Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water Quality Management1

Vidon, Philippe, Craig Allan, Douglas Burns, Tim P. Duval, Noel Gurwick, Shreeram Inamdar, Richard Lowrance, Judy Okay, Durelle Scott, and Steve Sebestyen, 2010. Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water Quality Management. Journal of the American Water Resources Association (JAWRA) 46(2):278-298. DOI: 10.1111/j.1752-1688.2010.00420.x Abstract: Biogeochemical and hydrological processes in riparian zones regulate contaminant movement to receiving waters and often mitigate the impact of upland sources of contaminants on water quality. These heterogeneous processes have recently been conceptualized as “hot spots and moments” of retention, degradation, or production. Nevertheless, studies investigating the importance of hot phenomena (spots and moments) in riparian zones have thus far largely focused on nitrogen (N) despite compelling evidence that a variety of elements, chemicals, and particulate contaminant cycles are subject to the influence of both biogeochemical and transport hot spots and moments. In addition to N, this review summarizes current knowledge for phosphorus, organic matter, pesticides, and mercury across riparian zones, identifies variables controlling the occurrence and magnitude of hot phenomena in riparian zones for these contaminants, and discusses the implications for riparian zone management of recognizing the importance of hot phenomena in annual solute budgets at the watershed scale. Examples are presented to show that biogeochemical process-driven hot spots and moments occur along the stream/riparian zone/upland interface for a wide variety of constituents. A basic understanding of the possible co-occurrence of hot spots and moments for a variety of contaminants in riparian systems will increase our understanding of the influence of riparian zones on water quality and guide management strategies to enhance nutrient or pollutant removal at the landscape scale.     

Herbicide Transport in Goodwater Creek Experimental Watershed: II. Long‐Term Research on Acetochlor,Alachlor, Metolachlor,and Metribuzin1

Lerch, R.N., E.J. Sadler, C. Baffaut, N.R. Kitchen, and K.A. Sudduth, 2010. Herbicide Transport in Goodwater Creek Experimental Watershed: II. Long‐Term Research on Acetochlor, Alachlor, Metolachlor, and Metribuzin. Journal of the American Water Resources Association (JAWRA) 1‐15. DOI: 10.1111/j.1752‐1688.2010.00504.x Abstract: Farmers in the Midwestern United States continue to be reliant on soil‐applied herbicides for weed control in crop production, and herbicide contamination of streams remains an environmental problem. The main objective of this study was to analyze trends in concentration and load of acetochlor, alachlor, metolachlor, and metribuzin in Goodwater Creek Experimental Watershed (GCEW) from 1992 to 2006. A secondary objective was to document the effects of best management practices (BMPs) implemented within GCEW on herbicide transport trends. Median relative herbicide loads, as a percent of applied, were 3.7% for metolachlor, 1.3% for metribuzin, 0.36% for acetochlor, and 0.18% for alachlor. The major decrease in alachlor use and increase in acetochlor use caused shifts in flow‐weighted concentrations that were observed over the entire concentration range. The smaller decrease in metolachlor use led to a consistent decreasing time trend only for the upper end of the concentration distribution. Metribuzin also showed moderate decreases in concentration with time since 1998. Annual loads were generally correlated to second quarter discharge. Despite extensive education efforts in the watershed, conservation BMPs within GCEW were mainly implemented to control erosion, and therefore had no discernable impact on reducing herbicide transport. Overall, changes in herbicide use and second quarter discharge had the greatest effect on trends in flow‐weighted concentration and annual load.     

The Regionalization of National‐Scale SPARROW Models for Stream Nutrients1

Schwarz, Gregory E., Richard B. Alexander, Richard A. Smith, and Stephen D. Preston, 2011. The Regionalization of National‐Scale SPARROW Models for Stream Nutrients. Journal of the American Water Resources Association (JAWRA) 47(5):1151‐1172. DOI: 10.1111/j.1752‐1688.2011.00581.x Abstract: This analysis modifies the parsimonious specification of recently published total nitrogen (TN) and total phosphorus (TP) national‐scale SPAtially Referenced Regressions On Watershed attributes models to allow each model coefficient to vary geographically among three major river basins of the conterminous United States. Regionalization of the national models reduces the standard errors in the prediction of TN and TP loads, expressed as a percentage of the predicted load, by about 6 and 7%. We develop and apply a method for combining national‐scale and regional‐scale information to estimate a hybrid model that imposes cross‐region constraints that limit regional variation in model coefficients, effectively reducing the number of free model parameters as compared to a collection of independent regional models. The hybrid TN and TP regional models have improved model fit relative to the respective national models, reducing the standard error in the prediction of loads, expressed as a percentage of load, by about 5 and 4%. Only 19% of the TN hybrid model coefficients and just 2% of the TP hybrid model coefficients show evidence of substantial regional specificity (more than ±100% deviation from the national model estimate). The hybrid models have much greater precision in the estimated coefficients than do the unconstrained regional models, demonstrating the efficacy of pooling information across regions to improve regional models.     

基于模型模拟的成都市PM2.5污染来源解析

在建立成都市大气污染物排放清单的基础上,采用源开关敏感性分析法,设置8个排放情景,基于WRF-CMAQ模型模拟分析了2015年1、4、7和10月这4个典型代表月份的大气污染传输和不同行业对成都市PM_(2.5)污染贡献.结果表明成都市PM_(2.5)污染较重,特别是1月达到130μg·m~(-3)以上;浓度的高值集中在中心城区,且与周边城市PM_(2.5)污染连接成片.由于气团比较稳定,大气污染物的区域传输能力较弱,成都市PM_(2.5)污染以本地源的贡献为主,占比为61%.从行业贡献来看,移动源、扬尘源和生活源对成都市PM_(2.5)年均浓度贡献率分别为29%、26%和24%,是影响PM_(2.5)污染的主要污染源,下一步应强化对这3类源的污染控制.     

碘普罗胺降解菌Pseudomonas sp. I-24共代谢降解性能研究

菌株Pseudomonas sp.I-24(I-24)难以利用碘普罗胺(IOP)作为唯一的碳源和能源进行生长和代谢,因此本研究选用淀粉、麦芽糖、葡萄糖和甘油作为I-24共代谢IOP的外加碳源,考察了在摇瓶实验中,不同外加碳源对I-24生长及降解IOP的影响.结果表明,I-24共代谢IOP符合一级反应动力学特征,淀粉对共代谢过程的促进作用最为显著,IOP的五日降解率可达到92.7%,I-24的IOP降解酶活力在培养第3 d达到最高0.182 mU,淀粉投加的最佳浓度为1 g·L-1,然而葡萄糖和麦芽糖分别对I-24的生长和电子传递系统活性(ETSA)有着最佳促进作用,表明降解菌生长过快将导致竞争性抑制,降低IOP降解率,同时ETSA与共代谢作用无直接关联.此外,从空白样表现出的酶活力得出IOP降解酶即使在低基质条件下同样可被诱导产生.     

城市生活垃圾集装箱转运过程中污染物产生状况研究

以上海市某生活垃圾中转站垃圾集装箱为研究对象,分析了1 a不同季节中转站集装箱内垃圾二次污染物的产生和变化规律.结果表明,集装箱内产生的主要气体指标中,H2S的变化范围为0.3~10.3 mg·m-3;CH4的变化范围为0.02%~2.97%;NH3的变化范围为0.7~4.5 mg·m-3,浓度峰值都出现在夏季.产生的渗滤液水质指标中,pH值在5.4~6.3之间变化,呈现酸性;SS在9 120~32 475 mg·L-1之间变化,波动较大;有机物COD的变化范围为41 633~84 060 mg·L-1,BOD5在18 116~34 130 mg·L-1之间变化,呈现出冬季高于夏季的特点;氨氮和总磷的变化范围分别为537~1 222 mg·L-1和17.98~296 mg·L-1之间,季节变化不明显.极端温度特别是夏季高温对箱体内气体污染物的产生影响明显,警示夏季要谨防在高温暴露和过长的停留时间,以防止易燃易爆气体和其他污染物的大量产生.     

北京城区冬季空气污染时期C2~C6碳氢化合物含量特征

本研究于2015年冬季,在北京市东南城区开展了C2~C6碳氢化合物大气环境浓度在线监测,研究共检出25种C2~C6碳氢化合物,但鉴于分析仪器的局限性,未包含苯这一重要物种.检出的25种碳氢化合物含量之和(C2~C6 HCs)在12.4~297.5×10~(-9)范围内,不同的空气质量条件下,C2~C6 HCs平均含量分别为29.4×10~(-9)(Ⅰ级,PM_(2.5):35μg·m~(-3))、63.2×10~(-9)(Ⅱ级,PM_(2.5):35~75μg·m~(-3))、85.5×10~(-9)(Ⅲ级,PM_(2.5):75~150μg·m~(-3))、94.9×10~(-9)(Ⅳ级,PM_(2.5):150~250μg·m~(-3))、131.8×10~(-9)(Ⅴ级,PM_(2.5):250μg·m~(-3)),且碳氢化合物的化学组成亦有所差异,烷烃、烯烃、乙炔的摩尔比分别从Ⅰ级条件的47%、45%、7%,变为Ⅴ级条件的59%、30%、12%,烷烃和乙炔的比重上升;烯烃的比重下降.碳氢化合物日变化规律显示,C2~C6 HCs在优良日(PM_(2.5)小时浓度均低于75μg·m~(-3))和污染日(PM_(2.5)小时浓度均高于75μg·m~(-3)),均在08:00~09:00、17:00~18:00存在两个明显的峰值,与日交通峰值时间一致,显示了道路源对局地碳氢化合物浓度的显著影响.通过HCs与CO浓度比值研究,发现随着污染情况的加重,HCs/CO(×10~(-9)/×10~(-6))呈显著下降趋势:90.6(Ⅰ级)、63.8(Ⅱ级)、56.9(Ⅲ级)、37.4(Ⅳ级)、36.4(Ⅴ级).具体化合物与CO比值在污染条件(Ⅲ~Ⅴ)与优良条件(Ⅰ~Ⅱ)的变化率,与各化合物的OH反应速率关联性很差(R=-0.31),由此判断污染时期C2~C6碳氢化合物并未发生强烈的化学衰减.HCs/CO比值变化更多反映了污染源贡献的变化,后向轨迹分析表明,在优良日北京城区多受北部和西北部清洁气团影响,北部地区燃烧源较少,其气团HCs/CO比值较高;而在污染日北京城区受南部和西南部污染气团输送,南部地区工业燃烧源和散煤燃烧源均偏多,其气团HCs/CO值偏低.综上所述,本研究认为重污染过程,北京城区C2~C6碳氢化合物(未包含苯)未体现出显著的化学衰减,碳氢化合物浓度的大幅提升,不仅源于本地污染源的排放累积,还受到南部污染气团的输送贡献.     

离子类型、强度和铁氧化物影响下微塑料的迁移行为及模型计算

土壤中的微塑料（MPs）作为一种新型污染物而被广泛关注,其迁移行为受到自身理化性质、土壤溶液化学组成和土壤矿物等因素的影响.目前,铁氧化物存在时,离子类型和离子强度对MPs迁移行为的影响机制尚不明确.通过稳定性实验和迁移实验,重点考察了离子类型、离子强度和铁氧化物对带有不同官能团聚苯乙烯微塑料（PSMPs）迁移行为的影响,并用胶体迁移模型、CD-MUSIC模型及DLVO理论探讨其迁移机制.结果表明,PSMPs在NaH₂PO₄背景下的稳定性最强,标准化浓度（c/c₀）达到0.99,而在CaCl₂背景下的稳定性相对弱,c/c₀降低至0.94.不同离子种类对PSMPs的迁移行为产生不同影响,对于阳离子Na⁺和Ca²⁺,二价Ca离子有架桥作用和较强的电荷中和作用,更能阻滞PSMPs在石英砂中的迁移,出水溶液中PSMPs回收率低至（43.83±1.71）%且第二动力学位点上的一级保留系数k_2a为1.54 min^-1,铁氧化物会进一步加剧阻滞作用,回收率降低为（6.04±0.40）%且k_2a升高为5.33 min^-1;对于阴离子Cl^-和PO₄^3-,PSMPs在纯石英砂柱中的迁移主要受其自身表面电负性的控制,Cl^-离子下PSMPs电负性更低,回收率升高［（92.95±0.63）%］且k_2a降低（0.19 min^-1）,而当铁氧化物存在时,PSMPs的迁移则受控于载铁石英砂表面的Zeta电位.CD-MUSIC模型计算结果显示PO₄^3-容易吸附在铁氧化物表面形成内圈络合物,降低载铁石英砂表面的电负性,因此PSMPs在PO₄^3-背景下的回收率升高［（76.22±1.39）%］且k_2a降低（0.66 min^-1）;同时,该内圈络合物的形态受PO₄^3-浓度的控制且不同形态的内圈络合物具有不同的表面负电荷数,因此高PO₄^3-浓度下载铁石英砂表面电负性反而高,不利于PSMPs迁移.此外,PSMPs的迁移均随着离子强度的增加而降低.最后,DLVO理论计算出不同条件下PSMPs和介质间的一级势垒变化趋势与PSMPs的迁移能力一致,即较高的一级势垒表明PSMPs和介质间较大的相互斥力有利于PSMPs的迁移,可以更好地阐明PSMPs的迁移行为.     

武汉地区2014年PM2.5时空分布与来源贡献的数值模拟研究

利用耦合了污染源在线追踪模块的化学传输模式NAQPMS （Nested Air Quality Prediction Model System）,结合地面细颗粒物（PM_2.5）的小时观测数据,模拟了2014年1、4、7、10月4个月份武汉地区PM_2.5浓度时空分布特征,量化了本地、武汉城市圈及远距离地区对武汉PM_2.5浓度贡献.研究发现,2014年武汉市PM_2.5年均浓度为85.3 μg·m^-3,污染天（PM_2.5日均值≥75 μg·m^-3）占全年总天数的47.9%.细颗粒物的月均值呈现出季节性特征,即冬季污染最为严峻,1月均值为199.1 μg·m^-3,PM_2.5浓度超标持续一整月;夏季空气质量最好,春秋介于两者之间.模拟的PM_2.5平均浓度在空间上大致呈现"城区高,郊区低"的分布态势.污染物区域来源解析发现,武汉市本地排放源贡献在1月最低,为34.1%,表明外来源贡献对长期灰霾的形成起决定性作用.7月本地源影响最显著（65.7%）,和毗邻城市源（23.1%）一起成为夏季污染物的主要来源.4月和10月本地排放贡献比分别为49.1%和42.1%.4个月份,武汉城市圈对该市PM_2.5浓度的贡献差异不大,范围在20.8%~24.1%.受大尺度天气系统的影响,远距离传输贡献率趋势与本地来源相反,占10.6%~35.3%.研究结果表明污染气团跨界输送对武汉不同季节PM_2.5浓度有重要贡献.在冬季大范围污染背景下,污染物区域大范围协同控制才能有效减缓武汉PM_2.5污染问题;而夏季对本地及近周边城市的减排措施可以有效改善武汉的空气质量.     

重庆南山表层岩溶泉与地下河三氮运移及氮通量估算

岩溶区特殊的地质构造使地下水系统存在多重水流.为研究三氮在表层岩溶带水流和地下河水流中的特征和运移方式,选取城市化进程中的重庆南山老龙洞地下河流域表层岩溶泉和地下河按月采样,分析水化学特征,结合SPSS的相关性分析,认为两种水流三氮特征差异很大.表层岩溶泉三氮质量浓度月变化小,受降水、污水影响较小,NO_3~--NNH_4~+-N;地下河水三氮质量浓度月变化大,受降水、污水影响较大,旱季NH_4~+-NNO_3~--N,雨季NO_3~--NNH_4~+-N.表层岩溶泉DIN主要来源于与农业活动有关的非点源污染,在土壤、表层岩溶带中经氨化、吸附、硝化作用等过程以扩散流形式运移至出露地表.地下河DIN随管道流、扩散流运移,并以管道流为主.DIN全年有点源的工业、生活污染物经落水洞、裂隙、溶隙进入.雨季同时存在占更大比例的非点源污染物,或由降雨产生的表面坡流、壤中流、表层岩溶带水流经落水洞进入,或经深裂隙、溶隙下渗进入,硝化作用明显.流域DIN输出通量为56.05 kg·(hm~2·a)~(-1),其中NH_4~+-N、NO_3~--N分别占46.03%、52.51%;根据径流分割法估算出点源污染、非点源污染的贡献率分别为25.08%、74.92%.