In order to reduce environmental risks and to ensure the safety of the food crop, it is a new problem to reveal the effects of blue-green algae toxin-microcystin in eutrophic enclosed water intake source irrigation on accumulation and growth of crops. As the impact on the flora and fauna of toxic blue-green algae occurring in irrigation water, there are accumulation and metabolism in fish, shellfish, absorption from roots microcystin cyclic peptide of hydroponic plants and crops, and accumulation in the terrestrial part of the plants and growth inhibition at a high concentration conditions in the plants. It is necessary to ensure the high quality and safety of agricultural products by performing a water quality improvement of irrigation water along with the toxic blue-green algae growth suppression by the introduction of bio-eco system aimed at risk reduction from microcystin In addition, to suppress toxic blue-green algae and the microcystin accumulation in the edible parts, it is important to establish the appropriate water use system of agricultural crops such as development on migrating to the method of water supply by irrigation method from spray irrigation to plants to penetration into the soil irrigation method

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Lakes Inawashiro, Hibara, Onogawa, and Akimoto are located around Mt. Bandai in Fukushima Prefecture, northeastern Japan. The changes in phytoplankton community composition in the acidotrophic lake Inawashiro, where neutralization in pH was observed in recent years, were estimated by analyzing the long-term dynamics of phytoplankton communities in these four lakes by using multivariate analyses. Canonical correspondence analysis (CCA) suggested that the differences in phytoplankton community composition across the four lakes could be predominantly explained by five environmental factors: pH, zooplankton density (ZOO), total nitrogen concentration (T－N), average monthly photosynthetically active radiation within the mixed layer (PAR.m), and nitrogen/phosphorus (N/P) ratio. The niche of species according to the habitat designated by six environmental factors, including water temperature (W.T.), was assessed by conducting outlying mean index (OMI) analysis, and 48 phytoplankton species were classified into the following four groups: widely distributed species, acidophilous species, circumneutral mesotrophic species, and circumneutral oligo-mesotrophic species. The niches of the four groups suggested that circumneutral mesotrophic species such as Microcystis sp. would occur in Lake Inawashiro and the phytoplankton community composition of this lake would approach that of Lakes Hibara, Onogawa, and Akimoto if eutrophication occurs in Lake Inawashiro.

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Many taxa similar to Navicula subalpina Reichardt var. subalpina which was represented as a valid publication by F. Reichardt （1988） were recorded and such taxa with different species name were recognized in Japan. On the other hand Navicula schweigeri Bahls （2012） was a taxon of valid publication recently. We research morphplogical variability of above two taxa in addition to the specimens from the Sagae River and the Kiso River. Approximately 260 valves were analyzed morphologically on the light photomicrographs from the samples collected from the two rivers referring to the photomicrographs and descriptions in the two taxa including holotype. As a result we suggest new rank and new combination as Navicula subalpina var. schweigeri （Bahls） H.Fukush., Kimura & Ts. Kobay. While this taxon is considered to be a indicator species of oligosaprobic～β－mesosaprobic waters.

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We analyzed small-eukaryote assemblages (size fraction: 0.2–5 μm) at a Japanese mesotrophic lake (Lake Kusaki) by sequencing cloned eukaryotic 18S rRNA genes. Clones belonging to 12 phyla of 18 classes were observed during the period of our study, from June 2009 to February 2012. Presence of small eukaryotes affiliated with Mychonastes (Chlorophyceae), Goniomonas (Goniomonadea), Chrysochromulina (Haptophyceae), Paraphysomonas (Chrysophyceae), Nerada (Bicoecea), Bodomorpha (Sarcomonadea) and Parastrombidinopsis (Spirotrichea) was determined in more than 7 libralies, and it is likely the classes and genera were representative of the small eukaryotes in Lake Kusaki. In 2011 and 2012, the detection frequency of the operational taxonomic units (OTUs) belonging to Chrysophyceae and Cercozoa was lower than that in 2009 and 2010. Sequence identities to known species were less than 95％ in 66％ of the OTUs, suggesting that there are many phylotypes of small eukaryotes in Lake Kusaki that have not yet been classified.

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