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Greenhouse gas (GHG) emissions from paddy fields depend on water management practices and rice varieties. Lysimeter experiments were conducted to determine the effect of rice varieties (lowland; Koshihikari (KH) and upland; Dourado Precoce (DP)) on GHG emissions under two water management practices: alternate wetting and drying (AWD) and continuous flooding (CF). A repeated cycle of drying and wetting in AWD irrigation was performed by drying the soil to −40 kPa soil matric potential and then rewetting. Consequently, the closed chamber method was used to measure direct emissions of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). The result revealed that water management significantly affected CH4 and N2O emissions (p < 0.05), while no significant effect was observed between different rice varieties. Although, AWD irrigation reduced CH4 emissions, it increased N2O emissions compared to CF irrigation, likely due to increased oxygen supply. AWD irrigation decreased GWP by 55.6% and 59.6% in KH and DP, respectively, compared to CF irrigation. Furthermore, CH4 and N2O emissions significantly correlated with soil redox potential and volumetric water content. These results suggest that AWD irrigation might be an effective water management method for mitigating GHG emissions from rice fields in central Japan. [ABSTRACT FROM AUTHOR]

Core samples to a depth of approximately 50 m and undisturbed soil samples were retrieved from eight locations in the Saga Plain, Japan, to investigate the effects of the depositional environment and post-depositional processes on the engineering properties of Quaternary clays in the Saga Plain. The engineering properties of these soil samples were measured, and the test results showed that the clays in the Saga Plain have a high void ratio, high water content, high compressibility, high sensitivity, and low stiffness. The one-dimensional compression curves plotted above the sedimentation compression line proposed by Burland, and the compression index was high, which indicated that the clays had been cemented to some degree. The clays have high strength sensitivity and high stress sensitivity, indicating that they have strong structures. It was considered that a considerable amount of volcanic ash from the four large volcanic eruptions that occurred during the deposition of these clays settled into the clays, resulting in a certain degree of cementation, which was attributed as the main driver of the strong structure in these clays. Comparisons of the NaCl concentration, pH, and oxidation-reduction potential (ORP) of the clay samples representing the initial depositional environment and the current ground environment showed that salt leaching occurred in the Ariake clay formation, and that the ground environment changed. When the NaCl concentration was less than approximately 2 g/L, the strength sensitivity of the Ariake clay samples with low-activity clay minerals significantly increased due to the decrease in the liquid limit and subsequent significant decrease in the remolded undrained shear strength. Therefore, salt leaching was probably a main cause of the high strength sensitivity of the clays in the Saga Plain. The depositional environment at some locations changed from an alkaline, reducing environment, to an acidic, oxidative environment, with the potential to change into a strongly acidic environment, which could have deteriorated the strength of the cement/lime-treated clays in the Saga Plain. [ABSTRACT FROM AUTHOR]

• Variation of hydrological connectivity of karst was assessed by intensive wells. • Chemicals and isotopes explain heterogeneity in surface–groundwater connectivity. • Coral limestone is porous and heterogeneous for water percolation and storage. Carbonate aquifers are critical for the health and well-being of human communities. Despite considerable efforts on the structure of karst aquifers, the variable and invisible flow paths or the vertical and spatial heterogeneity of karst systems remain too complex to be fully understood. An artificially constructed small limestone aquifer with an extensive network of observation wells in the Miyako Island, Japan, provides a unique opportunity to illustrate the vertical and spatial hydrological connectivity for water movement and storage. Water chemical data at two different depths over six years, including electrical conductivity (EC), dissolved oxygen (DO), oxidation–reduction potential (ORP), major ions (Na+, K+, Ca2+, Mg2+, SO 4 2−, and HCO 3 −), δ18O and δ2H capture water mixing processes during groundwater recharge in the aquifer influenced by irrigation pumping and recharge by precipitations throughout drying and wetting cycles. Results suggest that the intensive weathering of coral limestone under the impact of agricultural fertilization, as indicated by high EC values and high concentrations of Ca2+ and HCO 3 −. The high DO and low ORP values imply a lack of organic decomposition activity, which is typical in the karst groundwater condition. More importantly, groundwater recharge in the small aquifer was found to be influenced by following three processes. Spatially, both Cl− and NO 3 −−N indicate the large heterogeneity of water mixing as rainfall or drainage water percolates differently to various parts of the aquifer. Vertically, there are apparent differences in the concentration of Cl− and NO 3 −−N between the top and bottom layers in several wells, suggesting that, even within a single well, the vertical profile can be weakly connected between the top and the bottom layers. The bottom layer should have been recharged by lateral water inflow from fractures or conduits. And thirdly, the even distribution of Cl− over the long precipitation season from October 2016 and March 2021 and another nearly even distribution of NO 3 −−N in the low fertilization season in March 2021, demonstrate that the aquifer system is basically connected and porous. In summary, the insights gained from our study reveal that: 1) coral limestone can be treated as a well-developed porous aquifer and 2) the hydrological connectivity is highly heterogeneous and influenced by rock properties, including formation structure, degree of weathering, and clay content. Such findings are essential for understanding the hydrogeological properties of coral limestone aquifers globally. [ABSTRACT FROM AUTHOR]

Benthic invertebrates that inhabit the seafloor respond to anthropogenic and natural stresses, and are good indicators for assessing the benthic ecological status. We evaluated the ecosystem health of the Seto Inland Sea based on the multivariate AZTI Marine Biotic Index (M-AMBI), being its first application in a Japanese coastal sea with numerous endemic species. From the 415 locations studied, we were able to use M-AMBI in 384 sites (92.5% in all sites). The result revealed a statistically significant correlation among biotic indices including AMBI, M-AMBI, Richness, and H ' (p < 0.01). Most of the physico-chemical parameters of the sediment (water content, total organic carbon (TOC) content, sulfide content, mud content, and oxidation–reduction potential (ORP)) were significantly correlated with each other excluding sediment temperature. The M-AMBI was significantly correlated with physico-chemical variables including water content, TOC content, sulfide content, and ORP. We found that the sites classified into the organically enriched cluster, and having high contents of TOC, mud, and sulfide and negative ORP, corresponded with sites that had significantly low M-AMBI values (bad-poor ecological status). Conversely, sites in the unpolluted sandy cluster were assigned high M-AMBI values (high-good ecological status). Therefore, M-AMBI would be a useful biotic index in Japanese coasts due to the representation of the comprehensive sediment quality. • Ecological status of the Seto Inland Sea was evaluated using M-AMBI. • We evaluated the relationship of M-AMBI with physico-chemical variables. • M-AMBI values corresponded with comprehensive sediment quality. • M-AMBI can be a useful biotic index in Japanese coasts. [ABSTRACT FROM AUTHOR]

Biodiesel fuel (BDF) is a potentially carbon-neutral fuel that could play a potentially important role in preventing global warming. However, its high production cost poses a challenge for many BDF producers. To establish an efficient method for BDF production and increase its cost competitiveness, the production efficiencies of 35 BDF plants in Japan, which produce BDF from waste cooking oil, were evaluated. Moreover, the cost reduction potential associated with improved efficiency was estimated. The empirical analysis revealed that (1) approximately 92% of the BDF plants have inefficient production; (2) they exhibit two predominant types of inefficiencies, technical and scale inefficiencies, and (3) improvement of production inefficiency can lead to an average production cost reduction of 3.52 yen per liter of BDF. To increase the production efficiency, it is important to improve the quality of the waste cooking oil used and increase the production scale. It is recommended that operators of inefficient BDF plants learn the production activities of the most efficient plants identified in this study. Furthermore, government policies focused on efficient BDF plants are essential to increase BDF production with limited resources. • DEA for analyzing production efficiency of biodiesel fuel (BDF) plants using waste cooking oil in Japan. • Approximately 92% plants were inefficient, considering production technology and scale. • Improvements in production inefficiencies can reduce the production cost per liter of BDF by 3.52 yen on average. • Decision-makers in inefficient plants must refer to the technology of the most efficient plants. • Sharp energy policies prioritizing technological top runners were recommended to ensure the economic competitiveness of BDF. [ABSTRACT FROM AUTHOR]

An up-to-date techno-economic assessment was conducted on CO 2 emissions reduction potential in the Japanese iron and steel industry for 2030. The following mitigation measures were investigated: (i) maximized installation of best available technologies (BAT scenario), (ii) increased use of coke substitutes in blast furnaces, and (iii) increased use of obsolete steel scrap. For measure (iii), this study assessed the obsolete scrap use in the integrated steelmaking (BF-BOF) route, rather than increasing steel production from the electric arc furnace (EAF) route. CO 2 capture and storage (CCS) was not considered due to large deployment uncertainty. The results showed that 20 Mt–CO 2 of emissions reductions, equivalent to 12% of the industry's total emissions in 2010, can be achieved in 2030 compared with a frozen technology scenario. More than 9 Mt–CO 2 reduction was attributable to the enhanced use of obsolete scrap in the BF-BOF route. Consequently, the industry's emissions reduce by about 7 Mt–CO 2 or 4% below 2010 levels. Almost all domestically recovered obsolete scrap can be fully consumed solely by increasing the scrap use in basic oxygen furnaces (BOF). Moreover, the increase in average copper concentration in the BF-BOF steel due to the increased obsolete scrap use was found unlikely to limit the production of high-quality steel products. In comparison with a scenario that only considered measure (i) and assuming a 15% real interest rate, CO 2 mitigation cost curves for 2030 showed that the CO 2 mitigation costs were below US$ 2010 20/t-CO 2 for measure (ii) and around US$ 2010 110/t-CO 2 for measure (iii). Compared to the marginal abatement costs calculated for 2030 to reduce Japan's GHG emissions by 20%–25% from 1990 levels (about US$ 2010 67–640/t-CO 2 ) reported in the literature, all three measures may become economically viable. The increased use of obsolete scrap in the BF-BOF route can become an interesting option for Japanese steelmakers to stimulate the steel scrap market and achieve economical global CO 2 emissions reductions while maintaining international competitiveness in the midterm future. [ABSTRACT FROM AUTHOR]

Environmental noise can adversely affect human health and well-being. It is typically quantified by evaluation through strategic noise mapping, indicating the sound level; however, most of the local residents of an area do not understand the significance of sound level because they are unfamiliar with the relationship between sound level and health risks. Therefore, dissemination of information regarding the local health risks due to noise exposure is extremely important for effective risk communication. This study aims to transform noise maps into risk maps indicating the health risks to improve the risk communication with local residents. To this end, we developed a noise map, applied the exposure–response functions established by the World Health Organisation Regional Office for Europe to convert the sound levels into health risks and, finally, obtained the geospatial distribution of the health risks: health risk maps. Subsequently, we investigated the health risks due to road traffic noise in Sapporo City, Japan. High annoyance, high sleep disturbance, and ischaemic heart disease (IHD) were the observable health outcomes. In contrast to ordinary noise maps indicating the sound level, the health risk maps exhibited the percentages of highly annoyed and highly sleep-disturbed people and revealed the prevalence and mortality rates for IHD. In addition, the total number of residents affected by noise exposure was obtained using these health risk maps. To our knowledge, this is the first study showing health risks due to the road traffic noise of an entire city in Japan. The health risk maps can help the public realise the significant impact noise exposure has on general health. Furthermore, they can be utilised to demonstrate the potential reduction of the risks in future noise mitigation strategies. [ABSTRACT FROM AUTHOR]

Spatial patterns of the oxidation–reduction potential (Eh) of soil, water level and chemistry were examined in the fen area of the Tohfutsu mire, northern Japan, where horse pasturage has been carried out throughout the growing season every year. The fen vegetation consisted mosaically of communities mono- or codominated by Eleocharis kamtschatica, Iris setosa and Carex lyngbyei . The highest concentration of total dissolved nitrogen of soil water was observed in the dwarf community dominated by E. kamtschatica with smaller biomass, whereas the nutrient level was lower in the community monodominated by C. lyngbyei with larger biomass. Principal component analysis denoted well that Eh, N, K, and pH contributed to the differentiation of these communities significantly. During the growing season that was investigated, the highest nitrogen concentration was observed in midsummer, when plants are expected to absorb nutrients intensely, indicating that the supply of dissolved nitrogen far exceeded the nutrient uptake of plants. Multiple habitats with reduced soil were formed by submergence and by an excess of nitrogen due to pasturage, and the soil reduction indirectly inhibited the incursion of species with large biomass at such sites. It was demonstrated that soil Eh contributed to the anomalous pattern of vegetation where the supply of available nitrogen exceeds the uptake by plants. [ABSTRACT FROM AUTHOR]

The equipment energy efficiency improvement policy (EEEIP) is one of the important measures of energy conservation and emission reduction in various countries. However, due to the simultaneous implementation of variety policies, the effect of the single policy cannot be clearly reflected. In this paper, a method of identification and evaluation of EEEIP was proposed, and the application was verified by analyzing the example of EEEIP in Japan (Top Runner policy, TRP). Firstly, through the factor decomposition model, this paper studied the energy conservation and emission reduction potential of this policy area in Japan. Then, the TRP was identified by using moving windows and correlation analysis, and the impact of specific equipment in TRP was analyzed. Finally, through the calculation of the rebound effect of the carbon footprint (REC), this paper analyzed the energy consumption and emission reduction effects of TRP in the short-term and whole life cycle. It showed that the policy has a good effect in tertiary industry and transportation, while the effect in residential is poor. For life cycle, the TRP of air conditioning and passenger car can bring better CO2 emission reduction effect, but the emission reduction effect of lighting is basically offset. [ABSTRACT FROM AUTHOR]

In this study, a novel system named the third-generation wireless in-wheel motor (WIWM-3), which has a dynamic wireless power transfer (DWPT) system, is developed. It can extend the cruise range, which is one of the key specifications of electric vehicles. DWPT also reduces CO2 emission as the driving resistance is reduced due to light weight of the batteries. In this study, CO2 emission by an internal combustion vehicle, a long range drivable electric vehicle with the same cruise range, and an electric vehicle with WIWM-3 equipped with the DWPT system are analyzed using actual measurement data and calculated data based on actual measurement or specification data. A WPT system with WIWM-3 achieves 92.5% DC-to-DC efficiency as indicated by an actual measurement at the nominal position. Thus, the electric vehicle with DWPT can reduce up to 62% of CO2 emission in internal combustion vehicles, and the long-range drivable vehicle emits 17% more CO2 than the electric vehicle with DWPT. Moreover, it is expected that by 2050, electric vehicles with DWPT will reduce CO2 emissions from internal combustion vehicles by 95% in Japan. DWPT systems make electric vehicles more sustainable and, hence, more acceptable for consumers. [ABSTRACT FROM AUTHOR]