Greenhouse gases emissions from riparian wetlands: an example from the Inner Mongolia grassland region in China

Variation characteristics of soil respiration fluxes in four types of grassland communities under different precipitation intensity

Determining regional and global carbon cycles hinges on investigating the dynamic characteristics and influencing factors of soil respiration in various types of natural grasslands located in arid regions, and these characteristics are important indicators for assessing the structural and functional health of grassland ecosystems. Such investigations also provide theoretical support for carbon sink monitoring, energy conservation, emission reduction and low-carbon development in the western arid zone and are important for obtaining an in-depth understanding of the carbon cycle, as well as for ecosystem management, restoration and the reconstruction of arid areas. In this study, during the growing season (from May to October) of 2022, the LI-8100A automated soil CO2 flux system was used to measure the soil respiration rate (Rs), temperature from 1.5 m above the surface to depths of 5–25 cm (T, T5, T10, T15, T20 and T25) and the soil moisture content (SM) at a depth of 20 cm in four types of grasslands: lowland meadow, alpine meadow, temperate desert steppe and temperate steppe desert. Five replicates were established for each plot, and the responses of Rs to T and SM were fitted to construct the optimal regression model. The results revealed that (1) the daily average soil respiration was highest in the lowland meadow (0.07 to 5.76 μmol·m−2·s−1), followed by the alpine meadow (−0.57 to 0.95 μmol·m−2·s−1), the temperate desert steppe (−0.45 to 3.0 μmol·m−2·s−1) and the temperate steppe desert (−1.29 to 1.61 μmol·m−2·s−1); (2) the soil respiration rates of the four grassland types were significantly correlated with the temperature in the 5–15 cm soil layer, and the best model was an exponential function; the peak values generally appeared between 13:00 and 17:00 (h), with the minimum values at 2:00 or 8:00 (h); the maximum value was observed in July–August, and the minimum value was observed in October; and the soil respiration in the lowland meadow was higher than that in the other three types of grassland during the same period. The average variation intensities of the soil respiration from May to October were as follows: temperate steppe desert (91.78%) > temperate desert steppe (76%) > alpine meadow (58.77%) > lowland meadow (43.93%). (3) The partial correlation analysis revealed that when soil temperature was used as a control, the correlation between SM and soil respiration in the four types of grasslands changed, and the coefficient of determination (R2) increased to varying degrees, explaining up to 80% of the variation in the soil respiration in the lowland meadows. The correlation between soil respiration and the SM normalized to 10 °C explained up to 93.8% of the variation in soil respiration; the two-factor fitting equations revealed that the model with soil temperature and SM was superior to the single-factor model with either soil temperature or SM.

ABSTRACTThe open lots and manure stockpiles of dairy farm are major sources of greenhouse gas (GHG) emissions in typical dairy cow housing and manure management system in China. GHG (CO2, CH4 and N2O) emissions from the ground level of brick-paved open lots and uncovered manure stockpiles were estimated according to the field measurements of a typical dairy farm in Beijing by closed chambers in four consecutive seasons. Location variation and manure removal strategy impacts were assessed on GHG emissions from the open lots. Estimated CO2, CH4 and N2O emissions from the ground level of the open lots were 137.5±64.7 kg hd-1 yr-1, 0.45±0.21 kg hd-1 yr-1 and 0.13±0.08 kg hd-1 yr-1, respectively. There were remarkable location variations of GHG emissions from different zones (cubicle zone vs. aisle zone) of the open lot. However, the emissions from the whole open lot were less affected by the locations. After manure removal, lower CH4 but higher N2O emitted from the open lot. Estimated CO2, CH4 and N2O emissions from stockpile with a stacking height of 55±12 cm were 858.9±375.8 kg hd-1 yr-1, 8.5±5.4 kg hd-1 yr-1 and 2.3±1.1 kg hd-1 yr-1, respectively. In situ storage duration, which estimated by manure volatile solid contents (VS), would affect GHG emissions from stockpiles. Much higher N2O was emitted from stockpiles in summer due to longer manure storage.Implications: This study deals with greenhouse gas (GHG) emissions from open lots and stockpiles. It’s an increasing area of concern in some livestock producing countries. The Intergovernmental Panel on Climate Change (IPCC) methodology is commonly used for estimation of national GHG emission inventories. There is a shortage of on-farm information to evaluate the accuracy of these equations and default emission factors. This work provides valuable information for improving accounting practices within China or for similar manure management practice in other countries.

Aluminum production is a major energy consumer and source of greenhouse gas (GHG) emissions. The regional transfer of the primary aluminum (PA) industry, which mainly consists of the processes of electrolysis and aluminum ingot casting, is currently an important international trend in aluminum industrial development. However, the changes in GHG emissions from aluminum production for such transfers are unclear. This study has established a life cycle assessment model of aluminum industry based on regional transfers in the context of China, determined the GHG emissions of PA and secondary aluminum (SA) production, examined the GHG emission changes of PA production based on regional industry transfer between the years 2007 and 2017, and explored seven driving factors that affect GHG emissions in the aluminum industry. GHG emissions per unit PA and SA production in China decreased by 18.6% and 6.3%, respectively, but the total GHG emissions from aluminum industry still increased by 2.2 times between the years 2007 and 2017. The driving factor analysis showed that the major positive effects of GHG emissions from China's aluminum industry from 2007 to 2017 included the production scale effect of SA and the energy structure effect. Existing regional transfers (between the years 2007 and 2017) did not deliver significant annual GHG emissions reductions. Currently, Xinjiang, Henan, Shandong, and Inner Mongolia are the main PA production provinces in China, although regional transfers have been implemented. This study provides a basis for the improvement and sustainable development of the aluminum industry, suggests policies for regional aluminum development, and proposes a beneficial layout of the aluminum industry.

Rationale: Greenhouse gas (GHG) emissions from crop agriculture are of great concern in the context of changing climatic conditions; however, in most cases, data based on lifecycle assessments are not available for grain yield variations or the carbon footprint of maize. The current study aimed to determine net carbon emissions and sequestration for maize grown in Bangladesh. Methods: The static closed-chamber technique was used to determine total GHG emissions using data on GHG emissions from maize fields and secondary sources for inputs. A secondary source for regional yield data was used in the current study. GHG emission intensity is defined as the ratio of total emissions to grain yield. The net GHG emission/carbon sequestration was determined by subtracting total GHG emissions (CO2 eq.) from net primary production (NPP). Results: Grain yields varied from 1590 to 9300 kg ha−1 in the wet season and from 680 to 11,820 kg ha−1 in the dry season. GHG emission intensities were 0.53–2.21 and 0.37–1.70 kg CO2 eq. kg−1 grain in the wet and dry seasons, respectively. In Bangladesh, the total estimated GHG emissions were 1.66–4.09 million tonnes (MT) CO2 eq. from 2015 to 2020, whereas the net total CO2 sequestration was 1.51–3.91 MT. The net CO2 sequestration rates were 984.3–5757.4 kg ha−1 in the wet season and 1188.62–5757.39 kg ha−1 in the dry season. This study observed spatial variations in carbon emissions and sequestration depending on growing seasons. In the rice–maize pattern, maize sequestered about 1.23 MT CO2 eq. per year−1, but rice emitted about 0.16 MT CO2 eq. per year−1. This study showed potential spatiotemporal variations in carbon footprints. Recommendation: Special care is needed to improve maize grain yields in the wet season. Fertiliser and water use efficiencies need to be improved to minimise GHG emissions under changing climatic conditions. Efforts to increase the area under cultivation with rice–maize or other non-rice crop-based cropping systems are needed to augment CO2 sequestration. The generation of a regional data bank on carbon footprints would be beneficial for combating the impact of climate change.

Spring thawing can affect the soil carbon and nitrogen cycling processes and lead to changes in the emissions of greenhouse gases. The temporal variations and impact factors of soil GHGs fluxes were measured in Phragmites australis and Carex appendiculata with the static chamber from the end of March to the end of May in 2018 in riparian wetlands of Xilin River, which is typical inland river meandering through steppe region in Inner Mongolia, China. The results showed that soil CH4 and N2O emissions of the P. australis were significantly higher than those of the Carex appendiculata, whereas CO2 emissions were no significant difference. The responses of soil GHG fluxes to soil environmental factors in P. australis and Carex appendiculata differed. In the P. australis community, soil CO2 and CH4 emissions were influenced jointly by mainly the soil temperature and microbial biomass nitrogen, whereas soil N2O emission was mainly affected by the soil temperature. The dominant controlling factor for CO2 and N2O was soil temperature in the Carex appendiculata, whereas CH4 was mainly regulated by soil water content. The global warming potential of P. australis was significantly higher than that of Carex appendiculata. Those findings highlight the difference in soil greenhouse gas fluxes in different plant communities and the importance of CH4 and N2O emissions during the spring thaw, which contributes to predicting the riparian wetland soil greenhouse gases and their global warming potential under global climate changes.

Smallholder farmers struggle to achieve food security in many countries of sub-Saharan Africa (SSA). It is urgently required to find appropriate practices for enhancing crop production while avoiding large increases in greenhouse gas (GHG) emissions in SSA. This review aims to identify common smallholder farming practices for enhancing crop production, to assess how these affect GHG emissions and to identify strategies that not only enhance crop production but also mitigate GHG emissions in SSA. To increase crop production and ensure food security, smallholder farmers usually expand agricultural land, develop water harvesting and irrigation techniques and increase cropping intensity and fertilizer use. These practices may result in changing carbon stocks and GHG emissions, potentially creating trade-offs between food security and GHG mitigation. Agricultural land expansion at the expense of forests is the most dominant source of GHG emissions in SSA. While water harvesting and irrigation can increase soil organic carbon, they can trigger GHG emissions. Increasing cropping intensity can enhance the decomposition of soil organic matter, thus releasing carbon dioxide. Increasing nitrogen fertilizer use can enhance soil organic carbon, but also leads to increasing nitrous oxide emissions. An integrated land, water and nutrient management strategy is necessary to enhance crop production and mitigate GHG emissions. Among the most relevant strategies found, agroforesty practices in degraded and marginal lands could replace expanding agricultural croplands. In addition, water management, via adequate rainwater harvesting and irrigation techniques, together with appropriate nutrient management should be considered. Therefore, a land-water-nutrient nexus (LWNN) approach will enable an integrated and sustainable solution to increasing crop production and mitigating GHG emissions. Various technical, economic and policy barriers hinder implementing the LWNN approach on the ground, but these may be overcome through developing appropriate technologies, disseminating them through farmer to farmer approaches and developing specific policies to address smallholder land tenure issues and motivate long-term investment.

To establish a micro foundation to understand the impacts of greenhouse gas (GHG) emission regulations and financial development levels on firms’ GHG emissions, we build a two-stage dynamic game model to incorporate GHG emission regulations (in terms of an emission tax) and financial development (represented by the corresponding financing cost) into a two-echelon supply chain. With the subgame perfect equilibrium, we identify the conditions to determine whether an emission regulatory policy and/or financial development can affect GHG emissions in the supply chain. We also reveal the impacts of the strictness of GHG emission regulation, the financial development level, and the unit GHG emission rate on the operations of the supply chain and the corresponding profitability implications. Managerial insights are also discussed.

Salt-affected soils contain high levels of soluble salts (saline soil) and exchangeable sodium (alkali soil). Globally, about 932 million ha (Mha), including 831 Mha of agricultural land, is salt-affected. Salinity and sodicity adversely affect soil microbial diversity and enzymatic activities, and thereby carbon and nitrogen dynamics and greenhouse gas (GHG) emissions from soils. In this review article, we synthesize published information to understand the impact of salinity and sodicity on GHG production and emissions from salt-affected soils, and how various reclamation amendments (gypsum, phosphogypsum, organic manure, biochar, etc.) affect GHG emissions from reclaimed soils. Nitrous oxide (N2O) and methane (CH4) emissions are of greater concern due to their 298 and 28 times higher global warming potential, respectively, compared to carbon dioxide (CO2), on a 100-year time scale. Therefore, CO2 emissions are given negligible/smaller significance compared to the other two. Generally, nitrous oxide (N2O) emissions are higher at lower salinity and reduced at higher salinity mainly due to: (a) higher ammonification and lower nitrification resulting in a reduced substrate for denitrification; (b) reduced diversity of denitrifying bacteria lowered down microbial-mediated denitrification process; and (c) dissimilatory nitrate reduction to ammonium (DNRA), and denitrification processes compete with each other for common substrate/nitrate. Overall, methane (CH4) emissions from normal soils are higher than those of salt-affected soils. High salinity suppresses the activity of both methanogens (CH4 production) and methanotrophs (CH4 consumption). However, it imposes more inhibitory effects on methanogens than methanotrophs, resulting in lower CH4 production and subsequent emissions from these soils. Therefore, reclamation of these soils may enhance N2O and CH4 emissions. However, gypsum is the best reclamation agent, which significantly mitigates CH4 emissions from paddy cultivation in both sodic and non-sodic soils, and mitigation is higher at the higher rate of its application. Gypsum amendment increases sulfate ion concentrations and reduces CH4 emissions mainly due to the inhibition of the methanogenesis by the sulfate reductase bacteria and the enhancement of soil redox potential. Biochar is also good among the organic amendments mitigating both CH4 and N2O emission from salt-affected soils. The application of fresh organic matter and FYM enhance GHG emissions for these soils. This review suggests the need for systematic investigations for studying the impacts of various amendments and reclamation technologies on GHG emissions in order to develop low carbon emission technologies for salt-affected soil reclamation that can enhance the carbon sequestration potential of these soils.

Core Ideas Dynamics of redox potential were induced by water‐table changes in a lysimeter. The redox potential measurements well reflected the different GHG emission sources. Redox potential monitoring is a viable tool for better understanding of GHG emissions. Soil greenhouse gas (GHG) emissions contribute to global warming. To support mitigation measures against global warming, it is important to understand the controlling processes of GHG emissions. Previous studies focusing mainly on paddy rice fields or wetlands showed a strong relationship between soil redox potential and GHG emission (e.g., N 2 O). However, the interpretation of redox potentials for the understanding of the controlling factors of GHG emission is limited due to the low number of continuous redox measurements in most ecosystems. Recent sensor developments open the possibility for the long‐term monitoring of field‐scale soil redox potential changes. We performed laboratory lysimeter experiments to investigate how changes in the redox potential, induced by changes in the water level, affect GHG emissions from agricultural soil. Under our experimental conditions, we found that N 2 O emissions followed closely the changes in redox potential. The dynamics of redox potential were induced by changing the water‐table depth in a laboratory lysimeter. Before fertilization during saturated conditions, we found a clear negative correlation between redox potentials and N 2 O emission rates. After switching from saturated to unsaturated conditions, N 2 O emission quickly decreased, indicating denitrification as the main source of N 2 O. In contrast, the emissions of CO 2 increased with increasing soil redox potentials. After fertilization, N 2 O emission peaked at high redox potential, suggesting nitrification as the main production pathway, which was confirmed by isotope analysis of N 2 O. We propose that redox potential measurements are a viable method for better understanding of the controlling factors of GHG emissions, for the differentiation between different source processes, and for the improvement of process‐based GHG models.

Understanding the greenhouse gas emissions from China’s wastewater treatment plants: Based on life cycle assessment coupled with statistical data

Greenhouse gas emissions and land use from confinement dairy farms in the Guanzhong plain of China – using a life cycle assessment approach

Adopting appropriate cropping systems is an effective way to reduce greenhouse gas (GHG) emission, meanwhile GHG emission from farmland is a hot topic recently. In recent years, maize–soybean intercropping has been promoted in many regions in China. To explore the effects of maize-soybean intercropping on soil CO2 emission and carbon balance, we established three planting methods, namely, maize monoculture (M), soybean monoculture (S), and maize-soybean intercropping (MS). Results showed that the cumulative emissions of soil CO2 were M (21231 kg·hm-2) > S (19715 kg·hm-2) > MS (17321 kg·hm-2). The two-factor composite model of soil temperature and moisture content could explain the variation in soil CO2 emission rate well, which reached 58.36–68.54%. Correlation analysis showed that the soil CO2 emission rate was significantly correlated with peroxidase activity (P＜0.01). The soil carbon balance was favorable under different treatments, serving as a sink for atmospheric carbon. The soil carbon sequestration potential of M and MS treatments was significantly higher than that of S treatment (P<0.05), with increases of 37.11 and 34.02%, respectively. These results indicated that M and MS treatments had strong carbon sequestration potential . M treatment exhibited superior soil carbon balance compared with MS and S treatments, with increases of 29.80 and 359.31%, respectively. Therefore, maize treatment was a better planting method compared with soybean and maize-soybean treatments. Bangladesh J. Bot. 54(1): 113-122, 2025 (March)

Simple SummaryMinimizing the effects of climate change by reducing GHG emissions is crucial and can be accomplished by truly understanding the carbon footprint phenomenon. This study aims to improve the understanding of carbon footprint alteration due to agricultural management and fertility practices. It provides a detailed review of carbon footprint management under the impacts of environmental factors, land use, and agricultural practices. The results show that healthy soils have numerous benefits for the general public and especially farmers. These benefits include being stable and resilient, resistant to erosion, easily workable in cultivated systems, good habitat for soil micro-organisms, fertile and good structure, large carbon sinks, and hence lower carbon footprint. Intensive tillage is harmful to soil structure by oxidizing carbon and causing GHG emissions. If possible, no-till; if not, minimum tillage frequency and depth of tillage, and optimum moisture are recommended. The soil should be at an appropriate level of moisture when tillage takes place. Diverse cropping systems are better for the soil than monocultures. Minimizing machinery operations can help to avoid soil compaction. Building soil organic carbon in the most stable form is the most efficient practice of sustainable crop production.Global attention to climate change issues, especially air temperature changes, has drastically increased over the last half-century. Along with population growth, greater surface temperature, and higher greenhouse gas (GHG) emissions, there are growing concerns for ecosystem sustainability and other human existence on earth. The contribution of agriculture to GHG emissions indicates a level of 18% of total GHGs, mainly from carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Thus, minimizing the effects of climate change by reducing GHG emissions is crucial and can be accomplished by truly understanding the carbon footprint (CF) phenomenon. Therefore, the purposes of this study were to improve understanding of CF alteration due to agricultural management and fertility practices. CF is a popular concept in agro-environmental sciences due to its role in the environmental impact assessments related to alternative solutions and global climate change. Soil moisture content, soil temperature, porosity, and water-filled pore space are some of the soil properties directly related to GHG emissions. These properties raise the role of soil structure and soil health in the CF approach. These properties and GHG emissions are also affected by different land-use changes, soil types, and agricultural management practices. Soil management practices globally have the potential to alter atmospheric GHG emissions. Therefore, the relations between photosynthesis and GHG emissions as impacted by agricultural management practices, especially focusing on soil and related systems, must be considered. We conclude that environmental factors, land use, and agricultural practices should be considered in the management of CF when maximizing crop productivity.

Climate-smart management for increasing crop yield and reducing greenhouse gas emission in Beijing-Tianjin-Hebei region, China