琵琶湖南湖におけるホルミディウムの優占的発生と水質および気象要因等との相互関係 Relationship between the Occurrence of Phormidium tenue Bloom and Water Quality or Weather Factors in the South Basin of Lake Biwa
In the south basin of Lake Biwa, <i>Phormidium tenue</i> (Cyanophyceae) occurred in great portion sand the tap water had been damaged causing concern about the odor in early June of 1982, 1983, 1987, 1989, and 1990. The relationship between the abundance of P. tenue and water quality in the south basin and the weather condition of Lake Biwa were examined.<br>The changes of water quality in the south basin of Lake Biwa in early June of 1980-1993 showed that DIN (dissolved inorganic nitrogen) and DIN:DIP (dissolved inorganic phosphorus) ratio were comparatively low and TN (total nitrogen):DIN and TP (total phosphorus):DIP ratios were high in the years when <i>P. tenue</i> occurred abnormaly abundant.<br>The comparison of each average water quality among the dominant phytoplankton in early June of 1980-1993 showed that <i>P. tenue</i> occurred in the waters with low DIN and DIN:DIP ratio, and high WT (water temperature), TN:DIN and TP:DIP ratios. The species occurred in the years with the weather conditions of high air temperature and solar radiation, and low rain fall (precipitation) from 21 May to 10 June, before it become dominant. These features of <i>P. tenue</i> were remarkably contrac-tive as compared with those of <i>Uroglena americana</i>, with the exception of TP:DIP ratio.
日本水産学会誌 62(6), 872-877, 1996-11-15