Perturbations of a water column of Lake Onogawa by local heavy rainfall

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Abstract : The perturbations of a water column at the deepest part of Lake Onogawa by a local heavy rainfall were analyzed. Mixing throughout the water column (18.8-m deep) was indicated by changes in the distribution of water temperature. This mixing perturbed the hypolimnetic seasonal distributions of dissolved components. All particulate components peaked at 10m, suggesting a center of inflowing water. Compared with background levels, particulate nitrogen (PN), particulate carbon (PC), particulate phosphorus (PP), and suspended solids (SS) increased from 16-fold for PN to 100-fold fos SS. Soluble reactive phosphorus was the only dissolved component that formed a clear maximum at 10m, as did the particulate components. Assuming that SS consists mainly of mineral particles, SS can be classified into three categories: (1) A rapidly sinking fraction, the main body of the loaded SS, with a sinking rate exceeding 1m day~-1 and radii exceeding 2-3μm. (2) A slowly sinking fraction with a sinking speed of about 10cm day~-1 and radii of 0.7-0.9μm; this fraction is calculated to be about 4% of the total loaded SS at most. (3) A fraction that was essentially retained in the water column. The maximum estimate of this fraction was 0.5% of the total.　Key words : Heavy allochthonous load・Material distribution・Ventilation・SS sinking rate
山形大学の論文