Increments of COD, Total Nitrogen and Total Phosphorus Discharge to Isahaya Bay since the Embankment in 1997

克之, 佐々木; 義邦, 程木; 哲生, 村上

doi:10.5928/kaiyou.12.573

Cited by 13 publications

(4 citation statements)

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“…and Sasaki et al (2003) reported that average inflow from the Honmyo River is 14 m 3 s À1 , and average salinity of the upper and lower layers measured in the present study were 27.5 and 30.0 psu, respectively. Using equations (4) and (5), U 1 , U 2 and W were calculated to be 0.48, 0.31 and 2.44 Â 10 À4 cm s À1 , respectively.…”

Section: Measurement Of Water Hypoxiasupporting

confidence: 59%

“…Hypoxic water was not recorded in Isahaya Bay until 1997, and hypoxia may have developed only over the past decade as organic matter pollution increased in the bay (Azuma, 2000). Sasaki et al (2003) pointed out that the COD, TN and TP loads increased after the dyke construction because of the loss of the Isahaya tidal flat. According to their estimates, calculated on the basis of a box model, the COD load before the initiation of the reclamation project was 1046 t yr À1 (2.0% of the total load to Ariake Bay), and increased to 4000-5800 t yr À1 after the embankment was built (8.3-12.2% of the total load to Ariake Bay).…”

Section: Discussionmentioning

confidence: 99%

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Effects of tidal flat reclamation on sediment quality and hypoxia in Isahaya Bay

Hodoki

Murakami

2006

Aquatic Conserv: Mar. Freshw. Ecosyst.

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1. Ariake Bay, which is located in western Japan, has a large tidal range (>6 m) and a vast tidal flat (200 km 2 ). In the early 1990s, the government-managed Isahaya Reclamation Project began in the western part of Ariake Bay. A 16-km 2 area of tidal flat in the inner part of Isahaya Bay was destroyed through reclamation and separated from the sea by a dyke, which created land and a freshwater reservoir.2. Since the initiation of the project, fishery yields around Isahaya Bay have dramatically decreased. The objective of this study was to clarify the relationship between the work associated with the Isahaya Reclamation Project and the recent environmental deterioration in Ariake Bay, with references to present sediment thickness and organic matter content, and hypoxic water distributions in Isahaya Bay.3. The organic matter load from the reservoir has increased since the initiation of the reclamation project and has been associated with a thick layer of fine sediment at the bottom of Isahaya Bay. The thickness of fine sediment and the total organic carbon content were higher in Isahaya Bay than in the freshwater reservoir.4. Based on measurements in August 2001, hypoxic water spread widely in and around Isahaya Bay; the lowest dissolved oxygen (DO) concentration (0.53 mg L À1) was observed just outside the dyke. An analysis based on a two-layered box model using data obtained in August 2001 showed that the DO consumption rate in the bottom layer was high (0.61 mg O 2 L À1 day À1 ), and that 22-41% of the total organic carbon load needed to induce the hypoxic water was derived from the reclamation area.5. Our findings strongly suggest that enclosed seas may suffer from eutrophic and hypoxic conditions because of their low seawater-exchange rate. A comprehensive conservation programme and environmental assessment including physical and material transport processes in the system is needed to manage the environment of the enclosed sea.

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Section: Measurement Of Water Hypoxiasupporting

confidence: 59%

Section: Discussionmentioning

confidence: 99%

Effects of tidal flat reclamation on sediment quality and hypoxia in Isahaya Bay

Hodoki

Murakami

2006

Aquatic Conserv: Mar. Freshw. Ecosyst.

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“…This decreased the DO consumption rate due to organic matter decomposition. Sasaki et al (2003) also reported that strong currents at times of water discharge through the gates increased the COD load by resuspension of bottom sediment. Hayami and Hamada (2015) reported that gate-opening generated complicated flow in Isahaya Bay.…”

Section: Limitation Of the Present Modelmentioning

confidence: 94%

“…Since Nagao et al (2010) did not clarify the mechanisms that caused the DO difference, further studies are needed that consider the unsteady state conditions. Sasaki et al (2003) reported that inflow of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) to the Isahaya Bay increased significantly after the dike construction and promoted hypoxia/anoxia formation by the increase of DO consumption due to the deposition of organic matter on the seabed in the bay. Our simulation, however, revealed that the decrease in DO concentration in Isahaya Bay (BOX 2) was predominantly because of the decrease in DO supply by the vertical diffusion process ("VerDIf" in Fig.…”

Section: Limitation Of the Present Modelmentioning

confidence: 99%

Impact of Isahaya dike construction on DO concentration in the Ariake Sea

Yamaguchi

Hayami

2018

J Oceanogr

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In the Ariake Sea, dike construction in Isahaya Bay in 1997 for reclamation and disaster prevention was thought to cause big anthropogenic impacts on the marine ecosystem. Currently, hypoxia or anoxia occurs every summer in Isahaya Bay and the inner Ariake Sea. However, the effects of the dike construction on the DO concentration are unclarified. The present study evaluated the impact of the dike construction on the DO concentration by applying a numerical ecosystem model. The present calculation showed that the dike construction could affect the DO concentration in summer in a wider area than reported before in the steady state with a neap-spring tidal cycle. In Isahaya Bay, the dike construction caused a decrease of DO concentration greater than 2.0 mg l −1 , due to the decrease in DO supply from the vertical diffusion process with reduction of tidal current and the intensification of the density stratification. The dike construction also affected the DO concentration in the inner Ariake Sea by decreasing the DO concentration of the water transported by the estuarine circulation and the reduction of the diffusive supply of oxygen vertically with stratification enhanced by the dike construction. For the first time, this study showed with numerical simulation that the dike construction could affect the DO concentration in a wide area of the Ariake Sea.

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Influence of water discharged from a reservoir on reclaimed land into Isahaya Bay (Kyushu, Japan) on the regeneration of NH4+ in the water column

et al. 2019

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Increments of COD, Total Nitrogen and Total Phosphorus Discharge to Isahaya Bay since the Embankment in 1997

Cited by 13 publications

References 0 publications

Effects of tidal flat reclamation on sediment quality and hypoxia in Isahaya Bay

Effects of tidal flat reclamation on sediment quality and hypoxia in Isahaya Bay

Impact of Isahaya dike construction on DO concentration in the Ariake Sea

Influence of water discharged from a reservoir on reclaimed land into Isahaya Bay (Kyushu, Japan) on the regeneration of NH4+ in the water column

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