An approach to identify the spatiotemporal patterns of nitrogen flows in food production and consumption systems within watersheds

A Study on the Willingness of Industrial Ecological Transformation from China’s Zero Waste Cities Perspective

Based on the practice of a circular economy, China officially put forward the goal of building a “Zero Waste City” in 2018 and has formulated a series of measures to promote energy savings and emissions reduction in various sectors among which industry has received key attention due to its long-term high energy consumption and high pollution. The growth of an urban economy cannot be supported by industry, but the high energy consumption and high pollution of industry have become the keys to urban environmental management, and the need for ecological transformation of industry is very urgent. Based on the construction background of zero waste cities in China, this study analyzes the transformation factors of industrial producers’ willingness to make ecological transformation. The factors that influence industrial producers to make ecological transformation are perception of participation, perception of cost, perception of identity, and perception of government intervention. These factors have a positive moderating effect on the adoption of transformation strategies by industrial producers among which the perception of government involvement also plays a mediating role and has an important influence on the promotion of active ecological transformation by industrial producers.

Investigation of the nitrogen flows of the food supply chain in Beijing-Tianjin-Hebei region, China during 1978-2017

Reactive nitrogen (Nr) is an indispensable material for food production. However, it may cause serious environmental problems. The enhancement of nitrogen management in the food supply chain is an effective way to reduce Nr loss and increase Nr use efficiency. While Nr flows in association with the food chain have synergy in a mega-region, in-depth investigations at a cross-regional scale have remained relatively undocumented. This study developed a food-related Nr flow model based on a material flow analysis for the Beijing-Tianjin-Hebei region (BTH) during the years 1978-2017. A multi-regional input-output method was applied to investigate the Nr emissions embodied in the transboundary food supply. The results showed that the total Nr emissions from the food system during the years 1978-2017 in the BTH region increased until 2004 and subsequently decreased gradually. In 2017, Beijing exhibited the lowest Nr emissions per capita (2.3 kg N/cap) and per land use (3089 kg N/km²), while Hebei and Tianjin demonstrated the greatest Nr emissions intensity by capita (13.6 kg N/cap) and by land use (6392 kg N/km²), respectively. While farming and livestock husbandry dominated the regional Nr emissions (i.e., responsible for 90% of the total in 2017), food consumption and waste management have had an increasingly substantial role, as their shared percentage in the total increased by 22% over the study period. Nr emissions resulting from the inner-transboundary food supply chain decreased by 81% between 2012 and 2015 but dramatically increased by 231% between 2015 and 2017. This rebound effect partially resulted from the implementation of coordinated development planning for the BTH region in 2015. This study can facilitate the efficient regulation of regional nitrogen flows and the desired transition of food supply chain.

Nitrogen flow in the food production and consumption system within the Yangtze River Delta city cluster: Influences of cropland and urbanization

Intensive anthropogenic activities associated with the food production and consumption system (FPC) drive massive reactive nitrogen inputs to city clusters resulting in serious nitrogen (N) pollution. We conducted a substance flow analysis to examine N flows in the FPC within the Yangtze River Delta city cluster from 2011 to 2019. The total N input and output showed parabolic downward trends, with decreases from 4008.27 to 3472.57 Gg N yr^-1 and 3518.65 to 3061.29 Gg N yr^-1, respectively; chemical fertilizer (54.7%-57.3%) and N loss (87.1%-90.9%) were the primary components of N input and output, respectively. The decreased total N input was related to reductions in chemical fertilizers and livestock numbers. However, a notable increase in N input to the human subsystem was observed, and urbanization was associated with increased N inputs within the human subsystem via higher amounts of food N consumed per capita and proportions of animal-based food N consumed. Total N loss initially increased then decreased; Nantong, Jiaxing, Shanghai, Yancheng, Taizhou, and Yangzhou were the top six cities in N loss intensity. The proportion of cultivated land area, livestock numbers per unit area, and population density were important factors influencing the spatial heterogeneity of N loss intensity. Twenty-six cities were divided into six groups based on their N loss composition, and various N management strategies were proposed. This study highlights the strong influences of cropland and urbanization on N flows within the FPC, which can be used as a reference for N management at a city cluster scale.

Nitrogen and phosphorus trajectories (1998-2030) under regional development strategy of mainland China

A good understanding of the nutrient cycle under a regional development strategy is crucial for nutrient management decision-making. Quantitatively assessment of nutrient flow under the regional coordinated development strategy in mainland China can provide scientific reference for achieving global high-quality coordinated economic and agricultural development. In this study, the characteristics of nitrogen (N) and phosphorus (P) flows of agricultural systems in mainland China from 1998 to 2030 were quantified using nutrient flows in food chain environment and resource (NUFER) model. The results revealed that national N and P surplus intensity were 50.3 and 18.6 kg·hm^-2 in 2018, respectively, and there is still space for soil nutrient retention. The national input and output of N and P showed a continuous upward trend over the last two decades. Chemical fertilizer application and livestock rearing are the key points for nutrient management in China's agricultural systems. Under the regional development strategy, considerable geographical variation in N and P surplus intensity was observed across the country. From 1998 to 2013, the regional distribution of N and P surplus intensity was in accordance with regional economic characteristics. Areas with higher N and P surplus intensities were mainly in the eastern and central regions. From 2014 to 2018, equal emphasis on ecology and economy in the Yangtze River Economic Belt allowed development without aggravating the deterioration of the N and P surplus in the region. Over the next 10 years, our simulation predicts that future nutrient footprints tend to decrease, and coordinated governance of regional development and agricultural environment protection are the key to regional sustainable development.

Nitrogen cascade in the agriculture-food-environment system of the Yangtze Delta, 1998-2018

The nitrogen (N) cascade in rural areas of Changshu County should be measured and evaluated due to the large increase in anthropogenic disturbances in China's Yangtze Delta. Here, we developed a village-scale N flow model using Changshu County and its towns as a case study. The model included four subsystems and was used to describe the driving forces behind the N cascade from agricultural food production and household consumption to the environment (agriculture-food-environment) system. It was found that from 1998 to 2018 the N input increased from 274.63 to 848.65 kg N ha^-1. The cropland N use efficiency (NUEc) decreased by 10.35%, whereas the livestock feed N use efficiency (NUEa) increased by 51.84%. A relatively lower NUE, with a higher N input, was found in Shajiabang Town, which was attributed to hairy crab farming. Changes in dietary patterns led to the food N cost (FNC) being in the range of 4.59-7.74 kg kg^-1. Over the past two decades, the N losses from the agriculture-food-environment system decreased by 45.40% from 12,436.60 t N yr^-1 (1998). The contribution of the croplands, livestock-breeding, and household consumption to the N losses were 32.44%, 37.78%, and 29.78%, respectively. About 62.83% of the total N losses entered the water environment. Nitrogen emissions from the croplands accounted for 63.21% of the N losses into the atmosphere. Nitrogen oxide (NO_x) emissions accounted for 38.50% of the gas emissions, followed by NH₃ (28.36%) and N₂O (2.81%). The total N losses decreased annually but losses to the water environment increased by 5.10% from 60.16% (1998). The contribution of food production to the total N loss displayed a decreasing trend, while that of food consumption exhibited an increasing trend. Population growth and increased volumes of domestic waste in the Changsu area were the main driving forces for the increased contribution of household food consumption. The significant decline in cropland area and increase in built-up and heavily trafficked areas indicated an overall increase in anthropogenic disturbances, stimulating the N cascade in the Yangtze Delta from 1998 to 2018.

Linking Dietary Patterns to Environmental Degradation: The Spatiotemporal Analysis of Rural Food Nitrogen Footprints in China

Background: China has a large emerging economy that illustrates how dietary patterns can affect food-source nitrogen (N) cycling. The indicator of food nitrogen footprint (NF) reflects the amount of reactive nitrogen (Nr) emissions and impacts of these emissions on the environment. It is a result of food production and consumption to satisfy basic dietary demands of a given population. Different from urban food consumption with improved waste treatment, rural food consumption significantly affects the environment from food production to waste disposal. We therefore, performed a nationwide case study to link dietary patterns to environmental degradation based on rural food NF accounting. Methods: The N-Calculator model was adopted to reveal the spatiotemporal characteristics of food NFs per capita, and regional food NFs related to rural diets in China from 2000 to 2019. Then, food-source Nr emissions to regional environment were quantified based on food NF accounting and relevant inventory of regional Nr emissions. Results: (i) The average annual food NF per-capita in rural regions was lower than that of its national counterpart, but exhibited regional differences, mainly attributed to the dietary role of cereals. (ii) There existed significant spatiotemporal characteristics among regional food NFs that were mainly contributed by plant-derived food consumptions (73%). Sichuan, Henan, Shandong, and Hunan exhibited larger regional food NFs, and Beijing, Shanghai, and Tibet showed a growth in NFs, wherein rural diets were dominated by animal-derived food. (iii) Rural diets affected the environment by the pathways of ammonia and nitrous oxide volatilization processes, as well as Nr loss to water, accounting for a 33, 5, and 62% average of food NFs across regions. (iv) Although current rural dietary patterns suggest reliance on cereal and vegetable consumptions, more animal-derived types of food would be consumed as urbanization continues, especially in developed regions, creating a barrier for further reduction in national food NF. Conclusion: The findings of this study highlight the importance of changing dietary patterns to the human health-environment dilemma. Strategies that include improvements in N recycling rates, adjustments in dietary patterns, and reductions in food wastes could mitigate regional N pollution with rural dietary shifts.

Water-energy-nutrient nexus: Multi-sectoral metabolism analysis and technical path optimization for eco-towns

The multi-sectoral metabolisms of substance and energy in rural areas are complex, whose optimization is the key to realize resource recycling and energy cascade utilization. Through Substance Flow Analysis (SFA), we establish a Multi-sectoral Metabolism Analysis Model specific to rural areas (MMAM-rural), and investigated the multi-sectoral metabolisms of Liujiadian Town in Beijing city. We simulate the water, energy and nutrients (carbon, nitrogen and phosphorus) metabolisms of a total of five sectors (water, waste management, livestock husbandry, forestry, and residential sectors), and identify the key metabolic flows significant for improving regional metabolism performance of Liujiadian Town. For further technical path optimization, we construct an index system made up of resource utilization efficiency, environmental burden of production and recycling efficiency, and adopt Scenario Analysis to evaluate the water-energy-nutrient metabolism performance under multiple technical scenarios different from disposals of agricultural waste, livestock and poultry manure, and domestic waste. Results show that, for agricultural wastes disposal, the combination scenario of edible fungi cultivation, anaerobic fermentation and aerobic composting is optimal. For livestock and poultry manure, all pig manure should be composted after anaerobic fermentation. For domestic wastes, food wastes require anaerobic fermentation and composting for optimization. Our study provides a model to evaluate metabolism performance of water-energy-nutrient nexus in rural areas, and raises solutions for optimization in the process of eco-town construction.

Nitrogen flow patterns in the food system among cities within urban agglomeration: A case study of the Pearl River Delta region

Human activities along the entire food supply-consumption-waste treatment-recycling chain have an essential influence on Nitrogen (N) metabolic features, especially for densely-populated urban agglomeration. A few studies carried out research on detailed analysis and comparison of N flow patterns along the entire food chain among cities, to recognize these influences and accordingly explore effective measures for improving N use efficiencies. In this study, we developed an integrated N flow analysis model to quantify N flows in the food system illustrated by production, processing, consumption, and waste management sectors. Influence of anthropogenic activities on N flow patterns is recognized through comparison among cities and predictions of future scenarios. Using the Pearl River Delta (PRD) region as a case study, we find that (1) in 2016, the annual N import into the production sector in the food system in the PRD region was about 714.5 Gg, among which only 241.6 Gg entered food products. The removal rate of N pollution in all waste stream was about 62.3%, and only 9% of N became resources through reclamation. (2) Among the nine cities in the PRD region, the average amounts of N pollution emission to the air, water, and soil all range from 0.57-5.38 kg cap^-1 yr^-1, showing significant discrepancy among cities. Cities with relatively lower economic development undertake substantial N pollution embedded in their exported agricultural products. (3) Recycling of agricultural waste is the prior N management measure for Zhaoqing, Jiangmen, and Huizhou, while highly urbanized cities should mainly concentrate on recycling of food waste and sewage sludge. We further put forward suggestions such as cross-city resource recycling to realize better N resource recycling and pollution reduction on the whole urban agglomeration scale. This study provides an in-depth example of depicting N flow patterns and identifying proper N management measures for urban agglomerations.

Changes of urban nitrogen metabolism in the Beijing megacity of China, 2000-2016

Rapid growth in metropolitan areas is associated with high nitrogen (N) flows and subsequent environmental and human health consequences. Many studies on the contemporary aspects of urban N metabolism have conducted in recent years, but comprehensive analysis from life cycle perspective is limited. In this study, a detailed quantitative framework for a coupled human-natural N flow model, comprising a full cycle analysis based on the substance flow analysis approach to cover and integrate all specific N flows and stocks associated with N production, consumption and emission, was developed to study the temporal changing patterns of N metabolism in Beijing megacity during 2000-2016. The results show that total N inputs continuously increased from 413.3 to 529.5 Gg N during the study period, primarily attributing to fossil fuel combustion (53%), fertilizer/feed import (19%), and food import (15%). Agriculture subsystem contains the largest N internal flows, and a decreasing trend is exhibited by a widening gap between local production and household consumption, reflecting Beijing's increasing dependence on the external environment. Moreover, N outputs (394.9 Gg in 2016) contribute to upstream air emissions, landfills accumulation and downstream wastewater discharges. Furthermore, driving force analysis demonstrates that population growth has the largest positive effect on N inputs, and a decoupling of N input with GDP growth is identified. Overall, N flows exhibit an inefficient and unsustainable trend, and possible options for optimizing more sustainable situations while simultaneously minimizing negative consequences are discussed. This study provides decision-makers with an integrated view of N management at the city scale.

Recent insights on uncertainties present in integrated catchment water quality modelling

This paper aims to stimulate discussion based on the experiences derived from the QUICS project (Quantifying Uncertainty in Integrated Catchment Studies). First it briefly discusses the current state of knowledge on uncertainties in sub-models of integrated catchment models and the existing frameworks for analysing uncertainty. Furthermore, it compares the relative approaches of both building and calibrating fully integrated models or linking separate sub-models. It also discusses the implications of model linkage on overall uncertainty and how to define an acceptable level of model complexity. This discussion includes, whether we should shift our attention from uncertainties due to linkage, when using linked models, to uncertainties in model structure by necessary simplification or by using more parameters. This discussion attempts to address the question as to whether there is an increase in uncertainty by linking these models or if a compensation effect could take place and that overall uncertainty in key water quality parameters actually decreases. Finally, challenges in the application of uncertainty analysis in integrated catchment water quality modelling, as encountered in this project, are discussed and recommendations for future research areas are highlighted.