A biodiversity evaluation framework for restoration of aquatic macrophyte communities in shallow lakes driven by hydrological process management     

Shuhan Li  Tao Sun  Wei Yang  Baoshan Cui  Xinan Yin 《水文研究》2021,35(1):e13983

Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China's Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42–7.23 m; medium, 7.23–8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth (SD), and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Water level regime mainly influenced interspecific relationships by changing the TN and COD concentration. The water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability. The biodiversity evaluation framework would provide a deeper insight into the hydrological process management for restoration of aquatic macrophyte communities in shallow lakes.  相似文献   

Rainfall intensity affects runoff responses in a semi-arid catchment     

Ze Tao  Min Li  Bingcheng Si  Dyan Pratt 《水文研究》2021,35(4):e14100

The source and hydrochemical makeup of a stream reflects the connectivity between rainfall, groundwater, the stream, and is reflected to water quantity and quality of the catchment. However, in a semi-arid, thick, loess covered catchment, temporal variation of stream source and event associated behaviours are lesser known. Thus, the isotopic and chemical hydrographs in a widely distributed, deep loess, semi-arid catchment of the northern Chinese Loess Plateau were characterized to determine the source and hydrochemical behaviours of the stream during intra-rainfall events. Rainfall and streamflow were sampled during six hydrologic events coupled with measurements of stream baseflow and groundwater. The deuterium isotope (²H), major ions (Cl⁻, SO₄²⁻, NO₃⁻, Ca²⁺, K⁺, Mg²⁺, and Na⁺) were evaluated in water samples obtained during rainfall events. Temporal variation of ²H and Cl⁻ measured in the groundwater and stream baseflow prior to rainfall was similar; however, the isotope compositions of the streamflow fluctuated significantly and responded quickly to rainfall events, likely due to an infiltration excess, overland dominated surface runoff during torrential rainfall events. Time source separation using ²H demonstrated greater than 72% on average, the stream composition was event water during torrential rainfall events, with the proportion increasing with rainfall intensity. Solutes concentrations in the stream had loglinear relationships with stream discharge, with an outling anomaly with an example of an intra-rainfall event on Oct. 24, 2015. Stream Cl⁻ behaved nonconservative during rainfall events, temporal variation of Cl⁻ indicated a flush and washout at the onset of small rainfall events, a dilution but still high concentration pattern in high discharge and old water dominated in regression flow period. This study indicates rainfall intensity affects runoff responses in a semi-arid catchment, and the stored water in the thick, loess covered areas was less connected with stream runoff. Solute transport may threaten water quality in the area, requiring further analysis of the performance of the eco-restoration project.  相似文献   

Predicting quantiles of water quality from catchment characteristics     

Danlu Guo  Shuci Liu  Dhananjay Singh  Andrew W. Western 《水文研究》2021,35(1):e13996

Water quality is often highly variable both in space and time, which poses challenges for modelling the more extreme concentrations. This study developed an alternative approach to predicting water quality quantiles at individual locations. We focused on river water quality data that were collected over 25 years, at 102 catchments across the State of Victoria, Australia. We analysed and modelled spatial patterns of the 10th, 25th, 50th, 75th and 90th percentiles of the concentrations of sediments, nutrients and salt, with six common constituents: total suspended solids (TSS), total phosphorus (TP), filterable reactive phosphorus (FRP), total Kjeldahl nitrogen (TKN), nitrate-nitrite (NO_x), and electrical conductivity (EC). To predict the spatial variation of each quantile for each constituent, we developed statistical regression models and exhaustively searched through 50 catchment characteristics to identify the best set of predictors for that quantile. The models predict the spatial variation in individual quantiles of TSS, TKN and EC well (66%–96% spatial variation explained), while those for TP, FRP and NO_x have lower performance (37%–73% spatial variation explained). The most common factors that influence the spatial variations of the different constituents and quantiles are: annual temperature, percentage of cropping land area in catchment and channel slope. The statistical models developed can be used to predict how low- and high-concentration quantiles change with landscape characteristics, and thus provide a useful tool for catchment managers to inform planning and policy making with changing climate and land use conditions.  相似文献   

Finding KBO Flyby Targets for New Horizons     

Spencer  John  Buie  Marc  Young  Leslie  Guo  Yanping  Stern  Alan 《Earth, Moon, and Planets》2003,92(1-4):483-491

Development of the New Horizons mission to Pluto and the Kuiper Belt is now fully funded by NASA (Stern and Spencer, this volume). If all goes well, New Horizons will be launched in January 2006, followed by a Jupiter gravity assist in 2007, with Pluto arrival expected in either 2015 or 2016, depending on the launch vehicle chosen. A backup launch date of early 2007, without a Jupiter flyby, would give a Pluto arrival in 2019 or 2020. In either case, a flyby of at least one Kuiper Belt object (KBO) is planned following the Pluto encounter, sometime before the spacecraft reaches a heliocentric distance of 50 AU, in 2021 or 2023 for the 2006 launch, and 2027 or 2029 for the 2007 launch. However, none of the almost 1000 currently-known KBOs will pass close enough to the spacecraft trajectory to be targeted by New Horizons, so the KBO flyby depends on finding a suitable target among the estimated 500,000 KBOs larger than 40 km in diameter. This paper discusses the issues involved in finding one or more KBO targets for New Horizons. The New Horizons team plans its own searches for mission KBOs but will welcome other U.S, or international team who wish to become involved in exchange for mission participation at the KBO.  相似文献   

Three Super Active Regions in the Descending Phase of Solar Cycle 23   总被引：2，自引：0，他引：2  

Hong-Qi Zhang  Xing-Ming Bao  Yin Zhang  Ji-Hong Liu  Shu-Dong Bao  Yuan-Yong Deng  Wei Li  Jie Chen  Jin-Ping Dun  Jiang-Tao Su  Juan Guo  Xiao-Fan Wang  Ke-Liang Hu  Gang-Hua Lin  Dong-Guang WangNational Astronomical Observatories  Chinese Academy of Sciences  Beijing   《中国天文和天体物理学报》2003,3(6):491-494

We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle.  相似文献   

在BPL信道上增加数据广播内容的探讨   总被引：1，自引：1，他引：0  

吴海涛  边玉敬 《时间频率学报》2001,24(1):38-44

分析了现有罗兰C（包括BPL）在授时方面存在的不足，提出了在BPL信道上实现数据广播的主要目的。详细讨论了各种可能的数据信息的结构，并给出了有关参数和数据的计算方式和公式。认为发播内容的选择是由期望的系统功能决定的，广播内容的编排则与具体实现技术相关。最后给出了在不同调制方法下的传输速率，这是合理编排广播内容的基础。  相似文献   

First Post-Newtonian Angular Momentum In Relativistic Celestial Mechanics     

Jin-He Tao  Tian-Yi Huang  Zhao-Hua Yi 《Astrophysics and Space Science》1997,254(2):173-186

With a new theory on the 1PN celestial mechanics recently developed by Damour, Soffel and Xu (1991,1992,1993,1994), definitions and expressions of the 1PN spin angular momentum are investigated and analysed. The total spin angular momentum of a system of extended bodies such as the solar system is calculated and expressed as the function of local parameters and observables under reasonable assumptions, which would find its application in the evolution and dynamics of systems of celestial bodies. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

ELECTROCHEMICAL CORROSION BEHAVIOR OF STEEL IN THE JUNCTURE AREA OF SEA CLAY AND SAND     

张经磊  侯保荣  郭公玉  杨芳英  谢肖勃 《中国海洋湖沼学报》1993,11(2):171-175

Corrosion behavior of steel in the juncture area of sea clay and sand was studied. The results show that galvanic corrosion occurred between steel samples buried in sea clay and sand, and that the polarity of the galvanic cell reversed after some testing later. The cause of reversing of polarity is discussed.  相似文献   

Urban tourism research methodology     

Tao Wei  Zhong Wen-hui  Hong Yan 《中国地理科学(英文版)》2005,15(2):173-178

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在社会发展的层面上认识“数字地球”   总被引：1，自引：0，他引：1  

郭仁忠  林亨贵 《地球信息科学学报》2001,3(1):50-53

 本文讨论了“数字地球”的有关问题。指出“数字地球”是人类社会及其活动在网络空间的延伸和拓展,是信息技术带来的社会发展趋势。关于“数字地球”的讨论不应局限在空间信息技术领域,而应该在社会发展的层面上认识它  相似文献