Historical development, impact mechanism and future trends of nitrogen footprint in Wuxi City, China.

Human activities have changed the biogeochemical cycle of nitrogen, leading to a large amount of reactive nitrogen (Nr) into the environment, aggravating a series of environmental problems, affecting human and ecosystem health. Cities are the core areas driving nitrogen cycling in terrestrial ecosystems, however, there are numerous influencing factors and their contributions are unclear. The nitrogen footprint is an important index to understand the impact of human activities on the environment, however, the calculation of urban nitrogen footprint needs a simplified and accurate system method. Here we use a nitrogen footprint calculation model at the urban system level based on system nitrogen balance, and a multi-factor extended STIRPAT (stochastic impact by regression on population, affluence, and technology) model suitable for analyzing the impact mechanism of nitrogen footprint to estimate nitrogen footprint of Wuxi City during 1990-2050. We find that: (1) from 1990 to 2020, the total nitrogen footprint of Wuxi City was in an increasing trend, but the per capita nitrogen footprint was in a decreasing trend. The per capita nitrogen footprint of 22.36 kg capita-1 in 2020 was at a lower level globally. (2) Nr discharge from fossil fuel combustion and Haber-Bosch nitrogen fixation accounted for the main proportion of nitrogen footprint. (3) Dietary choice (Ad), GDP per capita (Ag), urbanization rate (Au), population (P), and fossil energy productivity (Te) were the key factors contributing to the increase of the nitrogen footprint, which resulted in an annual increase of 1.39 %. While nitrogen footprint productivity (Tn), nitrogen use efficiency in crop farming (Tc), and nitrogen use efficiency in animal breeding (Ta) were the key inhibit factors that inhibit the increase of nitrogen footprint, and these factors slow down the annual growth rate of nitrogen footprint by 0.39 %. (4) The continuous growth of nitrogen footprint in the baseline and population growth scenarios will bring more environmental problems and greater environmental governance pressure to Wuxi City, while the sustainable scenario that includes comprehensive means such as economic adaptation and technological improvement is more in line with the requirements of high-quality development in China. Several mitigation measures are then proposed by considering Wuxi's realities from both key impact factors and potential for nitrogen footprint reduction in different scenarios, which can provide valuable policy insights to other cities, especially lakeside cities to mitigate nitrogen footprint.

Scenario analysis of phosphorus flow in food production and consumption system in the Mwanza region, Tanzania.

Since the mineral, phosphorus (P), has dual properties of being limited resources for use, and being a pollutant for studying sustainable management of anthropogenic P flows in wetlands and soils, currently P receives the highest interests among researchers around the world. This study has successfully mapped P flows for a reference year (2017) and a future year (2030) using different scenarios of food production and consumption system (hereafter 'system') in the Mwanza region (Tanzania). The results showed that the total P input and output for 2017 alone were 9770 t and 7989 t, respectively. However, as high as 1781 tP accumulated in the system and the potentially recyclable P found, is yet to be recovered due to economic reasons and the lack of market. The main anthropogenic P input to the system occurred via imported feed, fertilizer, and crop food, accounting for about 99.72 % of the total input flow. The output was comprised of animal products exported with 3428 tP, and various P-contained wastes which were lost to water bodies with 4561tP. Analysis of the 2030 scenario showed that setting P management objectives from different perspectives such as the total P budget balance, potential recyclable P, and P emission, can help develop differentially preferred management strategies and measures in the Mwanza region. The combination of diet change, precision feeding, and integrated waste management practices presents the best prospects for decreasing P budget and losses, and the amount of P that can be potentially recovered from the system. We propose a package of integrated P management measures for the Mwanza region. Given the similarity of regional socio-economic development background around the Lake Victoria basin, the model can be used to guide the study of anthropogenic P flow analysis in other areas along the shore of Lake Victoria (Africa).

Sustainable nitrogen management strategies based on nitrogen flow in urban human system.

Urban nitrogen discharge has become an important factor leading to urban water environment deterioration, water crisis, and frequent air pollution. Human consumption is the driving force of nitrogen flow and the core of urban nitrogen research. Based on the process of nitrogen flow in the urban human system, combined with the relevant United Nations Sustainable Development Goals (SDGs) and taking Dar es Salaam as an example, we established a generic analytical framework for sustainable nitrogen management and put forward the strategies of sustainable nitrogen management in the urban human system. The main conclusions are as follows. (1) Waste nitrogen discharge affected the environment quality. 5286 t of N (5095 t of N-NH3, 86 t of N-N2O, and 105 t of N-NOx) was emitted into the atmosphere that affected air quality. 9304 t of N was discharged into surface water and 203 t of N was leaked, which had a negative impact on the prevention and control of surface water pollution. And 8334 t of N pose a potential threat to environmental quality. (2) Nitrogen management in Dar es Salaam faced huge challenges. From the perspective of nitrogen flow of the urban human system, the diet structure and household energy structure need to be optimized, and food waste is serious. Sewage treatment and garbage treatment are seriously insufficient, and the corresponding technologies are backward. In order to solve the existing problems of nitrogen flow in the urban human system and include sustainable nitrogen management under future challenges of growing population and economy, we proposed strategies including healthy diet guidance, reducing food waste, detailed assessment of household nitrogen accumulation, transformation of household energy structure to low nitrogen emission energy, increasing nitrogen recycling ratio, and infrastructure improvement of sewage treatment and garbage treatment, hence contributing to the achievement of related SDGs.

Examining key impact factors of energy-related carbon emissions in 66 Belt and Road Initiative countries.

Climate change with global warming as the main feature associated with fossil energy use has been recognized as a threat to public health and welfare. Energy-related carbon emission reduction is a more serious challenge for BRI (Belt and Road Initiative) countries with rapid economic development. Examining key impact factors is necessary and helpful. This paper is the first study providing detailed country-by-country analyses aiming to identify the key drivers and inhibitors of energy-related carbon emission in 66 BRI countries with more systematic impact factors. The results show that: (1) Economic development (A), population (Ps), urbanization (Pu), and industrialization (Ss) are the key drivers for 52%, 26%, 11%, and 6% countries of BRI countries. Technological progress (T), energy consumption structure (E), and tertiary industry proportion (St) serve as key inhibitors for 65%, 17%, and 8% countries of BRI countries. (2) Different carbon emission reduction strategies should be formed on different geographical scales. At the international level, carbon emission reduction consensus should be reached and carbon emission reduction targets should be formulated. At the regional level of the Belt and Road Initiative, a carbon emission reduction cooperation fund should be established, and carbon emission reduction technologies and measures should be exchanged and data should be shared to promote the green development of the Belt and Road. At the national level, there should be carbon emission reduction policies reflecting national characteristics. At the local level, there should be specific carbon reduction measures in line with local conditions.

Reactive nitrogen budgets in human-nature coupling system in lakeside area with insufficient data - A case study of Mwanza, Tanzania.

Nitrogen (N) is an essential nutrient element for life, and also a major element involved in the composition of greenhouse gases, surface water pollutants, air pollutants, etc. Quantifying and evaluating the nitrogen budget of a region is very important for effectively controlling the nitrogen discharge and scientifically managing the nitrogen cycle. In this paper, the urban Rural Complex N Cycling (URCNC) model was used to analyze the nitrogen budget of Mwanza region, a typical lakeside area with insufficient data, and the nitrogen flow process of livestock subsystem, cropland subsystem, human subsystem and landfill subsystem was clearly described and the nitrogen input sources of atmospheric subsystem and surface water subsystem were clarified. And the results demonstrated: (1) the cropland subsystem was the subsystem with the largest nitrogen flux, and the input, output and accumulation of nitrogen were 33,116 t of N, 31,925 t of N and 1191 t of N, respectively. Livestock subsystem was the second largest subsystem of nitrogen flux, and the input, output and accumulation of nitrogen were 31,013 t, 30,183 t and 830 t, respectively. The nitrogen flux of the human subsystem was also large, and the nitrogen input, output and accumulation were 17,905, 17,125 and 780 t, respectively. The nitrogen input, output and accumulation of the landfill subsystem were 3700 t, 770 t and 2930 t, respectively. (2) 8093 t of N, 6864 t of N, 3959 t of N, and 758 t of N emitted into the atmospheric subsystem from the livestock subsystem, cropland subsystem, human subsystem, and landfill subsystem, respectively. (3) The total Nr input of surface water subsystem increased from 18,545 t of N in 2010 to 20,174 t of N in 2020, with an increase of 8.78 % in the past decade. It was estimated that by 2030, the total Nr input of the surface water subsystem would reach 24,946 t of N with an increase of 23.65 % compared with 2020. The livestock subsystem was the largest source, the cropland subsystem was the second largest source and human subsystem was an important source. (4) Population growth, economic development and urbanization are the main nitrogen driving factor. (5) Technology and policy together have important contributions to the reduction of nitrogen pollution in surface water.

Influencing mechanism of non-CO2 greenhouse gas emissions and mitigation strategies of livestock sector in developed regions of eastern China: a case study of Jiangsu province.

The livestock sector not only provides people with meat, eggs, milk, and other nutrients but also causes a large number of non-CO2 greenhouse gas emissions. It is urgent to explore the influence mechanism of non-CO2 greenhouse gas emission from the livestock sector and formulate effective mitigation strategies. Taking Jiangsu province as an example, we analyzed the influencing factors of non-CO2 greenhouse gas emissions from the livestock sector based on sources and modified the STIRPAT (stochastic impact by regression on population, affluence, and technology) model, proposed the directions, designed the generally circular path, and determined the focus of non-CO2 greenhouse gas emissions reduction from the livestock sector. The results demonstrated: (1) the top priority of emission reduction of livestock sector in Jiangsu province was the reasonable treatment of manure produced by livestock (non-CO2 greenhouse gas emissions from manure had accounted for more than 60% of the total emissions from the livestock sector since 2007.), and the core was pig manure management (the CH4 and N2O emissions from pig manure accounted for more than 90 and 50% of the total CH4 and N2O emissions from all livestock manure, respectively). (2) The decrease of the agricultural population, the increase of livestock output value per capita of the agricultural population, and the improvement of livestock carbon productivity all reduced non-CO2 greenhouse gas emissions of the livestock sector. For every 1% decrease in agricultural population, for every 1% increase in livestock carbon productivity and livestock output value per capita of the agricultural population, non-CO2 greenhouse gas emissions from the livestock sector would be reduced by 0.0859%, 0.1748%, and 0.0400%, respectively. (3) To construct and improve the low carbon industrial chain of the livestock sector, to promote low carbon technology research and development and introduction are two focuses for non-CO2 greenhouse gas emission reduction in the livestock sector. The research can provide a basis for non-CO2 greenhouse gas emissions reduction from the livestock sector in China, especially in the developed eastern regions.

Spatial differentiation identification of influencing factors of agricultural carbon productivity at city level in Taihu lake basin, China.

Improving carbon productivity is the main way to deal with climate change under China's targets for carbon emissions to peak by 2030 and carbon neutrality by 2060. This study identified the spatial differentiation of influencing factors of agricultural carbon productivity at the city level in Taihu lake basin, and formed differentiated agricultural management strategies. The results show that: (1) Spatial differentiation of agricultural carbon productivity is obvious at city level. It can be divided into three echelons: the first echelon is Shanghai and Hangzhou (agricultural carbon productivity≥10,000 Yuan/t in 2019 with a growth rate ≥ 600% compared with 1992), the second echelon is Suzhou, Wuxi and Changzhou (9000 Yuan/t ≤ agricultural carbon productivity<10,000 Yuan/t in 2019 with 381% ≤ growth rate < 600% compared with 1992), and the third echelon is Zhenjiang, Huzhou and Jiaxing (agricultural carbon productivity<9000 Yuan/t in 2019 or a growth rate < 381% compared with 1992). (2) There is a synergetic evolution law between agricultural carbon productivity and agricultural economy, that is, agricultural economic development level is the first factor affecting agricultural carbon productivity, whether in the whole basin or in the city level. (3) There are significant differences in the influencing factors of agricultural carbon productivity at the city level. Finally, according to the spatial differentiation characteristics of influencing factors of agricultural carbon productivity at the city level in Taihu lake basin, we put forward different emphases of agricultural development in different cities.

Selecting low-carbon technologies and measures for high agricultural carbon productivity in Taihu Lake Basin, China.

In this paper, Delphi method was used to evaluate the low-carbon technologies and measures for high agricultural carbon productivity in Taihu Lake Basin. We established the selecting process and standards and obtained the final list of low-carbon technologies and management measures of high agricultural carbon productivity in Taihu Lake Basin: (1) the initial list of low-carbon technologies and measures of planting industry included 19 items, of which 10 items were included in the final list. The 10 technologies and measures included in the final list were reducing fertilizers, mixed use of organic fertilizer and chemical fertilizer, soil testing and formulated fertilization, application of controlled release fertilizer, deep application of fertilizers, cultivation of new variety, extension of conservation tillage, extension of midseason/alternate drainage, paddy-upland rotation (rice-rape/rice-wheat), and reducing pesticides. (2) The initial list of low-carbon technologies and measures of animal husbandry included 11 items, of which 4 items were included in the final list. The 4 technologies and measures included in the final list were reasonable ratio of concentrate to roughage in ration, treatment straw feed by silage/ammoniation/shredding, application of nutritive cube/dietary additives, and promotion of high productivity livestock breeds. (3) Low-carbon agricultural technologies and management measures need to be adapted to local conditions according to different geographical, climatic, and socio-economic development characteristics, and it is necessary to form a regionally differentiated system of low-carbon agricultural technologies and management measures. The final list of low-carbon technologies and management measures of high agricultural carbon productivity can provide decision-making reference for the formulation of agricultural carbon emission reduction technology system and low-carbon agricultural development planning of provinces and cities in Taihu Lake Basin. At the same time, the final list can be considered a priority for the promotion of agricultural low-carbon technologies and measures in China and even in the world.

Analysis of the influencing factors of energy-related carbon emissions in Kazakhstan at different stages.

This study analyzes Kazakhstan's influencing factors of energy-related carbon emissions in different stages, and the study period (1992-2014) was divided into four stages by using the logarithmic mean Divisia index (LMDI) method. In the low efficiency and high output stage, Kazakhstan had the most energy-related carbon emissions. The total energy-related carbon emissions might be positive or negative in the high efficiency and high output stage and the low efficiency and low output stage, and this was mainly determined by the energy intensity effect or the economic output effect. Different influencing factors had different effects in the different stages from 1992 to 2014. The economic output effect was the first contributor for promoting energy-related carbon emissions, and the energy intensity factor was the first contributor for suppressing energy-related carbon emissions from 1992 to 2014. Finally, policy recommendations in terms of the main influencing factors are put forward, including the low-carbon economic development mode transformation, technological innovation, and renewable energy development.

Extended STIRPAT model-based driving factor analysis of energy-related CO2 emissions in Kazakhstan.

Extended stochastic impact by regression on population, affluence, and technology model incorporating ridge regression was used to analyze the driving mechanism of energy-related CO2 emissions in Kazakhstan during 1992-2014. The research period was divided into two stages based on GDP of Kazakhstan in 1991 (85.70 × 109 dollars), the first stage (1992-2002), GDP < 85.70 × 109 dollars, the stage of economic recovery; the second stage (2003-2014), GDP > 85.70 × 109 dollars, the stable economic development stage. The results demonstrated that (1) population scale and the technological improvement were the dominant contributors to promote the growth of the CO2 emissions during 1992-2014 in Kazakhstan. (2) Economic growth and industrialization played more positive effect on the increase of the CO2 emissions in the stable economic development stage (2003-2014) than those in the stage of economic recovery (1992-2002). The proportion of the tertiary industry, the trade openness, and foreign direct investment were transformed from negative factors into positive factors in the stable economic development stage (2003-2014). (3) Due to the over-urbanization of Kazakhstan before the independence, the level of urbanization continued to decline, urbanization was the first factor to curb CO2 emissions during 1992-2014. Finally, some policy recommendations are put forward to reduce energy-related carbon emissions.

Changes in agricultural carbon emissions and factors that influence agricultural carbon emissions based on different stages in Xinjiang, China.

Xinjiang's agricultural carbon emissions showed three stages of change, i.e., continued to rise, declined and continued to rise, during 1991-2014. The agriculture belonged to the "low emissions and high efficiency" agriculture category, with a lower agricultural carbon emission intensity. By using the logarithmic mean divisia index decomposition method, agricultural carbon emissions were decomposed into an efficiency factor, a structure factor, an economy factor, and a labour factor. We divided the study period into five stages based on the changes in efficiency factor and economy factor. Xinjiang showed different agricultural carbon emission characteristics at different stages. The degree of impact on agricultural carbon emissions at these stages depended on the combined effect of planting-animal husbandry carbon intensity and agricultural labour productivity. The economy factor was the critical factor to promote the increase in agricultural carbon emissions, while the main inhibiting factor for agricultural carbon emissions was the efficiency factor. The labour factor became more and more obvious in increasing agricultural carbon emissions. Finally, we discuss policy recommendations in terms of the main factors, including the development of agricultural science and technology (S&T), the establishment of three major mechanisms and transfer of rural labour in ethnic areas.