RELATION OF NITRATE CONCENTRATIONS TO BASEFLOW IN THE RACCOON RIVER,IOWA1

ABSTRACT: Excessive nitrate‐nitrogen (nitrate) export from the Raccoon River in west central Iowa is an environmental concern to downstream receptors. The 1972 to 2000 record of daily streamflow and the results from 981 nitrate measurements were examined to describe the relation of nitrate to streamflow in the Raccoon River. No long term trends in streamflow and nitrate concentrations were noted in the 28‐year record. Strong seasonal patterns were evident in nitrate concentrations, with higher concentrations occurring in spring and fall. Nitrate concentrations were linearly related to streamflow at daily, monthly, seasonal, and annual time scales. At all time scales evaluated, the relation was improved when baseflow was used as the discharge variable instead of total streamflow. Nitrate concentrations were found to be highly stratified according to flow, but there was little relation of nitrate to streamflow within each flow range. Simple linear regression models developed to predict monthly mean nitrate concentrations explained as much as 76 percent of the variability in the monthly nitrate concentration data for 2001. Extrapolation of current nitrate baseflow relations to historical conditions in the Raccoon River revealed that increasing baseflow over the 20th century could account for a measurable increase in nitrate concentrations.     

岷江干流（成都段）水体污染防治对策研究

本文通过对岷江干流（成都段）地表水和地下水的综合研究，分别提出了地表水污染防治对策和地下水水质防护措施，划分出了地表水防治不同时期的目标以及地下水开采管理目标。     

天津地区表层土中饱和烃的组成与分布特征

为揭示天津地区不同环境功能区表层土壤中饱和烃污染特征及其来源,分析了该地区几个具代表性的环境功能区表层土(0～25cm)中饱和烃化合物的组成和分布特征,重点讨论了正构烷烃和甾、萜烷烃类化合物的组成、分布及环境意义,比较了不同层次(亚层)(0～5cm,5～10cm,10～15cm,15～20cm,20～25cm)中这些化合物及相关的地球化学参数的变化规律。结果表明,不同采样点以及同一采样点的不同亚层之间正构烷烃的组成特征存在不同程度的差别,而甾、萜烷烃类化合物组成与分布特征均较为接近。正构烷烃以及甾、萜类地球化学参数综合分析揭示,不同采样点之间正构烷烃的来源多样,中低分子量的正构烷烃主要来源于石油等化石燃料,高分子量正构烷烃主要来源于高等植物蜡的分解产物,但甾、萜烷烃类化合物的来源是一致的,且主要来源于石油烃污染。不同采样点表层土中饱和烃的来源及污染程度均存在一定的差别,市区、油田附近、经济开发区以及近郊区受石油源影响较重,北部山区污染较轻,且主要来源于高等植物的降解。除个别采样点外,同一采样点不同亚层之间饱和烃的组成特征基本一致,表明污染源是一致的,主要来源由表层污染物往下迁移所致。     

基于ANSYS-PDS的含缺陷压力容器可靠性分析

为更准确地分析含缺陷压力容器的可靠性,提出采用ANSYS软件中的PDS模块建模求解,从本质上克服API 581压力容器可靠性分析的局限性,采用将压力容器的内径、原始壁厚、缺陷深度、压力容器内压设置为服从正态分布的随机变量的方法,基于响应面法结合蒙特卡洛法抽样分析,通过编写APDL代码,探讨含缺陷压力容器的可靠性.结果表...     

表面漆对地板材料火灾初期热释放特性影响的研究

漆与木材是两种不同性质的材料,带有表面漆和不带表面漆的木地板在火灾初期的热释放特性有所不同。本文利用锥形量热计对不同辐射能量条件下的两类木地板的释热特性了实验研究,发现漆对木地板的点燃性和点燃初期的释热特性有较大的影响。这种影响与木材的种类和外部辐射能量的大小有密切的关系。     

煤层注水过程分析和煤体润湿机理研究

分析了煤层注水过程中水在煤体中的运动动力和过程,用界面化学理论分析了煤体表面的润湿过程,得出了煤体能够自行润湿的条件,即润湿过程的润湿功必须为正,同时得出了各种润湿过程的判断依据.根据上述理论分析,阐明了煤层注水降尘的润湿机理,为煤层注水提供理论基础.     

INCREASED BASEFLOW IN IOWA OVER THE SECOND HALF OF THE 20TH CENTURY1

ABSTRACT: Historical trends in annual discharge characteristics were evaluated for 11 gauging stations located throughout Iowa. Discharge records from nine eight‐digit hydrologic unit code (HUC‐8) watersheds were examined for the period 1940 to 2000, whereas data for two larger river systems (Cedar and Des Moines Rivers) were examined for a longer period of record (1903 to 2000). In nearly all watersheds evaluated, annual base flow, annual minimum flow, and the annual base flow percentage significantly increased over time. Some rivers also exhibited increasing trends in total annual discharge, whereas only the Maquoketa River had significantly decreased annual maximum flows. Regression of stream discharge versus precipitation indicated that more precipitation is being routed into streams as base flow than as storm flow in the second half of the 20th Century. Reasons for the observed stream flow trends are hypothesized to include improved conservation practices, greater artificial drainage, increasing row crop production, and channel incision. Each of these reasons is consistent with the observed trends, and all are likely responsible to some degree in most watersheds.     

Does the Temporal Resolution of Precipitation Input Influence the Simulated Hydrological Components Employing the SWAT Model?

This study aimed to evaluate the influence of sub‐daily precipitation time steps on model performance and hydrological components by applying the Green and Ampt infiltration method using the Soil and Water Assessment Tool (SWAT). Precipitation was measured at a resolution of 0.1 mm and aggregated to 5‐, 15‐, 30‐, and 60‐min time steps. Daily discharge data over a 10‐year period were used to calibrate and validate the model. Following a global sensitivity analysis, relevant parameters were optimized through an automatic calibration procedure using SWAT‐CUP for each time step. Daily performance statistics were almost equal among all four time steps (NSE ≈ 0.47). Discharge mainly consisted of groundwater flow (55%) and tile flow (42%), in reasonable proportions for the investigated catchment. In conclusion, model outputs were almost identical, showing simulations responded nearly independently of the chosen precipitation time step. This held true for (1) the selection of sensitive parameters, (2) performance statistics, (3) the shape of the hydrographs, and (4) flow components. However, a scenario analysis revealed that the precipitation time step becomes important when saturated hydraulic conductivities are low and curve numbers are high. The study suggests that there is no need in using precipitation time steps <1 h for lowland catchments dominated by soils with a low surface runoff potential if daily flow values are being considered. Editor's note : This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.     

微磁场条件下pH冲击对微氧活性污泥表面性质的影响

研究了微磁场条件下pH冲击对处理低负荷葡萄糖废水的微氧活性污泥表面性质的影响。在pH=6.0和9.0的条件下对添加磁粉和无磁粉反应器微氧活性污泥进行15 d的冲击,而后调整pH=7.5进行5 d的恢复实验。对pH冲击下污泥絮凝能力FA、疏水性RH和表面电荷SC的变化情况进行考察,结果表明,有磁粉反应器的各项指标均优于无磁粉反应器。经过5 d的恢复实验,添加磁粉反应器污泥的各指标均能恢复到接近初始值,而无磁粉反应器污泥难以恢复到接近初始值。     

地表水中微量氯代芳烃和硝基取代芳烃化合物的分析方法

建立了固相萃取、毛细管气相色谱-电子捕获检测、内标标准曲线法定量分析地表水中十三种氯苯、硝基氯苯和硝基苯类化合物的方法.该法对这些化合物的平均回收率在62%-101%之间,变异系数在3%-27%之间,方法最小检测浓度在0.01-1.31μg·1-1之间.应用本方法对太湖水中的氯代芳烃和硝基取代芳烃化合物进行了三次采样分析,定量重现性较好.