Papers by Takehiko Fukushima
Estuarine Coastal and Shelf Science, Jul 1, 2001
The concentrations of dissolved organic carbon (DOC) and hydrophilic DOC (Hil-DOC) in Hiroshima B... more The concentrations of dissolved organic carbon (DOC) and hydrophilic DOC (Hil-DOC) in Hiroshima Bay showed clear seasonal changes (high in summer and low in winter), suggesting the autochthonous production of Hil-DOC. The percentages of hydrophobic DOC (Hob-DOC) fractionated by XAD-8 resin were 33% for the bay waters and 41% for the river waters, whereas those of labile DOC (which decomposed during an incubation period of 100 days) were 20% and 24%, respectively. The increment of DOC to Chlorophyll a was calculated to be (0•014 mgl 1)/(gl 1). The mixing experiments suggested a negligible deposition of DOC at the estuaries of inflowing rivers. The Hob-DOC went through the bay with negligible changes in concentration in both summer and winter, but its chemical characteristics, e.g. spectrophotometric properties and mean molecular weight, differed from those of riverine origin. In contrast, both labile and refractory components of Hil-DOC were produced mainly in the inner part of the bay during summer, and although a significant percentage of the labile component was subjected to biodegradation during transport to the outer part of the bay, its chemical characteristics did not change dramatically.
Journal of Japan Society on Water Environment
The contributions of oxygen consumption by bottom-layer water and sediment were compared by inves... more The contributions of oxygen consumption by bottom-layer water and sediment were compared by investigating the oxygen consumption rates of bottom-layer water and sediment in Lake Kitaura and using in situ data on thermal stratification and hypoxic water. The oxygen consumption rate of bottom-layer water in Lake Kitaura was 2,550-2,910 mg m-3 d-1 and that of sediment was 652-1,080 mg m-2 d-1. These rates suggest that the contribution of oxygen consumption by sediment becomes greater when the height of the bottom-layer water column is less than 0.16 m. On the other hand, the contribution of oxygen consumption by bottom water becomes greater when the height of the bottom-layer water column exceeds 0.60 m. In addition, the in situ contribution of oxygen consumption was assessed using the vertical time-series data of thermal stratification and hypoxic water from July 28 to August 3, 2019, at Kamaya Observatory in Lake Kitaura. As a result, it was found that the contribution of oxygen consumption of by bottom-layer water was larger than that by sediment. However, it was considered that the effect of oxygen consumption by sediment could not be ignored, because hypoxic water formed gradually from the bottom of the lake.
Journal of Japan Society on Water Environment
Detailed distributions of oxygen-deficient water were observed using a high-resolution tow-yo ins... more Detailed distributions of oxygen-deficient water were observed using a high-resolution tow-yo instrument, YODA Profiler, in Lake Kitaura to investigate the formation of oxygen-deficient water. The results of observations showed that oxygen-deficient water widely appeared at a depth of deeper than 4 m, and the dissolved oxygen (DO) concentration in deep areas was particularly low. Furthermore, it was suggested that high phosphorus (PO 4-P) concentrations were eluted from sediments in areas of oxygen-deficient water. The DO concentration at 10 cm above the lake bottom tended to be lower than that at 50 cm above the lake bottom. The oxygen-deficient water in Lake Kitaura is greatly affected by the water depth, which implies that the ratio of the area of oxygen-deficient water can be inferred by lake bathymetry and observed DO profiles. The area of oxygen-deficient water reached 55.9％ at 50 cm above the bottom and 63.2％ at 10 cm above the bottom of the total area of Lake Kitaura.
Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research)
Indonesian Journal of Limnology
In general, the tropical lake in Indonesia is one of the unique ecosystems which are functioning ... more In general, the tropical lake in Indonesia is one of the unique ecosystems which are functioning in both ecological and economic services. This study aims to analyze the dissolved oxygen profile of caldera tropical lake represented by Lake Maninjau at West Sumatera, Indonesia, and its impacts. Lake Maninjau is not only for culture fisheries but also serves as important hydroelectricity power. Surveys at Lake Maninjau were conducted in August 2006, March 2014, September 2017, and April 2018. The results showed that the average depth is 105 m. It covers 13,260 ha of an area with an elevation of 461.5 m above sea level and a maximum depth of 165 m. The lake water comes from rainfall, small rivers, and the surrounding groundwater, with one outflow in the Batang Antokan River. Based on the measurement, it was observed that decreasing dissolved oxygen levels occurred at the surface to the depth of 40 m in 2006, and changed from surface to a depth of 12 m in 2018 indicating the worse condi...
Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research)
Estuarine Coastal and Shelf Science, Jul 1, 2001
The concentrations of dissolved organic carbon (DOC) and hydrophilic DOC (Hil-DOC) in Hiroshima B... more The concentrations of dissolved organic carbon (DOC) and hydrophilic DOC (Hil-DOC) in Hiroshima Bay showed clear seasonal changes (high in summer and low in winter), suggesting the autochthonous production of Hil-DOC. The percentages of hydrophobic DOC (Hob-DOC) fractionated by XAD-8 resin were 33% for the bay waters and 41% for the river waters, whereas those of labile DOC (which decomposed during an incubation period of 100 days) were 20% and 24%, respectively. The increment of DOC to Chlorophyll a was calculated to be (0•014 mgl 1)/(gl 1). The mixing experiments suggested a negligible deposition of DOC at the estuaries of inflowing rivers. The Hob-DOC went through the bay with negligible changes in concentration in both summer and winter, but its chemical characteristics, e.g. spectrophotometric properties and mean molecular weight, differed from those of riverine origin. In contrast, both labile and refractory components of Hil-DOC were produced mainly in the inner part of the bay during summer, and although a significant percentage of the labile component was subjected to biodegradation during transport to the outer part of the bay, its chemical characteristics did not change dramatically.
Journal of Japan Society on Water Environment
The contributions of oxygen consumption by bottom-layer water and sediment were compared by inves... more The contributions of oxygen consumption by bottom-layer water and sediment were compared by investigating the oxygen consumption rates of bottom-layer water and sediment in Lake Kitaura and using in situ data on thermal stratification and hypoxic water. The oxygen consumption rate of bottom-layer water in Lake Kitaura was 2,550-2,910 mg m-3 d-1 and that of sediment was 652-1,080 mg m-2 d-1. These rates suggest that the contribution of oxygen consumption by sediment becomes greater when the height of the bottom-layer water column is less than 0.16 m. On the other hand, the contribution of oxygen consumption by bottom water becomes greater when the height of the bottom-layer water column exceeds 0.60 m. In addition, the in situ contribution of oxygen consumption was assessed using the vertical time-series data of thermal stratification and hypoxic water from July 28 to August 3, 2019, at Kamaya Observatory in Lake Kitaura. As a result, it was found that the contribution of oxygen consumption of by bottom-layer water was larger than that by sediment. However, it was considered that the effect of oxygen consumption by sediment could not be ignored, because hypoxic water formed gradually from the bottom of the lake.
Journal of Japan Society on Water Environment
Detailed distributions of oxygen-deficient water were observed using a high-resolution tow-yo ins... more Detailed distributions of oxygen-deficient water were observed using a high-resolution tow-yo instrument, YODA Profiler, in Lake Kitaura to investigate the formation of oxygen-deficient water. The results of observations showed that oxygen-deficient water widely appeared at a depth of deeper than 4 m, and the dissolved oxygen (DO) concentration in deep areas was particularly low. Furthermore, it was suggested that high phosphorus (PO 4-P) concentrations were eluted from sediments in areas of oxygen-deficient water. The DO concentration at 10 cm above the lake bottom tended to be lower than that at 50 cm above the lake bottom. The oxygen-deficient water in Lake Kitaura is greatly affected by the water depth, which implies that the ratio of the area of oxygen-deficient water can be inferred by lake bathymetry and observed DO profiles. The area of oxygen-deficient water reached 55.9％ at 50 cm above the bottom and 63.2％ at 10 cm above the bottom of the total area of Lake Kitaura.
Limnology
In 2014, 2018 and 2021, we measured the vertical distributions of several water quality indicator... more In 2014, 2018 and 2021, we measured the vertical distributions of several water quality indicators in Lake Toba, a representative large tropical lake. This lake has a north basin (NB) and south basin (SB), connected by a strait. Similar water temperature profiles were observed in both basins, showing increasing trends. Shoaling of hypolimnetic DO (dissolved oxygen)-deficient waters was clearly observed in both basins except in the period from 2018 to 2021 during which the zero DO layer deepened in the SB. In 2014 and 2018, the middle-layer maximums (or minimums) of DO were found in the NB while the SB showed a monotonously downward decreasing tendency. Middle-layer minimums of electric conductivity adjusted to 25 °C (EC25) corresponded to the middle-layer DO maximums in the NB; significantly negative correlations between DO and EC25 were found in both basins. Based on horizontal distributions of EC25, water quality difference between the basins using satellite imagery and gradual change in the DO-EC25 relation, we consider the flow of hypolimnetic water from SB to NB and/or influence of worse water quality near the bottom of the strait with reference to the different behaviors of DO and EC25.
Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research)
Indonesian Journal of Limnology
In general, the tropical lake in Indonesia is one of the unique ecosystems which are functioning ... more In general, the tropical lake in Indonesia is one of the unique ecosystems which are functioning in both ecological and economic services. This study aims to analyze the dissolved oxygen profile of caldera tropical lake represented by Lake Maninjau at West Sumatera, Indonesia, and its impacts. Lake Maninjau is not only for culture fisheries but also serves as important hydroelectricity power. Surveys at Lake Maninjau were conducted in August 2006, March 2014, September 2017, and April 2018. The results showed that the average depth is 105 m. It covers 13,260 ha of an area with an elevation of 461.5 m above sea level and a maximum depth of 165 m. The lake water comes from rainfall, small rivers, and the surrounding groundwater, with one outflow in the Batang Antokan River. Based on the measurement, it was observed that decreasing dissolved oxygen levels occurred at the surface to the depth of 40 m in 2006, and changed from surface to a depth of 12 m in 2018 indicating the worse condi...
Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research)
Limnology
In 2014, 2018 and 2021, we measured the vertical distributions of several water quality indicator... more In 2014, 2018 and 2021, we measured the vertical distributions of several water quality indicators in Lake Toba, a representative large tropical lake. This lake has a north basin (NB) and south basin (SB), connected by a strait. Similar water temperature profiles were observed in both basins, showing increasing trends. Shoaling of hypolimnetic DO (dissolved oxygen)-deficient waters was clearly observed in both basins except in the period from 2018 to 2021 during which the zero DO layer deepened in the SB. In 2014 and 2018, the middle-layer maximums (or minimums) of DO were found in the NB while the SB showed a monotonously downward decreasing tendency. Middle-layer minimums of electric conductivity adjusted to 25 °C (EC25) corresponded to the middle-layer DO maximums in the NB; significantly negative correlations between DO and EC25 were found in both basins. Based on horizontal distributions of EC25, water quality difference between the basins using satellite imagery and gradual change in the DO-EC25 relation, we consider the flow of hypolimnetic water from SB to NB and/or influence of worse water quality near the bottom of the strait with reference to the different behaviors of DO and EC25.
Journal of Environmental Management
Journal of Environmental Management
Journal of Japan Society on Water Environment
The formation and disappearance of thermal stratification and hypoxic water were investigated by ... more The formation and disappearance of thermal stratification and hypoxic water were investigated by vertical and continuous observations of the water temperature, dissolved oxygen concentration, and oxidation-reduction potential from an automatic profiler sensor in Lake Kitaura in summer. Furthermore, the benthic flux of the dissolved inorganic phosphorus (PO 4-P) from sediment in Lake Kitaura was estimated from the results of water quality observations at short intervals using an automatic water sampler. The observed results showed that the conditions for forming thermal stratification were a temperature of 25 ℃ or higher and a wind velocity of less than 6.0 m s-1. Thermal stratification disappeared when the wind velocity exceeded 6.0 m s-1 for 2 h or more, internal Froude number (Fr i) increased from 0.3 to 1.0, and Wedderburn number (We) decreased from 0.5 to less than 0.1. Hypoxic water was formed 1-2 days after the formation of thermal stratification. The estimated benthic flux of PO 4-P from sediment in the field in summer may be 99.1 mg m-2 d-1 or higher.
Journal of Japan Society on Water Environment
The formation and disappearance of thermal stratification and hypoxic water were investigated by ... more The formation and disappearance of thermal stratification and hypoxic water were investigated by vertical and continuous observations of the water temperature, dissolved oxygen concentration, and oxidation-reduction potential from an automatic profiler sensor in Lake Kitaura in summer. Furthermore, the benthic flux of the dissolved inorganic phosphorus (PO 4-P) from sediment in Lake Kitaura was estimated from the results of water quality observations at short intervals using an automatic water sampler. The observed results showed that the conditions for forming thermal stratification were a temperature of 25 ℃ or higher and a wind velocity of less than 6.0 m s-1. Thermal stratification disappeared when the wind velocity exceeded 6.0 m s-1 for 2 h or more, internal Froude number (Fr i) increased from 0.3 to 1.0, and Wedderburn number (We) decreased from 0.5 to less than 0.1. Hypoxic water was formed 1-2 days after the formation of thermal stratification. The estimated benthic flux of PO 4-P from sediment in the field in summer may be 99.1 mg m-2 d-1 or higher.
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Papers by Takehiko Fukushima