[pp.97-106]

Evaluation of Water Quality Improvement by Dredging at Koya Pond

Nariaki WADA, Yasuhiro HEIKE and Yasuhiko WADA （Kobe University / Kansai University）

Abstract:
Pond eutrophication causes problems such as ugly landscapes, endangerment of aquatic life, and foul odors. Pond dredging is an effective solution to these problems and restores the multiple functions of ponds. Dredging was conducted at Koya Pond as a countermeasure to improve water quality. Field surveys were conducted to assess the quality of the water and sediment. The elution rate of nutrients from the sediment was computed using a simulated in situ method. Changes in the elution rate from the sediment and water quality before and after dredging were investigated, and the efficacy of dredging was evaluated. The elution rate of total nitrogen (T-N) decreased by 15.7–68.4%, whereas that of total phosphorus (T-P) increased by 163.6–1476.0% after dredging. Despite the increase in the elution rate of T-P, the improvement in the chemical oxygen demand (COD) and T-N and T-P concentrations confirmed that dredging improved the water quality.

Key Word:
evaluation of dredging, elution rate, nutrients, sediment, water quality

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