考虑残留氮对非稳定流场硝态氮淋失贡献的传递函数模型Ⅱ.农田应用

应用田间冬小麦-夏玉米生长条件下土壤硝态氮淋失动态的试验资料，对所提出的可估计表施和残留氮对土壤非稳定流场中硝态氮淋失贡献的传递函数模型进行了检验。首先，对所选定的农田中的两个土壤剖面，估算了硝态氮和氯离子的中值与均值迁移时间，然后，利用我们的模型，使用其中一个土壤剖面标定硝态氮和氯离子运移的概率密度函数的参数，接着，应用标定后的传递函数模型，模拟了另一个土壤剖面的硝态氮淋失浓度和累积淋失量动态，并分别估算了表施和残留氮占硝态氮总淋失量的分数。结果表明：提出的传递函数模型在农田条件下对土壤硝态氮累积淋失量模拟的相对误差为14．89％。     

考虑残留氮对非稳定流场硝态氮淋失贡献的传递函数模型Ⅱ农田应用

应用田间冬小麦-夏玉米生长条件下土壤硝态氮淋失动态的试验资料，对所提出的可估计表施和残留氮对土壤非稳定流场中硝态氮淋失贡献的传递函数模型进行了检验。首先，对所选定的农田中的两个土壤剖面，估算了硝态氮和氯离子的中值与均值迁移时间，然后，利用我们的模型，使用其中一个土壤剖面标定硝态氮和氯离子运移的概率密度函数的参数，接着，应用标定后的传递函数模型，模拟了另一个土壤剖面的硝态氮淋失浓度和累积淋失量动态，并分别估算了表施和残留氮占硝态氮总淋失量的分数。结果表明：提出的传递函数模型在农田条件下对土壤硝态氮累积淋失量模拟的相对误差为14.89%。     

土壤中硝态氮淋洗的传递函数模拟和预报

运用传递函数模型(Transfer Function Model,TFM)作为随机模拟工具，对灌溉入渗重分布条件下非饱和土壤中硝态氮的运移进行了数学模拟。获得了实验条件下土壤中硝态氮迁移时间的概率密度函数和中值与均值迁移时间及运移体积分数，仿真了实验期间硝态氮的出流浓度动态，估算了硝态氮的累积淋洗量。     

考虑残留氮对非稳定流场硝态氮淋失贡献的传递函数模型

本文通过引入溶质迁移距离的概率密度函数的修正系数，将Jury等提出的模拟非稳定流条件下土壤保守溶质运移的传递函数模型理论扩展到考虑土壤剖面存在残留氮分布的土壤中，构造了一个能估算表施和残留氮对土壤硝态氮淋失动态贡献的传递函数模型。通过与野外地中渗透计实验资料的对比，表明该模型具有一定的仿真精度，模拟的土壤硝态氮累积淋失量的相对误差小于15%。     

考虑残留氮对非稳定流场硝态氮淋失贡献的传递函数模型Ⅰ.地中渗透计验证

本文通过引入溶质迁移距离的概率密度函数的修正系数，将Jury等提出的模拟非稳定流条件下土壤保守溶质运移的传递函数模型理论扩展到考虑土壤剖面存在残留氮分布的土壤中，构造了一个能估算表施和残留氮对土壤硝态氮淋失动态贡献的传递函数模型。通过与野外地中渗透计实验资料的对比，表明该模型具有一定的仿真精度，模拟的土壤硝态氮累积淋失量的相对误差小于15％。     

亚热带农业小流域暴雨过程硝态氮迁移特征及水文示踪研究

为揭示亚热带丘陵区农业小流域暴雨过程中硝态氮迁移规律及其主要水文输送途径,本研究通过对紫色土丘陵区典型农业小流域典型暴雨过程跨尺度(从3~1 236 hm2)连续监测,分析径流硝态氮迁移动态特征及其尺度效应,并对比δ18O和硝态氮作为示踪剂的端元混合分析(EMMA)解析结果,探讨硝态氮作为暴雨过程水文示踪剂的可行性。结果表明:(1)两场暴雨事件中源头小流域苏荣小流域(含集镇污水)径流中硝态氮浓度最高,而到达梯级小流域出口处(万安小流域)硝态氮浓度最低,林地来水的贡献是较大尺度小流域径流硝态氮浓度降低的主要原因,坡耕地壤中流补给可能是径流消退过程中硝态氮出现浓度峰值的主要原因。(2)EMMA模型解析结果显示:δ18O与硝态氮均能示踪农业小流域径流消退期间壤中流补给过程;但硝态氮在受人居活动强烈影响子流域的示踪应用需谨慎。以农业为主的亚热带丘陵区小流域中,硝态氮具有同时作为环境效应指示剂和水文示踪剂的潜力,但其应用效果仍有待于进一步验证。     

土壤中硝态氮迁移转化的数值模拟研究

为了揭示不同灌溉强度下土壤中硝态氮浓度的变化规律,选取常德市典型浅层土壤为研究对象,以动态土柱淋滤试验和静态反硝化试验为基础,运用HYDRUS-1D软件建立数值模型对不同灌溉强度下硝态氮浓度的变化进行模拟分析。结果表明:当灌溉强度大于4 cm/d时,灌溉强度超过土壤下渗能力,灌溉水按下渗能力下渗,多余的水会形成地面积水,进而形成地表径流,模拟10 d各组土壤中硝态氮的浓度差异不大;当灌溉强度小于等于4 cm/d时,灌溉水全部下渗到土壤中,模拟10 d后土壤中硝态氮的浓度随灌溉强度的增加而增大。     

层施保水剂不同高度对土壤硝态氮运移的影响

通过室内层施保水剂的毛管水上升试验分析层施不同高度保水剂对毛管水上升和硝态氮运移的影响。结果表明:在土壤容重、初始含水率和硝酸铵浓度相同的情况下,层施保水剂的高度越高含水率越大,对硝态氮运移的影响也越明显;硝态氮在土壤中的的运移与水分的传输有着密切的关系。     

北京地区冬小麦-夏玉米轮作下土壤氮素的分布及对地下水影响分析

研究北京粮食作物种植区冬小麦—夏玉米轮作体系下不同施氮量对土壤氮素剖面分布、累积量、淋失量的动态变化过程的影响及对地下水的影响等。结果表明在喷灌条件下冬小麦试验季节硝态氮的累积主要在80 cm深度以上;而夏玉米季节,硝态氮的峰值运移到150 cm左右,硝态氮存在明显的深层淋失现象。硝态氮的剖面含量一般随着施氮量的增加而增加。单季施氮量低于110 kg/hm2,土壤氮素处于稍微亏损状态;而施氮量大于220 kg/hm2时,在0～200 cm土层内,硝态氮有明显的累积现象,硝态氮的累积量一般随着施氮量的增加而增加,因此建议该地区年施氮量为250kg/hm2以维持农田氮平衡。考虑到当地的地下水埋深一般在12.5m左右,可以初步得出冬小麦—夏玉米种植对地下水的影响较小,但是长期冬小麦—夏玉米种植施肥将对地下水产生影响。     

重庆典型岩溶槽谷区土壤氮素迁移过程分析

土壤-地下水系统中的硝氮污染和氮素的循环过程备受关注,但对岩溶区土壤氮素的迁移过程研究较少。选取重庆市典型岩溶槽谷区的灌丛和菜园地,分层取样分析土壤中各种形态的氮素,并用曲线拟合的方法分析氮素随土壤深度的变化,了解岩溶区土壤氮素的垂直分布情况。从分析结果看,硝态氮为土壤无机氮的主要存在和淋失形式;铵态氮垂直分布规律为表层多底层少,说明受土壤吸附作用的影响向下迁移较少;硝态氮的分布呈波峰波谷式变化,干燥时由于硝化作用产生积累,降雨时可能随雨水向下迁移而减少。研究结果可为指导岩溶区农业生产和氮素管理,以及科学治理石漠化提供理论依据。     

Habitat Suitability Criteria via Parametric Distributions: Estimation,Model Selection and Uncertainty

Previous methods for constructing univariate habitat suitability criteria (HSC) curves have ranged from professional judgement to kernel‐smoothed density functions or combinations thereof. We present a new method of generating HSC curves that applies probability density functions as the mathematical representation of the curves. Compared with previous approaches, benefits of our method include (1) estimation of probability density function parameters directly from raw data, (2) quantitative methods for selecting among several candidate probability density functions, and (3) concise methods for expressing estimation uncertainty in the HSC curves. We demonstrate our method with a thorough example using data collected on the depth of water used by juvenile Chinook salmon (Oncorhynchus tschawytscha) in the Klamath River of northern California and southern Oregon. All R code needed to implement our example is provided in the appendix. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

非稳定流条件下非饱和均质土壤溶质运移的传递函数解

根据溶质运移的传递函数模型Tromsfer Function Model, TFM理论，研究了非稳定流条件下非饱和均质土壤中表施和原有NO-3 N及原有Cl-的运移。由极大似然法估算了模型参数μ和σ2，求出了溶质运移的概率密度函数，计算了NO-3 -N的淋失量，并利用土壤中原有Cl-的动态，对NO-3 N的迁移过程进行了模拟，同时还估算了溶质的中值迁移时间tm和均值迁移时间相应的运移体积θst和θst。     

冬小麦生长条件下土壤氮素运移动态的数值模拟

将土壤溶质运移理论和土壤微生物化学、植物生理学有机地结合起来,建立了农田土壤氮素运移、转化与吸收的综合数学模型。运用该模型对中德合作项目试验田1999～2000年冬小麦优化施肥与传统灌溉和优化施肥与优化灌溉两小区的土壤水分和氮素运移动态及干物质产量进行了模拟。模拟结果与实测数据吻合较好。两小区土壤剖面埋深165cm处硝态氮淋失量的计算结果表明：与传统灌溉方式相比,优化灌溉方式的土壤硝态氮的淋失量明显减少。用验证后的数学模型在计算机上进行了几种不同灌溉方案下土壤水氮运移动态及干物质产量变化的数值试验,结果表明：在喷灌条件下,冬小麦以每l0d灌溉一次,每次20mm水量的灌溉方式较优。     

PROBABILITY DISTRIBUTION OF IN-LINE WAVE FORCES ON A PILE IN IRREGULAR WAVES

The probability distribution of in-line wave forces on a pile can bemathematically summed up to that of a theory and the assumption of wave period being constantare used and the above probability distribution is simplified to that of a single dimentsionfunction.The probability density functions of the peak values of total wave forces on a wholevertical pile in irregular waves are derived from that of wave height which is the Rayleighdistribution(deep water wave)or the Kerohovski distribution(shallow water waves)on the baseof the Morison Equation.The identification with experimental data shows that suchsimplification is successful.These distributions are compared with Weibull distribution andRayleigh distribution and the result shows that the shallow water distribution of wave forcesobtained here is the best one and can be used in practice.     

Products,Sums and Quotients of Upper Truncated Pareto Random Variables with an Application in Hydrology

Some hydrological quantities such as the rainfall intensity, which is defined as the quotient of the rainfall depth to the rainfall duration, are based on functions of random variables. At this point, the probability distribution of that quantity arises. Then one may take this distribution into account for the exact statistical inference without referring to a simulation study. There are a lot of works on the exact distributions of functions of random variables in the literature. One case is for the Pareto distributed random variables. Pareto distribution and its upper truncated version have many applications in hydrological modelling. In this paper, the exact distributions of the product, sum and quotient of two independently distributed upper truncated Pareto random variables are obtained. Although the probability density functions of the product and quotient are obtained in elementary mathematical functions, that for the sum is obtained in terms of a special function. Some characteristics of these functions such as moments and percentiles can be easily obtained. The distributions of the quotient and the sum are applied on a rainfall data set from hydraulic efficiency research of green roofs. The parameters are estimated by the method of maximum likelihood. The theoretical results of this paper may also be useful to other practitioners of the upper truncated Pareto distribution.

     

黄河口汛期泥沙分布特征及其对水流结构的影响

本文以黄河口汛期六船同步测验取得的水文泥沙资料为基础，得到含沙量与流速的垂向分布经验式，据此了解黄河口汛期的泥沙分布特征：泥沙异重流的含沙量垂向分布很不均匀，随水深的增加含沙星迅速增加；流速随水深分布均匀，无论是上层清水还是下层泥沙异重流流速都较大。并利用室内粒度分析资料研究泥沙对水流结构的影响。     

硝态氮和苯胺在渭河渗滤系统中的生物化学作用

采用自行设计的室内土柱实验装置模拟渭河渗滤系统,研究了含有硝态氮污染的河水以及苯胺污染的河水在渭河渗滤系统中的环境行为及净化机制,得出:河流渗滤系统对硝态氮污水有很大的净化作用,其净化机制主要是反硝化作用,对硝态氮的去除率达到100%;河流渗滤系统对硝态氮和苯胺共存的污水也有很大的净化能力,其净化机制主要是反硝化作用和生物降解作用,对硝态氮和苯胺的去除率均达到100%。最后定量研究了二者在河流渗滤系统中净化程度。     

泥石流冲击荷载的概率密度分布试验研究

建立浆体黏度和级配固相颗粒组合条件下的泥石流冲击室内模型,进行5种浆体黏度、5种固相比和4种颗粒粒径组合的85组试验。对试验数据进行概率统计,分析试验条件下泥石流体的冲击荷载概率密度分布特征。分析结果表明:冲击荷载概率密度曲线符合Gauss分布形式,拟合吻合度均达97%以上,中误差小于0.01;从形态上将实验中的概率密度曲线划分为单峰、奇异单峰、多峰及双驼峰分布形式,得到各种分布形式所对应的工况;仅考虑浆体黏度时,概率密度分布曲线随着浆体黏度的增大由单峰变为奇异单峰甚至多峰的分布形式;不考虑浆体黏度时,则是随固相颗粒粒径的增大同样由单峰变为奇异单峰及多峰的形式。     

Temporal scale effect of loading data on instream nitrate-nitrogen load computation

The temporal scale effect of loading data on nitrate-nitrogen load computation was examined using outputs of watershed modeling tool Hydrologic Simulation Program-FORTRAN (HSPF) for the Amite River in Louisiana, USA. The daily nitrate-nitrogen concentrations simulated using the HSPF were employed first to obtain daily, weekly, bi-weekly, and monthly average data and then to develop load duration curves for the data with four different temporal scales. The duration curves exhibited high variability in the load estimated using daily data as compared with those based on bi-weekly and monthly data. According to daily data, the nitrate-nitrogen load in the winter was found to be 2,780 kg. The nitrate-nitrogen load decreased with increasing temporal (daily, weekly, bi-weekly, and monthly) scale (commonly used in water quality monitoring) of the data. The coefficient of variation, used to quantify the effect of temporal scale on the load, was found to be linearly and inversely correlated with the logarithm of the time scale. Based on the finding, empirical equations were proposed to extrapolate near real-time data for flow and nitrate-nitrogen, greatly simplifying nutrient monitoring and reducing the cost involved in water quality monitoring.