Comparison of trace elements in freshwater pearls cultured in Japan, China, and USA

In this paper, we performed PIXE analysis of trace elements in freshwater pearls cultured in four different areas: Lake Biwa (Japan), Lake Kasumigaura (Japan), an unidentified lake in China, and Kentucky Lake (USA). We investigated the difference of trace elements contained in the four pearls from different aquaculture environments. The observed trace elements are Mn, Fe, Cu, Zn, and Sr. The major trace elements are Mn, Sr for all the samples. From comparison of the proportions of elements contained, we found the following features: (1) The Kasumigaura pearl has a nucleus with a high Mn/Sr ratio, (2) The Biwako pearl is low in iron content, and (3) The American pearl has high in Fe/Sr, Cu/Sr, and Zn/Sr ratios.

Relative impacts of increases of solar radiation and air temperature on the temperature of surface water in a shallow, eutrophic lake

We monitored lake surface water temperatures from 1992 to 2019 in Lake Kasumigaura, a shallow lake in Japan. We hypothesized that increases of shortwave radiation had increased surface water temperatures and heat fluxes more than had the increases of air temperature. We used the heat flux analyses and the sensitivity analyses to test the hypothesis. The fluxes of solar radiation gradually increased during the study period in a manner consistent with the phenomenon of global brightening. The increase was especially apparent in the spring. The rate of increase of surface water temperature was especially significant in May. Air temperature did not significantly increase in May, but it increased significantly in June (0.40 °C decade−1). A sensitivity analysis of the heat fluxes at the lake surface (shortwave radiation, longwave radiation, latent heat flux, and sensible heat flux) revealed that surface water temperature was more sensitive to changes of shortwave radiation than to air temperature during the spring. Although other factors such as inflows of groundwater and river water may also have impacted surface water temperatures, the increase of solar radiation appeared to be the major factor responsible for the increase of surface water temperature during the spring in Lake Kasumigaura.

Warming of water temperature in spring and nutrient release from sediment in a shallow eutrophic lake

We investigated whether recent springtime water temperature increases in a shallow eutrophic lake affected bottom sediment temperature and fluxes of ammonia (NH4+) and phosphate (PO43−) from the sediment. We conducted a lake-wide survey of Lake Kasumigaura, Japan, and analyzed the relationship between water temperature increases in spring and NH4+ and PO43− release fluxes. We also developed a numerical model to analyze how water temperature increase affects sediment temperature. Water temperature in May increased during 2010–2019 at a rate of 1.8–3.2 °C decade−1. The numerical simulation results showed that the water temperature increase was accompanied by a sediment temperature increase from a minimum of 18.3 °C in 2011 to a maximum of 21.6 °C in 2015. Despite the substantial difference in the observed sediment temperature (2.9 °C), no significant differences in NH4+ and PO43− fluxes in May between 2013/2014 and 2015 were found. These results suggest that both water and sediment temperatures are increasing in Lake Kasumigaura in spring, but it is unclear whether this warming has affected NH4+ and PO43− releases from the sediment. However, because a nonlinear response to sediment temperature was observed, future springtime warming may accelerate NH4+ and PO43− releases.

Impact of the municipal merger on watershed management: a study of Lake Kasumigaura, Japan

In the early 2000s, Japan instituted the Great Heisei Consolidation, a national strategy to promote large-scale municipal mergers. This study analyzes the impact that this strategy could have on watershed management. We select the Lake Kasumigaura Basin, the second largest lake in Japan, for the case study and construct a dynamic expanded input–output model to simulate the ecological system around the Lake, the socio-environmental changes over the period, and their mutual dependency for the period 2012–2020. In the model, we regulate and control the following water pollutants: total nitrogen, total phosphorus, and chemical oxygen demand. The results show that a trade-off between economic activity and the environment can be avoided within a specific range of pollution reduction, given that the prefectural government implements optimal water environment policies, assuming that other factors constraining economic growth exist. Additionally, municipal mergers are found to significantly reduce the budget required to improve the water environment, but merger budget efficiency varies nonlinearly with the reduction rate. Furthermore, despite the increase in financial efficiency from the merger, the efficiency of installing domestic wastewater treatment systems decreases drastically beyond a certain pollution reduction level and eventually reaches a limit. Further reductions require direct regulatory instruments in addition to economic policies, along with limiting the output of each industry. Most studies on municipal mergers apply a political, administrative, or financial perspective; few evaluate the quantitative impact of municipal mergers on the environment and environmental policy implications. This study addresses these gaps.

New insights from museum specimens: a case of Viviparidae (Caenogastropoda: Mollusca) in Iwakawa’s collection preserved in the National Museum of Nature and Science, Tokyo

In this study, we clarify the classification of museum specimens of the family Viviparidae, which is composed of six species/subspecies in Japan, including three endangered species. We examined Viviparus sclateri specimens from the Tomotaro Iwakawa collection (1855-1933) in the National Museum of Nature and Science, Tokyo. The Iwakawa's collection was catalogued in 1919 and Viviparus sclateri, labelled with Naga-tanishi, the current Japanese name for H. longispira, which was, at the time, equivalent to Viviparus sclateri, was listed in this catalogue. The catalogue noted localities of Viviparus sclateri (Naga-tanishi) from outside Lake Biwa, including occurrences in Lake Kasumigaura and Lake Suwa. However, Heterogen longispira (Naga-tanishi) is currently considered to be endemic to Lake Biwa drainage. The actual status of Viviparus sclateri in Iwakawa (1919) has not been clarified until now. Our examination revealed that Viviparus sclateri from Iwakawa’s catalogue included H. japonica, H. longispira and Sinotaia quadrata histrica, based on current taxonomy. Specimens assigned to H. longispira occurred only in Lake Biwa drainage. Heterogen japonica was confirmed to be present in all lots and some H. japonica from Lake Suwa had a distinctive morphology. Sinotaia quadrata histrica was only confirmed to occur in Lake Suwa. Furthermore, some specimens from southern Lake Biwa and the Seta River had intermediate characteristics between H. japonica and H. longispira and their populations are currently almost extinct.