Decadal-scale changes in suspended wood after riparian recruitment in managed stands in headwater streams of coastal British Columbia,Canada     

Felipe Rossetti de Paula  John S. Richardson  Alex C.Y. Yeung  Stephen J. Mitchell  Devesh Bahuguna 《地球表面变化过程与地形》2020,45(9):1974-1989

Large wood (LW) affects several ecological and hydrogeomorphic processes in streams. The main source of LW is riparian trees falling inside channels. However, in confined valley floors, falling trees are more likely to be suspended above the channel. Eventually, these suspended trees will decompose and break to finally fall into the channel to better provide functions for streams. We evaluated changes in wood decay, length, diameter, and suspended status (suspended or non-suspended) 17 years post-harvest and nine years after the first sampling occurred in 2006 in 12 headwater streams of coastal British Columbia, Canada. We also evaluated whether changes differed among riparian management treatments (no-harvest buffers of 10 and 30 m in width, thinning, and unharvested reference sites), and identified the factors affecting wood changes and suspended status. Wood pieces advanced in decay, became shorter, and 34% of them (n = 108) changed status from suspended to non-suspended. Non-suspended wood pieces were more decayed and shorter than suspended wood. Suspended wood was longer, thicker, less decayed, and represented 46.5% (n = 147) of the wood sampled in 2006. Our findings revealed limited influences of riparian management on many aspects of wood changes considered in this study. Changes in wood characteristics were more likely for pieces that were smaller in diameter, longer, and suspended closer to the water. The transition from suspended to non-suspended LW can be a long-term process that can increase wood residence time and reduce LW in-stream functions particularly in confined stream valleys. The suspended stage is also an important mechanism underlying time lags in stream ecosystem responses to riparian tree fall. © 2020 John Wiley & Sons, Ltd.  相似文献   

Drivers of variability in large wood loads along the fluvial continuum of a Mediterranean intermittent river     

Tomáš Galia  Tereza Macurová  Leonidas Vardakas  Václav Škarpich  Tereza Matušková  Eleni Kalogianni 《地球表面变化过程与地形》2020,45(9):2048-2062

Although in-channel and floodplain large wood (LW) has been recognized as an important component of lotic ecosystems, there is still limited knowledge on the recruitment, mobility and retention of LW in rivers with an intermittent hydrological regime. In this study, we analysed the LW characteristics and related reach-scale variables of 22 reaches in a Mediterranean intermittent river (Evrotas, Greece) in order to identify predictors of in-channel and floodplain LW distribution. Our results indicated high downstream variation in LW volumes in the fluvial corridor (0.05–25.51 m³/ha for in-channel LW and 0–30.88 m³/ha for floodplain LW). In-channel and floodplain LW retention was primarily driven by the hydrological regime of the studied reaches (i.e. perennial or non-perennial) with higher volumes of LW observed in perennial sections. The width of the riparian corridor was an important predictor of LW storage at the reach scale. Non-perennial reaches had a disproportionally larger number of relatively small-diameter living trees at the expense of mature trees with larger diameters typical for riparian stands functioning as LW recruitment areas in perennial reaches. The smaller dimensions of in-channel LW in non-perennial reaches, coupled with the dominance of loose LW pieces, implies frequent LW transport during ordinary flood events. Nevertheless, overall low LW retention in the fluvial corridor under non-perennial flow regime predicts low volumes of mobilized LW. In contrast, the recruitment of relatively long and large-diameter LW from mature riparian stands in perennial reaches, together with additional LW stabilization by banks, bed sediments, living trees or other LW pieces decreases the potential for further LW transport. © 2020 John Wiley & Sons, Ltd.  相似文献   

The effect of instream logs on river-bank erosion: Field measurements of hydraulics and erosion rates     

Nuosha Zhang  Ian D. Rutherfurd 《地球表面变化过程与地形》2020,45(7):1677-1690

This is the first substantial field measurement of river-bank erosion around fallen logs in rivers. Whilst numerous studies have established that living trees can stabilize river banks, and that fallen trees can cause scour of the river bed, knowledge of bank erosion effects from logs is largely restricted to qualitative observations. Recent flume studies suggest that a single log can increase near-bank velocity (and thus erosion) and this increase is related to the blockage ratio of the log and the distance between the log and bank. However, hydraulic interactions between logs can reduce this increase or even decrease the near-bank velocity. These theories, developed in a straight flume, have not been tested in the field. We measured erosion rates (relative to controls) on river banks adjacent to 35 large logs for 2 years, and velocity distributions around 11 logs during a near-bankfull flow in anabranching channels of the River Murray, SE Australia. These channels have abundant large instream logs, consistent bank material, and consistent regulated high flows. The field results generally supported the velocity changes caused by single and multiple logs in the flume studies, with single logs increasing near-bank velocity, but with the hydraulic interactions between successive logs tending to reduce this increase. Flow patterns caused by logs adjacent to curved banks were more complicated as the local effects of logs reinforced or weakened recirculating flows. Instream logs did not change overall, average, bank erosion rates, but they tended to shift the erosion from bank top to bank toe. However, individual logs increased or decreased bank erosion rates in patterns that generally concur with the near-bank velocity changes predicted in flume studies: that isolated logs increased erosion rates whilst hydraulically interacting logs did not increase erosion rates. © 2020 John Wiley & Sons, Ltd.  相似文献   

Large wood load and transport in a flood-free period within an inter-dam reach: a decade of monitoring the Dyje River,Czech Republic     

Zdeněk Máčka  Ondřej Kinc  Matej Hlavňa  David Hortvík  Lukáš Krejčí  Jana Matulová  Pavel Coufal  Pavel Zahradníček 《地球表面变化过程与地形》2020,45(14):3540-3555

This study examined the large wood (LW) load and transport during the non-flood period (2009–2018) following major floods that occurred in 2002 and 2006 within the inter-dam reach of the Dyje River (Czech–Austrian border). The LW load was examined in 36 river corridor segments scattered within the reach in the 2009–2018 period. Two whole-reach surveys (2011 and 2019) on LW frequency and distribution were conducted, and the export of LW to the downstream reservoir was analysed between June 2013 and December 2018. In the period of non-flood discharges, the recruitment and depletion of LW were highly variable processes in space and time, leading to a considerable change in the total LW quantity. Whereas the total number of LW pieces decreased, the total LW volume increased because of the increasing dimensions of newly recruited pieces. The annual variability in the quantity of newly recruited pieces was better explained by the variation in the maximum annual discharges (y = 41.043ln(x) + 3.2737, R² = 0.5352) than by the variability in the number of days with wind gusts >17.2 m/s (y = 1.5004x + 82.096, R² = 0.118). The land use change with the abandonment of human settlements after World War II and the progressive expansion of forest was the major historical factor driving the increased recruitment of LW to the river corridor. While the 2006 (>100-year RI) flood brought approximately 1,250 LW pieces to the reservoir, the 2013 (1.5-year RI) flood delivered 45 pieces. The long-term average monthly input of LW to the reservoir was 7.7 pieces. The exceptional low-magnitude flood of 2013, which occurred at the beginning of the monitoring period, was shown to be a threshold above which the number of LW pieces that floated to the dam significantly increased. © 2020 John Wiley & Sons, Ltd.  相似文献   

Dynamics of Wood Transport in Streams: A Flume Experiment     

Christian A. Braudrick  Gordon E. Grant  Yoshiharu Ishikawa  Hiroshi Ikeda 《地球表面变化过程与地形》1997,22(7):669-683

The influence of woody debris on channel morphology and aquatic habitat has been recognized for many years. Unlike sediment, however, little is known about how wood moves through river systems. We examined some dynamics of wood transport in streams through a series of flume experiments and observed three distinct wood transport regimes: uncongested, congested and semi-congested. During uncongested transport, logs move without piece-to-piece interactions and generally occupy less than 10 per cent of the channel area. In congested transport, the logs move together as a single mass and occupy more than 33 per cent of the channel area. Semi-congested transport is intermediate between these two transport regimes. The type of transport regime was most sensitive to changes in a dimensionless input rate, defined as the ratio of log volume delivered to the channel per second (Q_log) to discharge (Q_W); this ratio varied between 0·015 for uncongested transport and 0·20 for congested transport. Depositional fabrics within stable log jams varied by transport type, with deposits derived from uncongested and semi-congested transport regimes having a higher proportion of pieces orientated normal to flow than those from congested transport. Because wood input rates are higher and channel dimensions decrease relative to piece size in low-order channels, we expect congested transport will be more common in low-order streams while uncongested transport will dominate higher-order streams. Single flotation models can be used to model the stability of individual pieces, especially in higher-order channels, but are insufficient for modelling the more complex intractions that occur in lower-order streams. © 1997 John Wiley & Sons, Ltd.  相似文献   

Decadal changes in distribution and frequency of wood in a free meandering river,the Ain River,France     

Neil S. Lassettre  Herv Pigay  Simon Dufour  Anne‐Julia Rollet 《地球表面变化过程与地形》2008,33(7):1098-1112

This study examined the temporal dynamics and longitudinal distribution of wood over a multi‐decadal timescale at the river reach scale (36 km) and a meander bend scale (300–600 m) in the Ain River, a large gravel‐bed river flowing through a forested corridor, and adjusting to regulation and floodplain land‐use change. At the 36 km scale, more wood was recruited by bank erosion in 1991–2000 than since the 1950s. The longitudinal distribution of accumulations was similar between 1989 and 1999, but in both years individual pieces occurred homogeneously throughout the reach, while jam distribution was localized, associated with large concave banks. A relationship between the mean number of pieces and the volume recruited by bank erosion (r² = 0·97) indicated a spatial relationship between areas of wood production and storage. Wood mass stored and produced and channel sinuosity increased from 1993 to 2004 at three meander bends. Sinuosity was related to wood mass recruited by bank erosion during the previous decade (r² = 0·73) and both of these parameters were correlated to the mean mass of wood/plot (r² = 0·98 and 0·69 respectively), appearing to control wood storage and delivery at the bend scale. This suggests a local origin of wood stored in channel, not input from upstream trapped by preferential sites. The increase in wood since 1950 is a response to floodplain afforestation, to a change from braided to meandering channel pattern in response to regulation, and to recent large floods. We observed temporal stability of supply and depositional sectors over a decade (on a reach scale). Meander bends were major storage sites, trapping wood with concave banks, also delivering wood. These results, and the link between sinuosity and wood frequency, establish geomorphology as a dominant wood storage and recruitment control in large gravel‐bed rivers. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

The Phototropism of Jurassic Petrified Wood in North China Plate     

JIANG Zikun  LIU Benpei  HUANG Min  DENG Shenghui  LU Yuanzheng  LIU Lu  LI Mingming  DONG Shuxin  WANG Yongdong 《《地质学报》英文版》2014,88(5):1352-1355

Trees on the side directly exposed to sunlight generally grow faster than on the opposite side, a phenomenon termed plant phototropism. There are in situ vertical trunks of silicified wood in the Xiadelongwan area of Yanqing County, north Beijing, where the first National Geologic Park of Petrified Wood of China has been built since 2002. A few trunks have well-preserved growth rings. One petrified stump from the formation shows a positive phototropism direction of SW230°. As compared with the modern normal growth stumps in Beijing plain area, which have a positive phototropism direction of SW210 °± 5°, the evidence of wood phototropism supports the conclusion of previous palaeomagnetic studies that the North China Plate has rotated clockwise since the Late Jurassic. The known petrified wood stumps in the Yanshan-Liaoning area are mainly found from the strata of 165-136 Ma, which corresponds to the main stage of the Yanshanian Movement.  相似文献   

回收塑料-木材纤维复合材料的工艺及性能     

王正  赵行志  郭文静 《天文爱好者》2005,(1)

该文利用聚苯乙烯、聚乙烯和聚丙烯等 3种回收塑料与木材纤维复合制备复合材料 ,分析不同回收塑料种类、木材纤维与塑料不同质量比和热压温度等工艺条件对复合材料物理力学性能的影响 .结果表明 :3种回收塑料中回收聚苯乙烯塑料性能最好 ,回收聚丙烯塑料其次 ,回收聚乙烯塑料最差 .木塑质量比 5 0∶5 0效果最好 .塑料含量低时 ,内结合强度和拉伸强度低 ,吸水厚度膨胀率高 ;塑料含量过高时 ,静曲强度和弹性模量降低 .热压温度在1 90℃效果最好 .温度过低时 ,静曲强度、弹性模量、拉伸强度和内结合强度较差 ;温度过高时 ,木材纤维降解加剧 ,塑料少量溢出 ,性能反而有所下降 .通过极差和方差分析知 ,本研究F值的最佳工艺条件为 :采用回收聚苯乙烯、木塑质量比 5 0∶5 0、热压温度 1 90℃ .  相似文献   

云南省松材线虫病风险评估GIS平台开发   总被引：1，自引：0，他引：1  

沈安平  石雷  周汝良 《云南地理环境研究》2011,23(1):38-41,46

松材线虫病被称为松树的＂癌症＂。云南省针叶树种面积大,松材线虫寄主多,地形复杂,虫病防治难度大。综合运用.NET平台、ArcEngine组件技术、ArcSDE空间数据库引擎技术、SQL Server数据库技术,在云南省气象、空间、松材线虫数据基础上,建立一个云南省松材线虫病风险评估GIS平台,主要包括图层控制、风险评估、疫点操作、地图显示、专题图输出等功能,对云南省松材线虫病疫情进行更加精细化、标准化、可视化的评估。  相似文献   

三种裸子植物化石木的研究     

杨家驹  齐国凡  徐瑞瑚  杨礼茂 《国土资源》1996,(4)

本文研究了我国长江北岸湖北省武汉市新洲县阳逻镇北部晚第三纪的三种裸子植物化石木。它们是水松ＧｌｙｐｔｏｓｔｒｏｂｕｓｐｅｎｓｉｌｉｓＫ．Ｋｏｃｈ，武汉柏本ＣｕｐｒｅｓｓｕｓｗｕｈａｎｅｎｓｉｓＪ．ＪＹａｎｇｓｐ．ｎｏｖ．和武汉刺柏ＪｕｎｉｐｅｒｕｓｗｕｈａｎｅｎｓｉｓＪ．Ｊ．Ｙａｎｇｓｐ．ｎｏｖ，这些化石本的发现，给研究我国裸子植物提供了良好的依据．此外，对１９９０年发表于《林业科学》（２６卷４期）上的湖北柏木和河南松化石木也给了拉丁种名，它们分别是ＣｕｐｒｅｓｓｕｓｈｕｂｅｉｓｎｓｉｓＪ．Ｊ．Ｙａｎｇｓｐｎｏｖ．和ｐｉｎｕｓｈｅｎａｎｅｎｓｉｓＪ．Ｊ．Ｙａｎｇｓｐ．ｎｏｖ．  相似文献