Net Carbon Balance Research Articles

Use of Long-Term Soil Respiration Measurements for Calculating the Net Carbon Balance in Ecosystems of the Central Chernozemic Region

Use of Long-Term Soil Respiration Measurements for Calculating the Net Carbon Balance in Ecosystems of the Central Chernozemic Region

Soil net carbon balance depends on soil C: N: P stoichiometry

Exogenous carbon (C) input may induce priming effects, leading to the loss of soil organic C (SOC) by accelerating the decomposition of native soil organic matter (SOM), while also replenishing SOC through various mechanisms. However, the net C balance resulting from priming and replenishment of SOC under long-term nitrogen (N) fertilization and its stoichiometric regulation mechanisms remain largely undetermined. Soils subjected to 11 years of different N applications were used to investigate the net C balance following the addition of exogenous 13C-labeled glucose. The retention of glucose-derived C exceeded the loss of C caused by the priming effect, resulting in a positive net C balance, albeit attenuated by historical N application (ranging from 25.9 to 36.9 μg C mg−1 SOC). The application of increasing historical N levels resulted in a decrease in soil C:N imbalance and an increase in soil N:phosphorus (P) imbalance, as well as an increase in TERC:N and TERC:P. This suggested that the C and/or P limitations of soil microbial communities were intensified with increased N availability. Soil nutrient stoichiometric imbalance and available resource stoichiometry directly influenced the threshold element ratio, which in turn impacted glucose mineralization, subsequently affecting the net C balance. Collectively, our results provided solid evidence that labile C input could lead to a positive net C balance, which diminished with increased historical N application and was primarily regulated by soil C:N:P stoichiometry. This study highlights the significant implications for the soil C turnover and sequestration under long-term N application management in agroecosystems.

Soil Health Intensification through Strengthening Soil Structure Improves Soil Carbon Sequestration

Intensifying soil health means managing soils to enable sustainable crop production and improved environmental impact. This paper discusses soil health intensification by reviewing studies on the relationship between soil structure, soil organic matter (SOM), and ecosystem carbon budget. SOM is strongly involved in the development of soil structure, nutrient and water supply power, and acid buffering power, and is the most fundamental parameter for testing soil health. At the same time, SOM can be both a source and a sink for atmospheric carbon. A comparison of the ratio of soil organic carbon to clay content (SOC/Clay) is used as an indicator of soil structure status for soil health, and it has shown significantly lower values in cropland than in grassland and forest soils. This clearly shows that depletion of SOM leads to degradation of soil structure status. On the other hand, improving soil structure can lead to increasing soil carbon sequestration. Promoting soil carbon sequestration means making the net ecosystem carbon balance (NECB) positive. Furthermore, to mitigate climate change, it is necessary to aim for carbon sequestration that can improve the net greenhouse gas balance (NGB) by serving as a sink for greenhouse gases (GHG). The results of a manure application test in four managed grasslands on Andosols in Japan showed that it was necessary to apply more than 2.5 tC ha−1 y−1 of manure to avoid reduction and loss of SOC in the field. Furthermore, in order to offset the increase in GHG emissions due to N2O emissions from increased manure nitrogen input, it was necessary to apply more than 3.5 tC ha−1y−1 of manure. To intensify soil health, it is increasingly important to consider soil management with organic fertilizers that reduce chemical fertilizers without reducing yields.

Eddy covariance fluxes of greenhouse gasses observed in a renewed pasture in the southeast of Brazil

The recovery of degraded pastures and the increase in their capacity for storing carbon is a key strategy in Brazil's commitment to meeting its Nationally Determined Contribution (NDC) to the international effort to halt global warming. Here we report the fluxes of CO2, N2O and CH4 gasses and their balances, obtained by the eddy covariance method, from a representative pasture area in southeast Brazil. The measurements covered more than five years, starting with the old degraded pasture, covering the renewal process and then the re-establishment of pasture. The latter only received nitrogen fertilization once after the renewal – the common practice. The net ecosystem carbon balance (NECB), which considered the sum of the net ecosystem exchange (NEEpasture) of CO2 and methane (FCH4pasture) without the cattle respiration and enteric fermentation, as well the export/import of carbon by grazing and as feces (stocking rates of 1.8 to 3.3 AU ha−1), was positive in the old pasture (236 ± 104 g CO2m−2 year−1) representing a source to the atmosphere, but a sink (negative) during the first year of the renewal (-1603 ± 122 g CO2m−2 year−1) when it was fertilized and the recorded rainfall was normal. In the following two years it was neutral (77 ± 93 and 5 ± 100 g CO2m−2 year−1), partially a consequence of the lower rainfall received. In the fourth year it was a sink again (-736 ± 131 g CO2m−2 year−1). On average the cumulative fluxes of CH4 (42 ± 19 g CO2 eq. m−2 year−1) without the animals’ enteric fermentation and N2O (20 ± 10 g CO2 eq. m−2 year−1) were small and positive, being offset by the net carbon gain. The NECB for this site covering the period of measurements was an overall source of 671 ± 254 g CO2m−2.

Carbon balance analysis of agricultural production systems in oasis areas

China is the biggest emitter of greenhouse gases (GHGs) in the world, and agricultural GHG emission accounts for nearly a fifth of the total emission in China. To understand the carbon absorption and emission characteristics of agricultural production systems in those arid oasis areas, a typical representative city in northwestern China, Zhangye City, was selected for study.The emission factor method was used to analyze and calculate the characteristics of changing carbon emission dynamics in the whole agricultural production system in Zhangye city region (38,592 km2) from 2010 to 2021.The results revealed that carbon emissions during agricultural planting mainly come from fertilizers, which account for the highest proportion (47.9%) of total carbon emissions in agricultural planting. Animal enteric fermentation emissions from local livestock farming are the main contributor (86%) to GHG emissions. The annual average carbon absorption intensity is 4.4 t C-eq ha−1 for crop and 2.6 t C-eq ha−1 for the agricultural production system. The ratio of total carbon emissions from agricultural production to carbon sequestration of crops is 1:1.7. We find that the total carbon sequestration slightly exceeds its total carbon emissions in the study region, with an annual average of 41% for its sustainable development index. Carbon emissions of the agricultural production system in this oasis area are mainly driven by the livestock industry, mostly CH4 emissions from cattle raising.Reducing the local carbon emissions from the livestock industry, typically the cattle raising, will play a crucial role in reducing carbon emissions from this local agricultural production system and maintaining its net positive carbon balance.

Investigation of synergistic effects using alkanolamines on post-synthetic modification of metal-organic framework and CO2 adsorption capacity

The net global carbon balance is a key modern and even existential environmental issue to humans. Therefore, developing highly efficient gas separation technologies, e.g. based on the application of solid adsorbents, is critically important. Among the advanced solid adsorbents metal-organic frameworks (MOFs), especially MIL-101(Cr), which offers superior physicochemical properties, have proven to be highly promising porous materials for such purposes. In this approach, MIL-101(Cr) nanoadsorbent was functionalized using four alkanolamines (MIL-101(Cr)-alkanolamine) to enhance its CO2 adsorption capacity by increasing the polarity of its pores. Additionally, the synergistic effects of steric hindrance (-CH3 and –CH2CH2OH) and the basicity strength (pKa) of alkanolamines on post-synthetic modification (PSM) of MIL-101(Cr) were investigated. Alkanolamines were selected as the organic ligands because their nitrogen atoms (amino group) coordinate with the chromium ion in MIL-101(Cr), while the hydroxyl groups increase pore polarity and improve the CO2 adsorption capacity through creating weak hydrogen bonding (H-bonding) interactions, resulting in reduced energy consumption during regeneration. In this study, PXRD, IR, and FE-SEM results demonstrated that the crystal structure and morphology of nanoadsorbents remained intact after modification. CHN and ICP analyses were additionally employed to calculate the Nalkanolamine/Cr ratios. CO2 adsorption capacities of all MIL-101(Cr)-alkanolamine nanoadsorbents (∼30–∼45 %) and their selectivity profile (CO2:CH4 and CO2:N2) exhibited significant improvement as opposed to MIL-101(Cr). Investigations revealed that the adsorption capacities of all nanoadsorbents negligibly changed after five adsorption-desorption cycles.

Mountain Peatlands and Drought: Carbon Cycling in the Pyrenees Amidst Global Climate Change

AbstractThis study provides a multi‐year (2017–2022) Net Ecosystem Carbon Balance (NECB) of a Pyrenean mountainous peatland through the integration of field data, satellite imagery, and statistical modeling. Fluvial organic carbon export was measured at 30 min frequency, while gaseous (CO2 and CH4) exchanges were measured monthly using closed chambers. These measurements were combined with Sentinel‐2 derived chlorophyll index and in situ high frequency (1 hr) measurements of key environmental variables such as air temperature, photosynthetically active radiation, and water table level, to develop hourly gaseous carbon flux models (R2 = 0.69 for GPP, R2 = 0.84 for ER, R2 = 0.59 for CH4). Over the 2017–2022 period, modeled average GPP (610 ± 39 gC.m−2.year−1) and ER (641 ± 59 gC.m−2.year−1) showed that the peatland acted as a weak source of CO2 to the atmosphere, releasing 31 ± 73 gC.m−2.year−1. Considering fluvial carbon export and CH4 exchanges, the loss of carbon from the peatland increased to 55 ± 73 gC.m−2.year−1. Dissolved organic carbon constituted 8%–106% of the NECB. The estimated long‐term organic accumulation rate indicated a steady carbon accumulation rate of 16.4 gC.m−2.year−1, contrasting with the contemporary NECB, suggesting a recent shift in ecosystem functioning from a carbon sink to a source. The study underscores the role of water availability and air temperature through a drought index (DI), in shaping the NECB. The DI correlated significantly with annual carbon gaseous fluxes, except for 2022, marked by an intense drought. During this year the peatland became a large source of carbon (189 gC.m−2.year−1) to the atmosphere.

Topsoil dilution by subsoil admixture had less impact on soil organic carbon stock development than fertilizer form and erosion state

Enhancing the agroecosystems carbon (C) sink function for climate mitigation faced challenges, particularly with traditional measures with limited suitability for increasing soil organic carbon (SOC) stocks. Inducing a SOC undersaturation in the topsoil by abrupt subsoil admixture is a way to create an additional C sink. However, the deep tillage traditionally used for this topsoil dilution was not always successful. It was due to a lack of knowledge and suitable approaches to record the effect of all relevant factors in SOC recovery, including soil conditions and fertilizer forms.We addressed these problems by establishing a three-factorial experiment: I) “moderate topsoil dilution,” II) “N fertilization form,” and III) “soil erosion state,” representing three soil types in the hummocky ground moraine landscape of NE Germany. SOC dynamics were determined over a year of winter rye cropping using a novel robotic chamber system capable of measuring CO2 exchange on 36 experimental plots with a reduced methodological bias than previous measuring systems.The averaged net ecosystem carbon balance, a proxy for SOC stock change, indicated that topsoil dilution only reduced further SOC losses. The N fertilizer form had a significantly stronger and more differentiated effect. While the mineral N fertilization consistently produced only C sources, the organic fertilization, in combination with the diluted topsoil, led to a C sink. This C-sink function was, however, more pronounced in the eroded soil than in the non-eroded soil. Overall, the results have made clear that the impact of topsoil dilution on the further development of the SOC stock is only possible if the effect of other relevant factors, such as N fertilizer form and erosion state, are taken into account.

Effects of cover crops and nitrogen fertilizer on greenhouse gas emissions and net global warming potential in a potato cropping system

The study was conducted to investigate the effects of cover crops and different nitrogen levels on greenhouse gas emissions and net global warming potential in a potato production system during the 2018–2019 and 2019–2020 growing seasons at the Agricultural Research Farm of Razi University, Kermanshah, Iran. The experiment was arranged as a split plot based on a randomized complete block design with three replications. The main factor was cover crop including hairy vetch, rye, mixed (rye + hairy vetch), and control (no cover crop), and the sub factor was nitrogen fertilizer (as urea) at four levels consisted of 0 (control), 33, 66 and 100 % of the recommended nitrogen fertilizer based on the soil test. Results showed that the use of cover crops as green manures increased net ecosystem carbon balance (NECB) and the highest NECB was observed in the mixed treatment (rye + hairy vetch) along with the 66 % of nitrogen fertilizer. The mixed cover crops (hairy vetch + rye) along with the 100 % of nitrogen fertilizer showed higher CO2 emission and, while hairy vetch along with the 100 % of nitrogen fertilizer had higher emissions of N2O and CH4 during the potato growing season. It can be concluded that the use of cover crops as green manures before the planting of potato can notably increase greenhouse gas emissions and the net global warming.

Quantifying the negative effects of dissolved organic carbon of maize straw-derived biochar on its carbon sequestration potential in a paddy soil

Biochar of low-medium temperature may contain abundant dissolved organic carbon (BDOC), affecting its priming effect and carbon sequestration potential in soils. However, the direct and quantitative evidence for such impacts remains lacking. This study conducted incubation experiments on maize straw-derived 300/450 °C biochar, BDOC-extracted biochar residues and BDOC, and applied δ13C analysis to quantify biochar's mineralization and their priming effects on native soil organic carbon in a paddy soil. BDOC contained abundant lipid-, protein-, carbohydrate-like species, serving as nutrients for the metabolism of microorganisms, and thus enhanced native soil organic carbon's mineralization by 15–20%. After BDOC extraction, 300 °C biochar-trigged priming effect shifted from a positive (3.7 mg CO2–C kg−1 soil) to a negative state (−14.4 mg CO2–C kg−1 soil), and 450 °C biochar-induced negative priming effect increased by 31%; biochar's mineralization also decreased by 41–65%. Overall, after BDOC extraction, the net carbon balance in biochar-amended soils reduced by 7–8%. Furthermore, BDOC shifted the dominant priming mechanisms of biochar mainly by enhancing soil macro-aggregates while reducing sorptive protection for native soil organic carbon. Its extraction reduced the amount of soil macro-aggregates by 16–25% but enhanced the sorption affinity of native soil organic carbon by biochar by 68–122%. Additionally, after BDOC extraction, the microbial communities in biochar-amended soils contained more fungi and G+-bacteria. These findings proved that BDOC extraction appears a feasible strategy to enhance the short-period carbon sequestration potential of biochar.

Maintaining favourable carbon balance in boreal clay soil is challenging even under no-till and crop diversification

We explored the carbon balance, including both gaseous and waterborne carbon, of a long-term experimental site in 2019 and 2020. Additionally, we assessed earthworm abundance and soil aggregation, aiming to uncover potential factors influencing the decomposition and stabilization capacity of organic carbon in the soil. The heavy clay soil site in southern Finland was under long-term cereal monocropping with conventional tillage (CT) and no-till (NT) treatments. Short-term diversification with cover crop and winter rapeseed as a break crop were applied on parts of the site, and the effects of climate, carbon input and soil conditions on the carbon balance were assessed. Net ecosystem exchange (NEE) ranged from −0.32 to 1.91 Mg CO2-C ha−1 yr−1 in CT and from 0.22 to 2.40 Mg CO2-C ha−1 yr−1 in NT. Net ecosystem carbon balance ranged from 1.49 to 3.27 Mg C ha−1 yr−1 and 1.51 to 3.67 Mg C ha−1 yr−1 in CT and NT, respectively, indicating carbon loss from soil. The differences in NEE or carbon balance between CT and NT were not statistically discernible. Earthworm abundance was higher in NT than in CT and increased vastly in the NT management after diversification of the rotation with winter rapeseed. Soil erosion measurements showed remarkably lower carbon loss (44%) for NT compared to CT, however, the role of erosion in the carbon balance was minor, ranging from 50 to 120 kg C ha−1 yr−1. The mean size of soil aggregates decreased during the study period, and soil aggregates tended to enlarge in the summer and diminish in the winter. The results highlight the difficulty of maintaining a positive carbon balance in boreal agricultural soils with limited productivity. Furthermore, future climatic conditions may worsen the situation by promoting decomposition and restricting carbon protection in soil aggregates.

Effect of rice hull biochar treatment on net ecosystem carbon budget and greenhouse gas emissions in Chinese cabbage cultivation on infertile soil

Biochar, with its potential to enhance soil fertility, sequester carbon, boost crop yields and reduce greenhouse gas emissions, offers a solution. Addressing the challenges posed by climate change is crucial for food security and agriculture. However, its widespread adoption in agriculture remains in its infancy. This study assessed the effects of rice hull biochar on cabbage production and greenhouse gas emissions, especially nitrous oxide (N2O). A trial, employing a randomized block design in triplicate was conducted from September 13 to November 23, 2022, where "Cheongomabi" cabbage was cultivated with N-P2O5-K2O fertilization at 32-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-$$\\end{document}7.8-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-$$\\end{document}19.8 kg 10a−1. Additional fertilizer was applied twice post-sowing. The Biochar application rates were control = 0 ton ha−1, B1 = 1 ton ha−1, B3 = 3 ton ha−1, and B5 = 5 ton ha−1. The aboveground biomass of autumn cabbage harvested 82 days after sowing was 2.40–2.70 kg plant−1 in the control and biochar treatments (B1, B3, and B5), with no significant differences (p > 0.05). Cumulative CO2 emissions during cultivation varied across treatment groups, with initial and cumulative emissions of 10.40–17.94 g m−2 day−1 and 3.63–4.43 ton ha−1, respectively. N2O emissions decreased with higher biochar application: reductions of 2.9%, 25.4%, and 41.1% in the B1, B3, and B5 treatments, respectively, compared to the control. The biochar application had no significant impact on yield but curbed soil emissions, Net ecosystem carbon balance during cabbage cultivation ranged from 0.42 to 3.41 ton ha−1 for the B1, B3, and B5 treatments, respectively, compared to control. Overall, the study underscores biochar’s role in mitigating emissions and boosting soil carbon during cabbage cultivation in fall.

Progress and challenges in remotely sensed terrestrial carbon fluxes

ABSTRACT Accurate evaluation of terrestrial carbon balance is essential for designing climate change mitigation policies, and capabilities of remote sensing techniques in monitoring carbon fluxes are widely recognized for their great contributions to regional and global carbon budget accounting. In this review, we synthesized satellite-based data and methodologies to estimate the main flux components of terrestrial carbon balance and their uncertainties over the past two decades. The global gross primary production (GPP) during the period 2001–2022 is 134 ± 14 PgC yr−1, and nearly half of them occurs in tropical forest regions such as South America and Africa. Less than 2% of global GPP is converted into a net carbon sink of 2.28 ± 1.12 PgC yr−1 using satellite-based atmospheric inversion during 2015–2020, and this sink is comparable to the stock change-based estimate (2.49 PgC yr−1) but twice as large as model-based estimate (1.08 ± 0.78 PgC yr−1). By decomposing satellite-derived net carbon balance into different terms including satellite-derived carbon emissions from land-use change and wildfires (3.55 PgC yr−1), we inferred that ~ 43% of global GPP would be respired through soil microbes (57.1 PgC yr−1), but which is higher than the previous bottom-up estimate (39–46 PgC yr−1). We then propose that an accurate remote sensing of terrestrial carbon balance requires to enhance representations of photosynthetic responses to rising CO2 and disturbances, develop satellite-constrained belowground carbon dynamics and separate natural fluxes from anthropogenic CO2 emissions, by integrating multi-source satellite sensors in orbit, revolutionized remote sensing capabilities with focused field campaigns in data-scarce regions.

A Carbon Source in a Carbon Sink: Carbon Dioxide and Methane Dynamics in Open‐Water Peatland Pools

AbstractPeatlands store organic carbon available for decomposition and transfer to neighboring water bodies, which can ultimately generate carbon dioxide (CO2) and methane (CH4) emissions. The objective of this study was to clarify the biogeochemical functioning of open‐water peatland pools and their influence on carbon budgets at the ecosystem and global scale. Continuously operated automated equipment and monthly manual measurements were used to describe the CO2 and CH4 dynamics in boreal ombrotrophic peatland pools and porewater (Québec, Canada) over the growing seasons 2019 and 2020. The peat porewater stable carbon isotope ratios (δ13C) for both CO2 (median δ13C‐CO2: −3.8‰) and CH4 (median δ13C‐CH4: −64.30‰) suggested that hydrogenotrophic methanogenesis was the predominant degradation pathway in peat. Open‐water pools were supersaturated in CO2 and CH4 and received most of these dissolved carbon greenhouse gases (C‐GHG) from peat porewater input. Throughout the growing season, higher CO2 concentrations and fluxes in pools were measured when the water table was low—suggesting a steady release of CO2 from deep peat porewater. Higher CH4 ebullition and diffusion occurred in August when bottom water and peat temperatures were the highest. While this study demonstrates that peatland pools are chimneys of CO2 and CH4 stored in peat, it also shows that the C‐GHG concentrations and flux rates in peat pools are comparable to other aquatic systems of the same size. Although peatlands are often considered uniform entities, our study highlights their biogeochemical heterogeneity, which, if considered, substantially influences their net carbon balance with the atmosphere.

Projection of the Carbon Balance of the Hungarian Forestry and Wood Industry Sector Using the Forest Industry Carbon Model

As forest-based climate change mitigation has become a crucial element of international climate policy it is of increasing importance to understand the processes leading to the carbon offsetting capacity of the sector. In our study, we assessed the climate benefits of contrasting forest management strategies: decreasing harvest and enlarging the forest carbon stock, or increasing harvest to increase carbon uptake, wood product carbon pools, and substitution effects. We developed the Forest Industry Carbon Model (FICM) which is a new carbon accounting tool covering forest biomass, dead organic matter, soil, and harvested wood product pools, as well as avoided emissions through product and energy substitution. We modeled the carbon balance of the Hungarian forest industry under three different scenarios. In the business as usual (BAU) scenario, we assumed no changes in the current harvest and afforestation levels. In the extensification scenario, we assumed that the harvest and afforestation levels drop to half, while in the intensification scenario, we assumed an increase in afforestation, improved industrial wood assortments, and a gradual increase in logging, reaching the highest level as per sustainability criteria by 2050. Our results show that the intensification scenario is characterized by the largest net removals and the maximized product and energy substitution effects. By 2050, the net forest industry carbon balance reaches −8447 kt CO2 eq under the BAU scenario, while −7011 kt CO2 eq is reached under the extensification scenario and −22,135 kt CO2 eq is reached under the intensification scenario. Although substitution effects are not accounted for under the land-based (LULUCF) sector in the greenhouse gas inventory, the emission reductions in the industry and energy sectors have beneficial effects on the national carbon balance. Modeling results show that the 2030 LULUCF greenhouse gas removal target set by EU legislation for Hungary is reached under the intensification scenario. To achieve this outcome, widespread innovation is needed in the wood sector. The modeling results show that nonutilization of forests can only be a very short-term solution; however, its favorable effects will be reversed by 2050 resulting in additional emissions compared to the BAU scenario.

Harvest residues: A relevant term in the carbon balance of croplands?

Over the past two decades, major efforts have been made to quantify the extent to which and under what conditions croplands are sources or sinks for carbon. For this purpose, the net carbon stock change of the study site is typically quantified based on net CO2 fluxes monitored with an eddy covariance or chamber system, on measured C import by organic fertilizer and C export by harvest. While in cropland studies this balance is usually referred to as net biome productivity (NBP), we prefer to use the term net ecosystem carbon balance (NECB) here. NECB is basically the sum of the stock change of plant carbon (ΔPC) and soil organic carbon (ΔSOC). In the standard approach, the assumption is that at an annual cropland site the bulk of plant biomass is typically removed at harvest, and that ΔPC can therefore be neglected. In this case, ΔSOC equals NECB. In this paper we show that this assumption is problematic, particularly if in crop rotation systems the budget is determined over a single cropping period. The present contribution extends the concept of NECB to include harvest residues (HR) and applies it to a case study over a maize - winter wheat - winter wheat rotation at a cropland site in southwest Germany. In all three cropping periods, the sign of NECB was opposite that of ΔSOC. Accordingly, neglecting HR led to an incorrect result concerning the question whether the site is a sink or a source for soil carbon. Our findings demonstrate that for croplands HR must be included to obtain an accurate and meaningful carbon balance.

A drained nutrient-poor peatland forest in boreal Sweden constitutes a net carbon sink after integrating terrestrial and aquatic fluxes.

Northern peatlands provide a globally important carbon (C) store. Since the beginning of the 20th century, however, large areas of natural peatlands have been drained for biomass production across Fennoscandia. Today, drained peatland forests constitute a common feature of the managed boreal landscape, yet their ecosystem C balance and associated climate impact are not well understood, particularly within the nutrient-poor boreal region. In this study, we estimated the net ecosystem carbon balance (NECB) from a nutrient-poor drained peatland forest and an adjacent natural mire in northern Sweden by integrating terrestrial carbon dioxide (CO2 ) and methane (CH4 ) fluxes with aquatic losses of dissolved organic C (DOC) and inorganic C based on eddy covariance and stream discharge measurements, respectively, over two hydrological years. Since the forest included a dense spruce-birch area and a sparse pine area, we were able to further evaluate the effect of contrasting forest structure on the NECB and component fluxes. We found that the drained peatland forest was a net C sink with a 2-year mean NECB of -115 ± 5 g C m-2 year-1 while the adjacent mire was close to C neutral with 14.6 ± 1.7 g C m-2 year-1 . The NECB of the drained peatland forest was dominated by the net CO2 exchange (net ecosystem exchange [NEE]), whereas NEE and DOC export fluxes contributed equally to the mire NECB. We further found that the C sink strength in the sparse pine forest area (-153 ± 8 g C m-2 year-1 ) was about 1.5 times as high as in the dense spruce-birch forest area (-95 ± 8 g C m-2 year-1 ) due to enhanced C uptake by ground vegetation and lower DOC export. Our study suggests that historically drained peatland forests in nutrient-poor boreal regions may provide a significant net ecosystem C sink and associated climate benefits.

Microbial-explicit processes and refined perennial plant traits improve modeled ecosystem carbon dynamics

Globally, soils hold approximately half of ecosystem carbon and can serve as a source or sink depending on climate, vegetation, management, and disturbance regimes. Understanding how soil carbon dynamics are influenced by these factors is essential to evaluate proposed natural climate solutions and policy regarding net ecosystem carbon balance. Soil microbes play a key role in both carbon fluxes and stabilization. However, biogeochemical models often do not specifically address microbial-explicit processes. Here, we incorporated microbial-explicit processes into the DayCent biogeochemical model to better represent large perennial grasses and mechanisms of soil carbon formation and stabilization. We also take advantage of recent model improvements to better represent perennial grass structural complexity and life-history traits. Specifically, this study focuses on: 1) a plant sub-model that represents perennial phenology and more refined plant chemistry with downstream implications for soil organic matter (SOM) cycling though litter inputs, 2) live and dead soil microbe pools that influence routing of carbon to physically protected and unprotected pools, 3) Michaelis-Menten kinetics rather than first-order kinetics in the soil decomposition calculations, and 4) feedbacks between decomposition and live microbial pools. We evaluated the performance of the plant sub-model and two SOM cycling sub-models, Michaelis-Menten (MM) and first-order (FO), using observations of net ecosystem production, ecosystem respiration, soil respiration, microbial biomass, and soil carbon from long-term bioenergy research plots in the mid-western United States. The MM sub-model represented seasonal dynamics of soil carbon fluxes better than the FO sub-model which consistently overestimated winter soil respiration. While both SOM sub-models were similarly calibrated to total, physically protected, and physically unprotected soil carbon measurements, the models differed in future soil carbon response to disturbance and climate, most notably in the protected pools. Adding microbial-explicit mechanisms of soil processes to ecosystem models will improve model predictions of ecosystem carbon balances but more data and research are necessary to validate disturbance and climate change responses and soil pool allocation.

Freshwater wetland restoration and conservation are long-term natural climate solutions

Freshwater wetlands have a disproportionately large influence on the global carbon cycle, with the potential to serve as long-term carbon sinks. Many of the world's freshwater wetlands have been destroyed or degraded, thereby affecting carbon-sink capacity. Ecological restoration of degraded wetlands is thus becoming an increasingly sought-after natural climate solution. Yet the time required to revert a degraded wetland from a carbon source to sink remains largely unknown. Moreover, increased methane (CH4) and nitrous oxide (N2O) emissions might complicate the climate benefit that wetland restoration may represent. We conducted a global meta-analysis to evaluate the benefits of wetland restoration in terms of net ecosystem carbon and greenhouse gas balance. Most studies (76 %) investigated the benefits of wetland restoration in peatlands (bogs, fens, and peat swamps) in the northern hemisphere, whereas the effects of restoration in non-peat wetlands (freshwater marshes, non-peat swamps, and riparian wetlands) remain largely unexplored. Despite higher CH4 emissions, most restored (77 %) and all natural peatlands were net carbon sinks, whereas most degraded peatlands (69 %) were carbon sources. Conversely, CH4 emissions from non-peat wetlands were similar across degraded, restored, and natural non-peat wetlands. When considering the radiative forcings and atmospheric lifetimes of the different greenhouse gases, the average time for restored wetlands to have a net cooling effect on the climate after restoration is 525 years for peatlands and 141 years for non-peat wetlands. The radiative benefit of wetland restoration does, therefore, not meet the timeframe set by the Paris Agreement to limit global warming by 2100. The conservation and protection of natural freshwater wetlands should be prioritised over wetland restoration as those ecosystems already play a key role in climate change mitigation.

Trends in Water-Energy Nexus and Carbon Emissions Balance in Axarquia Region, Spain, in the Period 1990–2030

This research explores the dynamic interplay of water, energy, and carbon in Axarquia, Spain (1990–2030), focusing on the escalating water deficit and rising emissions. It seeks to comprehend the impact of subtropical crop expansion on regional resources. A comprehensive methodology integrates data on water demand, alternative sources and energy-intensive processes. Key methods include assessing the influence of subtropical crops on water requirements by calculating the FAO 56 crop coefficient (Kc), the total annual energy (GWh) as a consequence of the volume of water demanded, identifying the predominant water sources and quantifying CO2 emissions by calculating the carbon footprint balance, providing a holistic view of regional resource dynamics. The methodology developed here can be adapted to basins elsewhere and can be a useful tool to help the design of water management policies in basins where the balance of the Water, Food, Energy nexus is of particular interest. The study reveals a substantial 30% surge in water demand due to exponential growth in subtropical crops. Additionally, energy-intensive processes linked to alternative water sources contribute to a projected surge in emissions (2022–2030), indicating significant regional challenges. Axarquia faces imminent challenges with a widening water deficit and escalating emissions. However, the region emerges as a vital carbon sink, evidenced by the net carbon balance. With 176,413 tCO2eq sequestered by cultivated plant mass, the study underscores the potential for environmental improvement and climate change mitigation in the region.