Coarse Particulate Organic Matter Distribution in the Pools and Riffles of a Second-order Stream |
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Authors: | Takashi Nakajima Takashi Asaeda Takeshi Fujino Aung Nanda |
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Institution: | (1) Department of Environmental Science & Human Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, 338 Saitama-shi, Saitama, Japan |
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Abstract: | Coarse particulate organic matter distribution was investigated in a 270-m interval of a 2nd-order forest stream, the Yanase
River. The dominant tree type was Keyaki (Zelkova serrata). CPOM sampling was conducted, and the sampled CPOM was sorted into leaves and branches, and water depth and current velocity
were measured along with stone width, stone height and distance between the stones in the riffles. The collected CPOM was
categorized by their accumulation type: LSS, SLP, SLPi, SLPo and DD. LSS was leaf packs at the leading edge of the stones,
SLP was the sinking leaf packs in the pools, SLPi was the sinking leaf packs at the inner side of the stream bend in the pools,
while SLPo was the sinking leaf packs at the outer side of the stream bend, and finally, DD was the leaf packs in the debris
dams. The accumulated CPOM amounts at each leaf pack type were correlated with the measured physical stream variables. From
the results, CPOM accumulation in riffles is controlled by stones projecting above the water surface and by their arrangements.
In pools, CPOM accumulation occurs at high stream flow where the pools provide low velocities and a thick boundary layer of
relatively quiescent flow. At stream meandering points, CPOM accumulation occurs by production of a secondary flow. Finally,
CPOM accumulation in debris dams is important where they occur frequently. LSS was the largest in CPOM amount, and the stones
in the riffles were the most retentive structures. On the other hand, SLP and SLPo were the least CPOM amounts, and the pools
in the mainstream and at the outer side of the stream bend were the least retentive stream morphologies. |
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Keywords: | coarse particulate organic matter distribution forest stream pool riffle stream morphology stone |
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