Carbon Accounting of Weihe CSA Pilot Demonstration Area in Longjiang Forest Industry

<sec><title>Objective</title> The world is still in a phase of rapid industrialization and urbanization. Excessive carbon emissions has become the primary root cause of various urban or even global environmental problems, further impacting human physiological and psychological health. Cities are the largest sources of carbon emissions and are crucial regions for achieving carbon neutrality goals. Urban blue-green infrastructure (UBGI), comprising natural, semi-natural, or artificial green and blue spaces within cities, is considered as the most important carbon sink space in urban areas and has increasingly attracted widespread attention from researchers. However, there are still many unresolved issues regarding the effectiveness of UBGI in carbon sink enhancement and emission reduction: 1) How is the energy efficiency of carbon sink enhancement and emission reduction measured, and what factors influence it? 2) What are the mechanisms and pathways through which UBGI enhances carbon sink and reduces carbon emission? 3) How can UBGI be regulated to better enhance its effectiveness in carbon sink enhancement and emission reduction? 4) What are the limitations and potential directions for future research? This research aims to address these issues and propose scientifically sound planning strategies for UBGI construction to achieve urban carbon neutrality goals. </sec><sec><title>Methods</title> Through literature synthesis and deduction, this research organizes and analyzes the multi-scale measurement methods for UBGI’s efficiency in carbon sink enhancement and emission reduction, identifies corresponding influencing factors at each scale, and constructs multi-scale planning strategies for UBGI based on the logical framework of “measurement methods–influencing factors – planning strategies”. </sec><sec><title>Results</title> The research proposes UBGI planning strategies across three spatial scales (site, community and urban area), covering three key aspects: Carbon sequestration and sink enhancement, carbon reduction based on temperature reduction (or preservation), and travel-related carbon reduction. Based on current research gaps and planning needs, five major research topics are further identified. This research provides a detailed analysis of the measurement methods and influencing factors of UBGI’s efficiency in carbon sink enhancement and emission reduction from three perspectives: Carbon sequestration and sink enhancement, carbon reduction based on temperature reduction (or preservation), and travel-related carbon reduction. The research finds significant differences in the measurement methods for UBGI’s efficiency in carbon sink enhancement and emission reduction efficiency across different scales. Contradictory results may occur at different scales, and large-scale research often lacks characterization of internal features, leading to unclear mechanisms of influencing factors and obstructing practical planning. Based on the interpretation of UBGI’s mechanisms for carbon sink enhancement and emission reduction at different scales, this research formulates UBGI planning strategies across three spatial scales (site, community, and urban area). These strategies include: 1) At the site scale, for carbon sequestration and sink enhancement – carbon sink at the source, land balance, and ecological design; for emission reduction – symbiosis with buildings and integration into daily life. 2) At the community scale, for carbon sequestration – overall balance of revenue and expenditure, precise positioning, and proper interconnection of the carbon chain; for emission reduction – incorporation of cool islands and co-construction. 3) At the urban area scale, for carbon sequestration – enhancement of ecological space management and establishment of a carbon-safe pattern; for emission reduction – demand-based layout and organic dispersion. Finally, the research proposes five major research topics for the planning of UBGI’s carbon sink enhancement and emission reduction: How to construct unified measurement methods for UBGI’s efficiency in carbon sink enhancement and emission reduction across scales? How to measure UBGI’s efficiency in carbon reduction based on temperature reduction (or preservation) at the site scale? How to integrate the pathways of carbon sink enhancement and emission reduction for a life cycle assessment of UBGI? How to balance UBGI’s carbon sink enhancement and emission reduction with other functions to achieve the optimal layout for comprehensive benefits? How to achieve urban “carbon justice” through UBGI? </sec><sec><title>Conclusion</title> The carbon sink pathway of the strategy framework requires “carbon sink at the source – precise positioning – safe pattern”, and the emission reduction pathway requires “symbiotic integration – co-construction and sharing – organic dispersion”. The key trade-offs between these two pathways at three spatial scales may provide theoretical support and practical guidance for UBGI construction and management. The five major research topics mentioned above may offer valuable assistance for UBGI construction and future research. </sec>

In this study, we investigated the effect of carbon sequestration and sink on the environmental impact assessment of a housing redevelopment project. Through the case study, we found that the amount of carbon sequestration and sink increased with the increase of the area of park and green space and, furthermore, the amount of carbon emission decreased slightly with implementation of district heating and renewable energy. Therefore, it is necessary for its land use plan to be established to minimize the amount of net carbon emission, taking account of both the amount of present carbon emission and the amount of the future carbon sink, sequestration, and emission.

<sec><title>Objective</title> Ecosystem services are the link between ecosystems and social systems. While effectively coordinating regional ecological, social and economic needs and promoting carbon sequestration and emission reduction, ecosystem services can be transmitted to surrounding areas to boost regional ecological space optimization. Under the guidance of the carbon peaking and carbon neutrality goals, clarifying the positive impact of ecosystem services on net carbon sink efficiency in metropolitan areas and the spillover effect of ecosystem services can effectively contribute to regional ecosystem service enhancement, and realize efficient carbon sequestration and reduction in ecological space. </sec><sec><title>Methods</title> Supported by multi-source panel data spanning the period from 2010 to 2020, this research takes the Shanghai Metropolitan Area as the research object and divides the research area into 40 research units. Based on the multiple benefits of ecosystem services in synergistically promoting urban sink enhancement and emission reduction, this research constructs a net carbon sink efficiency indicator system. Then, utilizing the undesirable slacks-based measurement (SBM) model, the research evaluates the net carbon sink efficiency of each unit during the period from 2010 to 2020, and further explores the distributional characteristics and spatial-temporal changes of carbon sinks, carbon emissions, and net carbon sink efficiency from the geospatial perspective. In combination with the guiding content of spatial synergistic planning for the Shanghai Metropolitan Area, four important ecosystem services, namely water retention, water purification, soil retention and biodiversity maintenance, are quantitatively characterized with the InVEST model. Subsequently, based on the spatial decomposition effects (direct, indirect and total effects) obtained with spatial econometric model, the influencing mechanisms of ecosystem services and their interrelationship on the net carbon sink efficiency of 40 research units are analyzed. In addition, the spatial spillover effects of ecosystem services are innovatively revealed according to ecosystem service flow conduction mechanisms. </sec><sec><title>Results</title> Research results are summarized as follows. 1) During the 11 years from the 2010 to 2020, the growth of carbon dioxide emissions in the Shanghai Metropolitan Area gradually slowed down, while the net primary productivity of vegetation continued to increase, and the areas with high carbon emissions and high carbon sinks were partially overlapped; in addition, the net carbon sink efficiency of some core nodes, such as Shanghai City, maintained a steady improvement, effectively driving neighboring cities to reduce carbon emissions and increase carbon sinks; meanwhile, the areas with improved net carbon sink efficiency have some similar characteristics and can be divided into 2 types: areas with high production value, high carbon emissions, and high carbon sinks, and those with medium-high production value, low carbon emissions, and medium-high carbon sinks. 2) The four ecosystem services have significant spatial heterogeneity and relatively stable changes over the 11-year period, with the high values mainly distributed in the southwestern part of the area with high vegetation cover and the area around the Taihu Lake with concentrated water resources, while the low values mainly distributed in the concentrated urban construction areas and near the regional traffic arteries, and the total amount of the four ecosystem services has shown fluctuating characteristics. 3) Regarding the spatial decomposition effects of ecosystem services on net carbon sink efficiency, there are differences in the coefficients, directions and significance of the spatial effects of different ecosystem services. For the ecosystem service trade-off index and relationship index, the direct effects are significantly positive, while indirect effects significantly negative. </sec><sec><title>Conclusion</title> The research clarifies that water-related ecosystem services such as water retention and water purification services can significantly affect carbon reduction and sink enhancement in the Shanghai Metropolitan Area, and attention should be paid to water network system and its coupling effects with green and grey spaces, so as to further stimulate the ecological vitality of Jiangnan water vein. As there are differences in the spillover effects of different ecosystem services, it is necessary to differentiate the optimization and enhancement strategies for each type of ecological space and its ecosystem services according to local conditions, and the conservation of important ecological spaces in the metropolitan area should be continuously strengthened, followed by joint protection and control of ecological red lines in neighboring areas, so as to promote territorial spatial carbon reduction and sink enhancement activities, thus contributing to the steady improvement of the net carbon sink efficiency of the Shanghai Metropolitan Area in general. The research clearly demonstrates the positive effects of enhancing water-related ecosystem services and conserving important ecological spaces on regional carbon sinks and reduction, and effectively reveals an effective path for synergistic carbon reduction in the region, which may provide certain reference for improving territorial spatial management. </sec>

Assessing the potential of native tree species for carbon sequestration forestry in Northeast China

We analyzed the carbon sink status of different management modes of larch plantations in Liaoning Pro-vince using data from a second-class survey, and predicted the dynamics of carbon sink under different management modes by using tree ring data from sample plots. The main aim was to provide technical support for improving carbon sequestration capacity of larch plantations. The results showed that the maximum carbon densities of larch and Korean pine plantations were 70.24 and 63.33 t·hm-2, respectively. The carbon sequestration potential of current plantations was 11.66 Tg. With the cycle of forest management, carbon sequestration rates of larch (40 years) and Korean pine (80 years) plantations were 1.62 and 0.66 t·hm-2·a-1, respectively. The carbon maturity age of larch plantations was 22 years, and stopping the rotation at this age could increase carbon sequestration by 43.8%. Under the larch-Korean pine multi-storied forest model, it was best to plant Korean pine seedlings in 30-year-old larch plantations, and to remove larch trees between 45- and 50-year-old larch plantations. Compared to the larch continuous cropping model, it reduced accumulated stand carbon sink by 36.4% and increased stand carbon density by 18.1%. Under the larch-Korean pine-Fraxinus mandshurica multi-storied forest model, it was best to plant F. mandshurica seedlings in 60-year-old Korean pine plantations, and to selecting cut Korean pine trees in 130-year-old. It increased accumulated stand carbon sink by 2.6% than larch continuous cropping and by 28.1% than Korean pine continuous cropping, and increased stand mean carbon density by 12.6% than Korean pine continuous cropping. The multi-storied forest model could reduce soil carbon loss and maintain arbor and soil carbon sinks. Inducing larch plantations into Korean pine-broadleaf mixed forests would facilitate stand carbon density and carbon sink.

Carbon sequestration in soils: some cautions amidst optimism

Low-carbon agriculture is crucial for China's agricultural green transformation and the development of an ecological civilization. The net carbon sink of agriculture plays a vital role in this process. Here, we take China's 31 provinces （municipalities and autonomous regions） as the research object, select the data from 2000 to 2022, and discuss them from multiple perspectives around the three dimensions of time series, space, and coupling. Additionally, we constructed an environment-economy coupling index and refined it by phases to analyze the relationship between stages and regions. The study revealed the following： ① China's overall agricultural carbon emissions fluctuated and decreased, while the agricultural carbon sink continued to expand, showing steady growth. ② The net agricultural carbon sink was distributed among provinces, and the gap between provinces in terms of net carbon sink tended to widen. Agricultural net carbon sinks exhibited regional aggregation characteristics, forming two distinct growth areas. The traditional growth area comprised Shandong and Henan as the core and Hebei, Anhui, and Jiangsu as the neighboring radiation areas. The other emerging growth areas in Northeast China included Heilongjiang, Jilin, and Liaoning. ③ The net agricultural carbon sink demonstrated a clear positive spatial correlation. However, a tendency was observed for the spatial correlation to weaken and an increase in the spatial type of low-low form of aggregation over the years. ④ From 2000 to 2022, the coupling relationship between net agricultural carbon sinks and agricultural economic growth improved, with most provinces shifting from weak or strong decoupling to expanding negative decoupling. Six provinces, namely, Zhejiang, Fujian, Yunnan, Gansu, Xinjiang, and Inner Mongolia, have shown the most significant shifts. Overall, the net agricultural carbon sinks and agricultural economic growth are expected to be in a state of negative expansion or weak decoupling for a prolonged period in the future. While the contribution of agricultural carbon sinks to the resource reserve will be substantial, the sustainable growth of the agricultural economy will face challenges.

IntroductionGlobal climate change, increase in human activities, and prominence of ecological issues have led to uneven quantitative and spatial distributions of carbon emission and sequestration of terrestrial ecosystems. Such uneven distributions can lead to more negative impacts on the natural environment and human living conditions.MethodsTherefore, based on the carbon neutralization policy, we conducted geographically weighted regression (GWR) modeling in this study using panel data from 352 Chinese prefectural administrative districts in 2000, 2005, 2010, and 2017 to analyze and determine the impact factors and their spatial distribution for carbon emission and sequestration of terrestrial ecosystems.ResultsOur results showed that total population (TP), per capita gross domestic product (GDP) (PCG), proportion of secondary industry output (PSIO), scale of urban built-up area (SUB), green space proportion in city areas (GSP), normalized difference vegetation index (NDVI), and temperature (TEM) are factors driving carbon sequestration and carbon emission. The spatial distribution of these driving factors in mainland China is: (1) TP showed a negative correlation to carbon emission in most areas, while it exhibited a positive correlation to carbon sequestration in the southern, southwestern, and western parts of northwest China; however, in all other areas, TP showed a negative correlation with carbon sequestration; (2) PCG was positively correlated to carbon emission in most areas of China and to carbon sequestration in southwest, south, central, and northeast China; however, PCG demonstrated a negative correlation to carbon sequestration in the remaining areas; (3) PSIO and SUB presented a positive correlation to carbon emission and a negative correlation to carbon sequestration in most areas; (3) In contrast, GSP showed a negative correlation to carbon emission and a positive correlation to carbon sequestration in most areas; (5)NDVI showed a negative correlation to carbon emission and carbon sequestration in most areas toward the east of the “Heihe-Tengchong Line”; NDVI was positively correlated to both carbon emission and sequestration toward the west of this line; (6)TEM was positively correlated to carbon emission and sequestration in most parts of China.DiscussionBased on these results, we further divided the Chinese cities into 6 groups: (1) Groups 1, 2, 3, and 6 are areas where carbon emission and sequestration are governed by both socioeconomic and natural ecological factors. The major driving factors of carbon emission and carbon sequestration in group 1 are PSIO, GSP, and NDVI; the driving factors of group 2 are SUB and NDVI. Meanwhile, carbon emission and sequestration in group 3 are governed by PCG, GSP, and NDVI; for group 6, carbon emission and sequestration are controlled by PCG, SUB, GSP, and NDVI; (2) Group 4 represents areas where carbon emission and sequestration are majorly impacted by PCG and SUB, thereby rendering socioeconomic factors as the major driving forces. Group 5 represents areas where carbon emission and sequestration are sensitive to the natural environment, with GSP and NDVI being the driving factors. Considering the uneven distribution of carbon sequestration and emission and the diverse driving factors in different areas of China, we provided guidance for future environmental policies aimed at reducing the uneven distribution of carbon sequestration and emission in different areas to achieve carbon neutralization.

Flux of organic carbon burial and carbon emission from a large reservoir: implications for the cleanliness assessment of hydropower

Increasing the carbon sink capacity of terrestrial ecosystems is a primary strategy to mitigate climate change and achieve the "carbon neutrality" goal. Clarifying the status and future dynamics of carbon sink of terrestrial ecosystems in Northeast China is crucial for achieving "carbon neutrality" as this region is a core contributor to carbon sink in China's terrestrial ecosystems. Here, we systematically summarized current research on carbon sink of terrestrial ecosystems across Northeast China, including the measurements and spatial-temporal patterns of carbon sinks, driving mechanisms of carbon sinks, the assessments of carbon sink potential, and technologies for increasing carbon sequestration. There are substantial uncertainties in quantifying terrestrial ecosystem carbon sink in Northeast China due to differences in data sources and methods, especially for forest carbon sink measurements, ranging from 0.020 to 0.157 Pg C·a-1. Carbon sink function depends on carbon exchange processes across plant-soil-atmosphere interfaces. The key pathways to enhance carbon sequestration in Northeast China under different temporal and spatial scales remains unclear. Improving terrestrial ecosystem quality is the key and core of carbon sequestration and sink enhancement. However, there is an urgent need to develop a multi-ecosystem collaborative carbon sequestration and sink enhancement technology system for the "dual carbon" goal. Future research needs to develop an accurate carbon sink measurement system that integrates multi-source data and multi-scale technologies to accurately assess the function and potential of carbon sink in Northeast China, focus on the multi-scale driving mechanism of carbon sink functions, develop new technical systems for coordinated enhancement of carbon sink for the Northeast terrestrial ecosystems, and carry out demonstrations of carbon sink enhancement technologies. These efforts will provide the scientific and technological supports for achieving the "carbon neutrality" goal.

Conifers are considered to prefer to take up ammonium (NH4+ ) over nitrate (NO3- ). However, this conclusion is mainly based on hydroponic experiments that separate roots from soils. It remains unclear to what extent mature conifers can use nitrate compared to ammonium under field conditions where both roots and soil microbes compete for nitrogen (N). We conducted an in situ whole mature tree nitrogen-15 (15 N) labeling experiment (15 NH4+ vs 15 NO3- ) over 15d to quantify ammonium and nitrate uptake and assimilation rates in four 40-yr-old monoculture coniferous plantations (Pinus koraiensis, Pinus sylvestris, Picea koraiensis and Larix olgensis, respectively). For the whole tree, 15 NO3- contributed 39% to 90% to total 15 N tracer uptake among four plantations during the study period. At day 3, the 15 NO3- accounted for 77%, 64%, 62% and 59% by Larix olgensis, Pinus koraiensis, Pinus sylvestris and Picea koraiensis, respectively. Our study indicates that mature coniferous trees assimilated nitrate as efficiently as ammonium from soils even at low soil nitrate concentration, in contrast to the results from hydroponic experiments showing that ammonium uptake dominated over nitrate. This implies that mature conifers can adapt to increasing availability of nitrate in soil, for example, under the context of globalization of N deposition and global warming.

BackgroundConifers partition different N forms from soil, including ammonium, nitrate, and dissolved organic N (DON), to sustain plant growth. Previous studies focused on inorganic N sources and specific amino acid forms using 15N labelling, but knowledge of the contribution of DON to mature conifers’ N uptake is still scarce. Here, we quantified the contribution of different N forms (DON vs. NH4+ vs. NO3−) to total N uptake, based on 15N natural abundance of plant and soil available N, in four mature conifers (Pinus koraiensis, Pinus sylvestris, Picea koraiensis, and Larix olgensis).ResultsDON contributed 31%, 29%, 28%, and 24% to total N uptake by Larix olgensis, Picea koraiensis, Pinus koraiensis, and Pinus sylvestris, respectively, whereas nitrate contributed 42 to 52% and ammonium contributed 19 to 29% of total N uptake for these four coniferous species.ConclusionsOur results suggested that all four conifers could take up a relatively large proportion of nitrate, while DON was also an important N source for the four conifers. Given that DON was the dominant N form in study soil, such uptake pattern of conifers could be an adaptive strategy for plants to compete for the limited available N sources from soil so as to promote conifer growth and maintain species coexistence.

Carbon life cycle assessment of shelterbelts in Saskatchewan, Canada

A network-based framework for characterizing urban carbon metabolism associated with land use changes: A case of Beijing city, China

The farmland system in the global terrestrial ecosystem has dual attributes as both a carbon source and a carbon sink, playing a crucial role in controlling carbon emissions and mitigating global warming. Using carbon source and sink accounting of farmland ecosystems, we applied methods such as standard deviation ellipse, Tapio decoupling theory, and Markov chain to analyze the spatiotemporal changes, response mechanisms, and evolutionary trends of regional carbon effects. The results indicated that from 2011 to 2021, the farmland ecosystem in the middle and lower reaches of the Yangtze River consistently acted as a carbon sink. However, the net carbon sink showed slight fluctuations and significant spatial differences. The migration range of the net carbon sink center in the farmland ecosystem of the middle and lower reaches of the Yangtze River was relatively small, ranging from 115.52 to 115.77° E and 30.14 to 30.27° N. The decomposition of the Tapio decoupling index between the net carbon sink of the farmland ecosystem and agricultural output value showed the order of effects on their coupling relationship as follows: agricultural mechanization level &gt; agricultural mechanization efficiency &gt; agricultural output value &gt; planting scale. The probability of maintaining the original state of net carbon sink in various cities in the middle and lower reaches of the Yangtze River (over 77%) was much higher than the probability of transfer, making it difficult to achieve a leapfrog growth in net carbon sink. The net carbon sink at the city scale exhibits the Matthew effect and spatial spillover effect. The above research results clarify the spatiotemporal changes in carbon effects in agricultural production at multiple levels, including city, province, and region. They also provide a theoretical basis for formulating differentiated regional emission reduction and sink enhancement strategies in the middle and lower reaches of the Yangtze River, promoting the rapid development of low-carbon agriculture in China.