Kei Nishida

The present study investigates nitrogen (N) flows within the food system of Yamanashi Prefecture from 2000 to 2015, by longitudinally integrating Input–Output analyses with N flow models. By unveiling detailed N flows specifically in the food manufacturing sector (food processing, distribution, and food service), this study aims to analyse the recyclability of N losses quantitatively. Results showed approximately 60% of the total N input resulted in N loss. The N losses can be classified into highly recyclable nitrogen (high-RAN: 11%), low-recyclable nitrogen (low-RAN: 16%) and non-recyclable nitrogen (non-RAN: 73%). A comparative analysis was performed with three scenarios according to the Green Food System Strategy: a control scenario of 2050, Scenario l targeting chemical fertilizer reduction, and Scenario 2 targeting chemical fertilizer reduction and increased feed self-sufficiency. Compared to the control, both Scenario 1 and Scenario 2 demonstrated improvements in N recycling efficiencies by 4.9% and 15.0%, respectively. Notably, the Scenario 2, which separately reutilised high-RAN and low-RAN, expanded the N demand for recycling, achieving a 6.4% enhanced N loss reduction compared to the Scenario 1. In conclusion, this study provides the suggestion that the sophistication of the reutilisation network can promote the reduction of N losses.

An understanding of nitrogen processes in a paddy field, characterised by large water flux for irrigation and outflows under continuous irrigation, is required to manage adequate nitrogen inputs and outputs. This study identifies the effect of large water flux, especially high infiltration rate, on nitrogen processes in a paddy field under continuous irrigation. The developed nitrogen process model in this study was applied to two paddy fields having different infiltration rates (216 and 106 mm day^− 1 on average), and simulated physicochemical and biological nitrogen processes in ponded water, soil water and soil, including whole water flows as well as organic, and inorganic nitrogen forms. In each field, irrigation was found to be the major nitrogen input (153.2–461.5 kg N ha^− 1 year^− 1), and nitrogen outflow (65.2–284.3 kg N ha^− 1 year^− 1) found to be smaller than the input from irrigation. The irrigation water was primarily contaminated by dissolved organic nitrogen (DON) and nitrate. Nitrogen transportation from ponded water to soil water was four times greater under high infiltration condition than under low infiltration condition. High nitrogen transport to the soil layer increased air emission via denitrification and decreased outflows. In particular, DON and ammonium transported to soil water are sources of nitrite and nitrate, and denitrification was five times higher under high infiltration than low infiltration. The results of this study imply that paddy fields with high infiltration rates have a greater possibility of nitrogen removal from paddy water, rather than being a pollutant source for the water environment.

In regions suffering from water scarcity, residents commonly employ several coping strategies such as the use of multiple water sources, water storage and water sharing and borrowing. This study applies a hierarchical linear regression model to investigate the physical (i.e. water source and supply time) and non-physical (i.e. number of families, wealth status, education for household head, house ownership, water treatment and community involvement) factors associated with individual water consumption throughout the Kathmandu Valley, Nepal. During the baseline period (dry season before the 2015 Gorkha earthquake), the average water consumption was 91 litre/capita/day (LPCD) but there was a regional disparity in water consumption, ranging from 16 to 158 LPCD. The statistical analysis indicated that households using many water sources consumed more water regardless of the supply area even in an emergency. In addition, households with many family members used less water per person. During emergencies, households participating in the local community were found to consume more water than households not participating in the community, especially when the water being used was managed by the community.

The efficacy of a fine bubble (FB) diffuser in enhancing the performance of an attached biofilm hydrogenotrophic denitrification (HD) reactor was evaluated. HD reactors equipped with an FB diffuser (FB reactor) and an air stone (AS) diffuser that produced ordinary bubbles (AS reactor) were operated in parallel at different hydraulic retention times (HRTs) in a synthetic groundwater treatment experiment. A reduction in H₂consumption of approximately 77% was achieved using the FB diffuser to reach a gas-liquid mass transfer coefficient similar to that of the AS diffuser. The high gas dissolution efficiency of the FB diffuser resulted in an effective nitrogen removal rate (NRR) enhancement, requiring less H₂supply. The highest value of NRR at 53.0±9.8 g-N/m³/d was obtained in the FB reactor at a minimum HRT of 3 h, which was two-fold higher than the corresponding value from the AS reactor. The FB reactor also had the lowest requirement of H₂for denitrification reaching 0.1 m³-H₂/g-N in this condition, which was ten-fold lower than that in the AS reactor. Furthermore, the suspended sludge concentration in the FB reactor was lower than that in the AS reactor, indicating that the application of the FB diffuser can minimize excess suspended sludge accumulation inside the HD reactor. Microbial community analysis showed the predominance ofThaueraspp. reaching a relative abundance of 15.7–27.3% in the FB reactor, suggesting a contribution to the HD. This finding can provide insight into the application of the FB diffuser for optimizing nitrate-contaminated groundwater treatment technology by HD.

Isotopic tracing technique is one of the most effective methods to identify nitrogen source and fate in aquatic environments. Although dissolved organic nitrogen (DON) is a key component in nitrogen cycles, information on nitrogen stable isotope ratios in DON (δ¹⁵N-DON) is limitedly available for its low recovery through a direct measurement. Indirect measurement is based on mass balance calculations and easy to use with high recovery of DON. However, in theory, the result from mass balance calculation is sensitive to the level of DON content, and its applicability remains to be examined for waters containing a variety of DON content in total dissolved nitrogen (TDN). In this study, we established a protocol for indirect measurement of δ¹⁵N-DON values based on the combination of multiple analytical methods. Precision and accuracy in the measurement were assessed by varying the composition of DON and dissolved inorganic nitrogen, and quantitation thresholds were presented at different acceptable levels. The results illustrated an advantage of the developed protocol possibly applicable to water samples particularly with low DON content that is commonly detected in freshwater. This method is expected to expand the use of isotope tracing techniques for understanding the nitrogen cycle in water environments.

In Nepal, the number of diarrhoea hospitalizations in all ages is seriously high. According to the World Health Organization, diarrheal diseases can be substantially prevented through safe drinking water sources. In the Kathmandu Valley, because of the shortage of piped water, local residents use alternative water sources, such as groundwater, jars and tanker water. However, these alternative water sources can be contaminated. This study aimed to clarify the relationship between diarrhoea risk and the combinations of drinking water sources. A survey using multiple questionnaires on diarrhoea occurrence, water sources and water treatment was conducted three time between 2015 and 2016. The odds ratios (ORs) of developing diarrhoea were significantly high for drinking jar (OR 6.1) and tanker water (OR 8.4) compared with not drinking. The combined drinking of jar and tanker water obtained the 1 log higher OR compared with drinking only piped water. Conversely, drinking groundwater had a low OR, implying that the residents refrained from drinking polluted groundwater. In conclusion, diarrhoea occurrence was related not only to the level of water contamination, but also to a behavioural factor, i.e. people's careful management of the choice of multiple water sources.

Estimation of dissolved organic carbon (DOC) runoff load in forested watershed is important for the assessment of the global carbon cycle as well as for the control of regional water environments. A few process-based models have been proposed to estimate the DOC load to water environments, which assume DOC source in topsoil and transport processes to the river, however, these models exhibited difficulties with the availability of input data and applicability to short time-scale rainfall-runoff processes in the Asian monsoon area. This study presents a new process-based model that consists of two separate systems for determining DOC load enforced by DOC Source Area (DSA) concept. For the runoff system, a semi-distributed hydrological modelling unit (‘modified-TOPMODEL’) was installed, by which surface and subsurface water flows, representing for DSA, were sequentially simulated. For the soil system, a wet-dry cycle was successfully simulated by an advection-diffusion and dissolution formulation as well as seasonal temperature effect. The model is first evaluated upstream (98ha) and downstream (1798ha) in the Mizugaki Watershed, Yamanashi, Japan and then applied for a Miuchi (203ha) watershed, Aichi, Japan during 2014 to 2018. The results of cumulative DOC load at baseflow and stormflow periods that the model performed well between the simulations and observations for both study sites. Considering the stormflow periods, from 25.2% to 32.0%, and 31.1% of high flows contributed to 50% of the total DOC load at Mizugaki and Miuchi watershed, respectively. Overall, the proposed model successfully simulated DOC load under different geochemical and hydrological condition by capturing the DSA variability.

In the Kathmandu Valley of Nepal, locals depend on multiple water sources due to the limited access to safe water, which is a great global concern regarding its impact on human health. This study aimed to compare the infection risk of diarrhoea from multiple water sources with different concentrations of Escherichia coli among water supply areas and evaluate the impact of changing water sources due to the Gorkha earthquake on the infection risk. The concentration of enteropathogenic E. coli was estimated in samples of piped water, jar water, groundwater, and tanker water, which were collected in the Valley. The volume of each water ingestion was determined based on a questionnaire survey and considering drinking and bathing sources. The highest estimated risk was observed for households drinking groundwater from shallow dug wells, followed by tanker water. The estimated risk implied the regional disparity due to various water sources with different quality. After the earthquake, the ratio of households drinking only jar water increased, and the estimated risk decreased. The damage on piped water supply, the decrease of tanker water availability and the decrease of residents’ trust in groundwater quality presumably enhanced the consumption of jar water despite its high price.

The increasing concentration of nitrogen compounds in the groundwater is of a growing concern in terms of human health and groundwater quality. Although an excess of nitrogen compounds in the groundwater of the Kathmandu Valley has been reported, the seasonal variations of the fate of the nitrogen compounds and their relationships to the subsurface sediments are unknown. In this study, spatially distributed shallow dug well samples were collected during both the dry and wet seasons of 2016, and the nitrogen compound, chloride (Cl⁻), and iron (Fe²⁺) concentrations were analyzed. Two shallow dug wells and one deep tube well were monitored monthly for 2 years. Although NH₄-N concentrations were similar in the clay-dominated areas during both seasons (1 and 0.9 mg-N/L), they were lower in the gravel-dominated areas during wet season (1.8 > 0.6 mg-N/L). The NO₃-N concentration differed depending upon the soil type which increased during the wet season (clay 4.9 < 13.6 mg-N/L and gravel 2.5 < 6.8 mg-N/L). The Fe²⁺ concentration, however, was low during the wet season (clay 2.7 > 0.4 mg/L and gravel 2.8 > 0.3 mg/L). Long-term analysis showed higher fluctuation of nitrogen compounds in the gravel-bearing areas than in the clay-bearing areas.