Desirable Diet to Lower the Japanese Nitrogen Footprint: Analysis of the Saitama Prefecture Nutrition Survey 2017.

With the growing interest in healthy and sustainable diets, studying diets with high nutritional quality and low environmental impact is needed. We focused on the nitrogen footprint (NFP)-an indicator of reactive nitrogen loss that causes various environmental impacts-of Japanese diets using individual dietary records and identified the characteristics of lower NFP diets. This cross-sectional study was a secondary data analysis from the 2017 Saitama Prefecture Nutrition Survey. We analyzed the data obtained from a questionnaire and two-day dietary records of 479 men and women aged 30-65 y who had no misreported or missing data. The NFP was calculated using the virtual nitrogen factors of each food group reported in a previous study. After assessing NFP and its contributions, we conducted sub-group analysis for participants with appropriate weight status and adequate protein intake, classifying them into three groups according to tertiles of NFP to protein ratio. We compared NFP, its contributions, and nutrient intake between the groups. The total NFP (kg N/y) was 18.2±5.0 in men and 16.1±4.4 in women. In the sub-group analysis, total NFPs of the lower NFP group were 16.5±3.1 in men and 13.6±2.8 in women. Cereals, pulses, and fish and seafood contributed more significantly to the total NFP in the lower NFP group than in the higher NFP group. These results suggest that adequate protein intake from a variety of food sources is required to lower the environmental impact of adequate diets.

Comparison of spatial and temporal changes in riverine nitrate concentration from terrestrial basins to the sea between the 1980s and the 2000s in Japan: Impact of recent demographic shifts.

Nitrogen (N) is an essential nutrient but may become a pollution source in the environment when the N concentration exceeds a certain threshold for humans and nature. Nitrate is a major N species in river water with notable spatial and temporal variations under the influences of natural factors and anthropogenic N inputs. We analyzed the relationship between riverine N (focusing on nitrate) concentration and various factors (land use, climate, basin topography, atmospheric N deposition, agricultural N sources and human-derived N) in 104 rivers located throughout the Japanese Archipelago except small remote islands. We aimed to better understand processes and mechanisms to explain the spatial and temporal changes in riverine nitrate concentration. A publicly available river water quality database observed in the 1980s (1980-1989) and 2000s (2000-2009) was used. This study is the first to evaluate the long-term scale of 20 years in the latter half of Japan's economic growth period at the national level. A geographic information system (GIS) was employed to determine average values of each variable collected from multiple sources of statistical data. We then performed regression analysis and structural equation modeling (SEM) for each period. The forestland area influenced by the basin topography, climate (i.e., air temperature) and other land uses (i.e., farmland and urban area) played a major role in decreasing nitrate concentrations in both the 1980s and 2000s. Atmospheric N deposition (especially N oxides) and agricultural N sources (fertilizer and manure) were also significant variables regarding the spatial variations in riverine nitrate concentrations. The SEM results suggested that human-derived N (via food consumption) intensified by demographic shifts during the 2000s increased riverine nitrate concentrations over other variables within the context of spatial variation. These findings facilitate better decision making regarding land use, agricultural practices, pollution control and individual behaviors toward a sustainable society.

Changes in the nitrogen footprint of green tea consumption in Japan from 1965 to 2016.

Heavy application of nitrogen (N) in tea (Camellia sinensis (L.)) plantations causes various environmental problems. To date, studies on N flows have been limited to the tea plantation level, but the crucial drivers of N flows are consumers, not farmers. Therefore, this study aimed to evaluate changes in N flows concerning green tea production and consumption in Japan from 1965 to 2016 using the N footprint concept. Nitrogen use efficiency (NUE), virtual N factor (VNF), and N footprint were calculated using a Monte Carlo method from data for 17 parameters obtained from the literature review. The VNF for green tea in Japan decreased from 54.5 in 1991 to 30.8 in 2016. The major reasons for this decrease were (i) increased NUE in plantations and (ii) increased consumption of ready-to-drink (RTD) tea, matcha, and powdered tea, indicating an increase in the efficiency of N intake from green tea by consumers. The decrease in VNF resulted in a reduction in N footprint from green tea consumption. However, the decline in N footprint since 2004 is not derived from the decrease in VNF but mainly from reduced green tea consumption. A sensitivity analysis revealed that the parameters associated with the extraction efficiency of tea, powdered tea production, and the amount of tea leaves used for RTD production strongly affected VNF estimation.

Combined effects of oxygen and temperature on nitrogen removal in a nitrate-rich ex-paddy wetland.

Temperature is generally considered to be the primary factor controlling the nitrogen removal rate (NR) in nitrate (NO3-)-rich submerged sediments. Temperature stimulates both sediment oxygen (O2) respiration, to create anaerobic conditions, and microbial photosynthetic activity, to provide the organic carbon required for denitrification and expand the uppermost aerobic layer, i.e., the O2 penetration depth (OPD). The OPD serves as a diffusion barrier for NO3- to the underlying anaerobic layer for denitrification. The complex effects of O2 and temperature on the NR are unclear under field conditions with a wide range of temperatures and O2 suppliers. This study aimed to determine the combined effects of O2 and temperature on the NR in an NO3--rich, riparian ex-paddy wetland ("yatsu" environment) under long-term bare soil conditions. We used three years of field monitoring with occasional O2 microprofile measurements from undisturbed submerged soil cores. We observed vertical supersaturated O2 concentration plateaus up to 4.2 mm depth, which confirmed the presence of underground O2 producers, i.e., photosynthetic microorganisms forming habitat in the soil, and very large OPDs of up to 42.9 mm. A multiple regression analysis showed that temperature and dissolved O2 concentration in the flooded water were the key positive and negative influences, respectively, on the NR (332 kg N ha-1 year-1 on average), in association with the total N input. Microbial photosynthesis appeared to remain active regardless of the season, providing O2 to increase OPD and partly suppress the NR; however, photosynthesis has increased the soil C content and appears to have positively contributed to a sustained NR during the 20 years of bare soil conditions. Our results suggest that temporal no vegetation-shade (bare soil) conditions with periodic weed cutting is recommended to effectively remove N from the watershed, while maintaining high temperatures and soil organic C in yatsu environments.

Procedure for rapid determination of δ15N and δ18O values of nitrate: development and application to an irrigated rice paddy watershed.

The dual isotope approach using the stable isotope ratios of nitrate nitrogen (δ(15)N(NO3)) and oxygen (δ(18)O(NO3)) is a strong tool for identifying the history of nitrate in various environments. Basically, a rapid procedure for determining δ(15)N(NO3) and δ(18)O(NO3) values is required to analyze many more samples quickly and thus save on the operational costs of isotope-ratio mass spectrometry (IRMS). We developed a new rapid procedure to save time by pre-treating consecutive samples of nitrous oxide microbially converted from nitrate before IRMS determination. By controlling two six-port valves of the pre-treatment system separately, IRMS determination of the current sample and backflush during the next sample pre-treatment period could be conducted simultaneously. A set of 89 samples was analyzed precisely during a 25-h continuous run (17 min per sample), giving the fastest reported processing time, and simultaneously reducing liquid nitrogen and carrier helium gas consumption by 35%. Application of the procedure to an irrigated rice paddy watershed suggested that nitrate concentrations in river waters decreased in a downstream direction, mainly because of the mixing of nitrate from different sources, without distinct evidence of denitrification. Our procedure should help with more detailed studies of nitrate formation processes in watersheds.

Denitrification during vertical upwelling at an alluvium-diluvium interface below the upland perimeter of a riparian paddy.

Denitrification hotspots in riparian aquifers often develop in a relatively narrow zone at the upland-riparian interface, where nitrate-rich ground water of upland origin interacts with available soil organic carbon. In riparian paddy fields, denitrification in the aquifer has received less attention than that in the surface water and soil. This study aimed to determine the in situ activity of the denitrification hotspot formed at the vertical interface between the organic alluvial and the nitrate-rich diluvial aquifers around the depth of 2.0 m below the upland perimeter of riparian paddy, where vertical upwelling dominates the ground water recharge. The mass balances of water and solutes were approximately calculated from the one-dimensional vertical pressure head and water quality profiles with help of the stable isotopes analyses of water. The confined ground water of adjacent diluvial upland origin, with a high nitrate concentration of 1.72+/-0.42 mmol L(-1), mixed with the nitrate-deficient unconfined ground water at the alluvium-diluvium interface, and 63% of nitrate was removed by denitrification at a rate of 33 mg N m(-2) d(-1) and a nitrogen isotope fractionation factor of 0.988. The increase in bicarbonate concentration with the decrease in nitrate concentration suggested a heterotrophic denitrification with a stoichiometry of C:N=5:4. These results are the first to demonstrate the quantitative importance of denitrification in the aquifer below a riparian paddy in the removal of nitrate from the ground water of upland origin and emphasize the necessity of including this process in models for predicting watershed-scale surface water and ground water qualities.