>0.75, P<0.001 in all cases). This finding suggests that the biogeographical patterns exhibited by bacteria are fundamentally different from those of plants and animals, highlighting the need for the development of more inclusive concepts and theories in biogeography to explain these disparities.     

Genetically informed captive breeding of hybrids of an extinct species of Galapagos tortoise

Hybridization poses a major challenge for species conservation because it threatens both genetic integrity and adaptive potential. Yet, hybridization can occasionally offer unprecedented opportunity for species recovery if the genome of an extinct taxon is present among living hybrids such that selective breeding could recapture it. We explored the design elements for establishing a captive-breeding program for Galapagos tortoises (Chelonoidis spp.) built around individuals with admixed ancestry involving an extinct species. The target individuals were hybrids between the extinct species from Floreana Island, C. niger, and an extant species, C. becki, which were recently found in the endemic range of C. becki, from Wolf Volcano on Isabela Island. We combined genotypic data from 35 tortoises with high ancestry from C. niger with forward-in-time simulations to explore captive breeding strategies that maximized overall genetic diversity and ancestry from C. niger while accommodating resource constraints, species biology, and the urgency to return tortoises to Floreana Island for facilitating ecosystem restoration. Overall genetic diversity was maximized when in the simulation tortoises were organized in relatively small breeding groups. Substantial amounts of the C. niger genome were captured despite limited resources available for selectively breeding tortoises in captivity. Genetic diversity was maximized when captive-bred offspring were released to the wild rather than being used as additional breeders. Our results provide genetic-based and practical guidance on the inclusion of hybrids with genomic representation from extinct taxa into species restoration programs and informs the ongoing debate on the value of hybrids in biodiversity conservation.     

The role of environmental and spatial processes in structuring lake communities from bacteria to fish

We assessed the relative roles of local environmental conditions and dispersal on community structure in a landscape of lakes for the major trophic groups. We use taxonomic presence-absence and abundance data for bacteria, phytoplankton, zooplankton, and fish from 18 lakes in southern Quebec, Canada. The question of interest was whether communities composed of organisms with more limited dispersal abilities, because of size and life history (zooplankton and fish) would show a different effect of lake distribution than communities composed of good dispersers (bacteria and phytoplankton). We examine the variation in structure attributable to local environmental (i.e., lake chemical and physical variables) vs. dispersal predictors (i.e., overland and watercourse distances between lakes) using variation partitioning techniques. Overall, we show that less motile species (crustacean zooplankton and fish) are better predicted by spatial factors than by local environmental ones. Furthermore, we show that for zooplankton abundances, both overland and watercourse dispersal pathways are equally strong, though they may select for different components of the community, while for fish, only watercourses are relevant dispersal pathways. These results suggest that crustacean zooplankton and fish are more constrained by dispersal and therefore more likely to operate as a metacommunity than are bacteria and phytoplankton within this studied landscape.     

Conjunctive use of models to design cost-effective ozone control strategies

The management of tropospheric ozone (O3) is particularly difficult. The formulation of emission control strategies requires considerable information including: (1) emission inventories, (2) available control technologies, (3) meteorological data for critical design episodes, and (4) computer models that simulate atmospheric transport and chemistry. The simultaneous consideration of this information during control strategy design can be exceedingly difficult for a decision-maker. Traditional management approaches do not explicitly address cost minimization. This study presents a new approach for designing air quality management strategies; a simple air quality model is used conjunctively with a complex air quality model to obtain low-cost management strategies. A simple air quality model is used to identify potentially good solutions, and two heuristic methods are used to identify cost-effective control strategies using only a small number of simple air quality model simulations. Subsequently, the resulting strategies are verified and refined using a complex air quality model. The use of this approach may greatly reduce the number of complex air quality model runs that are required. An important component of this heuristic design framework is the use of the simple air quality model as a screening and exploratory tool. To achieve similar results with the simple and complex air     

National evaluation of the effect of graduated driver licensing laws on teenager fatality and injury crashes

ProblemAutomobile crashes remain a prominent cause of death and injury for teenagers in the United States. While it is generally agreed that graduated drivers licensing (GDL) influences crash rates, it is unclear which components have the strongest effect on any specific types of crashes.MethodWe analyze the relative effect of different stages of GDL on teenage fatal and injury crash risk via a negative binomial generalized linear model with random state effects. Overall, nighttime, and crashes with multiple teenage passengers are considered.ResultsThe strongest effects are seen by 16-year-olds, for which a strict permit stage is associated with a 58% reduction in fatal crash risk over a lenient permit stage. Similar reductions are seen for injury crashes. The intermediate stage, involving nighttime and passenger restrictions, is associated with a 44% reduction in fatalities but has relatively little effect on injury crashes. The strongest effects are generally seen for passenger crashes, followed by nighttime, and then overall crashes.Impact on IndustryThis study identifies stronger relationships between GDL and crash risk than has previously been discovered and captures the relative effects of permit and intermediate licensing restrictions, two high-level components of GDL which differ in intent and implementation.