Properties of small instream wood as a logjam clogging agent: Implications for clogging dynamics based on wood density, water content, and depositional environment
Properties of small instream wood as a logjam clogging agent: Implications for clogging dynamics based on wood density, water content, and depositional environment
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河道内小型木材作为堵塞剂的特性：基于木材密度、含水量和沉积环境的堵塞动态的影响
DOI：
10.1016/j.geomorph.2017.08.043
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发表时间：
2017
期刊：
影响因子：
3.9
通讯作者：
Fujimoto Takaaki
中科院分区：
文献类型：
--
作者：
Haga Hirokazu;Moriishida Takuya;Morishita Naoya;Fujimoto Takaaki
在木塞中，小的不规则木材（SW）与大的不规则木材（LW）合作，可以控制下游的沉积物和颗粒有机物的通量，可以在河流生态系统中发挥重要作用。然而，有关密度和水分含量的SW影响木材运输，木材腐烂，和质量负荷的信息是有限的。在这里，我们研究了SW属性，即，密度在现场条件下（原位密度），基本密度，体积含水量，和沉积环境的SW采样从五个logjams和他们的回水区在两个源头流（第二和第三级流）所包围的混合阔叶针叶林在日本西部。原位密度范围为0.49至1.25 g cm− 3，密度> 1.0 g cm− 3的碎片占所有样品的45%。此外，SW的原位密度与体积含水率密切相关（r ~ 2 = 0.76），而不是作为木材坚固性或腐朽状态指标的基本密度。部分浸没在水中的SW的体积含水量高于暴露在空气中的SW。这些结果表明，非漂浮运输是SW移动的一个重要机制，不能忽视，而且密度不取决于木材的坚固性，而是取决于SW的吸水性。浸水的SW应该很好地腐烂，因为它的基本密度比暴露在空气中的和沉积物低-我们得出结论，沉积环境的水分条件可以影响SW随后的传输和衰减过程。此外，大多数水淹和沉积物掩埋的西南，由于其高原位密度（> 1.0 g cm− 3），可能会导致河床和LW之间的堵塞，从而在未来的运动中引发堵塞。
In cooperation with large instream wood (LW) within logjams, small instream wood (SW) can control downstream flux of sediment and particulate organic matter and can play an important role for stream ecosystems. However, information regarding the density and moisture content of SW—which affects wood transport, wood decay, and mass loading—is limited. Here we investigated the SW properties, i.e., density under field conditions (in situdensity), basic density, volumetric water content, and depositional environment of SW sampled from five logjams and their backwater areas in two headwater streams (second- and third-order streams) surrounded by mixed broadleaf-conifer forests in western Japan. Thein situdensity ranged from 0.49 to 1.25 g cm− 3, and pieces with densities > 1.0 g cm− 3accounted for 45% of all samples. Additionally, thein situdensity of SW closely related to the volumetric water content (r2= 0.76) rather than the basic density as an index of solidity or decay condition of wood. The SW that was partially submerged in water had a higher volumetric water content than SW exposed to air. These results indicate that a nonfloating transport cannot be ignored as an important mechanism for SW movement and thatin situdensity depends not on the solidity of the wood but on water sorption by SW. However, waterlogged SW should be well decayed because it has a lower basic density than air-exposed and sediment-buried SW. We conclude that the moisture conditions of the depositional environment can affect subsequent transport and decay processes of SW. Moreover, most waterlogged and sediment-buried SW, because of its highin situdensity (> 1.0 g cm− 3), may contribute to clogging between the channel bed and LW that initiate a logjam during future movements.