Environmental impact of removal of a large-scale sluice gate on Nakaumi Lagoon and adjacent coastal waters, southwest Japan: Evidence from long-term foraminiferal monitoring.

A large-scale sluice gate, which was built in southwest Japan as a national project to reclaim and desalinate lagoon water in 1974, was removed between 2005 and 2009. To examine the impact of this removal on both Nakaumi Lagoon and the nearby coastal waters, we analyzed the foraminiferal assemblages of a coastal sediment core and of samples obtained during 10 years of lagoon monitoring (2001-2010). Detailed 210Pb(ex) dating of the sediment core revealed an increased sediment accumulation rate in the coastal waters, implying that discharge of fine-grained materials, including organic matter, was facilitated by removal of the sluice gate. The observed increase in agglutinated foraminifera and decrease in calcareous species was related to the sediment accumulation rate, and these changes occurred close to 2005, when sluice-gate removal began. In Nakaumi Lagoon, the sporadic presence of the coastal species Quinqueloculina seminula within the 6-m water column and the decline in the lagoon-adapted Ammonia "beccarii" have occurred since 2005. The removal of the sluice gate, plus the sea-level rise, allowed greater seawater inflow and stabilized the monthly deep-water salinity fluctuations in Nakaumi Lagoon.

Preliminary investigation of 222Rn in the Yakumo Wind-hole, an algific talus deposits, from Izumo, southwest Honshu, Japan.

The Yakumo Wind-hole in southwest Japan formed by landslip, and it is known as a cold air blowhole. This wind-hole consists of two parts, which have complementary relationships in regard to the flow of air, namely, topographically upper and lower holes that can be characterized as a warm wind-hole (WWH) and cold wind-hole (CWH), respectively. We carried out a preliminary investigation of radon behavior in the Yakumo Wind-hole. The data showed remarkable seasonal change from high 222Rn concentrations reaching to 7.6 ±â€¯0.1 kBq/m3 in the warm season (mid-May to October) to low 222Rn concentrations in the cold season (December to early May) at the CWH. The threshold in the regional atmospheric temperature was estimated as 16.2 °C for the beginning and 17.1 °C for the ending periods of air blow with higher 222Rn concentrations. These seasonal changes in 222Rn were not only associated with the dynamic convection caused by temperature differences in and out of the talus, but were also related to the relative humidity of air that is blown out. High 222Rn concentrations were formed in the high humidity environment, and the humidity may possibly be associated with melting ice. According to the known information on 222Rn behavior in relation to humidity, a radon trap in the growing ice in spring and in the melted water in summer are suggested. This study revealed that 222Rn measurements are a useful tool to understand the air dynamics in the talus.

A new late Eocene Bicornucythere species (Ostracoda, Crustacea) from Myanmar, and its significance for the evolutionary history of the genus.

The ostracode genus Bicornucythere (Ostracoda, Crustacea) is abundant in modern-day eutrophic marine bays, and is widely distributed in estuaries and inner bays throughout East Asia, including in China, Korea, Japan, and the Russian Far East. The evolutionary history of Bicornucythere is poorly understood. Here, we report on a new species of Bicornucythere (Bicornucythere concentrica sp. nov.) from the upper Eocene Yaw Formation in the Central Myanmar Basin. The oldest previously known Bicornucythere taxon, Bicornucythere secedens, was reported from lower Miocene strata in India, although a molecular phylogeny suggests that the genus first appeared in the Late Cretaceous. Bicornucythere concentrica sp. nov. is at least 10.9 million years older than the earliest known B. secedens. The new species occurs with Ammonia subgranulosa, a benthic foraminifer, an association that is representative of brackish water conditions in modern Asian bays. Our findings indicate that extant genera have inhabited Asian bays since the late Eocene. The paleobiogeography of Bicornucythere indicates that the taxon was dispersed onto Indian coasts during the collision between the Indian and Eurasian plates.

Anthropogenic impacts on meiobenthic Ostracoda (Crustacea) in the moderately polluted Kasado Bay, Seto Inland Sea, Japan, over the past 70 years.

Two sediment cores were obtained from Kasado Bay, a moderate-polluted enclosed bay in Japan, to examine anthropogenic impacts on Ostracoda over the past ca. 70 years. We analyzed ostracode abundance and diversity, grain size, and CHN, and used (210)Pb and (137)Cs as the dating method. The present study showed that cross-plot comparisons of ostracode abundance and each environmental factor, based on sediment core data, could be used to identify ostracode species as indicators for anthropogenic influences. Ostracode abundance reflected mainly the changes that had occurred in total organic carbon content in sediments related to eutrophication, but heavy metal concentration did not directly influence several ostracode abundance in the bay. Environmental deterioration because of eutrophication started in the 1960s. The regulations regarding the chemical oxygen demand in waters introduced in the 1980s probably influence ostracode abundance for certain species in this period. Currently, Kasado Bay is not experiencing severe degradation.

Opening of the closed water area and consequent changes of ²²8Ra/²²6Ra activity ratios in coastal lagoon Nakaumi, southwest Japan.

In Lake Nakaumi, the second largest coastal lagoon in Japan, artificially closed (Honjyo) area, which was left untouched for 28 years, was partly opened in May, 2009. (228)Ra/(226)Ra ratio of waters in Honjyo area and Lake Nakaumi showed a well-tuned seasonal variation exhibiting high value in summer. After the opening event, however, the (228)Ra/(226)Ra ratios in the Honjyo water showed an unclear seasonal variation in both surface and deep water. This opening event caused the change of active movement of lake and marine water.

The influences of various anthropogenic sources of deterioration on meiobenthos (Ostracoda) over the last 100 years in Suo-Nada in the Seto Inland Sea, southwest Japan.

This study focuses on the relationships of water and sediment quality with meiobenthos (Ostracoda) over the past 100 years, using a sediment core obtained from Suo-Nada in the Seto Inland Sea, Japan. We compared high-resolution ostracode results with geochemical and sedimentological data obtained from the study core as well as with rich environmental monitoring data that are available. R-mode cluster analysis revealed two bioassociations (BC, KA). Until the 1960 s, assemblages continued to show high diversity. They changed in approximately 1970, when excessive nutrients and organic matter began to be supplied, and most species decreased in number. All species of bioassociation BC were dominant again by the mid-1990 s; however, those of bioassociation KA containing infaunal species did not increase and have been absent or rare since the 1970s because organic pollution of sediments has continued to date. This study provided robust baseline for ostracode-based long-term environmental monitoring in East Asia.