基于小波分析的入库径流变化研究

基于桂林市青狮潭水库1958—2011年入库径流资料,采用Morlet小波分析方法对入库径流在不同时间尺度下的变换时频分布特征及丰枯变化的情况进行了分析。结果表明,青狮潭水库入库径流序列具有多时间尺度变化特性,主要存在8,15,22,32 a左右的周期变化。这4个主要周期变化,主导着青狮潭水库入库径流的趋势变化特性,尤其是以32 a的周期变化为主,入库径流大致经历了枯→丰→枯→丰→枯的变化。     

亚热带典型小流域总氮最大日负荷(TMDL)及影响因子研究——以金井河流域为例

本研究以亚热带红壤丘陵区为研究区域,选取10个典型小流域,根据土地利用和畜禽养殖密度分为4种类型(森林、森林-种植、养殖和种植-养殖小流域),并基于近3年小流域把口站的原位观测数据,采用负荷历时曲线模型(LDC)计算了不同类型小流域水体总氮(TN)的最大日负荷(TMDL),运用灰度分析法定量研究了不同流量阶段小流域主要因子对TN负荷消减率的影响.结果表明,小流域TN负荷特征与流域类型密切相关,10个小流域TN年均负荷为739.0~2798.4 kg·km-2·a-1,由小到大依次为森林、森林-种植、养殖、种植-养殖小流域,其中,养殖、种植-养殖小流域水质整体超标严重,且应针对中、低流量条件下(秋、冬季节)负荷进行消减,而森林-种植小流域TN负荷超标情况略好,但高流量阶段(春、夏)超标率过高.灰度分析结果表明,TN负荷消减率在高、中流量阶段下主要受农田面积比例影响,而低流量阶段受畜禽密度影响.农田面积比例对高、中流量段TN消减率影响显著,而畜禽养殖密度在低流量段具有更大影响,小流域景观越破碎、类型越丰富、斑块分布越零散、形状越复杂,TN负荷通量则越大.     

Observed Changes in Climate and Streamflow in the Upper Rio Grande Basin

Observed streamflow and climate data are used to test the hypothesis that climate change is already affecting Rio Grande streamflow volume derived from snowmelt runoff in ways consistent with model‐based projections of 21st‐Century streamflow. Annual and monthly changes in streamflow volume and surface climate variables on the Upper Rio Grande, near its headwaters in southern Colorado, are assessed for water years 1958–2015. Results indicate winter and spring season temperatures in the basin have increased significantly, April 1 snow water equivalent (SWE) has decreased by approximately 25%, and streamflow has declined slightly in the April–July snowmelt runoff season. Small increases in precipitation have reduced the impact of declining snowpack on trends in streamflow. Changes in the snowpack–runoff relationship are noticeable in hydrographs of mean monthly streamflow, but are most apparent in the changing ratios of precipitation (rain + snow, and SWE) to streamflow and in the declining fraction of runoff attributable to snowpack or winter precipitation. The observed changes provide observational confirmation for model projections of decreasing runoff attributable to snowpack, and demonstrate the decreasing utility of snowpack for predicting subsequent streamflow on a seasonal basis in the Upper Rio Grande Basin.     

Estimating Lag to Peak between Rainfall and Peak Streamflow with a Mixed‐Effects Model

We test the use of a mixed‐effects model for estimating lag to peak for small basins in Maine (drainage areas from 0.8 to 78 km²). Lag to peak is defined as the time between the center of volume of the excess rainfall during a storm event and the resulting peak streamflow. A mixed‐effects model allows for multiple observations at sites without violating model assumptions inherent in traditional ordinary least squares models, which assume each observation is independent. The mixed model includes basin drainage area and maximum 15‐min rainfall depth for individual storms as explanatory features. Based on a remove‐one‐site cross‐validation analysis, the prediction errors of this model ranged from ?42% to +73%. The mixed model substantially outperformed three published models for lag to peak and one published model for centroid lag for estimating lag to peak for small basins in Maine. Lag to peak estimates are a key input to rainfall–runoff models used to design hydraulic infrastructure. The improved accuracy and consistency with model assumptions indicates that mixed models may provide increased data utilization that could enhance models and estimates of lag to peak in other regions.     

页岩气钻屑固化填埋池监测与评价研究

为了探讨钻屑固化填埋池对周围土壤及水体环境的影响,以西南某页岩气田为例,分别选取了具有代表性的水基钻屑固化填埋池和油基灰渣固化填埋池,先对钻屑固化处置方式和效果进行了评价,再对钻屑固化填埋池土壤径流液及土壤进行了监测,分析了固化填埋池对周边土壤环境的影响。结果表明:钻屑固化体浸出液达到GB8978-1996《污水综合排放标准》一级排放标准,钻屑固化填埋池土壤径流液满足GB5084-2005《农田灌溉水质标准》旱作标准;水基钻屑固化填埋池和油基灰渣固化填埋池上覆土壤重金属综合污染指数分别是0.42、0.45,周边土壤重金属综合污染指数分别是0.45、0.54。钻屑固化填埋池各项监测指标均未超标,土壤重金属综合污染指数均小于0.7,钻屑固化填埋暂时未对周边土壤造成影响,属于清洁水平。短期内钻屑固化填埋效果较好,对周围土壤环境影响较小。     

上海市文教区屋面径流水质特性研究

在对2003～2006 年上海市文教区屋面径流进行监测的基础上,分析了屋面径流污染物的出流过程,并应用统计分析方法对屋面径流水质及其影响因素进行了探讨.结果表明,屋面径流污染物EMC的对数正态概率分布均呈现出良好的线性分布,说明污染物EMC具有较好的正态分布性;上海市文教区屋面径流污染物COD、SS、BOD5、NH4 -N、TP和TN的EMC中值浓度分别为42.6、76.9、15.2、1.61、0.14和4.8 mg/L;通过聚类分析可知,屋面径流水质整体上受大气沉降等污染物累积效应的影响最大,而受雨水冲刷作用的影响次之.     

西江河口段秋季表层水体CO2分压的变化特征

为了探讨西江河口段表层水体CO2分压(pco2)的分布特征,于2006年秋季在西江磨刀门至马口河段沿程实测了58个样点的表层水体理化参数.结果表明,河道表层水体Pco2值介于93.15-334.38Pa之间,平均值为174.00Pa,被测河段是个明显的大气CO2"源".河流水体的理化性质在向海输送过程中发生了明显的改变,并且导致表层水体Pco2随航程的增加而递减.样点水体接受的日照时间与其Pco2,有负相关关系,使得表层水体Pco2呈现出日周期变化.河段表层水体Pco2的这种时空变化与河口过程中河-海作用的弱化而引起水体理化参数(如水温、pH值、电导率、总溶解固体、氧化还原电位和碱度等)的变化以及水体内部碳的生物化学过程(如光合作用与呼吸作用以及有机物的分解转化等)密切相关.     

元江-红河干流径流时序特性及突变分析

以元江干流主要控制性水文站蛮耗站在1956～2000年观测记录共45年的径流量序列数据为基础,运用Mann Kendall、有序聚类和累积距平等统计方法分析元江径流分布规律及其变化的基本特征。结果表明：实测径流年内分配不均,年际变化不大,年径流变差系数为0263。实测径流量序列存在明显的阶段性和缓慢上升趋势。对元江实测径流序列进行还原处理得到天然径流量,发现其与实测径流的差异不大,多年平均水资源耗水量仅占天然径流量的292%。年径流量和径流系数在1965年和1994年前后都发生两次增加突变;而年降水量与流域年蒸散发量没有发生突变。归一化植被植物变化表明元江干流植被覆盖在1993年左右被破坏较为严重。因此,得出径流变化趋势主要与降雨有关,两次突变主要受人类对下垫面改变的影响。     

耕作措施对三峡库区土壤侵蚀和养分流失的影响

为研究三峡库区土地耕作措施对土壤侵蚀和营养物质流失的影响,在三峡库区张家冲小流域设置10个不同土地利用方式的试验小区,在自然降雨条件下,进行为期1 a的小区试验,研究不同土地利用方式下土壤侵蚀和径流中氮、磷流失特征.结果表明:在10个试验小区中,土坎梯种柑小区年均径流量和土壤侵蚀量最大,土坎篱种柑小区年均径流量最小,坡地种粮小区土壤侵蚀量最小;坡篱种粮小区总氮和总磷年流失量最大,坡地种柑小区年流失量最小;土壤侵蚀和营养物质流失主要发生在6-8月降雨集中的暴雨季节.在类似于研究区域的其他农业区域,适合于坡地种柑,而坡篱种粮和土坎梯种柑是不适合推广的种植方式.     

Impact of Grazing Intensity during Drought in an Arizona Grassland

Abstract:  The ecological benefits of changing cattle grazing practices in the western United States remain controversial, due in part to a lack of experimentation. In 1997 we initiated an experimental study of two rangeland alternatives, cattle removal and high-impact grazing, and compared grassland community responses with those with more conventional, moderate grazing practices. The study was conducted in a high-elevation, semiarid grassland near Flagstaff, Arizona (U.S.A.). We conducted annual plant surveys of modified Whittaker plots for 8 years and examined plant composition shifts among treatments and years. High-impact grazing had strong directional effects that led to a decline in perennial forb cover and an increase in annual plants, particularly the exotic cheatgrass ( Bromus tectorum L.). A twofold increase in plant cover by exotic species followed a severe drought in the sixth year of the study, and this increase was greatest in the high-impact grazing plots, where native cover declined by one-half. Cattle removal resulted in little increase in native plant cover and reduced plant species richness relative to the moderate grazing control. Our results suggest that some intermediate level of cattle grazing may maintain greater levels of native plant diversity than the alternatives of cattle removal or high-density, short-duration grazing practices. Furthermore, episodic drought interacts with cattle grazing, leading to infrequent, but biologically important shifts in plant communities. Our results demonstrate the importance of climatic variation in determining ecological effects of grazing practices, and we recommend improving conservation efforts in arid rangelands by developing management plans that anticipate this variation.