Impact of Channelization on Oyster Production: A Hydrodynamic-Oyster Population Model for Galveston Bay, Texas

A hydrodynamic-oyster population dynamics model was developed to assess the effect of a change in ship channel configuration under different freshwater inflow regimes and different future hydrologies on oyster (Crassostrea virginica) populations in Galveston Bay, Texas. The population dynamics model includes the effects of environmental conditions, predators, and the oyster parasite Perkinsus marinus on oyster populations. The hydrodynamic model includes the effects of wind stress, river runoff, tides, and oceanic exchange on the circulation of the Bay. Simulations were run for low, mean, and high freshwater inflow conditions under the present (1993) hydrology and predicted hydrologies for 2024 and 2049 that include anticipated water diversion projects to satisfy the freshwater demands of population growth in metropolitan Houston, Texas. Simulation results show that oyster biomass was predicted to increase after enlargement of the ship channel. Oyster biomass is expected to increase on about 53% of total reef acreage when averaged over a 50-yr time span. Oyster reef acreage characterized by increased biomass after channel enlargement increases moderately under the present hydrology and the 2049 hydrology, but decreases slightly in 2024. Lower biomass in 2024 is due to reduced freshwater inflow and increased saltwater intrusion that pushes the optimal areas for oyster growth somewhat farther upbay than in 2049. Declines in oyster biomass, noted in most simulations in downbay reaches, were more than balanced by increased oyster biomass upbay. The differential between upbay and downbay reefs can be explained by an increase in mortality from Perkinsus marinus downbay and saltwater intrusion upbay that expands the area characterized by moderate salinities. The 20th century history of Galveston Bay is one of expansion of isohaline structure and increased oyster production as a result of anthropogenic modification of bay physiography. The salinity gradient of the 1990s, however, is not in equilibrium with the distribution of hard substrate required for oyster growth, that reflects an earlier equilibrium with the pre-1900s hydrodynamics. Increased saltwater intrusion is normally disadvantageous to oyster populations; but, in this case, channel enlargement further expands the salinity gradient upbay and outward (east and west) from the channel. As a result, in most years, oyster biomass is increased because moderate salinities cover more of the pre-1900s reef tracts where hard substrate is plentiful.     

Numerical Modeling on the Effect of Dissolved Oxygen on Nitrogen Transformation and Transport in Unsaturated Porous System

Nitrogen pollution in groundwater resulting from wastewater application to land is a common problem, and it causes a major threat to groundwater-based drinking water supplies. In this study, a numerical model is developed to study the nitrogen species transport and transformation in unsaturated porous media. Further, a new mass transfer module for dissolved oxygen (DO) is incorporated in the one-dimensional numerical model for nitrogen species transport to describe the fate and transport of nitrogen species, dissolved oxygen, dissolved organic carbon (DOC), and biomass. The spatial and temporal variation of dissolved oxygen is incorporated in the model through the mass transfer from gaseous phase to water phase in an unsaturated porous system. The numerical results of the water flow model and single species and multispecies transport model in an unsaturated zone developed for this purpose have been validated with the available analytical/numerical solution. The developed model is applied in clay loam, silt, and sand soils to analyze the transport behavior of nitrogen species under unsaturated condition. The numerical results suggest that the high rate of oxygen mass transfer from the air phase to the water phase positively increases the dissolved oxygen in the applied wastewater and enhances the nitrification process. Because of this high oxygen mass transfer, the nitrate nitrogen concentration significantly increases in the unsaturated zone and the same is transported to a larger depth at higher simulation period. On the other hand, the low rate of oxygen mass transfer implicitly enhances the denitrification process and finally reduces the nitrate nitrogen concentration in the unsaturated zone. The numerical results also show that the nitrate nitrogen transport is rapid in sandy soil when compared with clay loam and silty soils under high oxygen mass transfer rate. In essence, the high oxygen mass transfer rate significantly increases the nitrate nitrogen in the unsaturated zone, especially at a greater depth at larger time levels and eventually affects the groundwater quality.     

Hydrogeochemical features of groundwater of semi-confined coastal aquifer in Amol–Ghaemshahr plain, Mazandaran Province, Northern Iran

Hydrogeochemical data of groundwater from the semi-confined aquifer of a coastal two-tier aquifer in Amol–Ghaemshahr plain, Mazandaran Province, Northern Iran reveal salinization of the fresh groundwater (FGW). The saline groundwater zone is oriented at an angle to both Caspian Sea coastline and groundwater flow direction and extends inland from the coastline for more than 40 km. Spearman’s rank correlation coefficient matrices, factor analysis data, and values of C ratio, chloro-alkaline indices, and Na⁺/Cl^? molar ratio indicate that the ionic load in the FGW is derived essentially from carbonic acid-aided weathering of carbonates and aluminosilicate minerals, relict connate saline water, and ion exchange reactions. Saline groundwater samples (SGWS) (n?=?20) can be classified into two groups. SGWS of group 1 (n?=?17) represent the saline groundwater zone below the Caspian Sea level, and salinization is attributed essentially to (1) lateral intrusion of Caspian seawater as a consequence of (a) excessive withdrawal of groundwater from closely spaced bore wells located in the eastern part of the coastal zone and (b) imbalance between recharge and discharge of the two-tier aquifer and (2) upconing of paleobrine (interfaced with FGW) along deep wells. SGWS of this group contain, on average, 7.9 % of saltwater, the composition of which is similar to that of Caspian seawater. SGWS of group 2 (n?=?3) belong to the saline groundwater zone encountered above the Caspian Sea level, and salinization of the groundwater representing these samples is attributed to irrigation return flow (n?=?2) and inflow of saline river water (n?=?1).     

固体进样-电热蒸发-原子吸收法测定土壤中的镉

采用固体进样原子吸收法直接测定土壤中的镉,可以避免传统酸消解预处理过程耗时长、试剂消耗大、操作步骤繁琐等缺点,提升镉的检测效率。通过优化测镉仪的仪器参数,确定了固体进样-电热蒸发-原子吸收法的优化仪器条件。采用优化条件测定了不同浓度的土壤样品,研究了该方法的检出限、正确度、精密度。研究结果表明:镉质量范围为0~200 ng时与峰面积的线性相关系数优于0.999 5,空气流下优化的灰化温度和热解温度均为800 ℃,优化的热解气体氢气流量为300 mL/min,当样品进样量为0.1 g时,检出限为0.009 mg/kg,7次连续测定相对标准偏差为1.4%~5.0%,加标回收率为96.2%~102.1%,分析时间小于4 min。该方法操作简便,用时短,无需高压气源,可以用于土壤中镉的高效检测。     

恒压氮气隔断连续流动分析法测定水中化学需氧量

为建立恒压氮气隔断连续流动分析法测定水样化学需氧量的分析方法,将连续流动分析法恒流空气隔断改为恒压氮气隔断,优化试剂配方和反应模块,结果表明：恒压氮气隔断法注入氮气的压力是0.06 MPa,仪器稳定时间是20～35 min,持续分析样品时间大于4 h,指标均优于恒流空气隔断法;标准曲线在2.5～40.0 mg/L范围内,相关系数大于0.999,方法检出限为0.44 mg/L,相对标准偏差为0.2%～2.6%,加标回收率在93.8%～103.8%之间,检出限优于恒流空气隔断法,精密度和正确度满足质量控制要求;实样和标样方法比对测定结果相对标准偏差小于5%,结果精密度优于标准的手工法。恒压氮气隔断连续流动分析法适用于大批量低浓度水样化学需氧量的快速检测,对于密度大、黏度大液流恒压氮气隔断具有更好的稳定性、灵敏度和正确度。     

Saturated and Unsaturated Water Flow in Inclined Porous Media

This paper considers the two-dimensional saturated and unsaturated flow of water through inclined porous media, namely a waste dump or hill slope. Since the partial differential equation governing this water flow transforms from being parabolic to elliptic as the water flow varies from unsaturated to saturated, an iterative, finite differencing scheme is used to develop a numerical solution. The model can be used to investigate the effects that hill slope angle, depth of soil cover and hilltop width have on water accumulation in the dump and the time required for saturation to occur at different areas in the dump domain. The accuracy and reliability of the computer based solution is tested for two different boundary conditions – (1) no flow on all boundaries (i.e., the internal redistribution of soil moisture to steady state) and (2) a constant rainfall flux on the dump surface. Numerical studies then show the effects of changing the hill slope angle, depth of layer, and dump geometry on the flow characteristics in the dump.     

平流层臭氧深度侵入对典型城区的影响过程分析

中纬度平流层臭氧深度侵入是造成对流层至近地面臭氧浓度突增的原因之一。筛选春夏季臭氧浓度升高时段的高分辨率大气再分析数据ERA5,以位涡值的下沉趋势分析了对流层顶折叠位置及变化过程;以AIRS数据反演了臭氧浓度、一氧化碳浓度和相对湿度的垂直廓线,并估计了其分布及相关性;以近地表污染物浓度变化、HYSPLIT模型后向轨迹分析结果证实了臭氧侵入气团的运移轨迹和局地效应;通过激光雷达监测结果观测臭氧垂直浓度分布,确定了臭氧浓度最大值所处高度,判定了受影响近地点的浓度升高时刻;以边界层高度变化、气象条件分析结果及当地与周边城市地面监测数据的逐小时变化情况等综合信息,进行了区域确认和近地面影响判定。通过以上数值综合分析,对城市地区受平流层臭氧深度侵入影响的过程和具体时间进行了详细再现,可为排除非人为排放因素导致的近地表臭氧浓度增加提供回溯分析,为臭氧污染防控决策提供依据。     

Can groundwater vulnerability models assess seawater intrusion?

This study examines the uncertainty associated with two commonly used GIS-based groundwater vulnerability models, DRASTIC and EPIK, in assessing seawater intrusion, a growing threat along coastal urban areas due to overexploitation of groundwater resources. For this purpose, concentrations of Total Dissolved Solids (TDS) in groundwater samples at three pilot areas along the Eastern Mediterranean were compared with mapped vulnerability predictions obtained through DRASTIC and EPIK. While field measurements demonstrated high levels of groundwater salinity depending on the density of urbanization, both vulnerability assessment methods exhibited a limited ability in capturing saltwater intrusion dynamics. In the three pilot areas, DRASTIC was only able to predict correctly between 8.3 and 55.6% of the salinity-based water quality ranges, while EPIK's predictions ranged between 11.7 and 77.8%. This emphasizing that conventional vulnerability models perform poorly when anthropogenic impacts induce lateral flow processes such as seawater intrusion caused primarily by vertical groundwater extraction.     

2015—2017年江苏省秋、冬季空气质量状况

采用2015—2017年秋、冬季江苏省环境空气质量监测数据,从空气质量优良(达标)率、首要污染物、主要污染物浓度分析空气质量现状及特点。结果表明,江苏省秋、冬季空气质量优良(达标)率在60%左右,其中沿海地区空气质量达标率最高(71.1%),西北地区达标率最差(52.2%)。污染日的首要污染物主要为PM 2.5,占比高达91.5%。ρ(PM2.5)/ρ(PM 10)存在地区差异,江苏西北地区扬尘源贡献较大,江苏南部地区的二次颗粒物贡献更明显。ρ(NO2)/ρ(SO2)逐年持续升高,表明大气污染类型从燃煤性污染转变为复合型污染。     

CO and NO2 pollution in a long two-way traffic road tunnel: investigation of NO2/NOx ratio and modelling of NO2 concentration

The CO, NO and NO2 concentrations, visibility and air flow velocity were measured using continuous analysers in a long Norwegian road tunnel (7.5 km) with traffic in both directions in April 1994 and 1995. The traffic density was monitored at the same time. The NO2 concentration exceeded Norwegian air quality limits for road tunnels 17% of the time in 1994. The traffic through the tunnel decreased from 1994 to 1995, and the mean NO2 concentration was reduced from 0.73 to 0.22 ppm. The ventilation fan control, based on the CO concentration only, was unsatisfactory and the air flow was sometimes low for hours. Models for NO2 concentration based on CO concentration and absolute air flow velocity were developed and tested. The NO2/NOx ratio showed an increase for NOx levels above 2 ppm; a likely explanation for this phenomenon is NO oxidation by O2. Exposure to high NO2 concentrations may represent a health risk for people with respiratory and cardiac diseases. In long road tunnels with two-way traffic, this study indicates that ventilation fan control based on CO concentration should be adjusted for changes in vehicle CO emission and should be supplemented by air flow monitoring to limit the NO2 concentration.     

大气乙醛碳同位素分析方法的研究

利用气相色谱/燃烧/同位素比值质谱(GC/C/IRMS)分析技术,采用NaHSO3与半胱胺衍生化方法,测定了气态乙醛在衍生化反应过程中的碳同位素效应,探讨了采用该方法测定大气乙醛碳同位素组成的可行性。试验测定了乙醛、衍生剂半胱胺及相应衍生物的碳同位素比值,结果表明,乙醛衍生物的δ13C测量值与理论值的偏差范围为0.11‰～0.35‰,在仪器精密度范围内(<0.50‰),即在衍生化过程中基本不会发生碳同位素分馏。采用该方法初步测定了大气中乙醛的碳同位素组成,实测数据显示,广州地化所和肇庆鼎湖山大气乙醛δ13C平均值分别为(-34.21±0.27)‰和(-31.23±0.16)‰,相同采样点的大气乙醛碳同位素组成基本不变,可见该方法可作为研究大气乙醛不同排放源的一种有效方法。     

COD adsorption capacity of the activated sludge — Its determination and application in the activated sludge process

Proper control of the activated sludge process is essential in ensuring production of good effluent. COD adsorption capacity (CAC) of the activated sludge could be used as a control parameter. CAC is determined by mixing the activated sludge with the settled sewage and measuring the instantaneous COD reduction per unit mass of activated sludge. CAC measures substrate removal by physical adsorption and reflects the quality of the activated sludge. CAC of a healthy activated sludge increases with the flow along the aeration units. CAC could be used for process decision on variation in air supply and feed pattern to the aeration units. In a modified process to cope with sludge bulking problem, CAC could be used to estimate the air supply to the aeration unit which is merely used for reaerating the returned sludge.     

化工厂场地酸化土壤工程化中和修复案例研究

对江苏某化工厂酸化地块进行了氧化钙中和修复工程研究。Ⅰ、Ⅱ、Ⅲ号地块剖面混合土样pH值分别为3.56、4.68和4.74,土壤修复目标定在pH值为6~8基本近中性。通过室内试验确定Ⅰ、Ⅱ、Ⅲ号地块土壤生石灰掺混比例为0.5%、0.3%和0.3%;现场中试后Ⅰ、Ⅱ、Ⅲ号地块石灰掺混比例调整为0.7%、0.35%和0.3%;中试结果用于场地机械搅拌工程修复,修复过程中定期随机采样对中和效果进行连续监测。监测结果基本达标后请第三方对修复效果进行评估,最后土壤回填压实。修复结果表明借助于科学的石灰添加量和工程机械混合措施,能快速有效地修复酸化地块土壤。     

Diode laser system for measurement of gaseous ammonia in ambient air

The use of a second harmonic diode laser system for monitoring gaseous ammonia in tropospheric air is discussed. Using a 96 m White cell operated at 13 torr pressure in flow mode, a minimum detectable concentration lower than 1 ppbv was obtained.The NH₃ mixing ratio was determined by simultaneous spectroscopic analysis of an atmospheric CO₂ line used as a built-in calibration standard.     

基于聚类分析的颗粒物监测网络优化研究

为了优化香港环境监测网络,收集香港14个监测站2011年1月1日至2015年11月30日的颗粒物PM_(2.5)、PM_(10)的小时数据进行统计分析。对PM_(2.5)进行聚类,并利用日均浓度变化图进行验证,结果表明,可将监测站分为4类(A、B、C、D类),A类位于城市郊区,B类则位于港口附近,且A、B类的PM_(2.5)日变化特征均呈现双峰型分布,峰值分别出现在09:00和21:00。对PM_(10)进行类似分析结果表明,监测站同样可以分为4类,A类位于九龙区,B类则位于港口附近,而且A、B类的PM_(10)日变化双峰分别出现在11:00和20:00左右。说明污染源头及地形的相似致使某些监测站颗粒物浓度的变化出现相同的趋势,导致监测设备的浪费和管理的冗余。建议建立更高效的空气管理系统,将冗余设备转移到其他地区,扩大空气监控区域。对PM_(2.5)/PM_(10)聚类结果表明,将监测站分为4类,B类均属于路边站,C类则位于居民区。同时还发现同类监测站PM_(2.5)/PM_(10)数值变化相同,并且可以用其中一个站的PM_(2.5)和PM_(10)浓度及另一个站的PM_(2.5)或PM_(10)浓度预测PM_(2.5)或PM_(10)浓度,为优化监测资源提供了一种新的思路。     

空气幕对抑制收费亭内污染物侵入作用的数值模拟

针对高速公路收费亭内空气质量差、污染严重的问题,为改善收费亭内工作环境、保障作业人员的身体健康,采用空气幕隔断方式抑制污染物进入亭内。运用Airpak软件对空气幕不同送风速度和送风角度下的抑制效果进行数值模拟,计算结果表明:空气幕可以有效抑制污染物侵入收费亭内;竖直向下送风时,随着送风速度的增加,抑制效果有所增加,当送风速度达到2.0 m/s时,继续增大送风速度对抑制效果的提升不明显;送风角度为0°、5°、10°时,空气幕能起到较好的抑制作用,当送风角度增大至15°、30°时,抑制效果有所降低。     

基于环境库兹涅茨曲线特征的桂林市大气环境状况研究

根据2006年-2012年桂林市经济发展主要指标和大气环境污染指标的统计资料，分析了该市人均 GDP 与SO2、NO x、烟（粉）尘排放量及 PM10质量浓度和 API优良率等大气环境指标的相关关系，建立了经济发展与大气环境指标之间的模拟曲线。模拟结果表明，桂林市处于工业时期，随着人均GDP增加，SO2和烟（粉）尘排放得到了一定程度的缓解，而NO x 和 PM10排放从长期看还处于上升趋势。建议改善能源结构，调整产业结构和工业布局，制定财税激励政策，开展环境综合整治，加大机动车排污防治力度，进一步控制大气污染。     

Optimizing environmental monitoring networks with direction-dependent distance thresholds

In the direction-dependent approach to location modeling developed herein, the distance within which a point of demand can find service from a facility depends on direction of measurement. The approach is effective for environmental location problems in which an underlying process with a prevailing gradient (e.g., wind or water flow) influences the interaction between sites in a modeled field. The utility of the approach is illustrated through an application to groundwater remediation.     

Determining the ventilation and aerosol deposition rates from routine indoor-air measurements

Measurement of air exchange rate provides critical information in energy and indoor-air quality studies. Continuous measurement of ventilation rates is a rather costly exercise and requires specific instrumentation. In this work, an alternative methodology is proposed and tested, where the air exchange rate is calculated by utilizing indoor and outdoor routine measurements of a common pollutant such as SO₂, whereas the uncertainties induced in the calculations are analytically determined. The application of this methodology is demonstrated, for three residential microenvironments in Athens, Greece, and the results are also compared against ventilation rates calculated from differential pressure measurements. The calculated time resolved ventilation rates were applied to the mass balance equation to estimate the particle loss rate which was found to agree with literature values at an average of 0.50 h^?1. The proposed method was further evaluated by applying a mass balance numerical model for the calculation of the indoor aerosol number concentrations, using the previously calculated ventilation rate, the outdoor measured number concentrations and the particle loss rates as input values. The model results for the indoors’ concentrations were found to be compared well with the experimentally measured values.     

Evaluating PM₂.₅ ionic components and source apportionment in Jinan, China from 2004 to 2008 using trajectory statistical methods

The mass concentrations and major chemical components of PM(2.5) in Jinan, Shandong Province, China from Dec. 2004 to Oct. 2008 were analyzed using backward trajectory cluster analysis in conjunction with the potential source contribution function (PSCF) model. The aim of this work was to study the inter-annual variations of mass concentrations and major chemical components of PM(2.5), evaluate the air mass flow patterns and identify the potential local and regional source areas that contributed to secondary sulfate and nitrate in PM(2.5) in Jinan. The annual mean concentrations of PM(2.5), sulfate and nitrate in 2004-2008 were almost the highest in the world. The most significant air parcels contributing to the highest mean concentrations of mass and secondary ions in PM(2.5) originated from the industrialized areas of Shandong Province. Clusters with a lower ratio of NO(3)(-)/SO(4)(2-) in PM(2.5) originated from the Yellow Sea, while a higher ratio was observed in the clusters passing through Beijing and Tianjin. PSCF modeling indicated that the provinces of Shandong, Henan, Jiangsu, Anhui and the Yellow Sea were the major potential source regions for sulfate, in agreement with the cluster analysis results. Regional and long-range transport of NH(4)NO(3) played an important role in the nitrate concentration of Jinan. By comparing the distributions of secondary sulfate and nitrate over three years, enhanced emission control management before and during the 29(th) Olympic Games led to a discernible decrease in source contributions from Beijing and its environs in 2007-2008.