Organic Carbon Storage Research Articles

UAV approaches for improved mapping of vegetation cover and estimation of carbon storage of small saltmarshes: examples from Loch Fleet, northeast Scotland

Abstract. Saltmarsh environments are recognised as key components of many biophysical and biochemical processes at the local and global scale. Accurately mapping these environments, and understanding how they are changing over time, is crucial for better understanding these systems. However, traditional surveying techniques are time-consuming and are inadequate for understanding how these dynamic systems may be changing temporally and spatially. The development of uncrewed aerial vehicle (UAV) technology presents an opportunity for efficiently mapping saltmarsh extent. Here we develop a methodology which combines field vegetation surveys with multispectral UAV data collected at two scales to estimate saltmarsh area and organic carbon storage at three saltmarshes in Loch Fleet (Scotland). We find that the Normalised Difference Vegetation Index (NDVI) values for surveyed saltmarsh vegetation communities, in combination with local tidal data, can be used to reliably estimate saltmarsh area. Using these area estimates, together with known plant community and soil organic carbon relationships, saltmarsh soil organic carbon storage is modelled. Based on our most reliable UAV-derived saltmarsh area estimates, we find that organic carbon storage is 15 %–20 % lower than previous area estimates would indicate. The methodology presented here potentially provides a cheap, affordable, and rapid method for saltmarsh mapping which could be implemented more widely to test and refine existing estimates of saltmarsh extent and is particularly well-suited to the mapping of small areas of saltmarsh environments.

CARBON STOCK, RATES OF CARBON ACCUMULATION AND DISTRIBUTION OF PARTICLES IN A LAKE OF THE ANAVILHANAS ARCHIPELAGO, NEGRO RIVER - AMAZON DURING THE LAST 1900 YEARS

Recent studies show that, despite great variability, the lake systems of the Amazon Basin have presented significant results in the accumulation and storage of organic carbon (TOC). However, the demonstration in the region is still limited and lacks more data to better estimate this non-carbon component of the region. The objective of this article was to estimate the carbon stock, the carbon accumulation rates and characterize the granulometric distribution of an Amazonian lake located in the Anavilhanas Archipelago, in the Lower Negro River region. Data were carried out using the 14C method and analyses of density, granulometry and TOC rate sof samples of a sediment core 1 meter deep. The results have shown that, during the period of 1900 cal years BP, Lake Boto presented two isolated peaks of sand particle sedimentation possibly related to major hydrodynamic events. Generally, well-defined characteristics of a lacustrine environment with sedimentation of fine silt and clay particles predominate. The sedimentation rate was 0.03 cm.year-¹ between approximately 1900 to 850 cal years BP and 0.07 cm.year-¹ in the last 850 cal years BP. It is estimated that Lake Boto has a stock of approximately 231,000 tons of TOC accumulated during the entire period. The stock of TOC is not significant as it is estimated for the soils of the Amazon. The results are an important indication of the role of the Anavilhanas Archipelago as a TOC sink.

Active microbial population dynamics and life strategies drive the enhanced carbon use efficiency in high-organic matter soils.

Microbial carbon use efficiency (CUE) is a critical parameter that controls carbon storage in soil, but many uncertainties remain concerning adaptations of microbial communities to long-term fertilization that impact CUE. Based on H218O quantitative stable isotope probing coupled with metagenomic sequencing, we disentangled the roles of active microbial population dynamics and life strategies for CUE in soils after a long-term (35 years) mineral or organic fertilization. We found that the soils rich in organic matter supported high microbial CUE, indicating a more efficient microbial biomass formation and a greater carbon sequestration potential. Organic fertilizers supported active microbial communities characterized by high diversity and a relative increase in net growth rate, as well as an anabolic-biased carbon cycling, which likely explains the observed enhanced CUE. Overall, these results highlight the role of population dynamics and life strategies in understanding and predicting microbial CUE and sequestration in soil.IMPORTANCEMicrobial CUE is a major determinant of global soil organic carbon storage. Understanding the microbial processes underlying CUE can help to maintain soil sustainable productivity and mitigate climate change. Our findings indicated that active microbial communities, adapted to long-term organic fertilization, exhibited a relative increase in net growth rate and a preference for anabolic carbon cycling when compared to those subjected to chemical fertilization. These shifts in population dynamics and life strategies led the active microbes to allocate more carbon to biomass production rather than cellular respiration. Consequently, the more fertile soils may harbor a greater microbially mediated carbon sequestration potential. This finding is of great importance for manipulating microorganisms to increase soil C sequestration.

Cover crops improve soil structure and change organic carbon distribution in macroaggregate fractions

Abstract. Soil structure is sensitive to intensive soil management. It can be ameliorated by a reduction in soil cultivation and stimulation of plant and microbial mediators for aggregate formation, with the latter being a prerequisite and measure for soil quality. Cover crops (CCs) are part of an integrated approach to stabilize or improve soil quality. Thereby, the incorporation of diverse CC mixtures is hypothesized to increase the positive effects of CC applications. This study entailed an investigation of the legacy effect of CCs on soil aggregates after three crop rotations in the second main crop (winter wheat) after the last CC treatment. Four CCs (mustard, phacelia, clover, and oat) cultivated in pure stands and with a fallow treatment were compared to a mixture of the four CC species (Mix4) and a highly diverse 12-plant-species mixture (Mix12) in a long-term field experiment in Germany. The organic carbon (OC) distribution within macroaggregate fractions (16–8, 8–4, 4–2, 2–1, and <1 mm) and their aggregate stability were measured by dry- and wet-sieving methods, and the mean weight diameter (MWD) was calculated from water-stable aggregates. The results showed that, compared to the fallow, all CCs increased the MWD between 10 % and 19 % in soil under the following main crop. The average MWD increase over the fallow was slightly higher for CC mixtures (16 %) than for single CCs (12 %). Most of the OC (67.9 % on average) was stored in the <1 mm aggregate fraction, highest in the topsoil and decreasing with soil depth. The intermediate fractions (8–4 mm, 4–2 mm, 2–1 mm) stored 8.5 %, 10.5 %, and 11.0 % of the total OC, while 2.1 % was stored in the 16–8 mm fraction. Higher MWD improvement at the 20–30 cm depth also indicates additional benefits from a reduction in the cultivation depth. Structural equation modelling (SEM) suggests that single CCs were more likely to increase OC storage in small macroaggregates <1 mm, while CC mixtures were more likely to increase OC in the largest fraction (8–16 mm). Different individual CC species or mixtures exhibited varying involvement in the formation of different aggregate fractions. We provide evidence that litter quality, root morphology, and rhizosphere input, which affect microbial mediators of aggregate formation, might be the main reasons for the observed differences between CC treatments. Cover crops are valuable multifunctional tools for sustainable soil management. Here, we showed that they contribute to structure amelioration in arable soils. Increasing the functional diversity of plant species in CC mixtures could be a strategy to further enhance the positive effects of CCs in agroecosystems.

Life on Earth can grow on extraterrestrial organic carbon

The universe is a vast store of organic abiotic carbon that could potentially drive heterotrophy on habitable planets. Meteorites are one of the transporters of this carbon to planetary surfaces. Meteoritic material was accumulating on early Earth when life emerged and proliferated. Yet it is not known if this organic carbon from space was accessible to life. In this research, an anaerobic microbial community was grown with the CM2 carbonaceous chondrite Aguas Zarcas as the sole carbon, energy and nutrient source. Using a reversed 13C-stable isotope labelling experiment in combination with optical photothermal infrared (O-PTIR) spectroscopy of single cells, this paper demonstrates the direct transfer of carbon from meteorite into microbial biomass. This implies that meteoritic organics could have been used as a carbon source on early Earth and other habitable planets, and supports the potential for a heterotrophic metabolism in early living systems.

SOIL CARBON STOCKS NOT LINKED TO ABOVEGROUND LITTER INPUT AND CHEMISTRY OF OLD-GROWTH FOREST AND ADJACENT PRAIRIE

ABSTRACT The long-standing assumption that aboveground plant litter inputs have a substantial influence on soil organic carbon storage (SOC) and dynamics has been challenged by a new paradigm for SOC formation and persistence. We tested the importance of plant litter chemistry on SOC storage, distribution, composition, and age by comparing two highly contrasting ecosystems: an old-growth coast redwood (Sequoia sempervirens) forest, with highly aromatic litter, and an adjacent coastal prairie, with more easily decomposed litter. We hypothesized that if plant litter chemistry was the primary driver, redwood would store more and older SOC that was less microbially processed than prairie. Total soil carbon stocks to 110 cm depth were higher in prairie (35 kg C m−2) than redwood (28 kg C m−2). Radiocarbon values indicated shorter SOC residence times in redwood than prairie throughout the profile. Higher amounts of pyrogenic carbon and a higher degree of microbial processing of SOC appear to be instrumental for soil carbon storage and persistence in prairie, while differences in fine-root carbon inputs likely contribute to younger SOC in redwood. We conclude that at these sites fire residues, root inputs, and soil properties influence soil carbon dynamics to a greater degree than the properties of aboveground litter.

Carbon and Nitrogen Stocks in Topsoil under Different Land Use/Land Cover Types in the Southeast of Spain

Land use plays a crucial role in the stock of soil organic carbon (SOC) and soil nitrogen (SN). The aim of this study was to assess and characterize the effects of various soil management practices on the physicochemical properties of soil in a Mediterranean region in southeastern Spain. Texture, soil moisture, bulk density, pH, electrical conductivity, equivalent CaCO3 (%), soil organic matter and carbon, and Kjeldahl nitrogen were determined for the surface topsoil (0–5 cm, 180 samples) under three types of land cover: cropland, grassland, and urban soil. The main soil textures were silt, silt loam, and sandy loam with low percentages of soil moisture in all soil samples and lower bulk density values in cropland and grassland areas. The pH was alkaline and the electrical conductivity as well as the equivalent calcium carbonate content were moderate to high. Organic matter estimated using the LOI and WB methods varied in the order cropland > grassland > urban soil. The results obtained for SOC and SN indicate that cropland presented the highest stocks, followed by grassland and urban soil. The values determined for the C/N ratio were close to 10 in cropland and grassland, indicating that organic matter readily undergoes decomposition at these sites. Our results emphasize the importance of evaluating the effects and identifying the impacts of different soil management techniques, and further research is needed to better understand the potential to improve soil organic carbon and nitrogen storage in semiarid regions.

A random forest model to predict soil organic carbon storage in mangroves from Southern Colombian Pacific coast

Mangrove ecosystems serve as significant reservoirs of carbon stocks, particularly within the soil. However, these ecosystems face widespread degradation globally, underscoring the necessity for comprehensive technical insights to facilitate effective management. Enhancing the precision of soil organic carbon estimates within mangroves necessitates access to precise field data. Hence, this study aimed to assess the soil organic carbon stored in mangrove ecosystems along the southern Colombian Pacific coast. Employing a Random Forest model, constructed with data from 28 soil profiles spanning a depth of 2 m and 16 predictor variables, we evaluated the model's performance using repeated 10-fold cross-validation (with 5 random repeats). Uncertainty in carbon storage predictions was quantified through 95% confidence intervals. Our model successfully accounted for 88% of the variability in soil organic carbon storage. Depth, cation exchange capacity, pH, and sand content emerged as the most influential predictors of soil organic carbon storage variation. The study estimated a mean of 270.32 ± 52.75 t C ha−1, with a total carbon reserve of 25458088 t in the study area. Notably, this value falls below global estimates, suggesting a potential overestimation of carbon stocks in mangrove soils by existing global models.

Organic Carbon Storage and Structural-Hydraulic Properties of Ultisol under Agricultural Land Use Systems at Umuahia

The extent and pattern of interaction among organic carbon, structural and hydraulic properties of soils under varying land use systems are of great concern in the overall management of soil fertility and productivity. This study was conducted to examine the relationship among soil organic carbon storage, structural and hydraulic properties of soils under different agricultural land use systems at Umuahia, Abia State. The treatments were the four (4) land use systems (continuously cultivated arable farmland, 3 – year fallow land, oil palm plantation, and forest land) in which nine (9) replicates each of disturbed and undisturbed soil samples were randomly collected to give thirty six observational units laid out in a randomized complete block design. The soil samples were prepared and analysed in the laboratory. Analyses of variance, regression and correlation analyses were conducted on the data collected using Genstat version 14 and SPSS version 20. Results show that organic carbon had significant positive relationship with saturated hydraulic conductivity, macro porosity and total porosity but significant negative relationship with bulk density at all the land use systems. However, the influence of organic carbon on the other parameters was greatest at continuously cultivated arable land followed by the 3 – year fallow land. There is need to increase organic matter input at the continuously cultivated arable land and 3 – year fallow land through increased organic manuring and extension of the fallow period, respectively.

Spring rest-grazing time affected soil organic carbon stability and storage in subalpine meadows of Carex

Scientific grazing management is essential to maintain soil organic carbon (SOC) stability in subalpine meadows on the Qinghai-Tibet Plateau (QTP). We studied the stability of SOC in Carex subalpine meadows in QTP with five rest-grazing treatments. (ST1: soil surfaces started thawing; ST2: soil thawing depth > 10 cm; RG1: re-greening coverage reached 30–40%; RG2: re-greening coverage reached 80%; CK: local traditional rest-grazing time). The results showed that rest-grazing at different times in spring affected the active SOC composition by affecting the stability of physical structure. The underground organic carbon storage was dominated by the root carbon storage, while the active organic carbon component had a significant correlation with the litter content. Compared with the traditional rest-grazing, ST1, ST2, RG1 and RG2 increased the topsoil SOC storage by 5.87%, 7.24%, 13.55%, 2.17%, and the topsoil root carbon storage by 32.77%, 36.25%, 9.91%, −0.79%. Rest-grazing at ST1 promoted the production of soil macro-aggregates, increased the hydrolase activity and active SOC contents in topsoil, and promoted the soil nutrient cycling. Continuing grazing after the plant re-green increased the physical structure stability and oxidase activity but decreased the active SOC and SOC storage. Although a late rest-grazing in spring has increased the SOC stability, it reduced soil carbon use efficiency and sequestration. It is necessary to rest-grazing subalpine QTP Carex meadows before soil thaw, which can promote SOC accumulation and nutrient cycling, and transport plant carbon into the deep soil through roots, which is beneficial for grassland productivity and grassland carbon sequestration.

AgriCarbon-EO v1.0.1: large-scale and high-resolution simulation of carbon fluxes by assimilation of Sentinel-2 and Landsat-8 reflectances using a Bayesian approach

Abstract. Soil organic carbon storage is a well-identified climate change mitigation solution. Quantification of the soil carbon storage in cropland for agricultural policy and offset carbon markets using in situ sampling would be excessively costly, especially at the intrafield scale. For this reason, comprehensive monitoring, reporting, and verification (MRV) of soil carbon and its explanatory variables at a large scale need to rely on hybrid approaches that combine remote sensing and modelling tools to provide the carbon budget components with their associated uncertainties at intrafield scale. Here, we present AgriCarbon-EO v1.0.1: an end-to-end processing chain that enables the estimation of carbon budget components for major and cover crops at intrafield resolution (10 m) and regional extents (e.g. 10 000 km2) by assimilating remote sensing data (e.g. Sentinel-2 and Landsat8) in a physically based radiative transfer (PROSAIL) and agronomic models (SAFYE-CO2). The data assimilation in AgriCarbon-EO is based on a novel Bayesian approach that combines normalized importance sampling and look-up table generation. This approach propagates the uncertainties across the processing chain from the reflectances to the output variables. After a presentation of the chain, we demonstrate the accuracy of the estimates of AgriCarbon-EO through an application over winter wheat in the southwest of France during the cropping seasons from 2017 to 2019. We validate the outputs with flux tower data for net ecosystem exchange, biomass destructive samples, and combined harvester yield maps. Our results show that the scalability and uncertainty estimates proposed by the approach do not hinder the accuracy of the estimates (net ecosystem exchange, NEE: RMSE =1.68–2.38 gC m−2, R2=0.87–0.77; biomass: RMSE =11.34 g m−2, R2=0.94). We also show the added value of intrafield simulations for the carbon components through scenario testing of pixel and field simulations (biomass: bias =-47 g m−2, −39 % variability). Our overall analysis shows satisfying accuracy, but it also points out the need to represent more soil processes and include synthetic aperture radar data that would enable a larger coverage of AgriCarbon-EO. The paper's findings confirm the suitability of the choices made in building AgriCarbon-EO as a hybrid solution for an MRV scheme to diagnose agro-ecosystem carbon fluxes.

Effects of fresh-salt water interaction on spatial variations of soil organic carbon in reed wetland of Yellow River Estuary.

Estuarine wetlands exhibit significant interaction between fresh and salt water, with long-term carbon sequestration capability. We set up 60 sampling sites in the reed wetlands of the fresh-salt water interaction zone of the Yellow River Estuary, covering four different zones of the weak-intensity fresh-salt water interaction zone (WIZ), medium-intensity fresh-salt water interaction zone (MIZ), high-intensity interaction fresh-salt water zone (HIZ) and strong-intensity fresh-salt water interaction zone (SIZ). We investigated how fresh-salt water interaction affected the spatial variation of soil organic carbon (SOC) storage. The results showed that the area of reed wetland accounted for 17.8% of the total area of the fresh-salt water interaction zone the Yellow River Estuary, which mainly distributed in the WIZ and MIZ. The SOC content of reed wetland in the fresh-salt water interaction zone ranged from 1.09 to 3.65 g·kg-1, the SOC density was between 1.85-5.84 kg·m-2, and the SOC storage was (17.32±3.64)×104 t. The SOC content and SOC density decreased with increasing fresh-salt water interaction. There were significant differences in surface SOC content between different subzones of the fresh-salt water interaction zone. The surface SOC content decreased significantly with the increases of fresh-salt water interaction intensity. SOC density was positively correlated with SOC, TN, NH4+-N, and biomass, but negatively correlated with salt ions, soil bulk density, pH, and EC. SOC storage in the 0-30 cm soil layer accounted for 50.9%-64.2% of that in the 0-60 cm soil layer, while SOC storage in the 0-60 cm soil layer occupied 19.1%-37.7% of that in the 0-400 cm soil layer. The results could provide a scientific basis for accurately evaluating SOC storage of estuarine wetlands, improving carbon sink function and wetland management.

Spatial changes of soil structural properties and organic carbon storage of arable farmland at Umuahia, Abia State

Precision agriculture requires that spatial changes of soil structural properties and soil organic carbon (SOC) accumulation be established for effective soil management. A research was carried out to ascertain the spatial variation of soil structural properties and organic carbon accumulation of an arable farmland at Umuahia. The experiment was conducted by delineating the land into three (3) portions. Three auger and core soil samples each were randomly collected from each portion, and this gave nine (9) observational points which were georeferenced. The soil samples were prepared and analysed in a laboratory for determination of parameters. The data generated were analysed for spatial variation using a GIS software package. The highest SOC accumulation of 26.46 ton / ha was obtained at the extreme north and northwestern regions of the land, while the lowest SOC accumulation of 19.71 ton / ha was obtained at extreme southeastern region of the land. The entire central area to the north western portion of the land had lowest bulk density (BD) of 1.33 kg / m3, while the southward to the north eastern portions of the land had the highest BD of 1.37 kg / m3. The highest hydraulic conductivity of 4.75 cm / mins was observed at the south western portion. The southward and extreme north eastern portions of the land had the highest mean weight diameter (MWD) of 0.95 mm, while the lowest MWD of 0.75 mm was observed at the central areaand extended to the north western portions of the land. There were also spatial changes in the total porosity, and micro aggregate stability indices across the land area. Suitable agronomic practices need to be adopted within the various portions of the land in managing the soil.

Connecting competitor, stress-tolerator and ruderal (CSR) theory and Lund Potsdam Jena managed Land 5 (LPJmL 5) to assess the role of environmental conditions, management and functional diversity for grassland ecosystem functions

Abstract. Forage offtake, leaf biomass and soil organic carbon storage are important ecosystem services of permanent grasslands, which are determined by climatic conditions, management and functional diversity. However, functional diversity is not independent of climate and management, and it is important to understand the role of functional diversity and these dependencies for ecosystem services of permanent grasslands, since functional diversity may play a key role in mediating impacts of changing conditions. Large-scale ecosystem models are used to assess ecosystem functions within a consistent framework for multiple climate and management scenarios. However, large-scale models of permanent grasslands rarely consider functional diversity. We implemented a representation of functional diversity based on the competitor, stress-tolerator and ruderal (CSR) theory and the global spectrum of plant form and function into the Lund Potsdam Jena managed Land (LPJmL) dynamic global vegetation model (DGVM) forming LPJmL-CSR. Using a Bayesian calibration method, we parameterised new plant functional types (PFTs) and used these to assess forage offtake, leaf biomass, soil organic carbon storage and community composition of three permanent grassland sites. These are a temperate grassland and a hot and a cold steppe for which we simulated several management scenarios with different defoliation intensities and resource limitations. LPJmL-CSR captured the grassland dynamics well under observed conditions and showed improved results for forage offtake, leaf biomass and/or soil organic carbon (SOC) compared to the original LPJmL 5 version at the three grassland sites. Furthermore, LPJmL-CSR was able to reproduce the trade-offs associated with the global spectrum of plant form and function, and similar strategies emerged independent of the site-specific conditions (e.g. the C and R PFTs were more resource exploitative than the S PFT). Under different resource limitations, we observed a shift in the community composition. At the hot steppe, for example, irrigation led to a more balanced community composition with similar C, S and R PFT shares of aboveground biomass. Our results show that LPJmL-CSR allows for explicit analysis of the adaptation of grassland vegetation to changing conditions while explicitly considering functional diversity. The implemented mechanisms and trade-offs are universally applicable, paving the way for large-scale application. Applying LPJmL-CSR for different climate change and functional diversity scenarios may generate a range of future grassland productivities.

Considering Historical Land Use When Estimating Soil Carbon Stock Changes of Transitional Croplands

Understanding changes to soil organic carbon storage (SOC) requires knowledge of detailed land use history. Many satellite-based analyses of land use change have been conducted over short periods (typically 5 to 10 years) to investigate causality to a demand increase in an agricultural commodity. However, statistically significant changes in SOC are not readily observable during this time and typically require decades for meaningful differences to accrue. This study aimed to determine land use and soil organic carbon stocks on land parcels over 36 years (1985–2021) located in areas where historical land use transitions between cropland and non-cropland are prevalent. Aerial and satellite imagery were analyzed across 25,992 hectares in ten counties across the Corn Belt. Grower interviews were conducted to solicit feedback on the drivers of land use change. Finally, SOC analyses associated with land use changes were determined using two process-based models. Analysis showed that 371 of the parcels had remained in cropland, 611 parcels transitioned into non-cropland, and 18 parcels were identified as non-cropland. The grower surveys indicated that the most common reasons for returning land to crop was the difficulty getting land re-enrolled in the CRP and reduced cattle prices. Both the SALUS and GREET-CCLUB models were parameterized to assess soil carbon changes for the respective land use history, and both models returned consistent SOC increases at the county level over time.

Influence of Forest Strips on Changes in Soil Properties in the Agrolandscape

Background: In Russia 5.2 million hectares of protective forest plantations were created on agricultural land. Forest strips optimize moisture turnover, heat and gas exchange of the territory and transform agrarian landscapes into more sustainable forest-agrarian ecosystems (agroforest landscapes). Studying the impact of shelterbelt forests on the transformation of soil properties in the context of climate change (organic carbon storage) is an important problem. The aim of our research was to study the effect of shelterbelt forests on soil indicators and to digitally map the contours of forest-meliorated soils on the test site using GIS-technology and field studies. Methods: In the present study, the methodology of soil studies in agroforested soils (1978) and the methodology of assessing the accumulation of substances in plants and soils in agroforested landscapes were used to study forest-meliorated soils. We proceeded from the position that the reclamation effect of forest belts occurs at a distance of 30 heights. The research was conducted from 2016 to 2022. Result: Research has established, that the soil profile under the forest belt has an organogenic horizon A0 (forest floor); the thickness of the humus horizon (A+B1) under the forest belt is 8-10 cm higher compared to other zones. Spatial distribution of humus content in the A+B1 horizon from the forest belt to the centers of inter-belt squares (zone 20H) is not characterized by great variability and clear patterns and on average makes 1.15-1.2%. The increase in calcium carbonate (CaCO3) content in the soil occurs in the direction from the forest belt to the 20H zone. The indicator of dense residue in terms of the content of readily soluble salts is not relevant in estimating the forest belt’s influence on transformation of soil properties. A preliminary digital map of the contours of forest-reclaimed soils has been compiled. The obtained materials will serve as a basis for modeling the spatial and temporal dynamics of soils under forest belts in the zonal section and improving soil fertility in the interstrip space.

Maximizing soil organic carbon stocks through optimal ploughing and renewal strategies in (Ley) grassland

Grassland management effects on soil organic carbon storage under future climate are unknown. Here we examine the impact of ley grassland durations in crop rotations on soil organic carbon in temperate climate from 2005 to 2100, considering two IPCC scenarios, RCP4.5 and RCP8.5, with and without atmospheric CO2 enhancements. We used the DailyDayCent model and a long-term experiment to show that ley grasslands increase soil organic carbon storage by approximately 10 Mg ha−1 over 96 years compared with continuous cropping. Surprisingly, extending ley duration from 3 to 6 years does not enhance soil organic carbon. Furthermore, in comparison with non-renewed grasslands, those renewed every three years demonstrated a notable increase in soil organic carbon storage, by 0.3 Mg ha−1 yr−1. We concluded that management of ploughing and renewal intervals is crucial for maximizing soil organic carbon stocks, through balancing biomass carbon inputs during regrowth and carbon losses through soil respiration.

Biomass Storage in Anoxic Marine Basins: Initial Estimates of Geochemical Impacts and CO2 Sequestration Capacity

AbstractIn combination with dramatic and immediate CO2 emissions reductions, net‐negative atmospheric CO2 removal (CDR) is necessary to maintain average global temperature increases below 2.0°C. Many proposed CDR pathways involve the placement of vast quantities of organic carbon (biomass) on the seafloor in some form, but little is known about their potential biogeochemical impacts, especially at scales relevant for global climate. Here, we evaluate the potential impacts and durability of organic carbon storage specifically within deep anoxic basins, where organic matter (OM) is remineralized through anaerobic processes that may enhance its storage efficiency. We present simple biogeochemical and mixing models to quantify the scale of potential impacts of large‐scale OM addition to the abyssal seafloor in the Black Sea, Cariaco Basin, and the hypersaline Orca Basin. These calculations reveal that the Black Sea in particular may have the potential to accept biomass storage at climatically relevant scales with moderate changes to the geochemical state of abyssal water and limited communication of that impact to surface water. Still, all of these systems would require extensive further evaluation prior to consideration of megatonne‐scale CO2 sequestration. Many key unknowns remain, including the partitioning of breakdown among sulfate‐reducing and methanogenic metabolisms and the fate of methane in the environment. Given the urgency of responsible CDR development and the potential for anoxic basins to reduce ecological risks to animal communities, efforts to address knowledge gaps related to microbial kinetics, benthic processes, and physical mixing in these systems are critically needed.

New perspectives on organic carbon storage in lake sediments based on classified mineralization

The burial amount of organic carbon (OC) in lake sediments is constantly changing owing to mineralization. Statically measured OC does not entirely reflect the dynamic OC processes in lake sediments. This study proposes a dynamic deposition and mineralization model for sedimentary OC (DMSOC) and applies it to eight sedimentary cores from two lakes to invert the history of OC in sediments. The results showed that the trophic level and temperature of the lake predominantly affected the amount of deposited OC (De-OC). The amount of mineralized OC in the sediments is adversely affected by the end sources, burial time, and trophic level of the lake. The OC end source mainly determined the mineralization rate in the following order: algae > aquatic > terrestrial sources. Burial time primarily affected the compositional characteristics of the remaining OC, owing to the asynchronous mineralization of OC from different sources. The De-OC of Dianchi Lake, a eutrophic lake, increased more than twice compared to that of the scenario 100 years ago. The De-OC content of Fuxian Lake, an oligotrophic lake, decreased by approximately 25 %. The greenhouse effect may further reduce the carbon sequestration capacity of lakes, particularly oligotrophic lakes. With a set burial age, the model results show that the increase in OC storage in lake sediments may be much lower than expected. Therefore, the roles of different types of lakes in the carbon cycle must be reassessed.

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 5 and 10 Tg, which corresponds to less than the 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.