Eshima Island is located in Lake Nakaumi, eastern Shimane Prefecture. A small-scale reclamation was performed for creating farmland in Eshima Island during the Edo–Meiji era. During the Showa era, in 1952, the “Eshima Island vicarious execution land reclamation project” was started by Shimane Prefecture. Furthermore, the “Government managed Lake Nakaumi land improvement project” was started in 1963, which continued until 2009 with some changes in the initial plan. The current landscape of Lake Nakaumi and Eshima Island was formed because of this project. In this study, we examined the history of land reclamation in Eshima Island using maps from the Edo and early Meiji era and several topographic maps that were published after 1901. In addition, we have quoted and explained various documents.

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Seawater backflow from the Sea of Japan is controlled by operating the flood gate on the Koyama River between the Sea of Japan and Lake Koyama-ike, a brackish lake in the Sanin region. An attempt was made to evaluate the salinity flux at the mouth of Lake Koyama-ike quantitatively, focusing on the effect of salinity on the ecosystem of the lake. The salinity and flow rates were monitored using electrical conductivity loggers and Doppler flow meter readings obtained every 10 min at various depths from August 8, 2021 to October 21, 2021. Based on the observed results, the salinity flux at the mouth of Lake Koyama-ike was estimated to be 0.09–5.82 kg/m2/s into the lake. When the salinity flux was high, the water level difference between the lake and the downstream site of the flood gate was large, the opening of the flood gate was large, and the salinity concentration was high at the downstream site of the flood gate. However, the results suggest that when the salinity flux is small, the flood gate opening is small, salinity concentration at the downstream site of the flood gate is low, and backflow time tends to be short.

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To verify the description of the Nakaura Channel described in Izumo no kuni fudoki (the topography of Izumo Province), I reconstructed the topography of the lake bottom in the waters surrounding Eshima island using hydrographic charts from a survey conducted in 1952.
The result revealed that a tombolo existed in the Nakaura Channel, and the area of this tombolo during the Nara Era was reconstructed.
Furthermore, the lake shallows in the Eshima north water area and the remains of dredging work from the Edo to Meiji Era in the Eshima northeast water area were detected.
Reclamation efforts in Eshima were undertaken on the tombolo in the Edo Era and on the lake shallow in the Showa Era.

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A macrobenthic community is sensitive to changes in the environment such as heavy rainfall and flooding. Lake Shinji is the largest fishing ground for the brackish water clam Corbicula japonica in Japan. The macrobenthic community of this lake has been surveyed for approximately 40 years since the 1980s, and it was surveyed in 2021. However, the amount of precipitation from June to September in 2021 was higher than ordinary years. The purpose of this study was to clarify the effects of the heavy rainfall and flooding on the macrobenthic community in Lake Shinji. Macrobenthic communities were compared between the heavy rainfall and flooding years (1997 and 2021) and ordinary year (1992). The amount of precipitation from June to September in 2021 was about 1279 mm (the average precipitation from 1981 to 2021 was 764.0 mm), which was the second highest value since the 1980s. In this study, we collected 21 macrobenthos species. Dominant macrobenthic species were Prinospio (Minuspio) japonica, Corbicula japonica, Iravadia elegantula, and Tanypus sp.. P. japonica and C. japonica were collected from the central area and the shoreline of the lake, indicating the effects of the heavy rainfall and flooding. Arcuatula senhousia was rarely collected, possibly due to low salinity. Results of cluster analysis showed that the ratios of brackish water polychaeta in the macrobenthic community were lower for the heavy rainfall and flooding years (1997 and 2021) than the ordinary year (1992). It is assumed that community structure and spatial distribution of macrobenthos in this lake was modified in the year 2021 due to heavy rainfall and flooding.

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Detailed lithology and tephra records in core sediment (Core HK19) from the eastern end of the Izumo Plain near the mouth of the Hii River in Shimane Prefecture revealed the formation history of the Izumo Plain and paleo-events of volcanic eruptions and great floods. Accelerator mass spectrometry (AMS) ¹⁴C dating indicates that sediment accumulation began about 10.1 cal. kyr BP under the low-salinity brackish condition. Once this site was under an open bay called Paleo-Shinji Bay, the bay had shifted to the semi-closed condition by sand bar development around 7.5 cal. kyr BP. After that, the laminated sediment started to be deposited in core HK19. Three tephra layers (K-Ah, S3-fa, and SOh) and a remarkable reworking of the K-Ah tephra layer were deposited in this laminated layer. The Sanbe (or Sambe) tephra units (S3-fa and SOh) occur as crypt-tephra layers, which were identified by soft X-ray and extremely high Sr content. The reworked K-Ah tephra was deposited around 6.86 cal. kyr BP. A correlative reworked layer was also found in the sediment layer of Paleo-Shinji Bay beneath the Shimane University campus east of Lake Shinji. This suggests that there was a huge flood in the Hii River basin at that time. The site of core HK19 was rapidly buried after 150 cal. yr BP under the progradation of the Hii River delta by the “kanna-nagashi” iron manufacturing activity.

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The tropical epibenthic holothurian Holothuria (Selenkothuria) erinaceus Semper, 1868 is reported for the first time; a single specimen has been collected from a subtropical mangrove forest on Ishigaki Island, Yaeyama Islands, southern Japan. The external/internal morphological features, including a calcareous ring and ossicles, are described and compared with literature descriptions of congeners. Holothuria (Selenkothuria) erinaceus Semper, 1868 has previously been recognized as a tropical species, distributed widely in the tropical Indian and West Pacific Oceans, including the Philippines and Fiji. Not only is the Ishigaki Island record the northernmost for the species, but also the collection site is the first recorded instance of an epibenthic sea cucumber inhabiting in a mangrove forest habitat.

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