Japanese Journal of Limnology (Rikusuigaku Zasshi)

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　In microbial ecology, technical challenges owing to the small cell size of organisms have been a bottleneck; however, new technologies have directly led to discoveries and breakthroughs, paving the way for novel insights. This review examines recent developments in lake microbial ecology, with a particular focus on their technological foundations and practical considerations for application in lakes. Amplicon sequencing and metagenomic analyses, which have emerged with the development of high-throughput DNA sequencing and analysis technologies, have revolutionized our understanding of the diversity and ecology of microbes that are difficult to culture in various environments. The significance of cell counting and microscopy, such as fluorescent in situ hybridization, has increased as nucleotide sequence data have become more comprehensive. Isolating difficult-to-culture microorganisms has also become a means of complementing information and testing the hypotheses obtained from sequencing data. We are now in an era in which we can determine “who is doing what” within complex microbial ecosystems at a high resolution, dispelling the notion that microbial ecosystems are "black boxes." The diverse expertise and approaches offered by the framework of limnology are key to making the best use of this vast amount of data.

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　T The reed communities along lakeshores are important for preventing shore erosion and enhancing biological production by phytoplankton and benthic invertebrates. However, if reed communities are located in inundated areas when the water level rises, they can dam up waste that would otherwise flow downstream. Additionally, unless the reeds are regularly mown and the cut vegetation is removed, the dead reeds can be carried downstream. In Lake Teganuma in Chiba Prefecture, the dead material washed out of the reed beds can stop the operation of the drainage pump station, and it can cause fishery damage if carried downstream into the Tone River. In this study, we used topographic maps and aerial photographs to clarify the formation and mechanisms of reed community development at the mouth of the Ohori River, the inflow river of Teganuma, and we confirmed their present condition through field surveys.
　The aerial photographs and old topographic maps showed that the field survey sites were located within water bodies from 1947 to 1955 and that the reed colonies were not as dense as they are today. The results of this study indicate that, since the 1960s, the reed colonies at the mouth of the Ohori River have been artificially altered from their natural state to their present form.

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