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921.
Feifei Pan Christa D. Peters‐Lidard 《Journal of the American Water Resources Association》2008,44(1):235-242
Abstract: The objective of this work was to explain an apparent contradiction in the literature related to the relationship between mean and variance (or standard deviation) of soil moisture fields. Some studies found an increase in soil moisture variance with decreasing mean soil moisture, while others showed a decrease. The evidence of maximum variance in the mid‐range of mean soil moisture was also reported in the literature. In this paper, we focus on the effects of spatial variability of soil texture on the relationship between variance and mean of soil moisture during soil dry‐down processes. Soil texture influences soil moisture mean and variance through its direct effects on evaporation and drainage, which are two main factors controlling soil drying. A differential equation describing soil moisture dry down is proposed and studied. Our study shows that as mean soil moisture is greater than a threshold, variance increases with decreasing mean soil moisture. If mean soil moisture is less than the threshold, variance decreases with decreasing mean soil moisture. The threshold depends on soil texture and is between the field capacity and the wilting point. The soil moisture dry‐down equation is also applied to explain the apparent contradiction with regard to the relationship between mean and variance of soil moisture fields reported in the literature. 相似文献
922.
复合垂直流与潜流人工湿地沿程脱氮除磷对比研究 总被引:4,自引:0,他引:4
针对复合垂直流和潜流人工湿地对COD、TP、NH_4~+-N、NO~3~--N和TN的沿程去除规律进行了对比研究.结果表明,夏季复合垂直流人工湿地的去除效果均好于潜流人工湿地.对于复合垂直流人工湿地,污染物的去除主要集中在下行流池,且在进水端0~20 cm对COD、TP、NH_4~+-N和TN都有快速降解的过程.对于潜流人工湿地,进水端0~40 cm主要是COD和TP的快速降解沉淀,之后硝化作用逐渐加强,潜流人工湿地沿程均会发生反硝化作用,TN浓度基本呈均匀下降趋势. 相似文献
923.
To understand the compositions and structures of microbial communities in different acid-aqueous environments, a PCR-based cloning approach was used. A total of five samples were collected from two mines in China. Two samples, named as G1 and G2, were acid mine drainage (AMD) samples and from Yunfu sulfide mine in Guangdong province, China. The rest of the three samples named as D1, DY and D3, were from three sites undertaking bioleaching in Yinshan lead-zinc mine in Jiangxi province, China. Phylogenetic analysis revealed that bacteria in the five samples fell into six putative divisions, which were α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Firmicutes, Actinobacteria and Nitrospira. Archaea was only detected in the three samples from Yinshan lead-zinc mine, which fell into two phylogenentic divisions, Thermoplsma and Ferroplasma. In addition, the results of principal component analysis (PCA) suggested that more similar the geochemical properties in samples were, more similar microbial community structures in samples were. 相似文献
924.
阐述了填埋气竖直井及渗滤液导排复合系统的构造及优势功能,分解了系统主要构造结构,主导排槽、支导排槽、竖直井、冷凝井等施工过程中的技术要点及参数控制,工程实践检验了系统的采气与导排效果,产生了较优的环境效益。 相似文献
925.
926.
一种节水灌溉新装置的研究 总被引:1,自引:0,他引:1
地下灌溉技术是新发展起来的一种高效节水灌溉技术。这种技术由于具有显著的节水、节肥、增产以及改善土壤环境等优点,因而倍受世界各国的关注。提出了一种节水灌溉新装置,通过在实验室进行下渗等实验,从蒸发和减少深层渗漏两个方面对其节水性进行了分析论证,并在此基础上对装置工作原理和特点进行了简要探讨。 相似文献
927.
Kim JY Lee BT Shin KH Lee KY Kim KW An KG Park YS Kim JY Kwon YH 《Environmental monitoring and assessment》2007,129(1-3):79-85
Ecological health in a temperate stream impacted by acid mine drainage (AMD) was evaluated by using a multimetric approach
of the Index of Biological Integrity (IBI) based on natural fish assemblage. Recently, this approach has been widely used
in many developed countries as a tool for ecological risk assessments of water environments. We used 10 metric systems, instead
of 12 metrics suggested by Barbour, M. T., Gerritsen, J., Snyder, B. D., & Stribling, J. B. (1999). Rapid Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, benthic Macroinvertebrates and Fish, 2nd edn. EPA 841-B-99-002. Washington, DC: U.S. Environmental Protection Agency, Office of Water, for a development of the
regional IBI model, and used trophic guilds, habitat guilds, and richness variables for the calculation of IBI values. In
the model, the attributes of four of 11 metrics were modified for the regional application. IBI values in the stream averaged
20.6 (n = 5), indicating a “poor condition” in terms of ecological health according to the modified criteria of U.S. EPA (1993).
Fish Field and Laboratory Methods for Evaluating the Biological Integrity of Surface Waters. EPA 600-R-92-111. Environmental Monitoring systems Laboratory – Cincinnati office of Modeling, Monitoring systems, and quality
assurance Office of Research Development, U.S. EPA, Cincinnati, Ohio, 45268. In particular, mean IBI values in the impacted
areas of sites 2 and 3 were 13, and this health condition was categorized as “very poor condition.” IBI values in the impacted
sites were significantly lower than the values found in the control. Also, we found that fishes in site sites 2 and 3 were
not present during the study, and morphological deformity of Rhynchocypris oxycephalus was observed in site 4, influenced directly by sites 2 and 3, indicating a chemical impact in the sites. From the results
of experiments in which AMD was treated with marine shells at stagnant condition, pH increased up to 6.0 from 3.1, and Fe
and Al were removed up to 99% within 6 h. In the reactor experiment considering field application, pH of effluent maintained
around 7.0. In addition, concentrations of Fe, Al, and heavy metals decreased remarkably in the effluents, and bottom-opened
screen between neutralizer basins showed high effectiveness in the treatment of AMD. 相似文献
928.
Melidis P Akratos CS Tsihrintzis VA Trikilidou E 《Environmental monitoring and assessment》2007,127(1-3):15-27
Thirteen field campaigns were undertaken in the period from December 2, 2002 until September 1, 2004 to collect water samples
in order to characterize the quality of rainfall and roof drainage in the city of Xanthi, a typical provincial city in Greece.
In each campaign, water samples were collected from 10 representative sites in the city (in total 130 samples), representing
areas of distinct land use and human activities (i.e., traffic volume, residence density and industrial activity). The water
samples were analyzed according to drinking water criteria for total coliform (not detected), temperature (range: 0.9–20°C),
pH (range: 3.6–11.4), alkalinity (range: 0–21.5 mg CaCO3/L), nitrate (range: 0–2456 μg/L), ammonium (range: 0–2628 μg/L), sulfate (range: 0–0.5 mg/L), calcium (range: 259.1–3064
μeq/L), magnesium (range: 0.8–488.8 μeq/L), potassium (range: 0.0–110.6 μeq/L) and dissolved heavy metals (Fe, range: 0.01–0.18
mg/L; Mn, range: 0.01–0.09 mg/L; Zn, range: 0.01–0.54 mg/L; Cu, Cr and Ni, not detected). Pollutant concentrations were generally
higher in roof drainage than in rainwater, but both were lower than drinking water standards. Dissolved heavy metal concentrations
were generally higher in the areas of intensive human activities, such as roads with high traffic volume and densely populated
residential areas. The satisfactory quality of rainwater, which results from this analysis, makes its use as grey water possible. 相似文献
929.
The potential effectiveness of a constructed passive net alkaline wetland in reducing human health risks from heavy metals
in surface waters was evaluated by using a multimedia model. Scenarios were developed using information available from site
reports, state, federal, and standard engineering sources. The scenarios replicated observed heavy metal concentrations in
the waters of a volunteer wetland and estimated the concentrations after implementation of a constructed passive net alkaline
wetland. The greatest reductions in risks are expected to occur soon after construction, with children benefiting more than
adults. 相似文献
930.
Fei Gao Gary Feng Ying Ouyang Huixiao Wang Daniel Fisher Ardeshir Adeli Johnie Jenkins 《Journal of the American Water Resources Association》2017,53(4):791-808
It is often necessary to find a simpler method in different climatic regions to calculate reference crop evapotranspiration (ETo) since the application of the FAO‐56 Penman‐Monteith method is often restricted due to the unavailability of a comprehensive weather dataset. Seven ETo methods, namely the standard FAO‐56 Penman‐Monteith, the FAO‐24 Radiation, FAO‐24 Blaney Criddle, 1985 Hargreaves, Priestley‐Taylor, 1957 Makkink, and 1961 Turc, were applied to calculate monthly averages of daily ETo, total annual ETo, and daily ETo in an arid region at Aksu, China, in a semiarid region at Tongchuan, China, and in a humid region at Starkville, Mississippi, United States. Comparisons were made between the FAO‐56 method and the other six simple alternative methods, using the index of agreement D, modeling efficiency (EF), and root mean square error (RMSE). For the monthly averages of daily ETo, the values of D, EF, and RMSE ranged from 0.82 to 0.98, 0.55 to 0.98, and 0.23 to 1.00 mm/day, respectively. For the total annual ETo, the values of D, EF, and RMSE ranged from 0.21 to 0.91, ?43.08 to 0.82, and 24.80 to 234.08 mm/year, respectively. For the daily ETo, the values of D, EF, and RMSE ranged from 0.58 to 0.97, 0.57 to 0.97, and 0.30 to 1.06 mm/day, respectively. The results showed that the Priestly‐Taylor and 1985 Hargreaves methods worked best in the arid and semiarid regions, while the 1957 Makkink worked best in the humid region. 相似文献