Net Carbon Sequestration Research Articles

Can citrus production in China become carbon-neutral? A historical retrospect and prospect

Reducing greenhouse gas (GHG) emissions and increasing carbon sequestration (CS) in agricultural systems are critical to realize carbon neutrality, and slowdown global climate change. However, a comprehensive analysis of GHG emissions, CS and the ways to achieve carbon neutrality of citrus production systems in China has not been reported. In this study, a NUFER-Citrus-LCA (citrus nutrient flows in food chains, environment, and resource use model combined with life cycle assessment) combined model was used to quantify the spatial and temporal characteristics of GHG emissions and CS from citrus production in China from 2004 to 2018 to determine the potential and the means to achieve carbon neutrality. The results showed that the GHG emissions varied remarkably among major citrus-producing provinces, with a decreasing trend in the last decade except for Guangdong province. However, the estimated emission for 2014–2018 (12,261 kg CO2-eq ha−1 yr−1) was 2–3 times greater than that of other countries, with Guangdong province recording the highest GHG emissions (24,403 kg CO2-eq ha−1 yr−1). Nitrogen fertilizer accounted for 71.5% of the total GHG emissions. The total carbon sequestration (TCS) during 2014–2018 was 24.1–74.5% of the total greenhouse gas (TGHG) emissions, depending on the province, indicating a net positive carbon emission in China’s citrus production system. The scenario analysis showed considerable potential for transforming the Chinese citrus production system from a carbon source to a carbon sink. This will, however, require a crop management system that combines optimized nitrogen fertilizer management, 50% replacement of chemical fertilizer with organic fertilizer and use of cover crops, resulting in a total net carbon sequestration of 15.2 Mt CO2-eq yr−1 nationally. Implementation of this crop management model is imperative for transitioning the Chinese citrus production toward carbon neutrality.

Creating economic incentives for agroforestry in Assam

Afforestation has been widely identified as the most affordable way to mitigate the worst effects of climate change by sequestering carbon and making ecosystems more resilient. However, developing countries like India have to deal with rising population and urbanization, often at the cost of its ecology. We propose that significant increase in afforestation and carbon sequestration can be achieved by shifting areas under crop cultivation to mixed variety afforestation. Private land can be diverted from crop cultivation to achieve afforestation targets. We suggest combining two existing Government of India schemes to ensure monthly payments to individual farmers for shifting away a portion of paddy cultivation, for a period of seven years in the state of Assam in India. Our calculations show that this model can increase average farm incomes through income transfers during the growth phase, along with net carbon sequestration. Varied maturity periods and uses of timber and non-timber forest produce will sustain farmer incomes beyond the initial support period and allow for increased forest cover and carbon sequestration over large areas in Assam, without putting any additional pressure on the exchequer.

Above- and belowground linkages during extreme moisture excess: leveraging knowledge from natural ecosystems to better understand implications for row-crop agroecosystems.

Above- and belowground linkages are responsible for some of the most important ecosystem processes in unmanaged terrestrial systems including net primary production, decomposition, and carbon sequestration. Global change biology is currently altering above- and belowground interactions, reducing ecosystem services provided by natural systems. Less is known regarding how above- and belowground linkages impact climate resilience, especially in intentionally managed cropping systems. Waterlogged or flooded conditions will continue to increase across the Midwestern USA due to climate change. The objective of this paper is to explore what is currently known regarding above- and belowground linkages and how they impact biological, biochemical, and physiological processes in systems experiencing waterlogged conditions. We also identify key above- and belowground processes that are critical for climate resilience in Midwestern cropping systems by exploring various interactions that occur within unmanaged landscapes. Above- and belowground interactions that support plant growth and development, foster multi-trophic-level interactions, and stimulate balanced nutrient cycling are critical for crops experiencing waterlogged conditions. Moreover, incorporating ecological principles such as increasing plant diversity by incorporating crop rotations and adaptive management via delayed planting dates and adjustments in nutrient management will be critical for fostering climate resilience in row-crop agriculture moving forward.

Processes underpinning natural capital account compilation highlight the potential for low-input grazing to mitigate farm carbon emissions while also improving biodiversity outcomes

Remnant woodland areas are commonly part of livestock grazing operations in temperate Australia. These remnant areas can store substantial amounts of carbon and have important biodiversity value, but are at risk of ongoing decline due to nutrient enrichment, overgrazing, clearing of woody debris and lack of tree recruitment. The process of compiling experimental farm-scale natural capital accounts (NCA) for 11 wool-growing businesses in temperate Australia demonstrated that some wool growers may be managing these areas in ways that sustained, and at times regenerated, carbon and other natural values. When managed sensitively, these largely native areas provide forage and shelter for livestock production while carbon and associated biodiversity is also protected, and in some cases regenerated. The farm-scale NCA process highlighted that for some farm businesses net sequestration of carbon can occur at a farm-scale, substantially owing to the management approach applied to these remnant areas. The process highlighted the potential for livestock grazing approaches underpinned by the ecosystem services provided by native grasses, forbs and woodlands (i.e. low-input rather than nutrient enrichment and pasture modification) to contribute to balancing carbon emissions from other areas of more intensive management within a farm business. With the current momentum worldwide aimed at achieving net zero emissions, there is an opportunity that has not existed previously to conserve, and sometimes regenerate, these remnant woodland areas on farmland. This could contribute to reversing a crisis of biodiversity loss in this threatened ecosystem while also helping farm businesses to reduce overall carbon emissions.

Feasibility of Planting Trees around Buildings as a Nature-Based Solution of Carbon Sequestration—An LCA Approach Using Two Case Studies

In response to Canada’s commitment to reducing greenhouse gas emissions and to making pathways to achieve carbon neutral buildings, this paper presents two real case studies. The paper first outlines the potential of trees to absorb CO2 emissions through photosynthesis, and the methods used for the estimation of their annual carbon sequestration rates. The net annual carbon sequestration rate of 0.575 kgCO2eq/m2 of tree cover area is considered in our study. Then, this paper presents the carbon life cycle assessment of an all-electric laboratory at Concordia University and of a single-detached house, both located in Montreal. The life cycle assessment (LCA) calculations were performed using two software tools, One Click LCA and Athena Impact Estimator for Buildings. The results in terms of Global Warming Potential (GWP) over 60 years for the laboratory were found to be 83,521 kgCO2eq using One Click LCA, and 82,666 kgCO2eq using Athena. For the single-detached house that uses natural gas for space heating and domestic hot water, the GWP was found to be 544,907 kgCO2eq using One Click LCA, and 566,856 kgCO2eq using Athena. For the all-electric laboratory, a garden fully covered with representative urban trees could offset around 17% of the total life cycle carbon emissions. For the natural gas-powered single-detached house, the sequestration by trees is around 3% of the total life cycle carbon emission. This paper presents limits for achieving carbon neutral buildings when only the emissions sequestration by trees is applied, and discusses the main findings regarding LCA calculations under different scenarios.

Nutrient-doped synthetic silicates for enhanced weathering, remineralization and fertilization on agricultural lands of global cold regions- A perspective on the research ahead.

There is now a dire demand for negative emissions technologies (which sequester CO2 from the atmosphere) that can be rapidly deployed, are scalable, and are demonstrably safe and effective. Enhanced weathering of silicate minerals has demonstrated a significant potential for CO2 capture and sequestration by the formation of pedogenic carbonates in soils, subsoils, and sediments. This technique has also been shown to deliver fruitful results in terms of improving soil health, and in turn plant health, through remineralization. The silicate minerals that possess the highest weathering rates (e.g., wollastonite), are relatively rare in nature, whereas the abundant ones (e.g., anorthite and forsterite) have a slower pace of weathering, especially in colder and drier climates such as found in the extensive agricultural lands of Western Canada and the Western United States. Herein, we offer a perspective on the opportunities for computational studies targeting atomic-scale interaction of CO2 with silicates and synthesis of fast-weathering silicates (such as larnite and bredigite), whose composition can be tuned to also support soil fertilization and remineralization, and whose production must be integrated with green and carbon-neutral technologies to ensure net-negative life cycle emissions.

Carbon sequestration via shellfish farming: A potential negative emissions technology

Negative emission technologies driven by nature with less energy input, lower costs, and long carbon storage capacities are essential for meeting ambitious global carbon mitigation goals. This paper evaluates the carbon sequestration potential of bivalve shellfish farming because its sequestration process is driven by nature, and it is cost-effective and energy efficient. The carbon in shells and the carbon that enters sediments via bio-deposition are long-lived forms of carbon. Using China as a case study, a preliminary estimation suggests that the carbon sequestration efficiency and intensity of cultivated shellfishes are much higher than those of artificial forests. In China, approximately 6.23 Mt CO2-eq a−1 was fixed via net carbon sequestration during shellfish growth from 2015 to 2019. In addition, the farmed shellfishes provided 0.37 Mt of harvested protein, and approximately 37.39 Mt CO2-eq a-1 were reduced compared to the same amount of protein provided by beef, and thus, shellfish farming has the win-win benefits of carbon sequestration and high-quality food provision. More importantly, a total of 5.64 Gt CO2-eq, accounting for 17.63% of the total emissions in 2020, can be potentially sequestrated at the global scale under the world's largest farming area scenario.

Carbon footprint of New Zealand beef and sheep meat exported to different markets

New Zealand (NZ) is the world's largest exporter of sheep meat and an important exporter of beef. Given the current concern about the impact of food production on climate change, it is important to understand the extent of greenhouse gas (GHG) emissions for NZ exported products. This Life Cycle Assessment study calculated the cradle-to-grave carbon footprint of beef and sheep meat produced in NZ and exported to different markets. Sensitivity analyses were performed to evaluate the effect of different Global Warming Potential (GWP) metrics, carbon sequestration by trees on farms and different allocation methods at the processing stage. The carbon footprint for the cradle-to-farm gate represented 90–95% of the cradle-to-grave for both beef and sheep. At the farm gate (not accounting for the sensitivity analysis studied), the beef results were influenced by the contribution of dairy beef, which showed a 34% lower footprint than traditional beef (8.97 and 6.88 kg CO2e kg−1 LW, respectively). Sheep meat had lower emissions than beef for the on-farm stage (6.01 kg CO2e kg−1 LW). For GWP*, the estimated footprint values were much lower, especially for sheep, where the national flock decreased over the last 20 years. National data on net carbon sequestration by trees within farms was significant and equated to 29% of the total on-farm GHG emissions. The meat processing stage contributed 2–4% of the carbon footprint, while post-processing was 2–6%. Despite the long shipping distances involved, NZ beef and sheep meat supplied to international markets have a full life-cycle carbon footprint at the lower end of other published estimates.

Carbon sequestration and greenhouse gas emissions for different rice cultivation practices

Traditional rice farming systems require large amounts of water for irrigation, labour for transplanting culms and tending fields, and therefore, emit large amounts of greenhouse gases such as carbon dioxide (CO 2 ), nitrous oxide (N 2 O) and methane (CH 4 ). Adopting alternative rice farming practices could reduce greenhouse gas emissions and increase carbon (C) sequestration. In this study, an on-site field experiment was conducted to assess the contribution of carbon by farm operations involved in the three types of rice cultivation practices: conventional (CVN), the system of rice intensification (SRI), and zero-tillage (ZTL). The study was aimed to examine the carbon indices under three different rice cultivation methods to assess the ecosystem services and disservices associated with carbon sequestration and emission. Results showed that fertilizer application significantly contributed to GWP among the three cultivations. In the CVN and ZTL plots, the GWP was higher for CH 4 and N 2 O. However, all three cultivation strategies acted as carbon sinks, with SRI cultivation yielding the highest sequestration values. The lower CF, higher CS, and higher CER values were obtained for SRI field plots than the other two cultivation practices. The ratio between ecosystem services and disservices in terms of US$ was highest for SRI, followed by ZTL and CVN cultivations. In summary, sustainable agriculture could promote by applying organic manure in the context of SRI cultivation in the water-scarce zones and ZTL cultivation in the tropical upland zones, where such cultivation is not yet practised. Not only will this increase net carbon sequestration, but it will also benefit farmers soon in terms of yield.

Dynamic Changes and Regional Differences of Net Carbon Sequestration of Food Crops in the Yangtze River Economic Belt of China.

The carbon sequestration of food crops is of great significance to slow down agricultural greenhouse gas emissions in agricultural production and management. This paper analyzes the dynamic change and regional differences of net carbon sequestration of food crops from temporal and spatial perspectives for the case study area of the Yangtze River economic belt (YREB) in China. We use the calculation formula of carbon sequestration and carbon emission to calculate the net carbon sequestration in the Yangtze River economic belt. On this basis, we analyze the dynamic trend and regional differences of net carbon sequestration in the Yangtze River economic belt. Furthermore, we use the Gini coefficient to measure the quantitative gap of net carbon sequestration of grain crops in different regions of the Yangtze River economic belt. The results show that: (1) from 2000–2018, the net carbon sequestration of food crops keeps rising within the studied area, while the carbon emission shows a fluctuating downward trend; (2) remarkable regional differences in the net carbon sequestration of food crops have occurred, and most provinces (cities) show an upward trend for the studied area; (3) the unequitable distribution of net carbon sequestration of food crops is clearly displayed in the upper, middle, and lower reaches of the studied area. Moreover, the most uneven place is located on the lower reaches, and the least uneven place is in the upper reaches. These findings are important points of reference for reducing the carbon emissions of the agricultural industry in the Yangtze River economic belt of China and in China more generally.

Holistic tool for ecosystem services and disservices assessment in the urban forests of the Real Bosco di Capodimonte, Naples

A tool for urban forest Ecosystem services (ES) and disservices (ED) assessment has been developed to visualize (i) overall ES and ED value, (ii) ES–ED trade-off and (iii) explore principal influences in ES and ED provision. The Real Bosco di Capodimonte (RBC) (Naples, Southern Italy) has been chosen as a case study. ES and ED linked to urban forest plant cover were: biodiversity, carbon storage, gross and net carbon sequestration, lessen runoff, oxygen production, air pollution removal, UV effects reduction, pollen-related allergenicity risk, and volatile organic compounds (VOCs) emissions. A phytosociological survey was conducted and biodiversity value was evaluated. ES and ED were assessed by i-Tree Eco model and Index of Urban Green Zones Allergenicity (IUGZA). Results showed that 441 different plant species occur in the RBC and the most represented genera are Quercus and Trifolium, while the largest family was Asteraceae. Carbon storage and pollution removal were highest in natural forest, while remaining ES were greater in managed forest areas. Highest value for VOCs emission and allergenicity were assigned to managed and natural forest, respectively. Managed forest scored the highest ES–ED value, while managed grassland scored the lowest. Results highlighted the greater influence of plant cover structure in overall ES and ED provision levels, and management influence considering the same type of plant cover. The model could be a valuable tool for ES and ED effective management generally applicable in urban forests.

Modelling spatial-temporal changes in carbon sequestration by mangroves in an urban coastal landscape

Mangrove deforestation by land use conversions is the greatest threat to the conservation of coastal ecosystems, ranking Brazil as a country with high gross annual CO2 emissions. Despite the recognized socio-ecological importance in providing essential ecosystem services (e.g., erosion prevention, protection against extreme weather events, provision of habitats for estuarine species, and blue carbon storage), mangroves have been converted from blue carbon sinks to sources. Here, we modelled and evaluated the spatial-temporal changes in blue carbon stocks and net sequestration potential in mangrove forests in Santos and São Vicente, Brazil, from 1988 to 2050. We used classified images obtained from MapBiomas and the InVEST Coastal Blue Carbon model, which quantifies the potential carbon sequestered in the study area based on changes in the land use and land cover over the determined study period. We found an increased trend in carbon stocks and net sequestration of mangroves in both municipalities. Over the analysis period, carbon stocks in the mangroves of the city of Santos increased 29% in total, while we found a smaller rise (14%) in São Vicente. We found that land use changed substantially during 1988 until 2018, with mangrove extent varying in the region from 3,375 ha in 1988 to 3,764 ha in 2018 within the entire study region. Overall, the net carbon sequestration was approximately 925,393 Mg CO2e and 287,130 Mg CO2e, in Santos and São Vicente, respectively, over a period from 1988 to 2050. To our knowledge, this study is the first to quantify soil carbon stock and accumulation in mangroves along an urban coastal landscape in Brazil and emphasizes the current and future role of mangroves in climate change mitigation. Our findings can support the development of public policies for mangrove conservation and restoration actions to mitigate climate impacts.

Benthic alkalinity fluxes from coastal sediments of the Baltic and North seas: comparing approaches and identifying knowledge gaps

Abstract. Benthic alkalinity production is often suggested as a major driver of net carbon sequestration in continental shelf ecosystems. However, information on and direct measurements of benthic alkalinity fluxes are limited and are especially challenging when biological and dynamic physical forcing causes surficial sediments to be vigorously irrigated. To address this shortcoming, we quantified net sediment–water exchange of alkalinity using a suite of complementary methods, including (1) 224Ra budgeting, (2) incubations with 224Ra and Br− as tracers, and (3) numerical modeling of porewater profiles. We choose a set of sites in the shallow southern North Sea and western Baltic Sea, allowing us to incorporate frequently occurring sediment classes ranging from coarse sands to muds and sediment–water interfaces ranging from biologically irrigated and advective to diffusive into the investigations. Sediment–water irrigation rates in the southern North Sea were approximately twice as high as previously estimated for the region, in part due to measured porewater 224Ra activities higher than previously assumed. Net alkalinity fluxes in the Baltic Sea were relatively low, ranging from an uptake of −35 to a release of 53 µmolm-2h-1, and in the North Sea they were from 1 to 34 µmolm-2h-1. Lower-than-expected apparent nitrate consumption (potential denitrification), across all sites, is one explanation for our small net alkalinity fluxes measured. Carbonate mineral dissolution and potentially precipitation, as well as sulfide re-oxidation, also appear to play important roles in shaping net sediment–water fluxes at locations in the North Sea and Baltic Sea.

The climate change mitigation potential of annual grasslands under future climates.

Composted manure and green waste amendments have been shown to increase net carbon (C) sequestration in rangeland soils and have been proposed as a means to help lower atmospheric CO2 concentrations. However, the effect of climate change on soil organic C (SOC) stocks and greenhouse gas emissions in rangelands is not well understood, and the viability of climate change mitigation strategies under future conditions is even less certain. We used a process-based biogeochemical model (DayCent) at a daily time step to explore the long-term effects of potential future climate changes on C and greenhouse gas dynamics in annual grassland ecosystems. We then used the model to explore how the same ecosystems might respond to climate change following compost amendments to soils and determined the long-term viability of net SOC sequestration under changing climates. We simulated net primary productivity (NPP), SOC, and greenhouse gas fluxes across seven California annual grasslands with and without compost amendments. We drove the DayCent simulations with field data and with site-specific daily climate data from two Earth system models (CanESM2 and HadGEM-ES) and two representative concentration pathways (RCP4.5 and RCP8.5) through 2100. NPP and SOC stocks in unamended and amended ecosystems were surprisingly insensitive to projected climate changes. A one-time amendment of compost to rangeland acted as a slow-release organic fertilizer and increased NPP by up to 390-814 kg C ha-1 year-1 across sites. The amendment effect on NPP was not sensitive to Earth system model or emissions scenario and endured through the end of the century. Net SOC sequestration amounted to 1.96 ± 0.02 Mg C ha-1 relative to unamended soils at the maximum amendment effect. Averaged across sites and scenarios, SOC sequestration peaked 22 ± 1 years after amendment and declined but remained positive throughout the century. Though compost stimulated nitrous oxide (N2 O) emissions, the cumulative net emissions (in CO2 equivalents) due to compost were far less than the amount of SOC sequestered. Compost amendments resulted in a net climate benefit of 69.6 ± 0.5 Tg CO2 e 20 ± 1 years after amendment if applied to similar ecosystems across the state, amounting to 39% of California's rangeland. These results suggest that the biogeochemical benefits of a single amendment of compost to rangelands in California are insensitive to climate change and could contribute to decadal-scale climate change mitigation goals alongside emissions reductions.

Seasonal Variations in Grain Yield, Greenhouse Gas Emissions and Carbon Sequestration for Maize Cultivation in Bangladesh

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.

Oxygen Production and Carbon Capturing Capacity of Various Tree Species in Coimbatore City, India

Climate change, environment pollution, rapid urbanization and industrialization have been recognized as major environmental threats of the present-day scenario. These environmental issues cause severe socio-economic implications across the globe. The living space and human settlements are increasing rapidly in urban areas of India. Simultaneously the existing green cover and tree population are declining in the name of developments. Trees are considered to be one of the important assets in cities, they provide myriad benefits. Considering the importance of trees the cities and their role in reducing the pollution besides adding fresh oxygen to the atmosphere, the present investigation focused with the aim of documenting various tree species in Coimbatore city and to assess their carbon capturing and oxygen release potential. There are about 58 tree species comprising of 27 families, that have been documented and classified into four age classes. Further these tree species were subjected to total biomass, carbon stock, CO2 (eq.), net carbon sequestration and net oxygen release assessment using standard non-destructive method. Among the 58 tree species studied, Albizia lebbeck (2.745 ton tree-1year-1), Tamarindus indica (2.156 ton tree-1year-1), Parkia biglandulosa (1.921 ton tree-1year-1), Delonix regia (1.027 ton tree-1year-1), Kigelia Africana (1.009 ton tree-1year-1), Peltophorum pterocarpum (1.006 ton tree-1year-1), Ficus religiosa (0.906 ton tree-1year-1), Leucaena leucocephala (0.804 ton tree-1year -1) of net oxygen were found to release, Pterospermum acerifolium (0.827 ton tree-1year-1) and Azadirachta indica (0.804 ton tree-1year-1) were found to release high oxygen with more carbon capturing capacity.

Production of dissolved carbon and alkalinity during macroalgal wrack degradation on beaches: a mesocosm experiment with implications for blue carbon

Marine macroalgae are a key primary producer in coastal ecosystems, but are often overlooked in blue carbon inventories. Large quantities of macroalgal detritus deposit on beaches, but the fate of wrack carbon (C) is little understood. If most of the wrack carbon is respired back to CO2, there would be no net carbon sequestration. However, if most of the wrack carbon is converted to bicarbonate (alkalinity) or refractory DOC, wrack deposition would represent net carbon sequestration if at least part of the metabolic products (e.g., reduced Fe and S) are permanently removed (i.e., long-term burial) and the DOC is not remineralised. To investigate the release of macroalgal C via porewater and its potential to contribute to C sequestration (blue carbon), we monitored the degradation of Ecklonia radiata in flow-through mesocosms simulating tidal flushing on sandy beaches. Over 60 days, 81% of added E. radiata organic matter (OM) decomposed. Per 1 mol of detritus C, the degradation produced 0.48 ± 0.34 mol C of dissolved organic carbon (DOC) (59%) and 0.25 ± 0.07 mol C of dissolved inorganic carbon (DIC) (31%) in porewater, and a small amount of CO2 (0.3 ± 0.0 mol C; ca. 3%) which was emitted to the atmosphere. A significant amount of carbonate alkalinity was found in porewater, equating to 33% (0.27 ± 0.05 mol C) of the total degraded C. The degradation occurred in two phases. In the first phase (days 0–3), 27% of the OM degraded, releasing highly reactive DOC. In the second phase (days 4–60), the labile DOC was converted to DIC. The mechanisms underlying E. radiata degradation were sulphate reduction and ammonification. It is likely that the carbonate alkalinity was primarily produced through sulphate reduction. The formation of carbonate alkalinity and semi-labile or refractory DOC from beach wrack has the potential to play an overlooked role in coastal carbon cycling and contribute to marine carbon sequestration.Graphical abstract

Sea level rise drives carbon and habitat loss in the U.S. mid-Atlantic coastal zone

Coastal marshes and seagrass beds store millions of tons of carbon in their sediments and sequester carbon at higher per-area rates than most terrestrial ecosystems. There is substantial interest in this “blue carbon” as a carbon mitigation strategy, despite the major threat that sea level rise (SLR) poses to these habitats. Many projections of habitat and carbon change with SLR emphasize the potential for inland marsh migration and increased rates of marsh carbon sequestration, but do not consider carbon fluxes associated with habitat conversion. We integrated existing data and models to develop a spatial model for predicting habitat and carbon changes due to SLR in six mid-Atlantic U.S. states likely to face coastal habitat loss over the next century due to low tidal ranges and sediment supply. Our primary model projection, using an intermediate SLR scenario (1.2 m SLR by 2104), predicts loss of 83% of existing coastal marshes and 26% of existing seagrasses in the study area. In addition, 270,000 hectares of forest and forested wetlands in low-lying coastal areas will convert to coastal marshes. These SLR-driven habitat changes cause the study area to shift from a carbon sink to a source in our primary model projection. Given the many uncertainties about the habitat and carbon changes represented in our model, we also identified the parameters and assumptions that most strongly affected the model results to inform future research needs. These included: land availability for inland marsh migration, the baseline extent and location of coastal marshes, proportion of stored carbon emitted from lost habitats (coastal marsh sediments or terrestrial biomass carbon), and methane emissions from freshwater habitats. The study area switched from a net carbon sink to a net carbon source under SLR for all but three model runs; in those runs, net carbon sequestration declined by 57–99%.

Current status of carbon neutrality in Chinese rice fields (2002–2017) and strategies for its achievement

China has pledged to achieve carbon neutrality by 2060 to address global climate change, and achieving carbon neutrality in rice fields is a vital component of this commitment. However, the current status of carbon neutrality in rice fields in China is unclear, and there are few feasible strategies to achieve its successful implementation. Therefore, this study calculated the net carbon sequestration rate (NCSR, i.e., carbon sequestration minus carbon emissions) of rice fields in China from 2002 to 2017 to clarify the carbon neutrality status of Chinese rice fields. Furthermore, the effects of field management measures, rice sown area, and rice yield on NCSR were analyzed to identify suitable carbon neutralization pathways in Chinese rice fields. Our findings indicated that the annual carbon sequestration rate in rice fields was lower than the carbon emissions, resulting in continuous net emissions of 195.49 Tg CO2-eq yr−1. The NCSR of paddy fields increased first and then decreased with increases in rice sown area and yield. Meta-analysis indicated that management measures such as water conservation and biochar significantly increased NCSR by ~5766.50 kg CO2-eq ha−1 yr−1 and 22,296.62 kg CO2-eq ha−1 yr−1, respectively. Our findings suggests that proper control of rice sown area and the adoption of reasonable field management measures (water conservation and biochar) can promote carbon neutrality in Chinese rice fields.

The influence of discounting ecosystem services in robust multi-objective optimization – An application to a forestry-avocado land-use portfolio

Discounting is standard in economics to consider time preferences of people and account for future market changes. However, so far discounting has mainly been applied to monetary flows and ignored for many ecosystem services. In multi-objective optimization, selectively disregarding time preference for some non-monetary services create bias. Here we study how discounting a range of ecosystem service indicators influences a public planner's optimal land allocation. We used a robust multi-objective optimization approach to model a mixed forestry-avocado farm portfolio in South Africa. The objectives for optimization were the provisioning of various ecosystem services and disservices represented by four indicators: net present value, payback period, carbon sequestration, and fertilizer use. To account for time preferences concerning indicator flows, we applied specific discount rates to each ecosystem service indicator, depending on its character (non-monetary or monetary indicators). We demonstrate that discounting reduces the standard deviations of the discounted sum of the indicators, which leads to less diversified land-use portfolios. To account for discount rate uncertainty, we introduced three indicator sets simultaneously, each using a different discount rate, which was off setting the effect of decreasing diversification.