Is There Any Correlation Between Landscape Characteristics and Total Nitrogen in Wetlands Receiving Agricultural Drainages?

In the case of increasing fragmentation of wetlands, the study of the relationship between wetland landscape characteristics and total nitrogen(TN) in water is of great significance to reveal the mechanism of wetland water purification. Taking the Naoli River(NR) wetlands in Northeast China as the research object, 10 uniformly distributed sampling sites in the study area were sampled in August 2015 to test the TN concentration and interpret the images of NR wetlands in the same period. Taking the sampling site as the control point, the whole wetlands were divided into 10 regions, and the landscape index of each region was extracted. In order to reveal whether the landscape characteristics are related to the TN concentration in the wetlands water body, the landscape index and the TN concentration in the control point water body were analyzed by correlation analysis, step-by-step elimination analysis and path analysis to reveal whether the landscape characteristics are related to the TN concentration under wetlands receiving agricultural drainages. The results showed that the correlation coefficients between four area indexes or eight shape indexes and TN concentration did not reach a significant correlation level(P > 0.05), indicating that TN removal was not only determined by a single landscape index. The path coefficient of edge density(ED) index is –0.41, indicating that wetland patch connectivity is the primary factor of TN removal, and there is no relationship between the larger patch area and the higher TN removal. The removal of TN in wetlands is restricted by the synergistic effect of landscape area and shape characteristics.

Calculations and Sensitivity Analysis of Chlorine-,NO_(x)-,and Bromine-Depleting Cycles of Stratospheric Ozone

This paper presents an engineering system approach using a 2D model of conservation of mass to study the dynamics of ozone and concerned chemical species in the stratosphere.By considering all fourteen photolysis,ozone-generating,and-depleting chemical reactions,the model calculated the transient,spatial changes of ozone under different physical-chemical-radiative conditions.Validation against the measured data demonstrated good accuracy,close match of our model with the observed ozone concentrations at both 20°S and 90°N locations.The deviation in the average concentration was less than 1% and in ozone profiles less than 17%.The impacts of various chlorine-(Cl),nitrogen oxides-(NO_(x)),and bromine-(Br)depleting cycles on ozone concentrations and distribution were investigated.The chlorine catalytic depleting cycle was found to exhibit the most significant impact on ozone dynamics,confirming the key role of chlorine in the problem of ozone depletion.Sensitivity analysis was conducted with levels of 25%,50%,100%,200%,and 400% of the baseline value.The combined cycles(Cl+NO_(x)+Br)showed the most significant influence on ozone behavior.The total ozone abundance above the South Pole could decrease by a small 3%,from 281 DU(Dubson Units)to 273 DU for the 25% level,or by a huge thinning of 60%to 114 DU for the 400% concentration level.When the level of chlorine gases increased beyond 200%,it would cause ozone depletion to a level of ozone hole(below 220 DU).The 2D Ozone Model presented in this paper demonstrates robustness,convenience,efficiency,and executability for analyzing complex ozone phenomena in the stratosphere.

The impact of land use and cover change on soil organic carbon and total nitrogen storage in the Heihe River Basin: A meta-analysis

Land use and cover change(LUCC) is an important indicator of the human-earth system under climate/environmental change,which also serves as a key impact factor of carbon balance,and a major source/sink of soil carbon cycles.The Heihe River Basin(HRB) is known as a typical ecologically fragile area in the arid/semi-arid regions of northwestern China,which makes it more sensitive to the LUCC.However,its sensitivity varies in a broad range of controlling factors,such as soil layers,LUCCs and calculation methods(e.g.the fixed depth method,FD,and the equivalent mass method,ESM).In this study,we performed a meta-analysis to assess the response of soil organic carbon(SOC) and total nitrogen(TN) storage to the LUCC as well as method bias based on 383 sets of SOC data and 148 sets of TN data from the HRB.We first evaluated the calculation methods and found that based on the FD method,the LUCC caused SOC and TN storage to decrease by 17.39% and 14.27%,respectively;while the losses estimated using the ESM method were 19.31% and 18.52%,respectively.The deviations between two methods were mainly due to the fact that the FD method ignores the heterogeneity of soil bulk density(BD),which may underestimate the results subsequently.We then analyzed the response of SOC and TN storage to various types of the LUCC.In particular,when woodland and grassland were converted into cultivated land or other land types,SOC and TN suffered from heavy losses,while other LUCCs had minor influences.Finally,we showed that increasing the depth of the soil layers would reduce the losses of SOC and TN storage.In summary,we identified a series of controlling factors(e.g.soil layer,the LUCC and calculation method) to evaluate the impact of the LUCC on SOC and TN storage in the HRB,which should be considered in future research.

Effects of land use, climate, topography and soil properties on regional soil organic carbon and total nitrogen in the Upstream Watershed of Miyun Reservoir, North China

Soil organic carbon （SOC） and total nitrogen （TN） contents as well as their relationships with site characteristics are of profound importance in assessing current regional, continental and global soil C and N stocks and potentials for C sequestration and N conservation to offset anthropogenic emissions of greenhouse gases. This study investigated contents and distribution of SOC and TN under different land uses, and the quantitative relationships between SOC or TN and site characteristics in the Upstream Watershed of Miyun Reservoir, North China. Overall, both SOC and TN contents in natural secondary forests and grasslands were much higher than in plantations and croplands. Land use alone explained 37.2% and 38.4% of variations in SOC and TN contents, respectively. The optimal models for SOC and TN, achieved by multiple regression analysis combined with principal component analysis （PCA） to remove the multicollinearity among site variables, showed that elevation, slope, soil clay and water contents were the most significant factors controlling SOC and TN contents, jointly explaining 70.3% of SOC and 67.1% of TN contents variability. Only does additional 1.9% and 3% increase in the interpretations of SOC and TN contents variability respectively when land use was added to regressions, probably due to environment factors determine land use. Therefore, environmental variables were more important for SOC and TN variability than land use in the study area, and should be taken into consideration in properly evaluating effects of future land use changes on SOC and TN on a regional scale.

基于Meta-analysis的土壤氮素对采伐的响应研究

[目的]研究采伐影响下土壤氮素的变化规律,探究森林合理的采伐强度,维持森林资源的可持续性。[方法]通过Review Manager 5.3软件,以标准化均数差(SMD)作为衡量效应尺度的统计学指标,对搜集到的1983—2017年初有关采伐对土壤氮素影响的31篇文献数据进行了Meta分析。[结果]采伐可有效降低土壤全氮含量[SMD=-0.55(95%CI,-1.04-0.07)<0],显著增加土壤铵态氮和硝态氮含量[SMD=0.99(95%CI,0.51 1.47)>0;SMD=2.34(95%CI,0.49 4.19)>0],而对土壤水解性氮含量影响不明显[SMD=-0.30(95%CI,-1.060.47)]。土壤氮素变化因采伐强度不同而异,皆伐对其影响较大。[结论]森林采伐时,在相同林型研究成果的基础上,合理控制采伐强度,减少高强度择伐,积极推广低强度择伐,避免皆伐。

芡实对沿淮富营养化水体的净化效果研究

为了解乡土水生植物芡实对沿淮农村富营养化河流净化效果,在模拟沿淮农村地区富营养化河流的水池中种植芡实,定期监测水体中的总氮(TN)、氨氮(NH_(4)^(+)-N)、总磷(TP)、化学需氧量(COD_(Cr))、酸碱度(pH)、可溶性盐含量(EC)、溶解氧(DO)的数值变化,综合分析芡实对富营养化河流的净化效果。结果表明,芡实作为沿淮地区乡土水生植物,对富营养化的河流有着净化作用。芡实在生长过程中能吸收水体95.53%~98.45%的NH_(4)^(+)-N和99.50%~99.65%的TP,净化效果好。芡实对富营养河流中TN和COD_(Cr)的净化效果不明显,而且水体中的pH上升11.05%~11.61%,EC值增加21.12%~22%,DO增加3.82~21.77倍。芡实作为一种乡土水生植物,对沿淮地区富营养化河流具有显著的净化潜力。

氮化硼化学成分标准物质研制

研制3种氮化硼化学成分标准物质。以硼酸和三聚氰胺为原料,采用湿化学法合成固体前驱物,分别在空气和氮气气氛下高温热处理,制得质量分数为95%~99%的氮化硼候选物。随机抽取12瓶分装好的样品进行均匀性检验,组内和组间无显著性系统差异,样品均匀性良好。采用直线拟合法进行短期稳定性和长期稳定性检验,拟合直线斜率均小于临界值,样品稳定性良好。通过8家实验室采用两种不同原理的方法进行协作定值,统计评定出标准值和不确定度,定值组分包括总氮、总硼、氧化硼、铁、钙、钠,其中总氮质量分数为53.8%~55.9%,总硼质量分数为41.8%~43.7%,氧化硼质量分数为0.105%~2.37%,基本覆盖了常规氮化硼的纯度范围。该系列标准物质能够满足氮化硼相关产品的测量质量控制和测试需求。

益气养阴法联合西药治疗肾病综合征的疗效及安全性的Meta分析

【目的】系统评价益气养阴法联合西药治疗肾病综合征的有效性及安全性。【方法】检索中国知网(CNKI)、中国生物医学文献数据库(CBM)、万方(Wangfang)、维普(VIP)、PubMed、Web of Science、Cochrane Library、Embase等国内外主要文献数据库,筛选其中有关益气养阴法联合西药(试验组)对比单纯西药(对照组)治疗肾病综合征的临床随机对照试验(RCTs),采用Cochrane手册中的偏倚风险工具进行文献的质量评价,运用RevMan 5.3软件进行Meta分析。【结果】共纳入18个RCTs,包含1334例患者。Meta分析结果显示,益气养阴法联合西药在提高临床有效率(RR=1.24,95%CI[1.16,1.32],P<0.00001),改善24 h尿蛋白定量(24hUPRO)(MD=-0.92,95%CI[-1.09,-0.75],P<0.00001)、血清白蛋白(ALB)(MD=7.06,95%CI[4.73,9.39],P<0.00001)、尿素氮(BUN)(MD=-1.57,95%CI[-2.01,-1.13],P<0.00001)、血肌酐(SCr)(MD=-12.23,95%CI[-16.58,-7.88],P<0.00001)、总胆固醇(TC)(MD=-1.06,95%CI[-1.69,-0.43],P=0.0009)、甘油三酯(TG)(MD=-0.58,95%CI[-0.94,-0.21],P=0.002)水平,以及降低不良反应发生率(RR=0.50,95%CI[0.40,0.64],P<0.00001)方面优于单纯西药治疗。【结论】益气养阴法联合西药治疗肾病综合征在提高临床疗效及改善24hUPRO、ALB、BUN、SCr、TC、TG方面优于单纯西药治疗,且能降低激素产生的不良反应。因纳入文献较少,文献质量较低,潜在疗效需更多的高质量研究进行验证。

改装流动注射分析仪总氮分析模块测定亚硝酸盐氮的探讨

利用总氮分析模块通过调整管路和程序参数进行亚硝酸盐氮测定。用改装后的总氮分析模块绘制亚硝酸盐氮标准曲线,相关系数r>0.999,线性良好。根据《环境监测分析方法标准制订技术导则》(HJ 168-2020)的相关规定分别验证该方法的检出限、测定下限。结果表明,检出限为0.002 mg/L,测定下限为0.008 mg/L,测定上限为0.5 mg/L。同时对标准样品进行检测,标准样品的检测结果合格,相对标准偏差为0.3%~2.3%。地表水的加标回收率为98%。采用配对样本t检验法将该方法与(GB/T 7493-1987)《水质亚硝酸盐氮的测定分光光度法》进行比对,结果表明两种方法无显著性差异。此方法简单快捷,对于实际水样的测定结果令人满意。

连续流动分析法同时测定地表水中的总氮和氨氮

结合地表水特性,为充分了解连续流动分析法在其总氮和氨氮测定中的实用价值。本研究通过采集地表水样本,运用连续流动分析法和手工法进行测定,统计两种方法的检测结果。连续流动分析法检测总氮、氨氮的线性范围内的相关系数(r)分别为0.9998、0.9997,检出限均为0.04 mg/L。检出精密度总氮、氨氮相对标准偏差分别在1.11%~2.38%、0.76%~1.28%范围内。以手工方法为对照,连续流动分析法的中总氮、氨氮样品检出准确度误差更低,且准确度与要求相符合。证实在地表水检测中,连续流动分析法不仅操作更加简单方便快捷,且有着更高的精密度和更好的准确度,可以更好满足实验室质量控制要求,可应用于地表水大批量样品的测定。

抚河流域氮磷浓度时空分布特征及污染状况评价

及时掌握抚河流域氮、磷等营养盐浓度时空分布特征,是保障鄱阳湖水环境与水生态安全的关键。基于抚河抚州段干流及主要支流14个国控/省考监测断面近9 a的水质监测数据,研究抚河流域抚州段河流氨氮、总磷浓度的时空分布特征,并利用单因素分析、内梅罗综合污染指数和聚类分析法,对抚河抚州段干支流氨氮、总磷污染状况进行综合评价。结果表明:(1)抚河干流及主要支流断面氨氮、总磷浓度达到Ⅱ类标准比例分别为91.29%和86.19%。(2)抚河流域河流氨氮、总磷浓度年际间变化较小,但年内季节、月际变化较大,氨氮、总磷浓度均在夏季达到最大值。(3)抚河流域上游氨氮、总磷浓度普遍低于中下游地区。(4)抚河干流氨氮、总磷属轻度污染,支流临水、东乡水的氨氮、总磷属重度污染。研究成果对于抚河流域水环境保护和治理具有重要参考价值。

连续流动分析法测定淡水中亚硝酸盐氮、硝酸盐氮、氨氮、总氮的研究

含氮化合物是水质监测中的重要指标,因此需要可靠、精确、快速的监测方法作为支撑。采用连续流动仪法对亚硝酸盐氮、硝酸盐氮、氨氮、总氮进行监测,结果表明:标准曲线相关系数均大于0.999,检出限、精密度、准确性、加标回收率、“四氮”关系均满足方法要求。说明连续流动分析仪具有较高的灵敏度和准确度,稳定性好,可实现样品在线消解、连续检测,简化了样品前处理过程,更适用于大批量含氮化合物的水质监测工作。

紫外分光光度法和流动注射法测定水样中总氮的比对研究

针对实际样品总氮的测定,于实验室内对采用流动注射法代替紫外分光光度法进行测定的可靠性进行评估。分为两个实验:两种方法的质量控制实验与两种方法的比对实验。对于质量控制实验,测定结果均符合标准方法质控要求:曲线相关系数R≥0.999;计算检出限与计算测定下限分别小于方法检出限与测定下限;空白值、重复多次测定的相对标准偏差、加标回收率、有证标准样品测定均符合方法与证书要求。对于方法比对实验,采用两种方法对22组工业废水进行总氮测定,对其差异性进行t检验评估,其p值为0.054(大于0.05)。证明采用两种方法进行总氮测定无显著性差异,采用流动注射法代替紫外分光光度法是可靠的。此外,对影响总氮测定结果的可能因素(试剂品质与纯度、流动注射系统、pH、金属离子与非金属离子)也进行了探讨,得出干扰因素对此次实验的总氮测定影响较小的结论。

复合肥料中总氮含量的测定方法探讨

通过凯氏定氮法对复合肥料进行精密度试验和加标回收率试验,将复合肥料中总氮含量测定结果与蒸馏后滴定法(仲裁法)测定结果进行比较。实验表明,凯氏定氮法操作简单、耗时少、节约试验成本,并且准确率和重复率高,数据准确可靠。

IGOA-RBF模型在石门水库水质预测中的应用

文中以石门水库为例,通过改进蚱蜢算法(IGOA)增加局部值的泛化性,并对RBF神经网络模型进行参数优化,构建了运行效率高、预测精确度高的IGOA-RBF的水质预测模型。结果表明,IGOA-RBF水质预测模型误差均较小,可为水源地水环境的水质评价和治理提供重要参考。

利用可见光/近红外反射光谱估算土壤总氮含量的实验研究

利用土壤的室内反射率光谱,探讨土壤氮元素的高光谱机理。利用土壤光谱各吸收带的特征参数与总氮含量进行逐步回归运算,确定与氮元素关系比较密切的几个吸收带。计算出这几个特征吸收带内土壤反射率的变化形式:一阶导数(FDR)、倒数(1/R)、倒数之对数(log(1/R))、波段深度(Depth),并与总氮含量进行逐步回归分析,得到比较理想的结果:建模样本的Ra2(修正的判定系数)分别为0 789、0 753、0 736、0 699,验证样本的Ra2分别为0 759、0 468、0 794、0 725。可见土壤的反射率光谱与氮元素含量之间存在比较明显的相关性,可见光/近红外反射光谱具有快速估算土壤中氮元素含量的潜力。

用近红外漫反射光谱检测肉品新鲜度的初步研究

挥发性盐基氮一直以来是评定肉品新鲜程度的重要指标,通常其测定依据是半微量凯氏定氮法,这难以满足当前肉品快速非破坏性的检测要求。文章通过近红外漫反射光谱法(NIRS)建立了挥发性盐基氮(TVB-N)的预测模型,并通过聚类分析方法对光谱数据进行了分类处理。结果表明当猪肉样品中TVB-N含量超过11.6 mg.(100g)-1时,可以判定该肉品为次鲜肉,采用近红外漫反射光谱法建立预测模型,能够实现对肉品的新鲜程度非破坏性、快速检测。

基于电子鼻的带鱼货架期预测模型

为探索通过气味分析判断海产品贮藏品质的方法,利用电子鼻对带鱼在不同贮藏温度与贮藏时间下的挥发性气味变化进行了分析,对所获数据进行了主成分分析与货架期分析,并与理化品质指标值挥发性盐基氮(totalvolatile basicnitrogen,TVBN)相联系,建立了带鱼在273～283K下的货架期预测模型。结果表明:电子鼻18个金属传感器能很好地将贮藏于273与283K下的带鱼随着贮藏时间变化的气味进行区分。贮藏于不同温度条件下的带鱼的TVBN值与菌落总数值均随着贮藏时间的增加而增长,且均符合一级化学动力学模型(R2>0.9)。基于电子鼻货架期分析获得的273～283K下的气味变化结果与该温度下理化品质指标变化具有较好的对应关系,采用Arrhenius动力学模型推导公式求得带鱼在(273～283K)温度段内TVBN的Q10(温差为10K的货架寿命之比)值,对照该温度段下电子鼻货架期分析获得的气味变化货架期分析值,得到带鱼在该温度段内的Q10货架期预测模型,经验证,其预测误差小于20%。可根据获得的货架期预测模型对带鱼在273～283K条件下的货架期进行预测。

水溶性糖、烟碱、总氮含量与烤烟吃味品质的关系研究

通过数理统计系统分析了烟叶中水溶性糖 (包括还原糖和总糖 )、烟碱、总氮含量与烤烟吃味品质的关系。结果表明 ,水溶性糖、烟碱、总氮含量对烤烟吃味品质都产生极显著的影响 ,其中还原糖、烟碱为目前制约烤烟吃味品质的主要化学成分。生产中 ,控制烟碱的过高积累 ,提高还原糖相对于总糖的含量、减小两糖差值 ,能有效地提高烤烟吃味品质。两糖差值可作为评价烟叶吃味品质的重要指标。数据分析表明 ,用水溶性糖、烟碱、总氮及其派生值传统的含量或数值范围评价烟叶吃味品质是不够的 ,更深入地研究吃味品质优良的烟叶在化学成分上共同遵循的规律 。

基于降雨和地形特征的输出系数模型改进及精度分析

降雨是非点源污染产生的主要驱动条件,地形是非点源污染输移的重要影响因素,两者均与非点源污染紧密相关。输出系数模型是大尺度流域非点源污染模拟的常用模型,从降雨和地形对非点源污染产生、迁移的影响出发,对现有输出系数模型进行了改进,并给出了改进模型中降雨影响因子和地形影响因子的确定方法,以提高模型在大尺度流域的模拟精度。最后,以长江上游1990和2000年TN负荷估算为例,分析了模型改进前后的精度变化。精度对比表明,通过模型改进,流域综合相对误差从45.02%和42.49%减小到23.93%和18.38%,直门达站、沱江大桥站和罗渡溪站控制流域的相对误差有明显减小。改进后的输出系数模型结构更合理,模拟更符合实际。