Decadal shifts in Qingzang Plateau lake carbon dynamics (1970-2020): From predominant carbon sources to emerging sinks

The evasion of carbon dioxide (CO2) from lakes significantly influences the global carbon equilibrium. Amidst global climatic transformations, the role of Qingzang Plateau (QZP) lakes as carbon (C) sources or sinks remains a subject of debate. Furthermore, accurately quantifying their contribution to the global carbon budget presents a formidable challenge. Here, spanning half a century (1970-2020), we utilize a synthesis of literature and empirical field data to assess the CO2 exchange flux of QZP lakes. We find markedly higher CO2 exchange flux in the southeast lakes than that in the northern and western regions from 1970 to 2000. During this time, both freshwater and saltwater lakes served primarily as carbon sources. The annual CO2 exchange flux was estimated at 2.04 ± 0.37 Tg (Tg) C yr-1, mainly influenced by temperature fluctuations. The CO2 exchange flux patterns underwent a geographical inversion between 2000 and 2020, with increased levels in the west and decreased levels in the east. Notably, CO2 emissions from freshwater lakes diminished, and certain saltwater lakes in the QTP transitioned from carbon sources to sinks. From 2000 to 2020, the annual CO2 exchange flux from QZP lakes is estimated at 1.34 ± 0.50 Tg C yr-1, with solar radiation playing a more pronounced role in carbon emissions. Cumulatively, over the past five decades, QZP lakes have generally functioned as carbon sources. Nevertheless, the total annual CO2 emissions have declined since the year 2000, indicating a potential shift trend from being a carbon source to a sink, mirroring broader patterns of global climate change. These findings not only augment our understanding of the carbon cycle in plateau aquatic systems but also provide crucial data for refining China's carbon budget.

Mixing of pine and arbuscular mycorrhizal tree species changed soil organic carbon storage by affecting soil microbial characteristics

Pure and mixed pine forests are found all over the world. The mycorrhizal type affects soil microbial activity and carbon sequestration capacity in pure forests. However, the effects of mycorrhizal type on microbial characteristics and carbon sequestration capacity in pine mixed forests remain untested. Further, making it difficult to predict carbon storage of the conversion from pure pine forests to mixed forests at larger scales. Herein, a meta-analysis showed that the contents of soil microbial biomass, mineral-associated organic carbon, and soil organic carbon in pine mixed forests with introduced arbuscular mycorrhizal tree species (PMAM) increased by 26.41 %, 58.55 %, and 27.41 %, respectively, compared to pure pine forests, whereas those of pine mixed forests without arbuscular mycorrhizal tree species (PMEcM) remained unchanged. Furthermore, the effect size of microbial biomass, mineral-associated organic carbon and organic carbon contents in subsoil of PMAM are 56.48 %, 78.49 % and 43.05 %, respectively, which are higher than those in topsoil. The improvement of carbon sinks throughout the PMAM soil profile is positively correlated with increases in microbial biomass and mineral-associated organic carbon in subsoil, according to regression analysis and structural equation modelling. In summary, these results highlight that the positive effects of introducing arbuscular mycorrhizal tree species rather than ectomycorrhizal tree species into pure pine forests on soil microbial biomass and carbon sequestration. The positive link between microbial biomass, mineral-associated organic carbon, and soil organic carbon suggests an underlying mechanism for how soil microorganisms store carbon in pine mixed forests. Nevertheless, our findings also imply that the soil carbon pool of PMAM may be vulnerable under climate change. Based on the above findings, we propose that incorporating mycorrhizal type of tree species and soil thickness into mixed forests management and biodiversity conservation.

Karst carbon sink mechanism and its contribution to carbon neutralization under land- use management

The chemical weathering process of carbonate rocks consumes a large quantity of CO2. This has great potential as a carbon sink, and it is one of a significant pathway for achieving carbon neutrality. However, the control mechanisms of karst carbon sink fluxes are unclear, and there is a lack of effective and accurate accounting. We took the Puding Shawan karst water‑carbon cycle test site in China, which has identical initial conditions but different land use types, as the research subject. We used controlled experiments over six years to evaluate the mechanisms for the differences in hydrology, water chemistry, concentrations and fluxes of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). We found that the transition from rock to bare soil to grassland led to increases in the DIC concentration by 0.08-0.62 mmol⋅L-1. The inorganic carbon sink flux (CSF) increased by 3.01-5.26 t⋅C⋅km-2⋅a-1, an increase amplitude of 30-70 %. The flux of dissolved organic carbon (FDOC) increase by 0.28 to 0.52 t⋅C⋅km-2⋅a-1, an increase amplitude of 34-90 %. We also assessed the contribution of land use modifications to regional carbon neutrality, it indicate that positive land use modification can significantly regulate the karst carbon sink, with grassland having the greatest carbon sequestration ability. Moreover, in addition to DOC from soil organic matter degradation, DOC production by chemoautotrophic microorganisms utilizing DIC in groundwater may also be a potential source. Thus, coupled studies of the conversion of DIC to DOC processes in groundwater are an important step in assessing karst carbon sink fluxes.

A scoping review of human health co-benefits of forest-based climate change mitigation in Europe

Climate change is a pressing global challenge with profound implications for human health. Forest-based climate change mitigation strategies, such as afforestation, reforestation, and sustainable forest management, offer promising solutions to mitigate climate change and simultaneously yield substantial co-benefits for human health. The objective of this scoping review was to examine research trends related to the interdisciplinary nexus between forests as carbon sinks and human health co-benefits. We developed a conceptual framework model, supporting the inclusion of exposure pathways, such as recreational opportunities or aesthetic experiences, in the co-benefit context. We used a scoping review methodology to identify the proportion of European research on forest-based mitigation strategies that acknowledge the interconnection between mitigation strategies and human impacts. We also aimed to assess whether synergies and trade-offs between forest-based carbon sink capacity and human co-benefits has been analysed and quantified. From the initial 4,062 records retrieved, 349 reports analysed European forest management principles and factors related to climate change mitigation capacity. Of those, 97 studies acknowledged human co-benefits and 13 studies quantified the impacts on exposure pathways or health co-benefits and were included for full review. Our analysis demonstrates that there is potential for synergies related to optimising carbon sink capacity together with human co-benefits, but there is currently a lack of holistic research approaches assessing these interrelationships. We suggest enhanced interdisciplinary efforts, using for example multideterminant modelling approaches, to advance evidence and understanding of the forest and health nexus in the context of climate change mitigation.

Enhancement of carbon sink in the main marginal sea ice zone by cold season Arctic cyclones

The Arctic Ocean, as a significant carbon sink, is attracting increased attention within the scientific community. This study focused on the main marginal sea ice zone, which has been the most sensitive to environmental changes in recent decades. Using data from reanalysis, models, and on-site observations, the changes in air-sea CO2 flux (FCO2) were analyzed during the influence of Arctic cyclones (ACs) in 2021-2022. Results indicated that the passage of ACs tended to increase the average carbon sink in the main marginal ice zone, with a more pronounced effect during the cold season. During ACs, the average FCO2 could reach -6.95 mmolC m-2 d-1. This was mainly associated with the stronger and more concentrated distribution of ACs where there was lower pCO2 (air-sea gradient of CO2 partial pressure) in the cold season. Additionally, the change in FCO2 during ACs was primarily affected by the sea surface wind and sea-ice concentration in the cold season, while it was influenced by a variety of environmental factors in the warm season, including the sea surface wind, sea-ice concentration, and ecological factors.

Carbon cycle responses to climate change across China's terrestrial ecosystem: Sensitivity and driving process

Investigations into the carbon cycle and how it responds to climate change at the national scale are important for a comprehensive understanding of terrestrial carbon cycle and global change issues. Contributions of carbon fluxes to the terrestrial sink and the effects on climate change are still not fully understood. In this study, we aimed to explore the relationship between ecosystem production (GPP/SIF/NDVI) and net ecosystem carbon exchange (NEE) and to investigate the sensitivity of carbon fluxes to climate change at different spatio-temporal scales. Furthermore, we sought to delve into the carbon cycle processes driven by climate stress in China since the beginning of the 21st century. To achieve these objectives, we employed correlation and sensitivity analysis techniques, utilizing a wide range of data sources including ground-based observations, remote sensing observations, atmospheric inversions, machine learning, and model simulations. Our findings indicate that NEE in most arid regions of China is primarily driven by ecosystem production. Climate variations have a greater influence on ecosystem production than respiration. Warming has negatively impacted ecosystem production in Northeast China, as well as in subtropical and tropical regions. Conversely, increased precipitation has strengthened the terrestrial carbon sink, particularly in the northern cool and dry areas. We also found that ecosystem respiration exhibits heightened sensitivity to warming in southern China. Moreover, our analysis revealed that the control of terrestrial carbon cycle by ecosystem production gradually weakens from cold/arid areas to warm/humid areas. We identified distinct temperature thresholds (ranging from 10.5 to 13.7 °C) and precipitation thresholds (approximately 1400 mm yr-1) for the transition from production-dominated to respiration-dominated processes. Our study provides valuable insights into the complex relationship between climate change and carbon cycle in China.

Quantifying carbon pool in ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia

Ex-mining lake-converted constructed wetlands play a significant role in the carbon cycle, offering a great potential to sequester carbon and mitigate climate change and global warming. Investigating the quantity of carbon storage capacity of ex-mining lake-converted constructed wetlands provides information and justification for restoration and conservation efforts. The present study aims to quantify the carbon pool of the ex-mining lake-converted constructed wetlands and characterise the physicochemical properties of the soil and sediment. Pearson's correlation and a one-way ANOVA were performed to compare the different sampling stations at Paya Indah Wetland, Selangor, Malaysia. An analysis of 23 years of ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia, revealed that the estimated total carbon pool in soil and sediment accumulated to 1553.11 Mg C ha-1 (equivalent to 5700 Mg CO2 ha-1), which translates to an annual carbon sink capacity of around 67.5 Mg C ha-1 year-1. The characterisation showed that the texture of all soil samples was dominated by silt, whereas sediments exhibited texture heterogeneity. Although the pH of the soil and sediment was both acidic, the bulk density was still optimal for plant growth and did not affect root growth. FT-IR and WDXRF results supported that besides the accumulation and degradation of organic substances, which increase the soil and sediment carbon content, mineral carbonation is a mechanism by which soil and sediment can store carbon. Therefore, this study indicates that the ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia have a significant carbon storage potential.

Weaker regional carbon uptake albeit with stronger seasonal amplitude in northern mid-latitudes estimated by higher resolution GEOS-Chem model

Terrestrial ecosystem in the Northern Hemisphere is characterized by a substantial carbon sink in recent decades. However, the carbon sink inferred from atmospheric CO2 data is usually larger than process- and inventory-based estimates, resulting in carbon release or near-neutral carbon exchange in the tropics. The atmospheric approach is known to be uncertain due to systematic biases of coarse atmospheric transport model simulation. Compared to a coarse-resolution inverse estimate at 4° × 5° using GEOS-Chem in the integrated region of N. America, E. Asia, and Europe from 2015 to 2018, the annual carbon sink estimate at a native high-resolution of 0.5° × 0.625° is reduced from -3.0±0.08 gigatons of carbon per year (GtC yr-1) to -2.15±0.08 GtC yr-1 due to prominent more carbon release during the non-growing seasons. The major reductions concentrate in the mid-latitudes (20°N-45°N), where the mean land carbon sinks in China and the USA are reduced from 0.64±0.03 and 0.35±0.02 GtC yr-1 to 0.14±0.03 and 0.15±0.02 GtC yr-1, respectively. The coarse-resolution GEOS-Chem tends to trap both the release and uptake signal within the planetary boundary layer, resulting in weaker estimates of biosphere seasonal strength. Since the strong fossil fuel emissions are persistently released from the surface, the trapped signal leads to the stronger estimates of annual carbon uptakes. These results suggest that high-resolution inversion with accurate vertical and meridional transport is urgently needed in targeting national carbon neutrality.

High organic carbon content constricts the potential for stable organic carbon accrual in mineral agricultural soils in Finland

Sequestering carbon into agricultural soils is considered as a means of mitigating climate change. We used agronomic soil test results representing c. 95% of the farmed land area in Finland to estimate the potential of the uppermost 15 cm soil layer of mineral agricultural soils to sequester organic carbon (OC) and to contribute to the mitigation of climate change. The estimation of the maximum capacity of mineral matter to protect OC in stable mineral-associated form was based on the theory that clay and fine-sized (fines = clay + silt) particles have a limited capacity to protect OC. In addition, we used the clay/OC and fines/OC ratios to identify areas with a risk of erosion and reduced productivity, thus indicating priority areas potentially benefitting from the increased soil OC contents. We found that 32-40% of the mineral agricultural soils in Finland have the potential to further accumulate mineral-associated OC (MOC), while in the majority of soils, the current OC stock in the uppermost 15 cm exceeded the capacity of mineral matter to protect OC. The nationwide soil OC sequestration potential of the uppermost 15 cm in mineral agricultural soils ranged between 0.21 and 0.26 Tg, which corresponds to less than 2% of annual greenhouse gas emissions in Finland. The fields with the highest potential for SOC accrual were found in the southern and southwestern parts of the country, including some of the most intensively cultivated high-clay soils. Although the nationwide potential for additional OC sequestration was estimated to be relatively small, the current OC storage in Finnish arable mineral soils (0-15 cm) is large, 128 Tg. Farming practices enabling maximum OC input into the soil play an important role as a tool for mitigating the loss of carbon from high-OC soils in the changing climate. Furthermore, especially in high-clay areas with potential for MOC accrual, efforts to increase soil OC could help improve soil structural stability and therefore reduce erosion and the loss of nutrients to the aquatic environments.

Maximizing the carbon sink function of paddy systems in China with machine learning

Developing low-carbon agriculture and alleviating the "carbon crisis" requires optimizing strategies that fully leverage the carbon sink function of paddy systems. Accurate assessment of the effects of various agricultural management practices (AMPs) on the carbon sink function of paddy systems is crucial to this end. Here, we have presented a soil organic carbon sequestration rate (SOCSR) database of paddy systems in China based on 1388 groups of experimental data from 143 peer-reviewed publications. We analyzed the impact trend of different AMPs on SOCSR, compared two traditional regression models, four classic machine learning models and two deep learning models, and established a data-driven SOCSR prediction model to quantify the impact of AMPs on SOCSR and provide the optimal strategies. Our model (Random Forest) had the characteristics of high accuracy (R2 = 0.71, RMSE = 0.53 Mg ha-1), strong flexibility, low time cost with a certain degree of interpretability for the regional scale of China. We found that inorganic N fertilizer, inorganic K fertilizer, organic fertilizer, tillage and residue management are relatively important AMPs for improving SOCSR. The carbon sink function of paddy systems would reach saturation when the application rate of inorganic N fertilizer, inorganic K fertilizer and organic fertilizer reached around 80 kg N ha-1, 40 kg K ha-1 and 2200 kg C ha-1, respectively. Compared to half residue returning and conventional tillage, full residue returning and no-tillage increased SOCSR by 39.8 % and 9.2 %, respectively. Our optimal combination of strategies could achieve SOCSR of 1.179 Mg ha-1 in paddy systems of China. Our work enables swift and precise evaluation of SOCSR in paddy systems, provides a new idea for assessing SOCSR of paddy systems on a regional scale, and serves as an essential part for the accurate assessment of the carbon footprint of rice production.

Saving the overlooked mangrove horseshoe crabs-A perspective from enhancing mangrove ecosystem conservation

Despite being widely distributed in Asia, Carcinoscorpius rotundicauda is often overlooked and, its population status remains unclear. Moreover, it is threatened by illegal harvesting and degradation of mangrove ecosystems. Protecting its habitat is essential for population and biodiversity conservation, as mangroves provide nursery grounds and food supply for C. rotundicauda. This review discusses the biological characteristics of C. rotundicauda, including ecology, nutrition, life history, toxicology, and immunology. It also presents information about its distribution and population status. The review emphasizes the challenges faced by C. rotundicauda and proposes a conservation framework that involves the participation of local residents to facilitate conservation efforts. Collaboration between local residents and communities is proposed to protect and monitor the mangrove ecosystem. Additionally, this framework can support field research, protect C. rotundicauda juveniles and other species, and ensure the livelihood of local residents through participation in carbon trading markets and eco-industries such as eco-farming and eco-tourism.

Multiple drivers for carbon stocks and fluxes in different types of mangroves

Mangroves are highly efficient in sequestering carbon from the atmosphere and can accumulate carbon in sediments for millennials. However, The fate of mangrove carbon has not been well constrained due to the lack of data on different pools of sediment carbon sinks and sources. This study examined the variation of carbon stocks and fluxes at the water-sediment-air interface in both estuarine mangroves (natural: Mai Po, restored: Gei Wai) and oceanic mangroves (Ting Kok). There are divergent patterns in biogeochemical variables at the sediment-water-air interface, likely due to significant variation within sites. Total sediment carbon stocks (TCs) ranked in the order of restored estuarine mangroves (392.5 ± 8.8 Mg ha-1), natural estuarine mangroves affected by aquaculture (315.2 ± 21.4 Mg ha-1) and oceanic mangroves (229.1 ± 32.3 Mg ha-1). Sediment organic carbon stocks (SOC) and inorganic carbon stocks (SIC) accounted for 84.1-90.2 % and 9.8-15.9 % of TC, respectively. The highest sediment-air CO2 and CH4 fluxes occurred in restored and natural estuarine mangroves affected by aquaculture, respectively. The isotope of CO2 fluxes (δ13C-CO2) indicates higher contributions from the degradation of mangrove-derived organic carbon in restored (-25.94 ‰ ± 3.37 ‰) and natural estuarine mangroves affected by aquaculture (-25.54 ‰ ± 0.96 ‰) than in oceanic mangroves (-21.55 ‰ ± 1.36 ‰). The isotope of CH4 fluxes (δ13C-CH4) indicates CH4 production dominated by acetate fermentation in restored estuarine mangroves but dominated by the reduction of CO2 for other sites. Future studies should better constrain the fate of mangrove carbon by considering local drivers.

Unveiling the potential for artificial upwelling in algae derived carbon sink and nutrient mitigation

Mariculture algae may present a crucial part of ocean-based solutions for climate change, with the ability to sequester carbon and remove nutrients. However, the expansion of mariculture algae faces multiple challenges. Here, we measure the changes in algae derived carbon sinks and nitrogen (N) and phosphorus (P) removal between 2010 and 2020 in Shandong Province, China. We further identify the key driving factors, namely area, algal species proportion, and yield, that influence the changes. The results show that algae derived carbon sinks and nutrient removal growth rates in Shandong Province have slowed significantly since 2014, mainly due to area limitations, laver-oriented species change, and unstable yields. Artificial upwelling (AU) has the potential to enhance the yield and subsequently offset the loss of carbon sinks and nutrient removal caused by negative driving factors. Scenario analysis indicates that a complete deployment of AU by 2030 will offset up to a 44.52 % decrease in the mariculture algae area, or a 72.57 % increase in the laver share of the algal species combination compared to 2020. Similar conclusions are reached regarding the role of AU in N and P removal. This study also identifies ancillary challenges such as low energy efficiency and high costs faced by applying AU.

Carbon sequestration and storage capacity of Chinese fir at different stand ages

In southern China, Chinese fir Cunninghamia lanceolata is one of the most important native conifer trees, widely used in afforestation programs. This area has the largest forestland atmospheric carbon sink, and a relatively young stand age characterizes these forests. However, how C. lanceolata forests evolved regarding their ability to sequester carbon remains unclear. Here we present data on carbon storage and sequestration capacity of C. lanceolata at six stand ages (5-, 10-, 15-, 20-, 30- and 60 - year-old stands). Results show that the carbon stock in trees, understory, vegetation, litter, soil, and ecosystem significantly increased with forest age. The total ecosystem carbon stock increased from 129.11 to 348.43 Mg ha-1 in the 5- and 60 - year-old stands. The carbon sequestration rate of C. lanceolata shows an overall increase in the first two stand intervals (5-10 and 10-15), peaks in the 15-20 stand intervals, and then decreases in the 20-30 and 30-60 stand intervals. Our result revealed that carbon sequestration rate is a matter of tree age, with the highest sequestration rates occurring in the middle age forest (15-20 - year-old). Therefore, this information may be useful for national climate change mitigation actions and afforestation programs, since forests are primarily planted for this purpose.

Chemical weathering in glacial catchment acting as a net carbon source

Over geological time scales, continental silicate weathering is considered as a critical carbon sink that regulates long-term climate feedback. By contrast, recent studies indicate that sulfide oxidation during weathering can be as a potential carbon source. However, whether chemical weathering in glacial conditions characterized by extreme erosion is a net carbon sink or source remains elusive. Here, we present the seasonal carbon cycle processes in a typical glacier catchment, via high-resolution (weekly) river water sampling during the whole 2017 in the Laohugou river, northeastern Tibetan Plateau. Our seasonal result shows that the release of CO2 by sulfide oxidation during the monsoon period can be much faster than CO2 consumption through weathering of silicate rocks, with maximum of ∼26 times. Extending to global glacial basins, we observed a consistent pattern that inorganic carbon releases in alpine glaciers are faster than atmospheric CO2 consumption. We propose that weathering in global glacial environment acts as a significant carbon source, and thus affects climate feedback.

Divergent response to abiotic factor determines the decoupling of water and carbon fluxes over an artificial C4 shrub in desert

Knowledge on relationship and determinants of water and carbon dioxide (CO2) exchange is crucial to land managers and policy makers especially for the desertified land restoration. However, there remains highly uncertain in terms of water use and carbon sequestration for artificial plantation in desert. Here, continuous water and carbon fluxes were measured using eddy covariance (EC) in conjunction with hydrometeorological measurements over an artificial C4 shrub, Haloxylon ammodendron (C. A. Mey.) Bunge, from July 2020 to 2021 in Tengger Desert, China. Throughout 2021, evapotranspiration (ET) was 189.5 mm, of which 85% (150 mm) occurred during growing season, that was comparable with the summation of precipitation (132.2 mm), dew (33.5 mm) and potential other sources (e.g. deep subsoil water). This ecosystem was a strong carbon sink with net ecosystem production (NEP) up to 446.4 g C m-2 yr-1, much higher than surrounding sites. Gross primary production (GPP, 598.7 g C m-2 yr-1) in this shrubland was comparable with that of other shrublands, whereas ecosystem respiration (Re, 152.3 g C m-2 yr-1) was lower. Random Forest showed that environmental factors can explain 71.56% and 80.07% variation of GPP and ET, respectively. Interestingly, environmental factors have divergent effect on water and carbon exchange, i.e., soil hydrothermic factors (soil moisture content and soil temperature) determine the magnitude and seasonal pattern of ET and Re, while aerodynamics factors (net radiation, atmospheric temperature and wind speed) determine GPP and NEP. As such, divergent response of abiotic factors resulted in the decoupling of water and carbon exchange. Our results suggest that H. ammodendron is a suitable species for large-scale afforestation in dryland given its low water use but high carbon sequestration. Therefore, we infer that artificial planting H. ammodendron in dryland could provide an opportunity for climate change mitigation, and the long-term time series data is needed to confirm its sustainable role of carbon sequestration in the future.

Macroalgae culture-induced carbon sink in a large cultivation area of China

Macroalgae culture-induced carbon sink in sediments has been little investigated. Here, total organic carbon (TOC), total nitrogen (TN), and δ13C were examined in sediments in a cultivation field of macroalgae (kelp and Gracilariopsis lemaneiformis) in Sansha Bay, Southeast China. Both proxies of C/N (TOC to TN ratio) and δ13C indicated a multisource of TOC. Based on a three-endmember model, macroalgae-derived TOC (TOCma) accounted for < 35% of the total TOC, averaging 16 ± 9% (mean ± SD). On average, terrestrial and phytoplankton-derived TOC showed much higher percentages of 24 ± 17% and 60 ± 20%, respectively (t-test, p < 0.02). A preliminary estimate suggested that TOCma represents a carbon sink of 8.2 × 103 tons per year, corresponding to about 22% of the sink associated with phytoplankton and macroalgae and 8 ± 6% of the macroalgae carbon production in Sansha Bay. Considering its production magnitude, the macroalgae-induced carbon sink seems to be insignificant, on a national or global scale, to phytoplankton, though it should be taken into account given the small cultivation area.

A carbon-neutrality-capactiy index for evaluating carbon sink contributions

The accurate determination of the carbon-neutrality capacity (CNC) of a region is crucial for developing policies related to emissions and climate change. However, a systematic diagnostic method for determining the CNC that considers the rock chemical weathering carbon sink (RCS) is lacking. Moreover, it is challenging but indispensable to establish a fast and practical index model to determine the CNC. Here, we selected Guizhou as the study area, used the methods for different types of carbon sinks, and constructed a CNC index (CNCI) model. We found that: (1) the carbonate rock chemical weathering carbon sink flux was 30.3 t CO₂ km^-2 yr^-1. Guizhou accounted for 1.8% of the land area and contributed 5.4% of the carbonate chemical weathering carbon sink; (2) the silicate rock chemical weathering carbon sink and its flux were 1.44 × 10³ t CO₂ and 2.43 t CO₂ km^-2 yr^-1, respectively; (3) the vegetation-soil ecosystem carbon sink and its flux were 1.37 × 10⁸ t CO₂ and 831.70 t CO₂ km^-2 yr^-1, respectively; (4) the carbon emissions (CEs) were 280 Tg CO₂, about 2.8% of the total for China; and (5) the total carbon sinks in Guizhou were 160 Tg CO₂, with a CNCI of 57%, which is 4.8 times of China and 2.1 times of the world. In summary, we conducted a systematic diagnosis of the CNC considering the RCS and established a CNCI model. The results of this study have a strong implication and significance for national and global CNC determination and gap analysis.

Importance of biochar as a key amendment to convert rice paddy into carbon negative

Biochar being made up of recalcitrant carbon (C) compounds is considered a negative emission technology (NET) due to its indirect removal of atmospheric carbon dioxide (CO₂). However, there is no clear report about how biochar remains a NET when organic amendment application in rice paddy results in a huge emission of greenhouse gases (GHG) particularly, methane (CH₄). To evaluate the net impact of biochar application on the net global warming potential (GWP) in rice paddy, no organic amendment (control), fresh manure, compost, and biochar treatments were selected during the whole investigation period. Compared to compost, biochar application decreased annual CH₄ and N₂O emissions by 55 and 31 %, respectively. In comparison to the control, biochar application increased CH₄ emission by 163 % but decreased N₂O emission by 19 %. Soil organic carbon (SOC) stock would annually deplete by 2.2 Mg C ha^-1 under control; however, biochar application could increase the SOC stock by 18.1 Mg C ha^-1 which was 63 and 33 % higher than fresh and compost treatments, respectively. As a result, the control had a net GWP of 10 Mg CO₂-eq ha^-1 however, this impact was increased with fresh manure and compost application by around 319 and 159 %, respectively. Interestingly, biochar application converted rice paddy into a C sink having a net GWP of -0.104 to -0.191 Mg CO₂-eq ha^-1. Since there was a comparable difference in grain yield among organic amendments, greenhouse gas intensity (GHGI) which is the net GWP per grain yield was significantly high in compost application of approximately 3.1 Mg CO₂-eq Mg^-1 grain being 127 % higher than control. However, the biochar application had a -0.02 Mg CO₂-eq Mg^-1 grain which was 1.4 Mg CO₂-eq Mg^-1 grain lower than the control. Conclusively, biochar application could be a considerable option in maintaining soil quality and productivity without contributing any GHG emissions and their associated impacts.

Current application of seaweed waste for composting and biochar: A review

To address the origins of ocean acidification, seaweed aquaculture is emerging as a key biosequestration strategy. Nevertheless, seaweed biomass is involved in developing food and animal feed, whereas seaweed waste from commercial hydrocolloid extraction is dumped in landfills, which together limit the carbon cycle and carbon sequestration. This work sought to evaluate the production, properties, and applications of seaweed compost and biochar to strengthen the "carbon sink" implications of aquaculture sectors. Due to their unique characteristics, the production of seaweed-derived biochar and compost, as well as their existing applications, are distinct when compared to terrestrial biomass. This paper outlines the benefits of composting and biochar production as well as proposes ideas and perspectives to overcome technical shortcomings. If properly synchronized, progression in the aquaculture sector, composting, and biochar production, potentially promote various Sustainable Development Goals.

Spatial-temporal variation of the carbon sequestration rate of afforestation in China: Implications for carbon trade and planning

Afforestation and reforestation (A&R) are nature-based and cost-effective solutions for enhancing terrestrial carbon sinks and facilitating faster carbon neutrality. However, the lack of hierarchical spatial-temporal maps for the carbon sequestration rate (CSR) from A&R at the national scale impedes the scientific implementation of forest management planning to a large extent. Here, we assessed the spatial-temporal CSR per area for A&R at the provincial, prefectural, and county levels in China using a forest carbon sequestration model under three climate scenarios. Results showed that the CSR of vegetation (CSR_Veg), soil (CSR_Soil), and the ecosystem (CSR_Eco) significantly varied across space and time. In China, the CSR_Veg, CSR_Soil, and CSR_Eco were primarily regulated by the spatial variations in temperature and precipitation. Additionally, CSR_Veg was found to be positively influenced by precipitation and temperature, whereas temperature had a negative influence on CSR_Soil. Therefore, the differences between the CSR_Veg and CSR_Soil should be emphasized in the future. These information on the spatiotemporal variation of CSR of A&R (vegetation, soil, and ecosystem) on unit area basis and at levels of province, prefecture, and county in China, can be used as a comparable protocol to estimate the carbon sinks of A&R at different scales. Overall, these hierarchical spatiotemporal maps for CSR on A&R may help to identify priority areas of forest management planning and carbon trade policy to achieve faster carbon neutrality for China in the future.

Interactions between dissolved organic matter and the microbial community are modified by microplastics and heat waves

Dissolved organic matter (DOM) exists widely in natural waters and plays an important role in river carbon cycles and greenhouse gas emissions through microbial interactions. However, information on DOM-microbe associations in response to environmental stress is limited. River environments are the main carriers of microplastic (MP) pollution, and global heat waves (HWs) are threatening river ecology. Here, through MP exposure and HW simulation experiments, we found that DOM molecular weight and aromaticity were closely related to initial microbial communities. Moreover, MP-derived DOM regulated microbial community abundance and diversity, influenced microorganism succession trajectories as deterministic factors, and competed with riverine DOM for microbial utilization. SimulatedHWs enhanced the MP-derived DOM competitive advantage and drove the microbial community to adopt a K-strategy for effective recalcitrant carbon utilization. Relative to single environmental stressor exposure, combined MP pollution and HWs led to a more unstable microbial network. This study addresses how MPs and HWs drive DOM-microbe interactions in rivers, contributes to an in-depth understanding of the fate of river DOM and microbial community succession processes, and narrows the knowledge gap in understanding carbon sinks in aquatic ecosystems influenced by human activities and climate change.

Water acidification weakens the carbon sink capacity of mixotrophic organisms

Mixotrophs combine both autotrophic and heterotrophic cell structures, and their highly plastic nutritional modes can shape the structure of food web and affect the carbon sink capacity of aquatic ecosystems. As pH affects the growth of phytoplankton by altering the carbonate balance system, water acidification caused by environmental pollution and global climate change may affect the nutritional modes of mixotrophs and bring a serious environmental consequence. In this study, we cultured mixotrophic Ochromonas gloeopara under autotrophic, mixotrophic, and heterotrophic conditions at different pH levels to test the tendency of its nutritional model and the changes in photosynthetic carbon fixation capacity. Results showed that: (1) with decreasing pH, carbon uptake of Ochromonas through phagocytosis gradually replaced the carbon fixation of photosynthesis; (2) with increasing pH, Ochromonas grazing rate decreased, and the relative contribution of photosynthetic carbon fixation to total carbon acquisition increased for Ochromonas; (3) Ochromonas became more heterotrophic under water acidification, which was involved in the up-regulated expression of genes encoding key enzymes that regulate nutrient perception, movement ability, and cell repair. These findings suggested that acidification caused mixotrophic organisms to become more heterotrophic, which can change their functional role and weaken their carbon sink capacity.

Assessment of greenhouse gases emissions and intensity from Chinese marine aquaculture in the past three decades

Marine aquaculture is increasingly gaining importance as a source of food with high nutritional value. However, the expansion of aquaculture could be responsible for water contamination that influences the environmental quality of coastal ecosystems, and emissions of greenhouse gases (GHG) that affect global climate. China is the world's largest producer of marine aquaculture protein, which demands robust studies to assess the corresponding GHG emissions and intensity. To fill in this knowledge gap, the current study quantifies and analyzes GHG emissions and intensity (emission intensity is defined as GHG emissions per unit of production) from Chinese marine aquaculture (marine aquaculture production) over the past 30 years (1991-2020). The production of marine aquaculture comes from the China Fisheries Statistical Yearbooks. And the GHG emissions and intensity were calculated based on five sectors (commercial feed, trash fish, N₂O, CH_4, and energy) by Emission-Factor Approach. The results suggest that, excluding shellfish and algae, GHG emissions of ten coastal provinces (excluding Shanghai, Hong Kong, Taiwan, and Macau) increased from 2 Mt (10⁹ kg) CO₂-eq in 1991 to 25 Mt CO₂-eq in 2020. In contrast, GHG emission intensity decreased in the same period from 7.33 (t CO₂-eq/t production) to 6.34 (t CO₂-eq/t production), indicating a progressive mitigation in GHG emissions per unit of product, hence sustainably satisfying a growing demand for food. As a result, China's marine aquaculture seems to be paving a promising way towards the neutrality of GHG emissions. In most provinces, GHG is on the rise, and only in Tianjin is on the decline in recent years. For the emissions intensity, the values of more than half provinces showed the downtrends. In addition, by considering the ratio of shellfish and algae, Chinese marine aquaculture can improve the net zero goal for GHG emissions of the sector. Finally, results also reveal for the first time the changes in taxonomic composition and spatial GHG emissions and intensity, providing new understanding and scientific bases to elaborate consistent mitigation strategies for an expanding global marine aquaculture.

Assessment of the sustainability of landcovers due to artisanal mining in Jos area, Nigeria

Environmental sustainability ensures that minerals are responsibly exploited to meet the present needs without depriving the future generations the ability to meet their needs. Unfortunately, environmental sustainability and artisanal mining seem unattainable in recent years with aggressive mining operations. It is on this premise that geospatial techniques with proven role in environmental studies were employed to assess the environmental sustainability due to artisanal mining in Jos area, Plateau State, Nigeria. Land surface temperature (LST) and seven geospatial indices used for land use land cover (LULC) estimation were generated. The mean LST values showed a steady increasing pattern from 23.98 to 25.88 °C and 29.46 °C in 1984, 2002, and 2020 respectively, as a result of exposed outcrops occasioned by mining and the expansion of mining communities. The mean value of the Normalized Difference Vegetation Index (NDVI) depicts a considerable increase from 0.179 in 1984 to 0.458 in 2002 and a slight decline to 0.438 in 2020. This is congruent with the mean Optimized Soil-Adjusted Vegetation Index (OSAVI) values, thus revealed that the Jos area is not densely vegetated implying that the course to revegetate the region has not been achieved to the tune of woodland populated vegetation. The resulting maps from Modified Normalized Difference Water Index (MNDWI) revealed a consistent decline in the mean values - 0.349, - 0.391, and - 0.411 in 1984, 2002, and 2020 respectively. Mineral recovery, mineral processing, and seasonal variations could be some of the reasons waterbodies are one of the most stressed natural resources in the study area. The mean values of Enhanced Built-up and Bareness Index (EBBI) decreased from 0.282 in 1984 to 0.202 in 2002, but increased from 0.202 in 2002 to 0.230 in 2020, which corroborated with the findings of NDBI. It was deduced that built-up areas in the study area are very low. This may be attributed to urban migration and the migration of artisanal miners to new mining sites across the state or country. The values of bare land mapped using Dry Bare Soil Index (DBSI) corresponds with that of Normalized Difference Bareness Index (NDBaI) and showed that bare land has reduced on the Jos Plateau due to improved vegetation growth. This study provided essential input and referential information for proper decision making on environmental sustenance, environmental management, and mineral resource conservation.

Variability of carbon stored in inland freshwater wetland in Northeast India

Inland freshwater wetland ecosystems are among the largest sink of carbon (C) in the biosphere. However, improved scientific understanding of the C stability and sequestration potential is required to predict response of C pool under environmental change and to identify priorities for lacustrine C sink management. This study analyses the concentration of organic C fractions based on their stability and estimates C stock along with depth and eco-zones of the Rudrasagar lake in Northeast India. Sediment samples up to 100 cm depth were collected from littoral, sub-littoral and deep layers, and analysed for organic C concentrations. Results showed that C concentration decreases with depth in the littoral layer but increases with depth in sub-littoral and deep layers. Two-way analysis of variance showed that concentrations of soil organic C (SOC) fractions were significantly different among the eco-zones but not between the soil depth. Average SOC stock was significantly higher in the deep layer (334.9 Mg C ha^-1) followed by sub-littoral (248.4 Mg C ha^-1) and littoral layer (106.1 Mg C ha^-1). Overall, we show that substantial spatial variability in SOC stock exists among the eco-zones and depth that may be driven by water inundation in deep layer and fluctuating hydrological conditions at the edges of the lacustrine ecosystem. Our study demonstrates that inland freshwater wetland is a major sink of organic C and if disturbed it can act as a carbon dioxide source.

Medium-term evaluation of the 4‰ initiative, soil organic carbon storage and stabilisation in a Mediterranean rainfed olive grove under conventional tillage: A case study

This study aims to show the effect of conventional tillage (CT) in olive orchards in the medium term (15 years) on carbon (C) storage considering the complete soil profile, on the soil C sequestration and stabilisation capacity and on the viability for the achievement of Objective 4‰. The results obtained showed important losses in soil organic carbon (SOC) and SOC stock (SOC-S), with a significant loss of total SOC-S of 42.3%. Concerning the SOC and the SOC-S linked to the fine soil fraction (<20 μm), the evolution over time led however to a SOC increase in depth (BC and C horizons) of 58.3% and 20.9% and increases in SOC-S of 17.2%, 34.7% and 27.3% for the Ap, BC and C horizons, respectively. Finally, it was seen that the goals set by the 4‰ initiative were not met, as losses of 2.1 Mg C ha^-1 yr^-1 were found when considering the entire soil profile and 0.8 Mg C ha^-1 yr^-1 when considering only the first 40 cm. Therefore, we can affirm that medium-term CT has not only conditioned C storage in the soils studied, but also their capacity for sequestration and stabilisation, which has repercussions not only on the failure to meet the objectives of the 4‰ initiative, but also on the amount of C lost in 15 years.

Exploring the spatiotemporal heterogeneity and influencing factors of agricultural carbon footprint and carbon footprint intensity: Embodying carbon sink effect

Due to the combined effects of carbon emission and carbon sink, agriculture is acknowledged as an essential contributor to achieve the Chinese government's carbon neutrality goal of 2060, and carbon footprint (CF) and carbon footprint intensity are substantial indicators to reveal the carbon emission level. For these reasons, the Theil index technique and extended STIRPAT model were employed to evaluate their spatiotemporal heterogeneity and influencing factors using panel data from 31 provinces for the period 1997-2019. The findings revealed that the CF showed an increasing trend with an annual growth rate of 24.6 %. The carbon footprint intensity (CFI) indicated an evident spatiotemporal heterogeneity and transferred over time, with an average growth rate of 19.82 %. The CFI Theil index and its contribution rate both confirmed that intra-regional difference is the main source of the overall difference, among which, the CFI Theil index displayed the distribution feature of "western (11.50 %) > central (11.12 %) > eastern (10.56 %) > northeast (6.61 %). The contribution rate of CFI illustrated the spatial pattern of "eastern (33.74 %) > central (21.07 %) > western (19.87 %) > northeast (5.24 %). Furthermore, the influencing effects of GDP per capita, planting structure, population density and urbanization level on CF and CFI also demonstrate evident spatiotemporal heterogeneity.

Determining whether hydrological processes drive carbon source and sink conversion shifts in a large floodplain-lake system in China

Lake carbon (C) cycling is a key component of the global C cycle and associated C source and sink processes. The partial pressure of carbon dioxide (pCO₂) and carbon dioxide (CO₂) exchange flux at the lake-air interface (F_c) are controlled by complex physical, chemical, and biological mechanisms. It would be instructively significant to determine whether hydrological processes drive conversion shifts between C sources and sinks in floodplain-lake systems. Findings from this study show that exogenous input and in situ metabolism related to photosynthesis, respiration, and organic matter degradation were the main driving mechanisms of CO₂ absorption and release in a large floodplain-lake system (i.e., Lake Poyang). Moreover, the intense and frequent water-level fluctuations inherent to floodplain-lakes may also have a direct or indirect impact on C cycling processes and CO₂ exchange rates in floodplain-lake systems via their effect on physical processes, inorganic C transport, in-situ metabolic processes. We confirmed the potential of C source and sink conversion in floodplain-lakes under hydrological fluctuations, and strengthen the understanding of driving mechanisms of C source and sink conversion in floodplain systems.

Environmental performance and shell formation-related carbon flows for mussel farming systems

This study examined the environmental performance of mussel (Mytilus galloprovincialis) farming in the view of reduction of greenhouse gas emissions, through the Life Cycle Assessment (LCA) methodology. The LCA has been integrated with the evaluation of the carbon sequestration potential of the biocalcification process. Three case studies of mussel farming sited along the coastal area in the north Adriatic Sea, Italy, were analyzed. Two of them concerned mussels that do not require a depuration process (area Class A), and one inspected mussel production in the rearing area of Class B, which imposes a depuration phase after harvesting. This study examined all the relevant flows of materials and energy across the systems and explored the potential role of mussel biocalcification in stocking seawater carbon into the shells. Global Warming (GW) -related emissions amounted to 0.07-0.12 kg CO2 eq for Class_A case studies and to 0.53 kg CO2 eq for Class_B case study. Through biogenic calcification, 0.19-0.20 kg CO2 kg-1 mussel is fixed in the shells, and 0.12 kg CO2 kg-1 mussel is released. These flows resulted in a net sequestration of about 0.08 kg CO2 kg-1 mussel. This study confirmed the good environmental performance of the mussel production in the farming systems analyzed. When considering greenhouse gasses emissions, the extent to which the seawater carbon fixed in the shell as calcium carbonate can be considered a carbon sink was discussed and substantiated by locally collected environmental data.

Urban development enhances soil organic carbon storage through increasing urban vegetation

Anthropogenic activities can lead to the loss of soil organic carbon (SOC) or improve its storage, hence they have the potential to exacerbate or help mitigate climate change. Urban expansion results in an initial loss of soil carbon, but long-term SOC changes during urban development are poorly understood. Herein, we studied SOC changes in the suburban and urban areas of cities with high levels of urbanization based on a long-term resampling campaign in Beijing, and a compilation of SOC content data from 21 other cities with high levels of urbanization across China over the past three decades. Our results revealed that the SOC of topsoils decreased by 17.2% in the suburban areas and increased by 104.4% in the urban areas of cities with high levels of urbanization. The changes in SOC were positively correlated with the changes in vegetation coverage and productivity. Partial least square method structural equation model analyses showed that changes in vegetation could directly affect SOC changes, and the changes in vegetation coverage and productivity were induced by human activities and climate changes in Beijing. The topsoils in the urban areas of cities with high levels of urbanization can act as carbon sinks due to the increase in vegetation. This study can help improve our understanding of the role of the SOC content of cities within the global C cycle and provide suggestions for achieving the goal of carbon neutrality in China.

Utilization of resources in abandoned coal mines for carbon neutrality

Under the new vista of carbon neutrality, all industries in China face new challenges. As the pillar industry for fossil energy, the coal industry cannot blindly "de-coal". It is necessary to combine the two-way force associated with abandoned mines to turn energy into resources and problems into solutions. Innovation that combines emission reduction and neutralization can overcome the bottlenecks in carbon neutralization in abandoned mines, and help achieve the national carbon peak in 2030 and carbon neutrality in 2060. This involves the entire life cycle of the mine, including the status quo of abandoned coal mines, and the development of downstream industries. The development mode of resource utilization in abandoned mines in accordance with the national situation was summarized, and the suggestion of carbon neutralization in abandoned mines was put forward, which involves three steps: (1) Define the value of abandoned mines, consolidate energy market share, enjoy the policy dividend, and realize carbon neutralization breakthrough; (2) list the development path of carbon neutralization in abandoned mines, utilize photosynthesis to sequester carbon, combine industrial advantages to promote the development of a new energy industry, promote the integration of carbon emission, gathering, sequestration and utilization, realize carbon sequestration and mineralization in terminals and participate in carbon sink market allocation; (3) promote multiple simultaneous measures to solve existing problems, develop abandoned mines, and implement carbon neutralization goals.

Spatio-temporal pattern of urban vegetation carbon sink and driving mechanisms of human activities in Huaibei, China

Carbon neutrality is a strategic choice for the sustainable development of global cities. Quantitatively assessing the spatio-temporal patterns of urban vegetation carbon sink and the impact of human activities has become an essential basis for adjusting urban carbon balance. We used Huaibei, a typical city with vigorous human coal resource mining activities, as the case study area. We regarded the net ecosystem productivity (NEP) as an indicator parameter of vegetation carbon sink and calculated it based on the improved Carnegie-Ames-Stanford approach (CASA). We then revealed the spatial-temporal evolution of vegetation carbon sink through trend analysis, coefficient of variation, and standard direction. Finally, we used geographic detectors to evaluate the impact of human activities on NEP. We found that net primary productivity (NPP) accuracy was good, and the R² value was 0.755 compared with MODIS NPP products. NEP was characterized by the first decrease and then increase, showing a slow increase overall, with an average trend coefficient of 0.15 gC·m^-2·a^-1. The average value in 2010 was the lowest at 18.30 gC·m^-2·a^-1. In terms of spatial characteristics, NEP showed a gradual decrease from north to south. High and severe fluctuations were distributed along the southeast, mainly concentrated in Duji District, Xiangshan District, and Lieshan District. The driving factors with reliable explanatory power for NEP were population density, GDP, and road density, while land use type, soil erosion intensity, and mining and collapse area had weak explanatory power. Meanwhile, factors of cooperative interaction enhanced the explanatory power of the results.

Growth performance and ecological services evaluation of razor clams based on dynamic energy budget model

Bivalve shellfish aquaculture has been proposed to abate eutrophication and increase carbon sink in integrated multi-trophic aquaculture ecosystems. An individual growth model for razor clams Sinonovacula constricta in an integrated aquaculture pond of Portunus trituberculatus- Penaeus japonicus- S. constricta was constructed based on dynamic energy budget (DEB) theory after parameter measurement and model validation. Goodness-of-fit indices (R-squared, mean difference, and absolute and relative root mean square error) showed that the DEB model accurately reproduced razor clam growth. The growth performance evaluation of razor clams under different environmental conditions showed that warming climate and food shortages inhibited the razor clam growth. The quantification results of ecological service showed that individual razor clam have the potential for nutrient (nitrogen and phosphorus) removal and CO₂ fixation, but exhibit a source of CO₂ in individual month. The possible applications and contribution of this aquaculture model in China are also discussed, and the assessment results can provide important support for the low carbon bivalve integrated aquaculture.

Net ecosystem CO2 exchange from jute crop (Corchorus olitorius L.) and its environmental drivers in tropical Indo-Gangetic plain using open-path eddy covariance technique

Present study is a maiden attempt to assess net ecosystem exchange (NEE) of carbon dioxide (CO₂) flux from jute crop (Corchorus olitorius L.) in the Indo-Gangetic plain by using open-path eddy covariance (EC) technique. Diurnal variations of NEE were strongly influenced by growth stages of jute crop. Daytime peak NEE varied from - 5 µmol m^-2 s^-1 (in germination stage) to - 23 µmol m^-2 s^-1 (in fibre development stage). The ecosystem was net CO₂ source during nighttime with an average NEE value of 5-8 μmol m^-2 s^-1. Combining both daytime and nighttime CO₂ fluxes, jute ecosystem was found to be a net CO₂ sink on a daily basis except the initial 9 days from date of sowing. Seasonal and growth stage-wise NEEs were computed, and the seasonal total NEE over the jute season was found to be - 268.5 gC m^-2 (i.e. 10.3 t CO₂ ha^-1). In different jute growth stages, diurnal variations of NEE were strongly correlated (R² > 0.9) with photosynthetic photon flux density (PPFD). Ecosystem level photosynthetic efficiency parameters were estimated at each growth stage of jute crop using the Michaelis-Menten equation. The maximum values of photosynthetic capacity (P_max, 63.3 ± 1.15 µmol CO₂ m^-2 s^-1) and apparent quantum yield (α, 0.072 ± 0.0045 µmol CO₂ µmol photon^-1) were observed during the active vegetative stage, and the fibre development stage, respectively. Results of the present study would significantly contribute to understanding of the carbon flux from the Indian agro-ecosystems, which otherwise are very sparse.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Design, production, and validation of the biological and structural performance of an ecologically engineered concrete block mattress: A Nature-Inclusive Design for shoreline and offshore construction

Over the past decade, the scientific community has studied, experimented, and published a notable body of literature on the ecological enhancement of coastal and marine infrastructure (CMI). The Nature-Inclusive Design (NID) approach refers to methods and technologies that can be integrated into the design and construction of CMI to create a suitable habitat for native species (or communities) whose natural habitat has been degraded or reduced. To examine the compliance of new environmentally sensitive technologies with structural requirements and fiscal restraints, while providing ecosystem and habitat value, this paper presents the findings of a structural-economical-biological analysis of ecologically engineered Articulated Concrete Block Mattresses (ACBMs). To evaluate the structural and biological performance of the Ecological Articulated Concrete Block Mattresses, a pilot project was deployed in April 2017 at Port Everglades, Florida, USA, and evaluated against controls of adjacent artificial structures and smooth-surface concrete blocks and monitored over a period of two years. The elements of ecological enhancement implemented in the fabrication and design of the ecologically enhanced ACBMs were comprised of bio-enhancing concrete additives and science-based designs. Based on the results of this study, these design alterations have increased the richness and diversity of sessile assemblages compared to control blocks and adjacent artificial structures and supported a higher abundance of mobile species. This ecological improvement was achieved within the operational limitations of conventional manufacturing and installation technologies, while complying with strict structural requirements for standard concrete marine construction. The results supported the working hypothesis and demonstrated that modifications of concrete composition, surface texture, and macro-design have the potential to increase the ecological value of concrete-based CMI and promote a more sustainable and adaptive approach to coastal and marine development in an era of climate resilience-building. Integr Environ Assess Manag 2022;18:148-162. © 2021 SETAC.

Significance of belowground production to the long-term carbon sequestration of intertidal seagrass beds

The high biomass and sediment features of seagrass beds can make their belowground portions critical sources of blue carbon sinks. However, seagrass belowground production and decomposition have rarely been quantified in the field. To assess the significance of seagrass belowground production to carbon sequestration, belowground carbon budgets were constructed in intertidal seagrass beds of the late-successional species Thalassia hemprichii and the early-successional species Haloduleuninervis in southern Taiwan. For both species, the turnover rates of the belowground portions were much longer than that of the aboveground portion, so the belowground biomass was much higher than the aboveground biomass. The leaf productivity of both species was significantly higher than the belowground productivity, but most of the leaf production decomposed within a year. The lower turnover and slower decomposition rates of the belowground portions allowed the late-successional seagrass T. hemprichii to store more carbon in the sediments than the early-successional seagrass H. uninervis. Long-term changes for the past 20 years in the sediment depth showed that the sediments of seagrass beds were increasing in the habitats at low elevation but were decreasing or had no clear trends in the habitats at high elevation or on the windward side. The carbon storage rates according to the belowground production of T. hemprichii and H. uninervis were 0.3-4.7 and 1.5-2.3 g C m^-2 yr^-1, respectively, which can potentially contribute 53% of the long-term organic carbon storage in the low-elevation sediments.

Country-level land carbon sink and its causing components by the middle of the twenty-first century

BACKGROUND

Countries have long been making efforts by reducing greenhouse-gas emissions to mitigate climate change. In the agreements of the United Nations Framework Convention on Climate Change, involved countries have committed to reduction targets. However, carbon (C) sink and its involving processes by natural ecosystems remain difficult to quantify.

METHODS

Using a transient traceability framework, we estimated country-level land C sink and its causing components by 2050 simulated by 12 Earth System Models involved in the Coupled Model Intercomparison Project Phase 5 (CMIP5) under RCP8.5.

RESULTS

The top 20 countries with highest C sink have the potential to sequester 62 Pg C in total, among which, Russia, Canada, USA, China, and Brazil sequester the most. This C sink consists of four components: production-driven change, turnover-driven change, change in instantaneous C storage potential, and interaction between production-driven change and turnover-driven change. The four components account for 49.5%, 28.1%, 14.5%, and 7.9% of the land C sink, respectively.

CONCLUSION

The model-based estimates highlight that land C sink potentially offsets a substantial proportion of greenhouse-gas emissions, especially for countries where net primary production (NPP) likely increases substantially and inherent residence time elongates.

Sizing the carbon sink associated with Posidonia oceanica seagrass meadows using very high-resolution seismic reflection imaging

Among blue carbon ecosystems, seagrass meadows have been highlighted for their contribution to the ocean carbon cycle and climate change mitigation derived from their capacity to store large amounts of carbon over long periods of time in their sediments. Most of the available estimates of carbon stocks beneath seagrass meadows are based on the analysis of short sediment cores in very limited numbers. In this study, high-resolution seismic reflection techniques were applied to obtain an accurate estimate of the potential size of the organic deposit underlying the meadows of the Mediterranean seagrass Posidonia oceanica (known as 'matte'). Seismic profiles were collected over 1380 km of the eastern continental shelf of Corsica (France, Mediterranean Sea) to perform a large-scale inventory of the carbon stock stored in sediments. The seismic data were ground-truthed by sampling sediment cores and using calibrated seismo-acoustic surveys. The data interpolation map highlighted a strong spatial heterogeneity of the matte thickness. The height of the matte at the site was estimated at 251.9 cm, being maximum in shallow waters (10-20 m depth), near river mouths and lagoon outlets, where the thickness reached up to 867 cm. Radiocarbon dates revealed the presence of seagrass meadows since the mid-Holocene (7000-9000 cal yr BP). Through the top meter of soil, the matte age was estimated at 1656 ± 528 cal yr BP. The accretion rate showed a high variability resulting from the interplay of multiple factors. Based on the surface area occupied by the meadows, the average matte thickness underneath them and the carbon content, the matte volume and total C_org stock were estimated at 403.5 ± 49.4 million m³ and 15.6 ± 2.2 million t C_org, respectively. These results confirm the need for the application of large-scale methods to estimate the size of the carbon sink associated with seagrass meadows worldwide.

Regional difference decomposition and its spatiotemporal dynamic evolution of Chinese agricultural carbon emission: considering carbon sink effect

The current study aims to analyze the regional differences and spatiotemporal dynamic evolution of carbon emission intensity (CEI) and carbon emission per capita (CEPC) of planting industry with consideration of carbon sink effect. The results indicate that: (i) The CEI and CEPC of China's planting industry present significant non-equilibrium distribution characteristic during the investigate period, provinces with high CEI are mainly distributed in major agricultural provinces, while high CEPC provinces are mainly located in northeast and individual central provinces with large planting industry. (ii) Inter-regional difference is the principal course of the total differences, the CEI Theil index demonstrates gradient decreasing pattern of "western > central > eastern > northeast," the contribution rate of CEI Theil index shows "northeast > eastern > central > western," the CEPC Theil index shows the spatial pattern of "northeast > central > western > eastern," and the contribution rate of CEPC Theil index presents the spatial pattern of "eastern > central > western > northeast." (iii) The dynamic evolution of CEI and CEPC curve presents polarization or multipolar differential phenomenon accompanies with distinct gradient characteristics, the regional difference of agglomeration level in CEI is gradually narrowing, while the CEPC gradually expanding and the dispersion level is increasing, which implies the "intra-regional convergence and inter-regional divergence." Consequently, differential carbon reduction policies have been put forward according to the study findings.

Defoliation-induced tree growth declines are jointly limited by carbon source and sink activities

Defoliation resulting from herbivory, storm, drought, and frost may seriously impair tree growth and forest production. However, a comprehensive evaluation of defoliation impacts on tree carbon (C) assimilation and growth has not been conducted. We performed a meta-analysis of a dataset that included 1562 observations of 40 tree species from 50 studies worldwide, and evaluated defoliation impacts on photosynthetic capacity, C allocation, and tree growth. Our results showed that the reduced tree-level leaf area by defoliation outweighed the enhanced leaf-level photosynthesis, leading to a net reduction in tree C assimilation that was accompanied with decreases in nonstructural carbohydrates (NSCs) concentrations. The negative effects of defoliation on leaf NSCs decreased over time, but leaf production increased following defoliation, suggesting a shift in the C allocation towards shoots over roots. Defoliation intensity negatively affected tree growth, but post-defoliated recovery time did oppositely. The structure equation modelling showed that defoliation reduced tree growth mainly by indirectly reducing C assimilation (r = -0.4), and minorly by direct negative effect of defoliation intensity (r = -0.28) and positive effect of post-defoliated time (r = 0.33). These findings suggest that tree growth declines caused by defoliation are co-limited by C-source and sink activities, which provide a physiological basis of tree growth that is of significance in tree growth modelling and forest management under global changes.

Determining afforestation areas by using social, economic and ecological scales

Global anthropogenic damage is caused when humans aim to improve their welfare by social and economic activities. From this vantage, this paper seeks to determine priority locations for afforestation areas and carbon sinks by using socio-economic and ecological variables. Factor analysis is performed on degraded forest areas (DEGFRST), the ratio of non-forest areas to provincial general area (NFL), average of total monthly rainfall (ATMR), air pollution (PM10), the amount of migration (AMGR), annual average population density (AAPD), gross domestic product by industrial activity (I_GDP), socio-economic development index (SEDI) of provinces, export (EXP) and import (IMP) amount of provinces, average number of cars per one thousand people (ACNPT), and average electricity consumption per person (AECPP) variables for all provinces in Turkey (KMO = 0.802, Bartlett's χ² = 832.191, and p < 0.0001). Principal component analysis is used as a factor extraction method. Based on the three components obtained (explaining 74.730% of the total variance), the factor scores of 81 provinces were analyzed geostatistically using the Kriging interpolation method. The final map of potential afforestation areas was created using three-factor maps and factor variances, according to weighted overlay analysis. As a result of this study, afforestation priority areas in Turkey were identified based on three components. In subsequent studies, by increasing the number of variables used in this study, strategies for increasing Turkey's carbon sinks can be planned. Evaluating socio-economic and ecological factors together in afforestation studies can contribute to balancing human impact and conservation through alternative approaches.

Impacts of bark beetle-induced tree mortality on pyrogenic carbon production and heat output in wildfires for fire modeling and global carbon accounting

Forests store significant quantities of carbon, and accurate quantification of the fate of this carbon after fire is necessary for global carbon accounting. Pyrogenic carbon (PyC) encompasses various carbonaceous products of incomplete combustion formed during fires and has potential to act as a carbon sink for up to millennia, but current estimates of PyC production in wildfires vary widely. Northern hardwood forests have changed dramatically in recent decades due to insect epidemics, such as the bark beetle epidemic in the Rocky Mountain Region which has caused widespread mortality. This study assessed impacts of bark beetle-induced mortality on fuel pyrolysis kinetics, carbon partitioning of combustion products, and net heat output to aid in forest fire modeling and carbon accounting by comparing healthy and beetle-killed lodgepole pine tree boles burned in a 2018 forest fire in southeast Wyoming, USA with unburned boles. Results showed charring predominantly restricted to the bark and cambium. Significant differences between burned and unburned healthy and beetle-impacted bark/cambium compositions were identified, and PyC production and energy output were quantified. Charring extent and PyC content were found to be greater in beetle-impacted boles due to a reduction in bark/cambium resistance to heating and charring, with 80 times more PyC produced in a beetle-killed bark/cambium than in a healthy bark/cambium. Upon scale-up, total PyC production in the fire-affected area was estimated to be 0.71 GgPyC (82.5 kgPyC/ha). This was found to be significantly enhanced compared to an estimated PyC production of 0.036 GgPyC (4.12 kgPyC/ha) in a hypothetical healthy lodgepole pine ecosystem of equal area. The results of this investigation concluded that the 58% beetle-induced mortality in the Badger Creek Fire area resulted in 3 times more carbon released to the global atmosphere, 20 times more PyC retained onsite and 32% greater heat output during wildfire.

Dynamics in riverine inorganic and organic carbon based on carbonate weathering coupled with aquatic photosynthesis in a karst catchment, Southwest China

Carbonate mineral weathering coupled with aquatic photosynthesis, herein termed 'coupled carbonate weathering' (CCW), represents a significant carbon sink which is determined by riverine hydrochemical variations. The magnitudes, variations and mechanisms responsible for the carbon sink produced by CCW are still unclear. In this study, major ions, TOC and discharge data at the Darongjiang, Lingqu, Guilin and Yangshuo hydrologic stations in Li River basin, a karst catchment typical of this geographic region, were analysed from January 2012 to December 2015 to elucidate the temporal variations in riverine inorganic and organic carbon and their controlling mechanisms. The results show that (1) HCO₃^- was sourced from carbonate weathering and silicate weathering, carbonate weathering by carbonic acid being predominant; (2) TOC was created chiefly by the transformation of bicarbonate to organic carbon by aquatic phototrophs during the non-flood period; (3) The carbon sink produced by coupled carbonate weathering in the Li River basin was calculated to be 14.41 tC·km^-2·yr^-1, comprised of the sink attributable to carbonate weathering (12.17 tC·km^-2·yr^-1) and sink due to the "biological carbon pump" (S_BCP) (2.24 tC·km^-2·yr^-1). The S_BCP thus accounted for approximately 15.54% of the total carbon sink, indicating that the proportion of riverine TOC sourced by the transformation from bicarbonate to organic carbon by aquatic phototrophs may be high and must be considered in the estimation of carbonate weathering-related carbon sinks elsewhere.

Response of the weathering carbon sink in terrestrial rocks to climate variables and ecological restoration in China

The weathering carbon sink (CS) of rocks has a sensitive response to different influencing factors, and it is important to accurately distinguish this response in the global carbon cycle. However, no quantitative analysis of the response mechanism has been performed. In this study, the CS of the 12 types of terrestrial rocks in China from 2000 to 2014 is estimated using the GEM-CO₂ model. The relative contribution rates of climate change and ecological restoration to the CS are quantitatively evaluated using the Lindeman-Merenda-Gold model. Results showed that: (1) The CS of terrestrial rocks in China was 17.69 Tg C yr^-1, and the CS flux (CSF) was 2.53 t C km^-2 yr^-1; mixed sedimentary rocks had the highest CS (6.89 Tg C yr^-1), and carbonate rocks had the highest CSF (5.8 t C km^-2 yr^-1). (2) The average annual CSF slightly decreased at a rate of 5.4 kg C km^-2 yr^-1; the areas of the CSF that decreased in the south were the areas where water budget decreased significantly, and it was the areas with a reduced water budget and ecological deterioration in the north. (3) The relative contribution rates of water budget and precipitation reached 57% and 35%, respectively; the response of the CSF to temperature was evident in areas with low or decreasing temperatures, and the influence of fractional vegetation cover (FVC) on the CSF in low value area was evident. (4) Mixed sedimentary rocks and carbonate rocks displayed a more evident reduction trend in the CSF than other rocks. This research verified the applicability of the GEM-CO₂ model in China and presented a scientific basis for quantitative assessment of the impact of climate change and ecological restoration on the CSF.

Sources and selective preservation of organic matter in the karst watershed: evidence from sediment records in a plateau deep lake, Southwestern China

Human activities have greatly altered terrestrial carbon (C) dynamics associated with vegetation cover and land use changes, thereby influencing the C sink in downstream ecosystems. However, the transport and preservation of organic C from soils that experience serious erosion in the karst area are scarce, particularly at catchment scales. In this study, chemical characteristics of organic matter (OM) isolated from the topsoil, overlying water, and lake sediments, as well as subsequent source identification, were inferred from the molecular, spectroscopic, and carbon isotopic (δ¹³C) signatures in a typical karst catchment, Southwestern China. The results indicated that the elemental compositions of the calcareous soil and paddy soil significantly differed from the yellow soil. High similarities existed in the fluorescence spectra of humic substances (HS) extracted from the front two soil types with those of lake sediments, indicating the homogeneous nature of OM molecular structure. The C/N ratios of six dissolved OM fractions and sedimentary HS along with δ¹³C values consistently reflected the primary terrestrial source. It was estimated to account for 60% of total organic C in sedimentary OM by end-member mixing modeling in accordance with soil erosion intensity and large recharge coefficient of this catchment. The evolution of soil loss and lake productivity can be well deduced from sediment records of organic C content, C/N ratio, and the specific information of HS. This research highlighted that the composition, source, and fate of OM in the karst lake was mainly dominated by the terrestrial C flux, rather than in-lake production. Furthermore, soil type and erosion intensity have significant effects on the nature of eroded OM and ultimate preservation.

Seasonal variation of net ecosystem CO2 exchange and its influencing factors in an apple orchard in the Loess Plateau

The Loess Plateau is the largest apple cultivation region in the world. However, the role of rain-fed apple orchards as carbon sinks or sources, including the dynamic variation and influencing factors, are still unclear. In this study, the net ecosystem CO₂ exchange (NEE) was monitored by an eddy covariance (EC) system in Loess Plateau apple orchards during 2016-2017. The results demonstrated that the annual NEE was higher in 2016 (- 698.0 g C m^-2 year^-1) than in 2017 (- 554.0 g C m^-2 year^-1). Particularly, the amount of orchard CO₂ uptake was significantly greater in 2016 (- 772.0 g C m^-2) than in 2017 (- 642.1 g C m^-2) during the carbon sink period. This difference may be attributed to the higher NEE in 2016 compared to 2017 during the fast and slow growth periods. In addition, a higher daily NEE occurred to the higher air temperature (T_a), which promoted early sprouting in 2016 (- 3.91 g C m^-2 day^-1) compared to 2017 (- 2.86 g C m^-2 day^-1) during the fast growth period. The daily NEE in 2016 (- 2.59 g C m^-2 day^-1) was remarkably higher than that in 2017 (- 1.41 g C m^-2 day^-1) during the slow growth period, owing to the greater number of cloudy and rainy days and lower temperatures in 2017. Overall, the present study demonstrated the key role played by the amount of precipitation and temperature in regulating the NEE during the growth season and provided accurate quantitative information on the carbon budget in apple orchards. Graphical abstract.

Seismic interval velocity in the matte of Posidonia oceanica meadows: Towards a non-destructive approach for large-scale assessment of blue carbon stock

High-resolution seismic reflection data have been used over the last decades to estimate the thickness of the long-term Blue Carbon sink associated to the below-ground sediment deposit (matte) of the Posidonia oceanica meadows. Time-to-depth conversion of these geophysical datasets was usually performed assuming a sound velocity in this structure, but appropriate seismic interval velocity measurements is necessary to achieve accurate calibration. This study describes the first methodology to estimate the seismic interval velocity in the matte. This approach performed on the eastern continental shelf of Corsica island (France, NW Mediterranean) is based on measurements of the vertical matte profile from high-resolution seismic reflection profiles (s TWTT) and from seafloor morpho-bathymetric DTM (multibeam echosounders - MBES and Light Detection and Ranging - LiDAR surveys) calibrated with ground-truthing data. A biogeosedimentological analysis of horizontal cores sampled in vertical matte escarpments has been undertaken to identify the potential relationship of sediment and environmental parameters with sound velocity. The cross-comparison and the data intercalibration show significant correlation of MBES (R² = 0.872) and LiDAR datasets (R² = 0.883) with direct underwater measurements. Seismic interval velocities (n = 367) have been found to range between 1631.9 and 1696.8 m s^-1 (95% confidence interval) and are estimated on average at 1664.4 m s^-1, which is similar to the literature for unconsolidated marine sediments. The prediction map provided by the ordinary kriging method emphasized, however, a high variability of sound velocity within the study area. The results showed that changes in sound velocity in the matte are positively and strongly correlated with sand and gravel content and environmental factors such as distance to coastal river mouths and coastline. However, it was found that a negative relationship linked sound velocity with total and coarse organic content of matte deposits.

Can more carbon be captured by grasslands? A case study of Inner Mongolia, China

Grasslands cover a large part of the Earth's surface and play an important role in the global carbon cycle. Previous studies have indicated that nearly half of the grassland vegetation cover has experienced degradation on a global scale; if this degradation is reversed, grasslands can act as potential carbon sinks. However, the question of how much more carbon (carbon gap) could be sequestrated by grassland vegetation by regulating human activities remains unanswered. Here, we present an innovative approach to assess the achievable carbon gap through focal analysis of long-term Moderate Resolution Imaging Spectroradiometer (MODIS) Net Primary Production (NPP) dataset or observed NPP (ONPP). In focal analysis, region segmentation was done to produce spatially homogeneous patches of the same types of soil, topography, and vegetation, referred to as S-T-V units, to minimize the variation in environmental conditions and their impacts on the NPP. Then, the ONPP within each S-T-V unit was rectified by offsetting the variations in potential NPP determined by the climate-oriented Miami NPP model. Hence, spatial variations in the climate-rectified ONPP (ONPP_CR) in an S-T-V unit were solely determined by different human activities across locations. In a case study of the Inner Mongolia grassland of China, three focal statistics, namely mean (Mean), 95% percentile threshold (95%PCT), and maximum (Max) within each S-T-V unit were computed for ONPP_CR for each year from 2000 to 2014 to assess the annual carbon uptake that was achievable by updating grassland management practices. The carbon gaps were assessed to be 11.8, 58.9, and 74.6 gC/m² per year based on Mean, 95%PCT, and Max, respectively, compared to 65.0 gC/m² per year based on the traditional pixel-based approach. We conclude that the carbon gap patterns identified from focal analysis are practically achievable and are more valuable in formulating policy-related decisions for grassland management. Implementing sustainable management practices that are currently being practiced at locations with high ONPP_CR in neighboring degraded areas is expected to increase the carbon sequestration by grassland vegetation by one-third.