Water budget and the consequent duration of canopy carbon gain in a teak plantation in a dry tropical region: Analysis using a soil–plant–air continuum multilayer model

A soil–plant–air continuum multilayer model was used to numerically simulate canopy net assimilation (A_n), evapotranspiration (ET), and soil moisture in a deciduous teak plantation in a dry tropical climate of northern Thailand to examine the influence of soil drought on A_n. The timings of leaf flush and the end of the canopy duration period (CDP) were also investigated from the perspective of the temporal positive carbon gain. Two numerical experiments with different seasonal patterns of leaf area index (LAI) were carried out using above-canopy hydrometeorological data as input data. The first experiment involved seasonally varying LAI estimated based on time-series of radiative transmittance through the canopy, and the second experiment applied an annually constant LAI. The first simulation captured the measured seasonal changes in soil surface moisture; the simulated transpiration agreed with seasonal changes in heat pulse velocity, corresponding to the water use of individual trees, and the simulated A_n became slightly negative. However, in the second simulation, A_n became negative in the dry season because the decline in stomatal conductance due to severe soil drought limited the assimilation, and the simultaneous increase in leaf temperature increased dark respiration. Thus, these experiments revealed that the leaflessness in the dry season is reasonable for carbon gain and emphasized the unfavorable soil water status for carbon gain in the dry season. Examining the duration of positive A_n (DPA) in the second simulation showed that the start of the longest DPA (LDPA) in a year approached the timing of leaf flush in the teak plantation after the spring equinox. On the other hand, the end appeared earlier than that of all CDPs. This result is consistent with the sap flow stopping earlier than the complete leaf fall, implying that the carbon assimilation period ends before the completion of defoliation. The model sensitivity analysis in the second simulation suggests that a smaller LAI and slower maximum rate of carboxylation likely extend the LDPA because soil water from the surface to rooting depth is maintained longer at levels adequate for carbon gain by decreased canopy transpiration. The experiments also suggest that lower soil hydraulic conductivity and deeper rooting depth can postpone the end of the LDPA by increasing soil water retention and the soil water capacity, respectively.     

Pollution characteristics of lead,zinc, arsenic,and cadmium in short-term storm water roof runoff in a suburban area

Pollution of hazardous elements in roof runoff has been a potential danger to aquatic ecosystem as documented in previous studies. In this study, concentrations of lead (Pb), zinc (Zn), arsenic (As), and cadmium (Cd) in roof runoff were measured for short-term rainfall events. The concentrations of the selected elements varied to a high degree during the rainfall period, and the well-known first-flush phenomenon was not observed due to the short-term rainfall patterns. Based on event mean concentrations (EMCs) and fluxes, the elemental pollution may be ranked as Zn >> Pb > As > Cd. The average levels of Pb and Zn exceeded the fourth class value and fifth class value of the environmental quality standards for surface water in China. The relative high pollution could be caused by atmospheric deposition and the erosion of crust steel appurtenance installed above the rooftop. Furthermore, elements in particulate form dominated the roof runoff pollution, and the ratios of elements in particulate form to total amounts were 0.6 (As), 0.9 (Pb), 0.7 (Cd), and 0.5 (Zn). This study cleared the pollution characteristics of hazardous elements in short-term storm water roof runoff; it was useful for the selection of best management practices.     

Removal of non-point pollutants from bridge runoff by a hydrocyclone using natural water head

A hydrocyclone using natural water head provided by bridge was operated for the treatment of stormwater runoff. The hydrocyclone was automatically controlled using electronic valve which is connected to a pressure meter. Normally the hydrocyclone was open during dry days, but it was closed after the capture of the first flush. The results indicated that the average pressure and the flow rate were directly affected by the rainfall intensity. The pressure head was more than 2 m when the rainfall intensity was above 5mm·h^-1. The percentage volume of underflow with high solids concentration decreased as the pressure and flow rate increased, but the percentage volume of overflow with almost no solids showed the opposite behavior. The total suspended solids （TSS） concentration ratio between the overflow and inflow （TSSover/TSSin） decreased as a function of the operational pressure, while the corresponding ratio of underflow to inflow （TSSunaer/TSSi,） increased. The TSS separation efficiency was evaluated based on a mass balance. It ranged from 25% to 99% with the pressure head ranging from 1.4 to 9.7 m, and it was proportional to pressure and flow rate. Normally, the efficiency was more than 50% when the pressure was higher than 2 m. The analysis of the water budget indicated that around 13% of the total runoff was captured by the hydrocyclone as a first flush, and this runoff was separated as underflow and overflow with the respective percentage volumes of 29% and 71%. The pollutants budget was also examined based on a mass balance. The results showed that the percentage of TSS, chemical oxygen demand （COD）, total nitrogen （TN）, and total phosphorus （TP） in underflow were 73%, 59%, 7.6%, and 49%, respectively. Thus, it can be concluded that the hydrocyclone worked well. It separated the first flush as solids-concentrated underflow and solids-absent overflow, and effectively reduced the runoff volume needing further treatment. Finally, four types of optional post treatment design are presented and compared.     

Sustainability of urban drainage management: a perspective on infrastructure resilience and thresholds

Urban wastewater infrastructures have been threatened by natural and socioeconomic disturbances. This study investigates infrastructure resilience against the risks of long-term changes rather than natural disasters. Urban expansion that leads to an increased urban runoff and massive population movements that cause fluctuations in domestic emissions are considered in this study. Pollution permits for water bodies are adopted as constraints on wastewater infrastructures. A land use-based accounting method, combined with a grid-based database, is developed to map domestic discharge and urban runoff to service areas of wastewater treatment plants. The results of a case study on downtown Sanya, the most famous seashore tourist attraction in China, show that the average resilient values of three sub-catchment areas in 2010 were -0.57, 0.10 and 0.27, respectively, a significant spatial variation. The infrastructure in the Sanya River sub-region is the least flexible, and is more likely to fail due to unstable inflows. The resiliencies will increase to 0.59, 1.01 and 0.54, respectively, in 2020, a considerable improvement in robustness. The study suggests that infrastructure resilience needs to be taken into further consideration for urban planning and the related realm of urban governance to foster more robust wastewater management under various risks.     

户用沼气池建设对改善农村生态环境效果分析

通过对河南省9个县(市)中9个乡(镇)的非沼气户和沼气户土壤、地表径流和室内空气进行监测,定量对比分析了户用沼气池建设对农村生态环境改善效果。结果显示,沼气户土壤中的速效磷、速效钾、有机质和全氮含量要高于非沼气户,且"四位一体"生态模式沼气户土壤中4种养分含量明显高于"三位一体"生态模式;沼气户地表径流中的COD、NH₃-N、 TP浓度均低于非沼气户;沼气户室内空气中的CO、SO₂、NH₃、PM₁₀浓度均低于非沼气户,且室内空气中的4项污染物浓度随季节变化而不同。这说明户用沼气池建设对于增加土壤养分、减轻农村面源污染、改善农户居住环境、实现节能减排效果显著。     

SCS-CN模型中土壤参数的作用机制研究

土壤参数是地表径流模型中的关键参数,对径流过程模拟有重要影响,因此有必要明确土壤参数的作用机制。论文结合SWAT (Soil and Water Assessment Tool) 模型,以广泛应用的径流曲线数模型(SCS-CN) 为例,对土壤参数在SCS-CN模型中的作用进行了理论推导、分析和实例研究。分析表明,土壤饱和含水量参数与田间持水量参数的比值,是影响不同土壤湿度下地表产流能力的重要因素,两者比值越大,土壤含水量对地表产流能力的调节越弱,导致基于不同土壤模拟的地表径流量随土壤湿度的波动而上下反转。以实际流域为例,发现不同土壤数据模拟地表径流间差别的显著季节性特征;阐明该差别季节性变化的内在机制,验证了理论分析结论。为深入理解产流过程、合理选择土壤数据、模型参数优化及模拟结果解释提供了参考。     

从潮白河年径流频率分布变化看北京市水资源安全问题

密云水库是北京市生活供水的唯一地表水源,而潮白河流域又是密云水库的径流形成区,因此,潮白河流域年径流量的变化直接关系到北京市的水资源安全。根据变化环境下非一致性年径流序列的水文频率计算原理,对潮白河水资源分区年径流序列的确定性成分和随机性成分进行分解,并分别对确定性成分进行拟合计算,对随机性成分进行频率计算;将确定性的预测值和随机性的设计值进行合成,得到潮白河水资源分区在过去、现在和未来年径流量的频率分布;从年径流量的频率分布变化上,分析了北京市所面临的水资源安全问题。分析结果表明潮白河流域年径流量变化的总体趋势是逐年减小,密云水库在平水年和枯水年的入库径流量也将随之减小,因此密云水库不能成为北京21世纪可持续发展的水资源保障。     

EXPORT COEFFICIENT MODELING TO ASSESS PHOSPHORUS LOADING IN AN URBAN WATERSHED1

ABSTRACT: An export coefficient modeling approach was used to assess the influence of land use on phosphorus loading to a Southern Ontario stream. A model was constructed for the 1995–1996 water year and calibrated within ± 3 percent of the observed mean concentration of total phosphorus. It was found that runoff from urban areas contributed most to the loading of phosphorus to the stream. When the model was assessed by running it for the 1977–1978 water year, using water quality and land use data collected independently, agreement within ± 7 percent was obtained. The model was then used to forecast the impact of future urban development proposed for the watershed, in terms of phosphorus loading, and to evaluate the reduction in loading resulting from several urban best management practices (BMP). It was determined that phosphorus removal will have to be applied to all the urban runoff from the watershed to appreciably reduce stream phosphorus concentration. Of the BMP designs assessed, an infiltration pond system resulted in the greatest phosphorus load reduction, 50 percent from the 1995–1996 baseline.     

突发事故危害期估算模式研究

针对大气环境突发事故造成的危害,在高斯扩散模式基础上,引入危害半径变化与时间及危害期变化与横风向距离呈线性关系的假设,得出危险源附近各处受危险源突发事故危害的危害时间长短（危害期）一系列定量估算公式,使用方便,结果精确,为环境风险评价提供了有效的工具,可广泛应用于环境风险评价与管理、风险工程设计、风险责任保险等各个领域与事故应急计划制定、事故抢险工作实施.     

不同植被类型及土壤对径流水化学特征的影响

在不同植被类型覆盖条件下,对降雨形成地表径流和地下径流的化学成分变化及其与土壤剖面性质的关系进行分析,结果表明:地表径流和地下径流的化学特征与雨水基本相同,阳离子主要以Ca²⁺为主,离子排序为Ca²⁺>K⁺>Na⁺>Mg²⁺>NH₄⁺,阴离子以SO₄^2-为主,SO₄^2->NO₃^->Cl^-.降雨形成地表径流和地下径流后,各成分浓度发生了明显的变化,水体中主要的阴阳离子如Ca²⁺、Mg²⁺、K⁺、Na⁺、SO₄^2-、Cl^-等浓度增加,与雨水相比为内贮型化学成分,地下径流中Ca²⁺、Mg²⁺、SO₄^2-和Cl^-增加的幅度显著高于地表径流.相关分析结果显示,地下径流pH受到土壤pH的强烈影响,受土壤胶体吸附的影响,水体中Ca²⁺、Mg²⁺、K⁺、Na⁺等阳离子与土壤交换性阳离子之间一般呈负相关的关系,由于阴离子容易随水流失,水体中SO₄^2-、NO₃^-和Cl^-与土壤相关离子之间普遍呈正相关关系.