Modeling Parent and Metabolite Fate and Transport in Subsurface Drained Fields With Directly Connected Macropores1

Abstract: Few studies exist that evaluate or apply pesticide transport models based on measured parent and metabolite concentrations in fields with subsurface drainage. Furthermore, recent research suggests pesticide transport through exceedingly efficient direct connections, which occur when macropores are hydrologically connected to subsurface drains, but this connectivity has been simulated at only one field site in Allen County, Indiana. This research evaluates the Root Zone Water Quality Model (RZWQM) in simulating the transport of a parent compound and its metabolite at two subsurface drained field sites. Previous research used one of the field sites to test the original modification of the RZWQM to simulate directly connected macropores for bromide and the parent compound, but not for the metabolite. This research will evaluate RZWQM for parent/metabolite transformation and transport at this first field site, along with evaluating the model at an additional field site to evaluate whether the parameters for direct connectivity are transferable and whether model performance is consistent for the two field sites with unique soil, hydrologic, and environmental conditions. Isoxaflutole, the active ingredient in BALANCE^® herbicide, was applied to both fields. Isoxaflutole rapidly degrades into a metabolite (RPA 202248). This research used calibrated RZWQM models for each field based on observed subsurface drain flow and/or edge of field conservative tracer concentrations in subsurface flow. The calibrated models for both field sites required a portion (approximately 2% but this fraction may require calibration) of the available water and chemical in macropore flow to be routed directly into the subsurface drains to simulate peak concentrations in edge of field subsurface drain flow shortly after chemical applications. Confirming the results from the first field site, the existing modification for directly connected macropores continually failed to predict pesticide concentrations on the recession limbs of drainage hydrographs, suggesting that the current strategy only partially accounts for direct connectivity. Thirty‐year distributions of annual mass (drainage) loss of parent and metabolite in terms of percent of isoxaflutole applied suggested annual simulated percent losses of parent and metabolite (3.04 and 1.31%) no greater in drainage than losses in runoff on nondrained fields as reported in the literature.     

Density functional theory (DFT) studies of vanadium-titanium based selective catalytic reduction (SCR) catalysts

Based on density functional theory (DFT) and basic structure models, the chemical reactions on the surface of vanadium-titanium based selective catalytic reduction (SCR) denitrification catalysts were summarized. Reasonable structural models (non-periodic and periodic structural models) are the basis of density functional calculations. A periodic structure model was more appropriate to represent the catalyst surface, and its theoretical calculation results were more comparable with the experimental results than a non-periodic model. It is generally believed that the SCR mechanism where NH₃ and NO react to produce N₂ and H₂O follows an Eley-Rideal type mechanism. NH₂NO was found to be an important intermediate in the SCR reaction, with multiple production routes. Simultaneously, the effects of H₂O, SO₂ and metal on SCR catalysts were also summarized.     

滇池水中细菌和古菌氮代谢功能基因的空间分布

氮代谢在滇池水生态系统氮素循环和转化过程中起到重要的作用,不仅真核生物参与氮素转化,原核生物作为氮素循环的主要驱动者,在氮素生物化学循环中的作用更不容忽视.基于16S rDNA高通量测序技术,监测滇池草海和外海区域13个点位,分析滇池水中原核生物氮循环功能关键基因的分布特征.结果发现,滇池水中细菌35门, 427属,主要以变形菌门和拟杆菌门为优势门类;古菌14门, 61属,主要以广古菌门为优势门类;β多样性指数显示滇池整体细菌丰富度指数高于古菌,草海细菌多样性指数高于外海.PICRUSt功能解析表明细菌和古菌具有功能上的丰富性,细菌中有35个参与氮代谢的KO通路,涉及氮异化硝酸盐还原基因nirB、一氧化氮还原酶基因norB和硝酸还原酶基因nasK等关键基因;古菌中有23个参与氮代谢的KO通路,涉及固氮酶基因nifH、nifK和nifD,古菌固氮酶基因拷贝数显著高于其它氮代谢基因,草海中古菌氮代谢能力整体高于外海,滇池水中古菌比细菌固氮潜能更大.本研究从原核生物氮循环中功能基因的角度,探讨滇池不同区域水中细菌和古菌氮循环差异,为进一步揭示氮循环机制,解决氮素污染引起的富营养化提供理论参考.     

低温下丝状菌膨胀污泥的微生物多样性

为探究低温下丝状菌污泥膨胀过程中微生物多样性的变化特征,实验采用低温-SBR反应器成功诱发污泥膨胀,并借助Illumina MiSeq高通量测序技术,考察了不同沉降性能下活性污泥微生物群落的整体变化特征、各特定菌群及特定菌属的变化特征.结果表明,在系统运行温度降至(14±1)℃后可成功诱发丝状菌污泥膨胀,SVI可恶化至663.99 mL·g~(-1),且膨胀后COD去除率和TN去除率仍能维持在90%和86%左右.低温下污泥膨胀的发生不仅会导致系统内微生物整体多样性和均一性的降低,使特定菌群中丝状菌群的丰度由0.49%增至26.04%,还会使脱氮菌群的丰度由21.04%减少至13.99%、除磷菌群的丰度由4.25%减少至1.93%.发现的5种丝状菌属中,以Thiothrix为代表的3种菌属的丰度递增,仅Haliscomenobacter的丰度递减;发现的19种脱氮菌属中,以Nitrosomonas为代表的5种菌属的丰度递增,以Nitrospira为代表的7种菌属的丰度递减;发现的8种除磷菌属中,Pseudomonas和Tetrasphaera的丰度递增,以Candidatus_Competibacter为代表的5种菌属的丰度递减.虽然污泥膨胀对微生物菌群结构产生较大影响,但不同泥样中始终存在的477个OTUs和227个菌属说明膨胀过程中反应器内主体微生物仍呈相对稳定状态.     

基于不同废污泥源的短程反硝化快速启动及稳定性

为探究不同废污泥源快速启动短程反硝化和实现稳定NO_2~--N积累的可行性,在3个完全相同的SBR反应器(S1、S2和S3)分别接种:实验室城市污水反硝化除磷系统排泥、城市污水厂剩余污泥及河涌底泥,比较其短程反硝化启动快慢和NO_2~--N积累特性,考察系统短程反硝化活性和NO_3~--N→NO_2~--N转化性能,并从微生物学角度分析反应器功能菌群特征.结果表明,在乙酸钠为唯一碳源、高碱度和适宜COD/NO_3~--N比进水条件下,3个SBR短程反硝化反应器在短时间内均能够成功启动,系统平均NO_3~--N→NO_2~--N转化率为S1 S2 S3(75. 92% 73. 36% 69. 90%).同时发现持续低温条件下S1和S2呈现不同程度的短程反硝化性能恶化趋势,但S3能够稳定维持良好NO_2~--N积累性能.微生物高通量测序表明,变形菌门和拟杆菌门居PD系统主导地位,3个短程反硝化反应器NO_2~--N积累关键功能菌属Thauera属丰度差异明显:S3 S1 S2(25. 09% 4. 71% 3. 60%),表明S3具备稳定高效的NO_2~--N积累性能,同时高丰度Thauera属可能是维持低温短程反硝化活性的重要原因.     

不同轮作模式下作物根际土壤养分及真菌群落组成特征

为研究宁夏中部干旱带不同轮作模式下土壤养分及真菌群落组成的特征,以谷子轮作大豆（MRG）、轮作籽粒苋（MRA）、轮作藜麦（MRQ）及谷子连作（CK）为对象,测定了土壤养分含量,并利用Illumina MiSeq高通量测序平台测定了土壤真菌的ITS变异区序列.结果表明,不同轮作模式对土壤养分的影响存在差异.3种轮作模式下土壤pH和电导率均有所下降,土壤全氮、全钾、全磷和有机质含量均上升,OTUs数和α多样性指数均高于连作.真菌群落组成研究结果显示,子囊菌门（Ascomycota）为4种模式下的优势菌群.聚类分析显示MRA和MRG的真菌属组成最为相似,其次是MRQ,CK与3种轮作模式相差较大.相关性分析显示,土壤养分与几种优势真菌属呈显著相关性（P<0.05或P<0.01）,土壤全氮、全钾、硝态氮和有机质含量是影响土壤真菌群落最主要的因子.主成分分析（PCA）表明,MRG轮作模式优于MRA和MRQ模式.综上所述,轮作提高了真菌群落多样性指数,改变了土壤真菌群落结构,改善了土壤肥力状况,其中以谷子与大豆轮作效果最佳,建议将谷豆轮作作为中部干旱带杂粮产业中主要的轮作模式之一进行推广.     

基于稳定氢同位素的太原市大气单环芳烃来源

采集太原市城北和城南区域环境空气和5类污染源挥发性有机物样品,测定样品中典型单环芳烃稳定氢同位素（δD）组成,基于同位素质量平衡原理计算单环芳烃从源到环境空气受体的δD初始混合值,探讨单环芳烃来源.结果表明,柴油挥发源、溶剂挥发源、汽油挥发源（97^#）、汽油挥发源（95^#）、机动车尾气（97^#）、机动车尾气（95^#）和民用燃煤源中单环芳烃δD范围依次为：（-138.7‰~-115.5‰）、（-147.0‰~-121.0‰）、（-150.8‰~-117.6‰）、（-131.8‰~-113.8‰）、（-171.2‰~-120.0‰）、（-138.9‰~-102.7‰）和（-168.3‰~-142.3‰）,民用燃煤源中单环芳烃δD显著贫重氢同位素（D）组成,机动车尾气源与汽油挥发源中苯的δD相比显著贫D,可用于探索污染物转化过程;城北和城南环境空气中δD范围为（-131.7‰~-115.1‰）和（-131.9‰~-74.9‰）,δD初始混合值为-138.4‰和-173.9‰,体现了其来源差异.     

乡村振兴视域下农村土地利用利益相关者分析

乡村振兴的实施使得农村土地利用与管理面临更多的挑战。应用利益相关者分析、博弈均衡分析和实证案例分析,探讨乡村振兴视域下土地利用各利益相关者的关系演变。研究结果显示：（1）1949年至今,农村地区土地利用利益相关者主体数量增加,博弈关系呈现复杂化、多样化和多向化;（2）乡村振兴时期主要有六种博弈关系,并探讨了案例村实施下山脱贫、发展乡村旅游、新型经营主体进驻、城市居民促进农村发展四种博弈决策过程;（3）乡村振兴视域下,农村地区发展应关注基础设施配套、土地利用效率与生态环境协调、农户生计可持续性等问题。乡村振兴中应注重实现土地利用各利益相关者的最优均衡,降低各方风险,保护生态环境并寻求多方利益平衡。     

2006—2018年中国省级以上开发区的空间分布特征变化

以新的国土空间规划语境为背景,基于核密度估计、标准差椭圆法和分类统计对我国2006—2018年省级以上开发区的密度分布特征变化、发展重心轴向的变化和主体功能区视角下的分布变化做了分析。研究表明：该阶段我国省级以上开发区空间分布的东西差距得到一定缓解,仍存在东部连片集聚、西部据点集中的模式差异。开发区分布的总体重心已经向西北方向移动,发展轴向则由原来的南北轴向转向了东南—西北轴向。从主体功能区视角来看,开发区空间分布格局呈现出外围扩散与局部缩减的动态调整。开发区规模的增长主要集中在重点开发区域,缩减主要发生在生态功能区域。这些新变化将为我国国土空间土地利用优化和国土空间管控实践提供重要参考。     

Pt-Sn/Al2O3蜂窝催化剂催化氧化C6烃

采用等体积分浸法制备Pt-Sn/Al₂O₃蜂窝催化剂（Pt含量仅为0.06wt%）.运用X射线衍射（XRD）、透射电镜（TEM）等技术对催化剂理化性质进行表征,并选取4种代表性C₆烃（苯、环己酮、环己烷和正己烷）对催化剂性能进行评价.活性评价试验中,Pt/Sn比为3/1催化效果最佳.此时4种C₆烃转化率达到90%的温度（T₉₀）较Pt催化剂均降低约20℃,其原因在于Sn可将Pt分割为较小的团簇提高Pt分散度.寿命评价试验以环己烷为例同Pt-Sn蜂窝催化剂连续运行720h,催化活性无明显变化,其原因在于,Sn可有效抑制其粒径增长;Pt₃Sn合金降低表面对C₆烃的吸附,减少催化剂表面积炭.