半干旱黄土丘陵区退化人工林群落结构 调整下细根特征分析          下载免费PDF全文

李浩  胡婵娟  冯德显  赵荣钦  郭雷  满洲 《干旱区地理》2020,43(6):1523-1533

根系尤其细根在植物的生长发育中起着重要作用，以甘肃省定西市巉口镇龙滩流域的白 杨及山杏 2 种典型退化人工林为研究对象，研究了人工林群落结构调整后形成的白杨+5 年生油 松、白杨+10 年生油松及山杏+云杉、山杏+樟子松混交林与单一纯林相比不同深度、不同径级下细 根的根长密度、根面积密度、根生物量密度、比根长及比根面积，以期揭示不同人工林恢复模式下 的细根分布特征。结果表明：（1）混交恢复模式起到了一定的积极作用，大部分混交林相较于纯林 细根的根长密度、根面积密度及根生物量密度在土壤表层均有所提高。混交林细根在浅层的占比 得到了提高，且随恢复年限的增加而升高。（2）细根根长密度、根面积密度及根生物量密度与土壤 全碳、全氮、含水量及有机碳之间以及比根长及比根面积与土壤全碳、土壤全氮及有机碳之间均存 在显著正相关关系。  相似文献   

Factors controlling the temporal variability in dissolved oxygen regime of salmon spawning gravels          下载免费PDF全文

D. A. Sear  I. Pattison  A. L. Collins  M. D. Newson  J. I. Jones  P. S. Naden  P. A. Carling 《水文研究》2014,28(1):86-103

Dissolved oxygen (DO) plays a critical role in the development of the juvenile stages of benthic spawning fish and salmonids in particular. Factors influencing the DO regime within spawning gravels include the accumulation of fine sediment, penetration of groundwater or surface water into the gravels, thermal regime, and the consumption of oxygen by sediment and its associated organic fractions. In this field study, we quantify the DO regime within an artificial salmon redd at high temporal resolution. The environment within the redd is shown to be complex, with large variations in DO. Application of a numerical model (SIDO‐UK) enables for the first time, the quantification of the relative contributions to DO consumption from thermal regime, sediment accumulation and sediment oxygen demand. Sediment accumulation is shown to have a minor impact on DO in the redd whereas upwelling groundwater is identified as the most likely cause of the major changes in DO. Bed mobility has a minor impact on DO regime of the redd. The effects of fine sediment and oxygen supply on salmon embryo survival are estimated. Implications for river catchment management and prospects for future research are discussed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Storage,properties and seasonal variations in fine‐grained bed sediment within the main channel and headwaters of the River Sanginjoki,Finland          下载免费PDF全文

H. Marttila  B. Kløve 《水文研究》2014,28(17):4756-4765

Lowland catchments in Finland are intensively managed, promoting erosion and sedimentation that negatively affects aquatic environments. This study quantified fine‐grained bed sediment in the main channel and upstream headwaters of the River Sanginjoki (399.93 km²) catchment, Northern Finland, using remobilization sediment sampling during the ice‐free period (May 2010–December 2011). Average bed sediment storage in river was 1332 g m^?2. Storage and seasonal variations were greater in small headwater areas (total bed sediment storage mean 1527 g m^?2, range 122–6700 g m^?2 at individual sites; storage of organic sediment: mean 414 g m^?2, range 27–3159 g m^?2) than in the main channel (total bed sediment storage: mean 1137 g m^?2, range 61–4945 g m^?2); storage of organic sediment: mean 329 g m^?2, range 13–1938 g m^?2). Average reach‐specific bed sediment storage increased from downstream to upstream tributaries. In main channel reaches, mean specific storage was 8.73 t km^?1, and mean specific storage of organic sediment 2.45 t km^?1, whereas in tributaries, it was 126.94 and 34.05 t km^?1, respectively. Total fine‐grained bed sediment storage averaged 563 t in the main channel and 6831 t in the catchment. The proportion of mean organic matter at individual sites was 15–47% and organic carbon 4–455 g C m^?2, with both being highest in small headwater tributaries. Main channel bed sediment storage comprised 52% of mean annual suspended sediment flux and stored organic carbon comprised 7% of mean annual total organic carbon load. This indicates the importance of small headwater brooks for temporary within‐catchment storage of bed sediment and organic carbon and the significance of fine‐grained sediment stored in channels for the suspended sediment budget of boreal lowland rivers. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Surveyed and modelled one‐year morphodynamics in the braided lower Tana River          下载免费PDF全文

Eliisa Lotsari  David Wainwright  Geoffrey D. Corner  Petteri Alho  Jukka Käyhkö 《水文研究》2014,28(4):2685-2716

Field measurements and morphodynamic simulations were carried out along a 5‐km reach of the sandy, braided, lower Tana River in order to detect temporal and spatial variations in river bed modifications and to determine the relative importance of different magnitude discharges on river bed and braid channel evolution during a time span of one year, i.e. 2008–2009. Fulfilling these aims required testing the morphodynamic model's capability to simulate changes in the braided reach. We performed the simulations using a 2‐D morphodynamic model and different transport equations. The survey showed that more deposition than erosion occurred during 2008–2009. Continuous bed‐load transport and bed elevation changes of ±1 m, and a 70–188‐m downstream migration of the thalweg occurred. Simulation results indicated that, during low water periods, modifications occurred in both the main channel and in other braid channels. Thus, unlike some gravel‐bed rivers, the sandy lower Tana River does not behave like a single‐thread channel at low discharge. However, at higher discharge, i.e. exceeding 497 m³/s, the river channel resembled a single‐thread channel when channel banks confined the flow. Although the spring discharge peaks caused more rapid modifications than slower flows, the cumulative volumetric changes of the low water period were greater. The importance of low water period flows for channel modifications is emphasized. Although the 2‐D model requires further improvements, the results were nevertheless promising for the future use of this approach in braided rivers. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Stream and bed temperature variability in a coastal headwater catchment: influences of surface‐subsurface interactions and partial‐retention forest harvesting          下载免费PDF全文

S. M. Guenther  T. Gomi  R. D. Moore 《水文研究》2014,28(3):1238-1249

Stream temperature was recorded between 2002 and 2005 at four sites in a coastal headwater catchment in British Columbia, Canada. Shallow groundwater temperatures, along with bed temperature profiles at depths of 1 to 30 cm, were recorded at 10‐min intervals in two hydrologically distinct reaches beginning in 2003 or 2004, depending on the site. The lower reach had smaller discharge contributions via lateral inflow from the hillslopes and fewer areas with upwelling (UW) and/or neutral flow across the stream bed compared to the middle reach. Bed temperatures were greater than those of shallow groundwater during summer, with higher temperatures in areas of downwelling (DW) flow compared to areas of neutral and UW flow. A paired‐catchment analysis revealed that partial‐retention forest harvesting in autumn 2004 resulted in higher daily maximum stream and bed temperatures but smaller changes in daily minima. Changes in daily maximum stream temperature, averaged over July and August of the post‐harvest year, ranged from 1.6 to 3 °C at different locations within the cut block. Post‐harvest changes in bed temperature in the lower reach were smaller than the changes in stream temperature, greater at sites with DW flow, and decreased with depth at both UW and DW sites, dropping to about 1 °C at a depth of 30 cm. In the middle reach, changes in daily maximum bed temperature, averaged over July and August, were generally about 1 °C and did not vary significantly with depth. The pre‐harvest regression models for shallow groundwater were not suitable for applying the paired‐catchment analysis to estimate the effects of harvesting. However, shallow groundwater was warmer at the lower reach following harvesting, despite generally cooler weather compared to the pre‐harvest year. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Benthic control upon the morphology of transported fine sediments in a low‐gradient stream          下载免费PDF全文

James Fox  William Ford  Kyle Strom  Gabriele Villarini  Michelle Meehan 《水文研究》2014,28(11):3776-3788

The structure of fluvial sediments in streams has environmental implications to contaminant fate, nutrient budgeting and the carbon flux associated with fine particulate organic matter (FPOM). However, the influence of sediment structure is lacking in environmental predictive models. To this end, the present study links field‐based results of sediment aggregate structure to seasonal biological functions in the surface fine‐grained laminae (SFGL) of a low‐gradient stream. Fluvial sediment collection, microscopy and image analysis are used to show that aggregates collected over a 20 month time period support the concept that aggregate structure can vary seasonally in low‐gradient streams where temporarily stored sediment is prominent. Results show that the structure of the transported aggregates is more irregular in the summer with the structure being elongated about the long axes. In the winter, the aggregate structure is compacted and more spherical. Statistical analysis and results suggest that heterotrophic and autotrophic biological activity within the SFGL exhibits seasonal control upon the morphology of transported sediments. Implications of this research are highlighted through calculations of the reactive surface area of the transported suspended sediment load. The surface area of transported sediment is estimated to be 40% greater in the summer as compared to the winter time period, which implies that (i) the affinity of sediments to sorb contaminants is higher in summer months and (ii) the downstream reactivity of FPOM in large rivers, lakes and estuaries is not just a function of microbial drivers but also the seasonally dependent structure of transported FPOM derived from low‐order streams. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

三维点云数据拼接中ICP及其改进算法综述   总被引：5，自引：0，他引：5  

解则晓  徐尚 《中国海洋大学学报(自然科学版)》2010,40(1)

ICP算法是三维点云数据精确拼接过程中的主流算法.文章对目前国内外ICP及其各种改进算法的发展现状进行了系统地分析与研究.将ICP算法分为4个主要阶段:(1) 对原始点云数据进行采样;(2) 确定初始对应点集;(3) 去除错误对应点对;(4) 坐标变换的求解.分别对各个阶段中典型方法的基本思想和关键技术进行了分类与分析,并在精度与效率等方面对这些算法进行了比较.最后对目前算法研究中的难点问题及未来的研究重点进行了展望.  相似文献   

应用测距三角高程法进行跨河水准测量     

夏月晖 《北京测绘》2020,(3):314-318

为将三角高程法跨河水准测量的技术规范要求对应到工程案例中,有效指导技术人员实际操作,本文通过工程实例,按测距三角高程法跨河水准测量的作业流程、计算公式、各未知数据求值展开,逐层解构分析,细致阐述跨河水准测量中测距三角高程法的要点,实例验证了利用测距三角高程测量实现二等跨河水准测量的可行性。同时对“跨河垂直角观测时视线长”的简易计算公式进行了推导,探讨了计算结果的准确性和有效性,对跨河二等水准测量具有较好的推广价值。  相似文献   

The response of a gravel‐bed river planform configuration to flow variations and bed reworking: a modelling study          下载免费PDF全文

Gabriel Kaless  Luca Mao  Johnny Moretto  Lorenzo Picco  Mario A. Lenzi 《水文研究》2015,29(17):3812-3828

A 2D depth‐averaged model has been developed for simulating water flow, sediment transport and morphological changes in gravel‐bed rivers. The model was validated with a series of laboratory experiments and then applied to the Nove reach of the Brenta River (Northern Italy) to assess its bed material transport, interpret channel response to a series of intensive flood events (R.I. ≈ 10 years) and provide a possible evolutionary scenario for the medium term. The study reach is 1400 m long with a mean slope of 0.0039 m m^?1. High‐resolution digital terrain models were produced combining LiDAR data with colour bathymetry techniques. Extensive field sedimentological surveys were also conducted for surface and subsurface material. Data were uploaded in the model and the passage of two consecutive high intensity floods was simulated. The model was run under several hypotheses of sediment supply: one considering substantial equilibrium between sediment input and transport capacity, and the others reducing the sediment supply. The sediment supply was then calibrated comparing channel morphological changes as observed in the field and calculated by the model. Annual bed material transport was assessed and compared with other techniques. Low‐frequency floods (R.I. ≈ 1.5 years) are expected to produce negligible changes in the channel while high floods may erode banks rather than further incising the channel bed. Location and distribution of erosion and deposition areas within the Nove reach were predicted with acceptable biases stemming from imperfections of the model and the specified initial, boundary and forcing conditions. A medium‐term evolutionary scenario simulation underlined the different response to and impact of a consecutive sequence of floods. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

煤层气井排采扰动下局部水动力场对排采的动态影响          下载免费PDF全文

张兆民  史国萍  廉永彪 《山东国土资源》2018,34(9)

煤层气主要以吸附态存在于煤层中,其产出需要历经解吸—扩散—渗流的过程。煤层气的产出过程说明,煤岩储层压力低于煤层气的临界解吸压力是煤层气解析产出的关键。排水降压是降低煤岩储层压力最为行之有效的方法,在排水降压的过程中会对地下原始水动力场产生扰动,在井周围形成局部水动力场,从而影响排水降压的效能。该文根据地下水的流动状态、区域构造发育状态,结合煤储层与含水层的组合关系,提出了煤储层排水降压过程可能出现有效扰动型、含水层水入侵型、地表淡水入侵型等3种局部水动力场,并结合实例分析了不同种类水动力场对煤层气排采的动态影响,对指导煤层气的排采具有实际意义。  相似文献