High Carbon Input Research Articles

Evaluation of RothC model for predicting soil organic carbon stock in north-west Ethiopia

Assessing soil organic carbon (SOC) is vital for water retention, soil health, nutrient cycling, greenhouse gas emissions, and pollutant reduction and thereby contributes to sustainable agricultural production and food security. Thus, using long-term climate, soil, and land management inputs, the Rothamsted Carbon (RothC) model was applied to assess the current and future SOC stocks in the Anjeni watershed using long term climate, soil and land management data. RothC was calibrated with long-term SOC, land management, and climatic data from the Anjeni watershed in north-west Ethiopia. The correlation coefficient between simulated and observed SOC in 1997 and 2021 were 0.77 and 0.86, respectively, suggesting that the model could characterize the SOC of the Anjeni watershed. Then, the RothC was used to estimate SOC in the watershed for 30 years, from 2022 to 2052, under three slope gradients and four land use type and carbon storage scenarios (business as usual (BAU), low, medium and high carbon inputs). The result indicated that in the lower slope gradient, the current SOC simulation is less than all future scenarios considered under all land use types. Grass/fallow land showed higher current and projected SOC than cultivated land and plantation forest. Moreover, grass/fallow land with a gentle slope gradient had higher SOC than the watershed's middle and high-elevation parts. Overall, the model projected an increase of SOC under different future scenarios that could be due to climate and land use cover changes, the long-term soil-water conservation camping works and better soil and land managements in the watershed. This future assists for water retention, soil health, nutrient cycling, soil aeration, and greenhouse gas emission reduction, which in turn could enhance agricultural productivity, food security, and sustainable development.

Active CO2 emissions from thermal springs in the Karakoram fault system and adjacent regions, western Tibetan Plateau

Large-scale intra-continental strike-slip faults provide the pathways for groundwater circulation and the release of CO2-rich fluids through thermal springs, which is a significant type of deep CO2 emissions into the atmosphere and hydrosphere. India-Asia collision created numerous strike-slip faults and thermal springs in the Tibetan Plateau and adjacent regions, but their CO2 origins and fluxes are still not well understood. Here, we present a quantitative study on CO2 emissions from thermal springs in the Karakoram fault system (KKFS) and adjacent regions, western Tibetan Plateau, with the aim of revealing the origins of CO2-rich fluids and estimating the dissolved and gaseous CO2 fluxes. Hydrogen and oxygen isotopic data show that the geothermal waters were recharged by local precipitation (e.g., rainfall and snow-melt water) and experienced variable degrees of water-rock interaction, giving rise to the dominant Na–HCO3 type and minor Na–Cl and Ca–HCO3 type waters discharging from thermal springs. Spatially, the thermal springs within or close to the KKFS (Group 1 and Group 2) have larger circulation depths of 1.3–5.1 km, while those away from the KKFS (Group 3) exhibit shallow (0.6−0.8 km) groundwater circulation. Mass balance calculations reveal high deeply-sourced carbon inputs (60.4−94.3%) to dissolved inorganic carbon (DIC) of the Group 1 and Group 2 samples, while the Group 3 samples have higher shallow carbon contributions (50.4−60.9%) to DIC via dissolution of carbonate and organic carbon. This is consistent with higher Δ14CDIC values (−788.6‰ to −692.1‰) in Group 3 samples and the lack of radioactive 14C in Group 1 and Group 2 samples (Δ14CDIC = −999.9‰ to −985.9‰). Based on chemical compositions and fluxes of spring water and bubbling gases, the total CO2 output from thermal springs (including dissolved and gaseous CO2) in the KKFS is estimated to be ∼2332 t a−1, in which the endogenic carbon such as metamorphic CO2 accounts for ∼1863 t a−1. Our results provide the first estimate of deep CO2 flux for the KKFS and would contribute to a better understanding of active CO2 emissions facilitated by strike-slip faulting processes in continental collision zone.

Modelling of Soil Organic Carbon Dynamic on Grassland Under Different Management and Climate Scenarios

Abstract Improperly used farming systems and agrotechnical practices with ongoing climate change can contribute to the reduction of the level of soil organic carbon (SOC) stocks not only in intensively cultivated arable soils but also in grasslands. One of the ways to track changes in the SOC stock is the use of mathematical models. The RothC model was validated at the locality Suchý vrch, which hosts long-term experiments on grassland. The soil type is sandy-loam textured Cambisol. Validation was done for the period 1993 – 2009 on grassland with various applications of mineral and organic fertilisers. Results of validation show that the RothC model appropriately predicts the development of grassland SOCs and can be used in forecasting SOC stock in the future. Five different management scenarios, with carbon input 2.3 to 6.4 t/ha and three climate scenarios (RCP 2.6, RCP 4.5, RCP 8.5) of the MPI climate model were used to track the changes of SOC stock on grassland in the period 2009 – 2100. Modelling results of SOC development show, that in the future, a relatively low-temperature increase (RCP 2.6) and a relatively high carbon input into the soil (6.4 t/ha) can ensure moderate carbon sequestration. However, between the low-carbon management scenarios (2.3 and 4.1 t/ha), SOC stocks are continuously decreasing in the RCP 2.6 climate scenario. At a significantly higher temperature (climate scenario RCP 8.5), that is expected in future, it will not be possible to maintain the current level of SOC stock not even at a high carbon input (6.4 t/ha).

Increased Soil Organic Carbon Losses Due to Soybean Monoculture in the Argentine Pampas: A Meta-Analysis

ABSTRACT Agricultural soils can act as a repository for atmospheric carbon and hence mitigate global warming. One of the best management practices that can increase the soil organic carbon (SOC) is the selection of high carbon input crops. Some crops like soybean would lead to SOC decrease due to its low residue production. This is the main crop in the Pampas region of Argentina. The objective of the present study was to determine how soybean monoculture impacts the SOC in the region. Data were collected from 11 long-term field experiments. Results of nine SOC comparisons of soybean monoculture with rotations and seven comparisons of other crop monocultures with rotations were extracted. Meta-analytic methods were used for the analysis. SOC stock in the 0–20 cm layer was 10% lower under monoculture of soybean than under rotations. The average duration of the experiments was 10 years. On the contrary, no differences of the SOC were detected when monocultures of wheat, corn or sunflower were compared with rotations. When the initial and final SOC stocks were compared in each treatment, it was estimated that in nearly all cases there were losses of SOC. The average loss of SOC was 8.1 t ha−1 under soybean monoculture and 3.9 t ha−1 under the corresponding rotations. Consequently, the reviewed experiments indicate losses of SOC due to agriculture in the Pampas that double with soybean monoculture.

Spatial and temporal variability of greenhouse gas ebullition from temperate freshwater fish ponds

Fish ponds with their typically high carbon and nutrient inputs are relevant sources of greenhouse gases. However, not much is known about gas bubble emissions (ebullition) and their high spatiotemporal variability. This is the first study which quantified diffusive and ebullitive greenhouse gas emissions from temperate fish ponds. To improve greenhouse gas estimates, we investigated the diurnal and spatial variability of diffusive and ebullitive fluxes in 12 extensively to semi-intensively managed fish ponds near Bautzen, Germany. Emissions differed greatly between the different ponds but methane was consistently the predominant greenhouse gas. The feeding sites were hotspots with one order of magnitude higher ebullition rates compared to other parts of the ponds. At these hotspots, ebullitive fluxes of up to 38 L/m2d were measured with a mean bubble methane content of 79%, corresponding to a methane flux of 1.24 mol/m2d. Methane accounted for 90% of the global warming potential in one fish pond but carbon dioxide emissions of up to 242 mmol/m2d at the feeding sites were also significant. Nitrous oxide fluxes, in contrast, were low with 5 ± 9 μmol/m2d. Greenhouse gas ebullition decreased exponentially along a transect from the feeding site into the pond and showed some diurnal fluctuations. While diffusion was higher during night, ebullition rates increased in the morning, presumably caused by higher benthivorous fish activity. Our results highlight the potential of temperate fish ponds as significant greenhouse gas sources and ebullition as a significant pathway. For robust quantification, both small scale spatial and temporal variability as well as the hotspot of the feeding area must be considered.

Aqueous habitats and carbon inputs shape the microscale geography and interaction ranges of soil bacteria

Earth’s diverse soil microbiomes host bacteria within dynamic and fragmented aqueous habitats that occupy complex pore spaces and restrict the spatial range of ecological interactions. Yet, the spatial distributions of bacterial cells in soil communities remain underexplored. Here, we propose a modelling framework representing submillimeter-scale distributions of soil bacteria based on physical constraints supported by individual-based model results and direct observations. The spatial distribution of bacterial cell clusters modulates various metabolic interactions and soil microbiome functioning. Dry soils with long diffusion times limit localized interactions of the sparse communities. Frequently wet soils enable long-range trophic interactions between dense cell clusters through connected aqueous pathways. Biomes with high carbon inputs promote large and dense cell clusters where anoxic microsites form even in aerated soils. Micro-geographic considerations of difficult-to-observe microbial processes can improve the interpretation of data from bulk soil samples.

THE INFLUENCE OF GENOTYPE, SOIL TILLAGE AND FERTILISATION ON CARBON SEQUESTRATION IN MAIZE

The increase in the concentration of greenhouse gases in the Earth’s atmosphere, especially that of CO2, is a major concern because it is the main source leading to global warming, and its impact on climate change is still widely studied. The intensity and frequency of drought and flooding increase due to the change in climate, which has a negative impact on crop productivity and food security. The aim of this paper was to demonstrate the role of corn in carbon sequestration based on plant biomass and soil organic carbon accumulation. We presented the main factors that contribute to carbon sequestration and concrete examples regarding the capacity of corn hybrids created at National Agricultural Research and Development Institute (NARDI) Fundulea, as well as aspects regarding the importance of soil tillage and fertilisation. In contrast to genotypes in which this ratio was lower, maize genotypes that demonstrated a rise in the root:stem ratio under drought stress conditions produced more biomass, suggesting that the roots of these genotypes can grow at water potentials where stem growth is inhibited, which are attributes that also prove their good potential for carbon sequestration under climate change conditions. The organic carbon content in the superficial soil layer decreased with the intensification of the degree of soil mobilisation (9.95% when working the soil with the chisel, 17.91% for ploughing), but fertilisation had a beneficial effect. The biomass was higher than that of the unfertilised soil. This means that a higher carbon input has a positive influence on the carbon stock in the soil.

Greenhouse gas emissions embodied in electric vehicle charging infrastructure: a method and case study of Georgia, US 2021–2050

Electric vehicle (EV) charging infrastructure buildout is a major greenhouse gas (GHG) mitigation strategy among governments and municipalities. In the United States, where petroleum-based transportation is the largest single source of GHG emissions, the Infrastructure Investment and Jobs Act of 2021 will support building a national network of 500 000 EV charging units. While the climate benefits of driving electric are well established, the potential embodied climate impacts of building out the charging infrastructure are relatively unexplored. Furthermore, ‘charging infrastructure’ tends to be conceptualized in terms of plugs and stations, leaving out the electrical and communications systems that will be required to support decarbonized and efficient charging. In this study, we present an EV charging system (EVCS) model that describes the material and operational components required for charging and forecasts the scale-up of these components based on EV market share scenarios out to 2050. We develop a methodology for measuring GHG emissions embodied in the buildout of EVCS and incurred during operation of the EVCS, including vehicle recharging, and we demonstrate this model using a case study of Georgia (USA). We find that cumulative GHG emissions from EVCS buildout and use are negligible, at less than 1% of cumulative emissions from personal light duty vehicle travel (including EV recharging and conventional combustion vehicle driving). If an accelerated EVCS buildout were to stimulate a faster transition of the vehicle fleet, the emissions reduction of electrification will far outweigh emissions embodied in EVCS components, even assuming relatively high carbon inputs prior to decarbonization.

Source and sequestration of sediment organic carbon from different elevation zones in estuarine wetland, North China

Estuarine wetland plays an important role in regulating global carbon cycle due to high terrestrial carbon input and burial. However, it is unclear how the source and sequestration of sediment organic carbon (SOC) in estuarine wetlands changes under the anthropogenic impact in the past century. In this study, combining parameters of TOC/TN ratios, δ13C, δ15N and 210Pb-chronology, temporal trends of SOC source and sequestration flux in Liaohe estuarine wetland were studied. The results showed that the source of organic carbon in Liaohe estuarine wetland was dominated by terrestrial input (contribution >60 %). Due to vegetation, TOC in shallow reed marsh was significantly higher than that of bare beach and subtidal flat. Affected by elevation, the sediment mass accumulation rate (MAR, kg·m−2·yr−1) showed differences in reed marsh (C1), bare beach (C2) and subtidal flat (C3), which were 6.57, 13.56 and 13.25 respectively in the past century. MAR fluctuated over time, it showed an overall increasing trend, especially since the 1980s. Correspondingly, the sequestration flux of SOC (SF-SOC, g·m−2·yr−1) showed an overall increasing trend with average of 82.84 (reed marsh), 151.93 (bare beach) and 123.71 (subtidal flat). Comparing to TOC, the higher MAR had a more distinct effect on carbon sequestration in Liaohe estuarine wetland. The difference in sedimentation rate and carbon sequestration are linked to the changes in sediment flux of riverine input and land utilization in the catchment area due to human activities in recent decades, including the construction of reservoirs, dams and local ditch wharf.

High nutrient loads amplify carbon cycling across California and New York coastal wetlands but with ambiguous effects on marsh integrity and sustainability.

Eutrophic conditions in estuaries are a globally important stressor to coastal ecosystems and have been suggested as a driver of coastal salt marsh loss. Potential mechanisms in marshes include disturbance caused by macroalgae accumulations, enhanced soil sulfide levels linked to high labile carbon inputs, accelerated decomposition, and declines in belowground biomass that contribute to edge instability, erosion, and slumping. However, results of fertilization studies have been mixed, and it is unclear the extent to which local environmental conditions, such as soil composition and nutrient profiles, help shape the response of salt marshes to nutrient exposure. In this study, we characterized belowground productivity and decomposition, organic matter mineralization rates, soil respiration, microbial biomass, soil humification, carbon and nitrogen inventories, nitrogen isotope ratios, and porewater profiles at high and low marsh elevations across eight marshes in four estuaries in California and New York that have strong contrasts in nutrient inputs. The higher nutrient load marshes were characterized by faster carbon turnover, with higher belowground production and decomposition and greater carbon dioxide efflux than lower nutrient load marshes. These patterns were robust across marshes of the Atlantic and Pacific coasts that varied in plant species composition, soil flooding patterns, and soil texture. Although impacts of eutrophic conditions on carbon cycling appeared clear, it was ambiguous whether high nutrient loads are causing negative effects on long-term marsh sustainability in terms of studied metrics. While high nutrient exposure marshes had high rates of decomposition and soil respiration rates, high nutrient exposure was also associated with increased belowground production, and reduced levels of sulfides, which should lead to greater marsh sustainability. While this study does not resolve the extent to which nutrient loads are negatively affecting these salt marshes, we do highlight functional differences between Atlantic and Pacific wetlands which may be useful for understanding coastal marsh health and integrity.

Large herbivores on permafrost— a pilot study of grazing impacts on permafrost soil carbon storage in northeastern Siberia

The risk of carbon emissions from permafrost is linked to an increase in ground temperature and thus in particular to thermal insulation by vegetation, soil layers and snow cover. Ground insulation can be influenced by the presence of large herbivores browsing for food in both winter and summer. In this study, we examine the potential impact of large herbivore presence on the soil carbon storage in a thermokarst landscape in northeastern Siberia. Our aim in this pilot study is to conduct a first analysis on whether intensive large herbivore grazing may slow or even reverse permafrost thaw by affecting thermal insulation through modifying ground cover properties. As permafrost soil temperatures are important for organic matter decomposition, we hypothesize that herbivory disturbances lead to differences in ground-stored carbon. Therefore, we analyzed five sites with a total of three different herbivore grazing intensities on two landscape forms (drained thermokarst basin, Yedoma upland) in Pleistocene Park near Chersky. We measured maximum thaw depth, total organic carbon content, δ13C isotopes, carbon-nitrogen ratios, and sediment grain-size composition as well as ice and water content for each site. We found the thaw depth to be shallower and carbon storage to be higher in intensively grazed areas compared to extensively and non-grazed sites in the same thermokarst basin. First data show that intensive grazing leads to a more stable thermal ground regime and thus to increased carbon storage in the thermokarst deposits and active layer. However, the high carbon content found within the upper 20 cm on intensively grazed sites could also indicate higher carbon input rather than reduced decomposition, which requires further studies including investigations of the hydrology and general ground conditions existing prior to grazing introduction. We explain our findings by intensive animal trampling in winter and vegetation changes, which overcompensate summer ground warming. We conclude that grazing intensity—along with soil substrate and hydrologic conditions—might have a measurable influence on the carbon storage in permafrost soils. Hence the grazing effect should be further investigated for its potential as an actively manageable instrument to reduce net carbon emission from permafrost.

Global warming readiness: Feasibility of enhanced biological phosphorus removal at 35 °C

Recent research has shown enhanced biological phosphorus removal (EBPR) from municipal wastewater at warmer temperatures around 30 °C to be achievable in both laboratory-scale reactors and full-scale treatment plants. In the context of a changing climate, the feasibility of EBPR at even higher temperatures is of interest. We operated two lab-scale EBPR sequencing batch reactors for > 300 days at 30 °C and 35 °C, respectively, and followed the dynamics of the communities of polyphosphate accumulating organisms (PAOs) and competing glycogen accumulating organisms (GAOs) using a combination of 16S rRNA gene metabarcoding, quantitative PCR and fluorescence in situ hybridization analyses. Stable and nearly complete phosphorus (P) removal was achieved at 30 °C; similarly, long term P removal was stable at 35 °C with effluent PO43-_P concentrations < 0.5 mg/L on half of all monitored days. Diverse and abundant Candidatus Accumulibacter amplicon sequence variants were closely related to those found in temperate environments, suggesting that EBPR at this temperature does not require a highly specialized PAO community. A slow-feeding strategy effectively limited the carbon uptake rates of GAOs, allowing PAOs to outcompete GAOs at both temperatures. Candidatus Competibacter was the main GAO, along with cluster III Defluviicoccus members. These organisms withstood the slow-feeding regime, suggesting that their bioenergetic characteristics of carbon uptake differ from those of their tetrad-forming relatives. Comparative cycle studies revealed higher carbon and P cycling activity of Ca. Accumulibacter when the temperature was increased from 30 °C to 35 °C, implying that the lowered P removal performance at 35 °C was not a direct effect of temperature, but a result of higher metabolic rates of carbon (and/or P) utilization of PAOs and GAOs, the resultant carbon deficiency, and escalated community competition. An increase in the TOC-to-PO43−-P ratio (from 25:1 to 40:1) effectively eased the carbon deficiency and benefited PAOs. In general, a slow-feeding strategy and sufficiently high carbon input benefited a high and stable EBPR at 35 °C, representing basic conditions suitable for full-scale treatment plants experiencing higher water temperatures.

Environmental impacts and resource use for sheep production in semi-arid India investigated by life cycle assessment

Agriculture is a major contributor of green house gas emissions and livestock component have significant contribution, sheep being an important part of animal husbandry also contributes to carbon footprints (CFs) of environment through enteric fermentation, manure emissions and inputs used in sheep husbandry. To augment productivity and lower environmental impact of livestock sector, intensive farming is a promising strategy; yet, the approach of feeding more amount of concentrate to increase the productivity of animals was less competent and severed environmental effects as compared to fodder production. Furthermore, to avoid dependence on grazing pastures and provide year round quality fodder to the animals, carbon foot print from forage production required for stall feeding should be taken in to consideration along with other agromonic practices for conducting life cycle assessment of sheep farming. In this study, rearing of popular sheep breeds (Malpura, Avishaan, Patanwadi and Kheri) along with dominant forage production systems (napier, perennial grasses, forage legumes and bajra) was assessed in terms of carbon foot prints and output of crops as well as sheep. Among the crops, perennial grasses required less input and very low CFs from inputs followed by forage legumes. The mean carbon foot print of finished lambs was 8.9, 9.5, 9.3 and 5.7 kg CO2e/kg live weight in Malpura, Avishaan, Patanwadi and Kheri, respectively. For production of 1 kg fodder on dry matter basis, Napier required around 224.6% higher carbon input than perennial grasses along with maximum productivity (carbon output) of 67.4% as compared to other crops. Grasses being marginal crops required very low carbon input approximately 794.5% lower as compared to Napier production. For meat, Avishaan proved its superiority in terms of higher meat production which resulted in higher CFs from meat in Avishaan which was around 89.9 and 85.5% higher than Malpura and Patanwadi, respectively. In case of milk, Patanwadi was the highest contributor having 20.1 and 14.3% higher CO2-e as compared to Malpura and Avishaan, respectively. The CFs for wool production was also more for Patanwadi by about 15.0 and 22.9% higher than Malpura and Avishaan, respectively. When the CFs of fodder production and sheep farming was studied together, it was revealed that Napier production with Patanwadi rearing contributed maximum CFs over other systems. Grass cultivation with Avishaan rearing resulted in least CFs contribution. The results suggest that environmental impact of animal production sector should be conducted considering the mean carbon footprints of all correlated farm variables for indepth information.

Legacy of plaggen agriculture: High soil organic carbon stocks as result from high carbon input and volume increase

Plaggic Anthrosols are anthropogenic soils formed by former plaggen agriculture in north-western continental Europe. Here, we present an inventory of organic carbon (OC) concentrations and stocks of Plaggic Anthrosols and of reference soils in the vicinity without plaggen fertilization history from eight sites in northwest Germany (Lower Saxony, North Rhine-Westphalia) and the eastern parts of The Netherlands (North Brabant, Overijssel). To evaluate the enrichment of Plaggic Anthrosols with OC and the implications for OC stocks, soils were analysed for basic soil properties (bulk density, pH, OC − and nitrogen (N) concentrations), texture, and acid oxalate-(FeOX) and dithionite-citrate-bicarbonate-extractable iron (FeDCB) concentrations. Organic C stocks and plant-available water capacity (PAWC) were calculated. The plaggic topsoils are characterized by high OC concentrations (6.5–36.9 mg g−1) and a thickness of 53–124 cm, in contrast to the modern cultivated ∼30 cm thick topsoils of the reference soils with 10.6–24.0 mg g−1 OC concentration. The plaggen agriculture formed a soil with improved properties and conditions for plant growth. The addition of plaggen material to the topsoils induced a volume increase as well as higher OC concentrations in the Ap horizons, resulting in significantly higher OC stocks in the Plaggic Anthrosols (6.3–14.5 kg m−2) compared to the reference soils (4.9–10.5 kg m−2). The additional soil volume amounted to 30–56% to the total soil profile depth (1.0 to 1.6 m) and comprised 25–62% of the total OC stocks. Compared to the reference soils, the volume increase of the plaggic topsoil increased the PAWC in the effective rooting zone by 1.6 to 3.4 times. Plaggic Anthrosols represent a relic of historical farming with preserved high OC concentrations and improved storage capacity for plant-available water, causing higher nutrient availability and an increase in yields, which in turn result in higher in-situ OM input, additionally contributing to high OC stocks. The results of this study demonstrate the potential of soil melioration practices similar to the former plaggen management to induce high OC concentrations and increase OC stocks in sandy agricultural soils.

Carbonate chemistry seasonality in a tropical mangrove lagoon in La Parguera, Puerto Rico.

We investigated the seasonal carbonate chemistry variability within a semi-enclosed tropical mangrove lagoon in southwestern Puerto Rico. Biweekly measurements of seawater temperature, salinity, total alkalinity (TA), and dissolved inorganic carbon (DIC) were conducted from 2014 to 2018. We describe the possible mechanisms driving the observed variability by correlating the DIC/TA ratio with pH and Ωarg, suggesting that the mean pH (7.87 ± 0.09) and aragonite saturation state (Ωarg, 2.96 ± 0.47) of the mangrove lagoon negatively affected calcification. The measured pCO2 and DIC/TA ratios indicate that heterotrophic activity was the primary driver for persistent acidification, which reached its maximum expression during the wet season. We conclude that mangrove lagoons with limited seawater exchange and high carbon input will not mitigate ocean acidification.

TOWARD A SOCIALLY JUST TRANSITION TO LOW CARBON DEVELOPMENT: THE CASE OF INDONESIA

In 2019, the Indonesian government released its post-Paris Agreement report Low Carbon Development: a paradigm shift towards a green economy in Indonesia, in which it set out an economic rationale for a move to low carbon growth. The core of the paradigm shift referenced in the report's title was that growth not only had to be decoupled from high carbon inputs but that in both practice and outcomes it had to be sustainable and inclusive. Yet the report does little to define social justice, equity practices, or inclusive outcomes in a green economy context. In this article, we foreground distributive, procedural and recognition aspects of social justice that are central to Indonesia's climate mitigation efforts and transition to a green, low carbon economy. We focus on two sectors that are key to this transition – forest and land-use, and energy. Our analysis shows that existing forms of injustice can exacerbate challenges for decarbonisation action and that low carbon transitions initiatives have been unable to overcome various forms of injustice and have, in some cases, created new injustices.

Carbon accumulation in a bare fallow Chernozem soil with high carbon input rates

AbstractA multitude of models for soil organic carbon (SOC) dynamics are available to predict management impacts on SOC dynamics in its interaction with environmental factors. Most models include one SOC pool that has no or a very slow, negligible turnover. For this pool of long‐term stabilized (LTS) organic matter, we assumed a dynamic physical protection, whereby organic matter is protected in micropores and exposed to microbial access due to soil structure dynamics. Dynamics of the LTS pool is of special interest because of its very long turnover time. Therefore, it is of special importance whether the size of this pool is unlimited or if it reaches a saturation state. We investigated this topic by applying the CCB (CANDY Carbon Balance) model on a dataset from a long‐term experiment that started in 1983 in Bad Lauchstädt, Germany on a Haplic Chernozem and includes bare fallow treatments with the application of farmyard manure at different rates from 5 to 20 kg m−2 year−1. Observations of SOC development over time supported our hypothesis about the existence of a saturation effect and were used to calibrate the CCB model with the hypothetical assumption of a limited LTS pool size. The model results suggest an upper limit of the LTS pool of 1.07 M% (percent of dry soil mass) SOC for the Bad Lauchstädt site. Furthermore, model calibration of LTS turnover revealed that organic matter in this pool is released from its protected state at a very low rate of 0.003 year−1.Highlights Long‐term bare fallow field experiment with FYM input rates up to 20 kg m−2 Predicted long‐term SOC dynamics reflect observations Proof of non‐linear relationship between SOC storage and carbon input rate Evidence for limited protection capacity for SOC (saturation effect)

Fate of Organic Carbon Burial in Modern Sediment Within Yangtze River Estuary

AbstractLarge river‐dominated margins play a potential key role in regulating global carbon cycle and budget due to high terrestrial organic carbon (Corg) inputs and sediment accumulation rates. Here bulk elements (Corg and TN), isotopic compositions (δ13Corg and δ15N), radioisotope 210Pb, sedimentary grain size, pH, Eh, and physicochemical properties were analyzed on samples from the Yangtze River Estuary to determine the mechanism involved in transporting sedimentary Corg offshore. In addition, nine box‐cores were analyzed to further reveal the potential effects of the declining sediment load on the modern depositional pattern of Corg. The statistical analyses indicate that the hydrodynamically driven sediment composition exerts a significant control on the transport, mobilization, and accumulation of sedimentary Corg from the river to the estuary, with respect to the redistribution of fine‐grained sediments. Furthermore, X‐radiographs and 210Pb indicate that reworked environment dominates carbon burial in the Yangtze proximal deposit, while a stable sedimentary environment of Corg (3.50–5.58 g cm−2 year−1) is observed in the Yangtze distal mud. Notably, the enhanced erosional inputs that contain terrestrial plant debris (mainly the coarse fractions) have tended to become important sources for Corg. Although reworked sediments in the Yangtze River Estuary are frequently exposed to oxygen during physical and biological processes, there appears to be a high potential for long‐term sedimentary Corg storage, due to its association with sediment particles (mainly the clay fractions) that provide physical protection against its degradation.

Intertwined effects of climate and land use change on environmental dynamics and carbon accumulation in a mangrove-fringed coastal lagoon in Java, Indonesia.

The identification and quantification of natural carbon (C) sinks is critical to global climate change mitigation efforts. Tropical coastal wetlands are considered important in this context, yet knowledge of their dynamics and quantitative data are still scarce. In order to quantify the C accumulation rate and understand how it is influenced by land use and climate change, a palaeoecological study was conducted in the mangrove-fringed Segara Anakan Lagoon (SAL) in Java, Indonesia. A sediment core was age-dated and analyzed for its pollen and spore, elemental and biogeochemical compositions. The results indicate that environmental dynamics in the SAL and its C accumulation over the past 400years were controlled mainly by climate oscillations and anthropogenic activities. The interaction of these two factors changed the lagoon's sediment supply and salinity, which consequently altered the organic matter composition and deposition in the lagoon. Four phases with varying climates were identified. While autochthonous mangrove C was a significant contributor to carbon accumulation in SAL sediments throughout all four phases, varying admixtures of terrestrial C from the hinterland also contributed, with natural mixed forest C predominating in the early phases and agriculture soil C predominating in the later phases. In this context, climate-related precipitation changes are an overarching control, as surface water transport through rivers serves as the "delivery agent" for the outcomes of the anthropogenic impact in the catchment area into the lagoon. Amongst mangrove-dominated ecosystems globally, the SAL is one of the most effective C sinks due to high mangrove carbon input in combination with a high allochthonous carbon input from anthropogenically enhanced sediment from the hinterland and increased preservation. Given the substantial C sequestration capacity of the SAL and other mangrove-fringed coastal lagoons, conservation and restoration of these ecosystems is vitally important for climate change mitigation.

Past aquatic environments in the Levant inferred from stable isotope compositions of carbonate and phosphate in fish teeth.

Here we explore the carbon and oxygen isotope compositions of the co-existing carbonate and phosphate fractions of fish tooth enameloid as a tool to reconstruct past aquatic fish environments and harvesting grounds. The enameloid oxygen isotope compositions of the phosphate fraction (δ18OPO4) vary by as much as ~4‰ for migratory marine fish such as gilthead seabream (Sparus aurata), predominantly reflecting the different saline habitats it occupies during its life cycle. The offset in enameloid Δ18OCO3-PO4 values of modern marine Sparidae and freshwater Cyprinidae from the Southeast Mediterranean region vary between 8.1 and 11.0‰, similar to values reported for modern sharks. The mean δ13C of modern adult S. aurata and Cyprinus carpio teeth of 0.1±0.4‰ and -6.1±0.7‰, respectively, mainly reflect the difference in δ13C of dissolved inorganic carbon (DIC) of the ambient water and dietary carbon sources. The enameloid Δ18OCO3-PO4 and δ13C values of ancient S. aurata (Holocene) and fossil Luciobarbus sp. (Cyprinidae; mid Pleistocene) teeth agree well with those of modern specimens, implying little diagenetic alteration of these tooth samples. Paired δ18OPO4-δ13C data from ancient S. aurata teeth indicate that hypersaline water bodies formed in the Levant region during the Late Holocene from typical Mediterranean coastal water with high evaporation rates and limited carbon input from terrestrial sources. Sparid tooth stable isotopes further suggest that coastal lagoons in the Eastern Mediterranean had already formed by the Early Holocene and were influenced by terrestrial carbon sources. Overall, combined enameloid oxygen and carbon isotope analysis of fish teeth is a powerful tool to infer the hydrologic evolution of aquatic environments and assess past fishing grounds of human populations in antiquity.