Variations in the quality of the coastal waters during recent 30 years in the Suo-Nada region off Yamaguchi prefecture [Japan]
2005
Wanishi, A.(Yamaguchi-ken. Fisheries Research Center, Nagato (Japan))
The quality of the coastal waters was monthly investigated in the Suo-Nada region off Yamaguchi Prefecture from 1973 to 2003. The long-term variations of the parameters such as transparency, dissolved oxygen (DO), dissolved inorganic nitrogen (DIN) and phosphate (PO4-P) were analyzed. Generally speaking, the water pollution in this area by plant effluent and living drainage have been gradually decreasing. For example, transparency and DO concentration at the bottom layers showed tendencies to increase or level off, while nutrients concentration and chemical oxygen demand (COD) showed tendencies to decrease or level off. Chlorophyll-a concentration in the surface layers, which represents the primary productivity of the waters, has also decreased. From the remarkable decline of the recent fisheries production, the present quality of the waters in this area may be relatively poor to maintain successful fisheries industry. Therefore, we should continue to make thorough investigations and discuss what are the suitable conditions of the waters for fishery in this area.
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