Effect of floating-leaved and emergent vegetation on flow and dissolved oxygen concentration: Case study of the lotus stand

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  • 浮葉および抽水植生が流動と溶存酸素濃度に与える影響 ～ハス群落を例に

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<p>　To compare the effects of floating-leaved and emergent vegetation on the flow and dissolved oxygen concentration in the bottom layer of lakes, we measured the density of the plants, average flow, dissolved oxygen concentration, and sediment quality inside and outside the lotus stand at Lake Teganuma. We measured sulfide and methane in the sediment as indicators of the redox condition. The floating leaves covered the water surface to suppress the blowing flow, and the flow decreased in both the bottom layer and the surface layer inside the stand area. Although the petiole cross-sectional area per unit area was lower when the leaves were floating than that at the time of emergent leaves, the resistance was the highest in the stand area when the leaves were floating. The flow velocity during emergent leaves and withering was relatively faster in the surface layer than in the bottom layer, and the resistance increased in proportion to the petiole cross-sectional area per unit area. Dissolved oxygen concentration decreased in the stand area in the presence of floating and emergent leaves. Although the water temperature was the highest at the time of emergent leaves, rate of decrease in dissolved oxygen concentration was significantly higher at the time of floating leaves. From the above, we concluded that the degree of reduction in the flow and dissolved oxygen concentration was greater in the lotus stand area in the presence of floating leaves than in the presence of emergent leaves. Since 95.0 % of the gas generated from the sediment collected in October and 74.5 % of the gas collected in December was methane, the sediment of the lotus stand is highly reduced during the entire year.</p>

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