No abstract

No abstract

No abstract

Cyanobacterial blooms, consisting mainly of Microcystis spp., occur during summer in Lake Kasumigaura, Japan. Some previous studies have suggested that these blooms are enhanced by the recruitment of overwintering cells from the lake sediment. However, the volume and distribution of Microcystis in the sediment of Lake Kasumigaura are unknown. The purpose of this research was to clarify the volume, distribution, and seasonal variation of Microcystis in Lake Kasumigaura using real-time polymerase chain reaction PCR . The results showed that cell densities differed among stations and seasons. Moreover, it was suggested that cell recruitment occurred in early June in Tsuchiura Bay. Additionally, the lake bottom sediment is an unsuitable environment for the accumulation of Microcystis cells because the cells decomposed immediately and/or were transported by disconcertion at the surface of the sediment in Lake Kasumigaura.

Cyanobacterial blooms in lakes cause serious environmental problems on a global scale. Planktothrix (a filamentous cyanobacterium) blooms occurred during winter and spring from 2007 to 2011 in Lake Kasumigaura, a eutrophic lake located in Japan. This study analysed water quality during the period of Planktothrix abundance (2007–2010) at the centre of Lake Kasumigaura and compared it to that in the succeeding period, which did not have Planktothrix blooms (2012–2015). The average phytoplankton biovolume during the abundance period was larger than that in the succeeding period, which would contribute to the high chemical oxygen demand (CODMn; annual average of 9.7 mg/L) in the abundance period, compared to the succeeding period (7.6 mg/L). The total phosphorus concentration peaked in spring and summer in the abundance period, but only in summer in the succeeding period, whereas the seasonal variation in total nitrogen concentration between the two periods was relatively small. The annual average transparency (Secchi disc depth) increased before the abundance period due to a decrease in fixed suspended solid, which is comprised mainly of inorganic matter. It is likely that the change in irradiance conditions affected the occurrence of Planktothrix blooms.