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

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 10 m, 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 for SS. Soluble reactive phosphorus was the only dissolved component that formed a clear maximum at 10 m, 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 1 m day Ϫ1 and radii exceeding 2-3 µm.(2) A slowly sinking fraction with a sinking speed of about 10 cm day Ϫ1 and radii of 0.7-0.9 µm; 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.

Potential capacity of coprecipitation of dissolved organic carbon (DOC) with iron(III) precipitates

“…Lake Onogawa (37°40′ N, 140°06′ E) lies on the Urabandai Plateau, northeast Japan (see map in Satoh et al 2001). It is a dammed dimictic lake formed at the time of the volcanic eruption of Mt.…”

“…Water samples from 40 cm above the lake bottom were collected from the same station as by Satoh et al (2001) using a handmade water sampler (Fig. 1).…”

Reverse process of coprecipitation of dissolved organic carbon with Fe(III) precipitates in a lake

“…Lake Onogawa (37°40 0 N, 140°06 0 E) lies on the Urabandai Plateau, northeast Japan (see map in Satoh et al 2001). It is a dammed dimictic lake formed at the time of the volcanic eruption of Mt.…”

“…The trophic status of this lake is on the boundary between meso-and eutrophic (Satoh et al 1996). The anoxic hypolimnion is formed from late July or early August to late October or early November (Satoh et al 1996(Satoh et al , 2001(Satoh et al , 2002(Satoh et al , 2006.…”

“…The sampling station was the same as that used in Satoh et al (1996Satoh et al ( , 2001Satoh et al ( , 2002Satoh et al ( , 2006. Water samples from 40 cm above the lake bottom were collected nine times from April to November 2007 using a hand-made vinyl tube sampler (Satoh et al 2006).…”