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Coastal ecosystems are recognized as important carbon reservoirs. However, assessments of coastal carbon dioxide (CO2) fluxes often neglect unvegetated tidal flats, particularly in peri-urban areas. This study investigated the gross primary production (GPP), net primary production (NPP), and total respiration (TR) of three tidal flats in Hong Kong, one of the largest cities in South China, during both summer and winter seasons to understand their CO2 fluxes. Results showed that GPP of three tidal flats was significantly higher in winter than in summer. However, no significant seasonal variations in TR were observed among the tidal flats. Structural equation modelling was used to examine the drivers of CO2 fluxes in the three tidal flats. The model showed that temperature and microphytobenthos abundance were identified as positive drivers of GPP, while sediment mud content had a positive effect on TR. The estimated daily NPP of these tidal flats ranged from -0.853 to 0.112 g C m−2 d−1, which is lower than the mean value reported for global vegetated coastal wetlands. Despite some seasonal and spatial variations, those peri-urban tidal flats may be considered as weak CO2 sources rather than CO2 sinks. [ABSTRACT FROM AUTHOR]

To assess the accuracy of satellite monitoring of anthropogenic CO 2 emissions, inversions of satellite data in SWIR are usually combined with the assimilation of the total CO 2 column into a Kalman filter that reconstructs the sources and sinks of atmospheric CO 2 . To provide error estimates of the total CO 2 column for multi-month assimilation experiments of simulated satellite data, we parametrise these errors using linear regressions. These regression are obtained from a database that links meteorological situations, albedos, and aerosols to the errors in the inversion of the total CO 2 column based on simulated satellite data for those conditions. The errors in this database are explicitly computed using the Bayesian estimation formalism, and the linear regressions are optimised by selecting appropriate predictors and predictants. For different levels of measurement noise, error simulations are performed over a period of several months using the albedo and aerosol data from MODIS. [ABSTRACT FROM AUTHOR]

In recent years, the rise in greenhouse gas emissions from agriculture has worsened climate change. Efficiently utilizing agricultural waste can significantly mitigate these effects. This study investigated the ecological benefits of returning peach branch waste to fields (RPBF) through three innovative strategies: (1) application of peach branch organic fertilizer (OF), (2) mushroom cultivation using peach branches as a substrate (MC), and (3) surface mulching with peach branches (SM). Conducted within a peach orchard ecosystem, our research aimed to assess these resource utilization strategies' effects on soil properties, microbial community, and carbon cycle, thereby contributing to sustainable agricultural practices. Our findings indicated that all RPBF treatments enhance soil nutrient content, enriching beneficial microorganisms, such as Humicola, Rhizobiales, and Bacillus. Moreover, soil AP and AK were observed to regulate the soil carbon cycle by altering the compositions and functions of microbial communities. Notably, OF and MC treatments were found to boost autotrophic microorganism abundance, thereby augmenting the potential for soil carbon sequestration and emission reduction. Interestingly, in peach orchard soil, fungal communities were found to contribute more greatly to SOC content than bacterial communities. However, SM treatment resulted in an increase in the presence of bacterial communities, thereby enhancing carbon emissions. Overall, this study illustrated the fundamental pathways by which RPBF treatment affects the soil carbon cycle, providing novel insights into the rational resource utilization of peach branch waste and the advancement of ecological agriculture. [ABSTRACT FROM AUTHOR]

Wetlands are characterised by distinct hydrological regimes and have significant importance in the global carbon cycle, having the potential to reduce carbon emissions through long-term carbon storage in the soil. In this study, carbon dynamics were simulated using a process-based model DeNitrification-DeComposition (DNDC), for two locations along Dâmbovița River case study area. These scenarios took into consideration the interconnection of soil parameters, hydrology, meteorological conditions and vegetation type. The findings showed that soil CO2 emissions are positively and strongly correlated with air temperature and soil moisture, with changes in the water content of the soil regime having the greatest impact on CO2 fluxes. Also, the model simulations have been validated by statistical analysis of uncertainties with the values of CO2 fluxes measured in situ using the dynamic closed chamber method. By comparing DNDC outputs with field measurements, the performance of the model was evaluated in different environmental conditions and the results were consistent, which increased confidence in its application for assessing wetland ecosystems. These results contribute to a more comprehensive understanding of the carbon cycle in wetlands and an improved estimation of the effects of climate change on the dynamics of carbon in these ecosystems. [ABSTRACT FROM AUTHOR]

Mangrove ecosystems play a significant role in carbon absorption. However, the accumulation of organic matter in mangrove sediments undergoes decomposition, which triggers the release of CO2 gas flux. This study aimed to analyze the CO2 gas flux in mangrove sediments of Negeri Passo, Ambon City. Gas data collection was performed using cylinder canopies at the three observation stations. Gas was passed through the syringe five times with an interval of 30s. Gas concentration analysis was carried out using the gas chromatography method, while CO2 flux was analyzed with flux equations referring to slope regression, volume and area of the scope, temperature, molecular weight of the gas, ideal gas settings, and time constants based on gas intake intervals. The results showed that the average CO2 concentration in St. 1 was 465.14 ± 96.52 ppm, and was the lowest compared to St. 2 and St. 3 with values of 638.60 ± 90.05 ppm and 630.98 ± 54.09 ppm, respectively. Meanwhile, the average CO2 flux was 50.44 mg/m2/hour. The largest CO2 gas flux was observed at St. 2 at 103.69 mg/m2/hour. Meanwhile, the lowest flux was found at St. 3, which was 16.24 mg/m2/hour. Based on this, it can be concluded that] the mangrove ecosystem in Negeri Passo has a higher concentration of CO2 gas than the average concentration of climate change stabilization scenarios. However, the CO2 flux was lower than that at other locations in the Ambon Dalam Bay area. In addition, the potential for significant carbon sequestration based on the Tier 1 model approach indicated that mangrove ecosystems in this location play an important role in climate change mitigation.

Across boreal forests, trees are the main living biomass carbon (C) stock, but the understory vegetation can contribute significantly to the C cycling and net forest carbon dioxide (CO2) balance. The patchy understory vegetation, which consists of sunlit (i.e. lichen‐like) and shaded habitats (i.e. dwarf shrub‐like), is often altered by ungulate grazers. Grazers may influence understory CO2 exchange and, consequently, the forest CO2 balance. Grazing affects differently the biomass of slow‐growing lichens compared to the faster‐growing mosses and dwarf shrubs, and therefore the effects of grazing on CO2 exchange in the patchy understory vegetation may vary temporally. We studied how excluding grazing for short and long periods affects the CO2 exchange and vegetation biomass in the understory of an oligotrophic Scots pine forest. We measured growing season (2019, 2020) CO2 exchange across sunlit and shaded habitats inside fences that had excluded large grazers for 0–1 and 25–26 years and in the adjacent grazed area. In addition, we measured the height of understory vegetation. We found that short‐term grazer exclusion increased ecosystem CO2 source fluxes only in the shaded habitats. However, long‐term exclusion of grazing decreased CO2 net release regardless of the habitat type. Furthermore, grazer exclusion increased moss depth immediately, which coincided with an abrupt intensification of CO2 net release. Considering the impacts of grazing over both short‐ and long‐term periods may help to forecast C fluxes more accurately, which may be relevant for informed climate solutions regionally and even on a larger scale. [ABSTRACT FROM AUTHOR]

Boreal forests nowadays act as a sink for atmospheric carbon dioxide; however, their sequestration capacity is highly sensitive to weather conditions and, specifically to ongoing climate warming. Extreme weather events such as heavy rainfalls or, conversely, heat waves during the growing season might perturb the ecosystem carbon balance and convert them to an additional CO2 source. Thus, there is an urgent need to revise ecosystem carbon fluxes in vast Siberian taiga ecosystems as influenced by extreme weather events. In this study, we focused on the soil CO2 pulses appearing after the rainfall events and quantification of their input to the seasonal cumulative CO2 efflux in the boreal forests in Central Siberia. Seasonal measurements of soil CO2 fluxes (both soil respiration and net soil exchange) were conducted during three consecutive frost-free seasons using the dynamic chamber method. Seasonal dynamics of net soil exchange fluxes demonstrated positive values, reflecting that soil respiration rates exceeded CO2 uptake in the forest floor vegetation layer. Moreover, the heavy rains caused a rapid pulse of soil emissions and, as a consequence, the release of additional amounts of CO2 from the soil into the atmosphere. A single rain event may cause a 5–11-fold increase of the NSE flux compared to the pre-rainfall values. The input of CO2 pulses to the seasonal cumulative efflux varied from near zero to 39% depending on precipitation patterns of a particular season. These findings emphasize the critical need for more frequent measurements of soil CO2 fluxes throughout the growing season which capture the CO2 pulses induced by rain events. This approach has inevitable importance for the accurate assessment of seasonal CO2 soil emissions and adequate predictions of response of boreal pine forests to climatic changes. [ABSTRACT FROM AUTHOR]

Urban rivers and lakes are major components of inland waters. A deeper understanding of how carbon dioxide (CO2) emissions are impacted in urban waters is important for quantifying the contributions of urban waters to the global carbon budget. Acidic polysaccharides (APS) are a major component of the carbon pool, though there is still much uncertainty associated with CO2 concentrations and fluxes. Here, we measured the dissolved APS (DAPS), particulate APS (PAPS), and CO2 concentrations and fluxes in a typical urban river (the Ganjiang River) and two lakes (Xiang Lake and Qingshan Lake) in China, and assessed the impact of different APS fractions on CO2 concentrations and fluxes. Our results show abundant DAPS and PAPS in urban waters, with PAPS being the main form in winter while DAPS the main component in other seasons. The Ganjiang River and the urban lakes were supersaturated with CO2 at concentrations of 35.67 ± 19.99 μmol·L−1 & 27.79 ± 17.52 μmol·L−1 and emissions of 64.52 ± 53.38 mmol·(m2 d)−1& 36.56 ± 56.97 mmol·(m2 d)−1 from river and lake waters, respectively. Linear mixed-effects model analysis further revealed that increased DAPS concentration led to significantly higher CO2 concentrations and fluxes, whereas PAPS exhibited a negative influence on CO2 concentrations and fluxes in the urban lakes. Our work provides deeper insight into CO2 evasion in inland freshwater ecosystems as well as carbon neutrality in urban waters.

To assess the accuracy of satellite monitoring of anthropogenic CO2 emissions, inversions of satellite data in SWIR are usually combined with the assimilation of the total CO2 column into a Kalman filter that reconstructs the sources and sinks of atmospheric CO2. To provide error estimates of the total CO2 column for multi-month assimilation experiments of simulated satellite data, we parametrise these errors using linear regressions. These regression are obtained from a database that links meteorological situations, albedos, and aerosols to the errors in the inversion of the total CO2 column based on simulated satellite data for those conditions. The errors in this database are explicitly computed using the Bayesian estimation formalism, and the linear regressions are optimised by selecting appropriate predictors and predictants. For different levels of measurement noise, error simulations are performed over a period of several months using the albedo and aerosol data from MODIS.

Accurate assessment of the size and distribution of carbon dioxide (CO2) sources and sinks is important for efforts to understand the carbon cycle and support policy decisions regarding climate mitigation actions. Satellite retrievals of the column-averaged dry-air mole fractions of CO2 (XCO2) have been widely used to infer spatial and temporal variations of carbon fluxes through atmospheric inversion techniques. In this study, we present a global spatially resolved terrestrial and ocean carbon flux dataset for 2015–2022. The dataset was generated by the Global ObservatioN-based system for monitoring Greenhouse GAses (GONGGA) atmospheric inversion system through the assimilation of Orbiting Carbon Observatory 2 (OCO-2) XCO2 retrievals. We describe the carbon budget, interannual variability, and seasonal cycle for the global scale and a set of TransCom regions. The 8-year mean net biosphere exchange and ocean carbon fluxes were −2.22 ± 0.75 PgC yr−1 and –2.32 ± 0.18 PgC yr−1, absorbing approximately 23 % and 24 % of contemporary fossil fuel CO2 emissions, respectively. The annual mean global atmospheric CO2 growth rate was 5.17 ± 0.68 PgC yr−1, which is consistent with the National Oceanic and Atmospheric Administration (NOAA) measurement (5.24 ± 0.59 PgC yr−1). Europe has the largest terrestrial sink among the 11 TransCom land regions, followed by Boreal Asia and Temperate Asia. The dataset was evaluated by comparing posterior CO2 simulations with the observations from Total Carbon Column Observing Network (TCCON) and Observation Package (ObsPack). Compared with CO2 simulations using the unoptimized fluxes, the bias and root mean square error of posterior CO2 simulations were largely reduced across the full range of locations, confirming that the GONGGA system improves the estimates of spatial and temporal variations in carbon fluxes by assimilating OCO-2 XCO2 data. This dataset will improve the broader understanding of global carbon cycle dynamics and their response to climate change. [ABSTRACT FROM AUTHOR]

Research focusing on seagrass ecosystems as carbon storage has been conducted in various Indonesian waters. However, an essential aspect that remains unexplored is the simultaneous analysis of blue carbon storage in seagrass alongside carbon dioxide (CO2) flux values, particularly within Karimunjawa waters. This study aims to assess the organic carbon stock and sea–air CO2 flux in seagrass ecosystems in Karimunjawa. Our hypothesis posits that although seagrass ecosystems release CO2 into the water, their role as blue carbon ecosystems enables them to absorb and accumulate organic carbon within seagrass biomass and sediments. This investigation took place in Karimunjawa waters, encompassing both vegetated (seagrass meadows) and unvegetated (non-seagrass meadows) areas during August 2019, 2020, and 2022. Over this period, the organic carbon stock in seagrass and sediment displayed an increase, rising from 28.90 to 35.70 gCorg m−2 in 2019 and from 37.80 to 45.25 gCorg m−2 in 2022. Notably, the expanse of seagrass meadows in Karimunjawa dwindled by 328.33 ha from 2019 to 2022, resulting in a total carbon stock reduction of the seagrass meadows of 452.39 tC to 218.78 tC. Sediment emerges as a pivotal element in the storage of blue carbon in seagrass, with sedimentary organic carbon outweighing seagrass biomass in storage capacity. The conditions in Karimunjawa, including a high A:B ratio, low dry bulk density, and elevated water content, foster a favorable environment for sediment carbon absorption and storage, facilitated by the waters' CO2 emission during the southeast monsoon season. Notably, our findings reveal that CO2 release within vegetated areas is lower compared to unvegetated areas. This outcome underscores how seagrass ecosystems can mitigate CO2 release through their adeptness at storing organic carbon within biomass and sediment. However, the presence of inorganic carbon in the form of calcium carbonate introduces a nuanced dynamic. This external source, stemming from allochthonous origins like mangroves, brown algae like Padina pavonica, and calcareous epiphytes, leads to an increase in sedimentary organic carbon stock of 53.2 ± 6.82 gCorg m−2. Moreover, it triggers the release of CO2 into the atmosphere, quantified at 83.4 ± 18.26 mmol CO2 m−2 d−1. [ABSTRACT FROM AUTHOR]

This modeling study intended to solve a part of the global scientific problem related to increased concentrations of carbon dioxide in the atmosphere via emissions from terrestrial ecosystems that, along with anthropogenic emissions, make notable contributions to the processes of climate change on the planet. The main stream of CO2 from natural terrestrial ecosystems is related to the activation of biological processes, such as the production/destruction of plant biomass. In this study, the Wetland-DNDC computer simulation model with a focus on nitrogen and carbon biogeochemical cycles was used to study the effect of hydrothermal conditions on greenhouse gas fluxes in West Siberian peatlands. The study was implemented on the site of the world's largest pristine wetland/peatland system, the Great Vasyugan Mire (GVM). The study was carried out based on data from permanent measurements at meteo stations and our own in situ measurements of hydrological and thermal parameters on sites, which allowed for testing different scenarios of changes in environmental conditions (temperature, precipitation, groundwater level) together with a change in GHG fluxes. The study revealed the air temperature and the level of groundwater as the main drivers controlling CO2 fluxes. The study of different scenarios of change in annual air temperature revealed the threshold of change in the wetland/peatland ecosystem from carbon sink to carbon source to the atmosphere to happen with an increase in the average annual air temperature by 3 °C with reference to the average annual air temperature values in 2019. Also, we found that the wetland/peatland ecosystem turned to act as an active carbon sink with about 7 cm increase in annual groundwater level, compared with its base level of −21 cm. [ABSTRACT FROM AUTHOR]

Grassland ecosystems are an important component of global terrestrial ecosystems and play a crucial role in the global carbon cycle. Therefore, it is important to study the carbon dioxide (CO2) process in the Middle Tien Shan grassland ecosystem, which can be regarded as a typical representative of the mountain grasslands in Xinjiang. Eddy covariance (EC) and the global carbon fluxes dataset (GCFD) were utilized to continuously monitor the Middle Tien Shan grassland ecosystem in Xinjiang throughout the 2018 growing season. The findings revealed notable daily and monthly fluctuations in net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco). On a daily basis, there was net absorption of CO2 during the day and net emission during the night. The grassland acted as a carbon sink from 6:00 to 18:00 and as a carbon source for the remaining hours of the day. On a monthly scale, June and July served as carbon sinks, whereas the other months acted as carbon sources. The accumulated NEE, GPP, and Reco during the growing season were −329.49 g C m−2, 779.04 g C m−2, and 449.55 g C m−2, respectively. On the half-hourly and daily scales, soil temperature (Ts) was the main contributor to CO2 fluxes and had the greatest influence on the variations in CO2 fluxes. Additionally, air temperature (Ta) showed a strong correlation with CO2 fluxes. The grassland ecosystems exhibited the strongest CO2 uptake, reaching its peak at soil temperatures of 25 °C. Moreover, as the air temperatures rose above 15 °C, there was a gradual decrease in NEE, while CO2 uptake increased. The applicability of GCFD data is good in the grassland ecosystem of the Middle Tien Shan Mountains, with correlations of 0.59, 0.81, and 0.73 for NEE, GPP, and Reco, respectively, compared to field observations. In terms of remote sensing spatial distribution, the Middle Tien Shan grassland ecosystem exhibits a carbon sink phenomenon. [ABSTRACT FROM AUTHOR]

Continuous long-term eddy covariance (EC) measurements of CO2 fluxes (NEE) in a variety of terrestrial ecosystems are critical for investigating the impacts of climate change on ecosystem carbon cycling. However, due to a number of issues, approximately 30–60% of annual flux data obtained at EC flux sites around the world are reported as gaps. Given that the annual total NEE is mostly determined by variations in the NEE data with time scales longer than one day, we propose a novel framework to perform gap filling in NEE data based on machine learning (ML) and time series decomposition (TSD). The novel framework combines the advantages of ML models in predicting NEE with meteorological and environmental inputs and TSD methods in extracting the dominant varying trends in NEE time series. Using the NEE data from 25 AmeriFlux sites, the performance of the proposed framework is evaluated under four different artificial scenarios with gap lengths ranging in length from one hour to two months. The combined approach incorporating random forest and moving average (MA-RF) is observed to exhibit better performance than other approaches at filling NEE gaps in scenarios with different gap lengths. For the scenario with a gap length of seven days, the MA-RF improves the R2 by 34% and reduces the root mean square error (RMSE) by 55%, respectively, compared to a traditional RF-based model. The improved performance of MA-RF is most likely due to the reduction in data variability and complexity of the variations in the extracted low-frequency NEE data. Our results indicate that the proposed MA-RF framework can provide improved gap filling for NEE time series. Such improved continuous NEE data can enhance the accuracy of estimations regarding the ecosystem carbon budget. [ABSTRACT FROM AUTHOR]

The Indian Ocean significantly influences the global carbon cycle but it is one of the undersampled regions with reference to surface ocean pCO2. As a part of the Regional Carbon Cycle Assessment and Processes‐2 (RECCAP2) project, several approaches, such as interpolated observational climatology, hindcast model, observation‐based surface CO2 (empirical models), and atmospheric inversion models have been employed for estimating net sea‐to‐air CO2 fluxes between 1985 and 2018. The seasonal, spatial and long‐term variability in sea‐to‐air fluxes of CO2 were compared with observational climatology. The mean value of CO2 in the Indian Ocean (north of 37.5°S) for the period of 1985–2018 using all models is estimated to be −0.19 ± 0.1 PgC yr−1 and it is consistent with the observational climatology (−0.07 ± 0.14 PgC yr−1). The Indian Ocean north of 18°S is found to be the mean annual source (0.04 ± 0.05 PgC yr−1) whereas a net sink (−0.23 ± 0.11 PgC yr−1) in the south of 18°S. All models captured observed spatial patterns but underestimated the net source of CO2 in the Oman/Somalia upwelling, the Equatorial Indian Ocean and the Bay of Bengal whereas CO2 sink is overestimated in the South Indian Ocean. Overall, all models captured the seasonality in pCO2 levels and CO2 fluxes but overestimated the amplitude of their variability. All models suggested the strengthening of the sink over the period between 1985 and 2018 by 0.02 PgC yr−1 decade−1. A significant increase in the collection of surface ocean pCO2 and atmospheric CO2 measurements improves the model simulations in the Indian Ocean. Plain Language Summary: The Indian Ocean is under‐sampled with reference to pCO2 levels and CO2 fluxes. We evaluated the CO2 fluxes simulated by different models based on observational CO2 flux climatology. The CO2 fluxes estimated by all models are close to climatological value; however under and/or overestimation of fluxes are noticed in several regions. Due to weaker monsoon mixing, accurate river discharge data and atmospheric deposition of pollutants in the model, they failed to reproduce actual CO2 fluxes. Inclusion of such processes in the model improves their performance in future. Key Points: Northern Indian Ocean is a source whereas South Indian Ocean (SIO) is a sink for CO2Mean uptake of CO2 using all models comes to −0.18 ± 0.1 PgC yr−1Net CO2 flux is underestimated off Somalia, Bay of Bengal and Equatorial Indian Ocean whereas sink is over estimated in SIO [ABSTRACT FROM AUTHOR]

Desert ecosystem CO2 exchange may play an important role in global carbon cycling. However, it is still not clear how the CO2 fluxes of shrub-dominated desert ecosystems respond to precipitation changes. We performed a 10-year long-term rain addition experiment in a Nitraria tangutorum desert ecosystem in northwestern China. In the growing seasons of 2016 and 2017, with three rain addition treatments (natural precipitation +0%, +50%, and +100% of annual average precipitation), gross ecosystem photosynthesis (GEP), ecosystem respiration (ER), and net ecosystem CO2 exchange (NEE) were measured. The GEP responded nonlinearly and the ER linearly to rain addition. The NEE presented a nonlinear response along the rain addition gradient, with a saturation threshold by rain addition between +50% and +100%. The growing season mean NEE ranged from −2.25 to −5.38 μmol CO2 m−2 s−1, showing net CO2 uptake effect, with significant enhancement (more negative) under the rain addition treatments. Although natural rainfall fluctuated greatly in the growing seasons of 2016 and 2017, reaching 134.8% and 44.0% of the historical average, the NEE values remained stable. Our findings highlight that growing season CO2 sequestration in desert ecosystems will increase against the background of increasing precipitation levels. The different responses of GEP and ER of desert ecosystems under changing precipitation regimes should be considered in global change models. [ABSTRACT FROM AUTHOR]

The South China Sea is a typhoon-prone region, and previous studies have shown that typhoons have significant impacts on air-sea CO _2 fluxes. However, the effect of typhoons on the northern coastal area of the South China Sea is not well understood owing to limited observational data. In this study, we used a coupled model to simulate the impact of four typhoons (Hato, Mangkhut, Nida, and Merbok) on the partial pressure of CO _2 in seawater (pCO _2sea ) and the CO _2 fluxes in this area. Our results show that the coupled model effectively reproduces the spatial pattern of pCO _2sea in this region. The response of pCO _2sea to typhoons was determined by typhoon-induced vertical mixing and coastal upwelling, along with initial oceanic conditions. Typhoon Nida caused a decrease in pCO _2sea with Total Alkalinity and Sea Surface Temperature being the primary factors. However, typhoons Hato, Mangkhut, and Merbok caused an increase in pCO _2sea with Dissolved Inorganic Carbon playing a more prominent role. The average CO _2 fluxes during the passage were approximately 6–14 times higher than those before typhoon passage. These results enhance our understanding of the effect of typhoons on air-sea CO _2 fluxes over the northern coastal area of the South China Sea.

There is significant spatial and temporal variability associated with greenhouse gas (GHG) fluxes in high-latitude Arctic tundra environments. The objectives of this study are to investigate temporal variability in CO2 and CH4 fluxes at Barrow, AK and to determine the factors causing this variability using a novel entropy-based classification scheme. In particular, we analyzed which geomorphic, soil, vegetation and climatic properties most explained the variability in GHG fluxes (opaque chamber measurements) during the growing season over three successive years. Results indicate that multi-year variability in CO2 fluxes was primarily associated with soil temperature variability as well as vegetation dynamics during the early and late growing season. Temporal variability in CH4 fluxes was primarily associated with changes in vegetation during the growing season and its interactions with primary controls like seasonal thaw. Polygonal ground features, which are common to Arctic regions, also demonstrated significant multi-year variability in GHG fluxes. Our results can be used to prioritize field sampling strategies, with an emphasis on measurements collected at locations and times that explain the most variability in GHG fluxes. For example, we found that sampling primary environmental controls at the centers of high centered polygons in the month of September (when freeze-back period begins) can provide significant constraints on GHG flux variability - a requirement for accurately predicting future changes to GHG fluxes. Overall, entropy results document the impact of changing environmental conditions (e.g., warming, growing season length) on GHG fluxes, thus providing clues concerning the manner in which ecosystem properties may be shifted regionally in a future climate.

In the high Arctic, plant community species composition generally responds slowly to climate warming, whereas less is known about the community functional trait responses and consequences for ecosystem functioning. The slow species turnover and large distribution ranges of many Arctic plant species suggest a significant role of intraspecific trait variability in functional responses to climate change. Here we compare taxonomic and functional community compositional responses to a long‐term (17‐year) warming experiment in Svalbard, Norway, replicated across three major high Arctic habitats shaped by topography and contrasting snow regimes. We observed taxonomic compositional changes in all plant communities over time. Still, responses to experimental warming were minor and most pronounced in the drier habitats with relatively early snowmelt timing and long growing seasons (Cassiope and Dryas heaths). The habitats were clearly separated in functional trait space, defined by 12 size‐ and leaf economics‐related traits, primarily due to interspecific trait variation. Functional traits also responded to experimental warming, most prominently in the Dryas heath and mostly due to intraspecific trait variation. Leaf area and mass increased and leaf δ15N decreased in response to the warming treatment. Intraspecific trait variability ranged between 30% and 71% of the total trait variation, reflecting the functional resilience of those communities, dominated by long‐lived plants, due to either phenotypic plasticity or genotypic variation, which most likely underlies the observed resistance of high Arctic vegetation to climate warming. We further explored the consequences of trait variability for ecosystem functioning by measuring peak season CO2 fluxes. Together, environmental, taxonomic, and functional trait variables explained a large proportion of the variation in net ecosystem exchange (NEE), which increased when intraspecific trait variation was accounted for. In contrast, even though ecosystem respiration and gross ecosystem production both increased in response to warming across habitats, they were mainly driven by the direct kinetic impacts of temperature on plant physiology and biochemical processes. Our study shows that long‐term experimental warming has a modest but significant effect on plant community functional trait composition and suggests that intraspecific trait variability is a key feature underlying high Arctic ecosystem resistance to climate warming. [ABSTRACT FROM AUTHOR]

The full understanding of variation and temporal changes in carbon dioxide (CO2) fluxes in cropland may contribute to a reduction in CO2 emissions from agriculture. The aim of this study was to determine the CO2 exchange intensity in the three most popular crops in Poland. The CO2 fluxes in summer maize, winter oilseed rape and winter wheat fields were measured using the eddy covariance system. The seasonal dynamics of CO2 fluxes for all studied crops varied from each other due to individual dynamics in atmospheric CO2 assimilation of each species through the growing season. The weighted average values of CO2 fluxes calculated for the entire vegetation period were −22.22 µmol CO2 m−2 s−1, −14.27 µmol CO2 m−2 s−1 and −11.95 µmol CO2 m−2 s−1 for maize, oilseed rape and wheat, respectively. All the studied agro-ecosystems were carbon sinks during the growing season. The highest negative values of CO2 fluxes (−36.31 µmol CO2 m−2 s−1 and −33.56 µmol CO2 m−2 s−1) were observed in the maize field due to the high production of biomass. However, the maize field was also the most significant carbon source due to slow growth of plants at the beginning of the growing season, and due to leaving the field fallow after harvest until the next sowing. In these two periods, the CO2 fluxes ranged from 0.59 µmol CO2 m−2 s−1 to 3.72 µmol CO2 m−2 s−1. CO2 exchange over wheat and oilseed rape fields was less intense, but more even throughout the growing season. In the wheat field, the CO2 fluxes ranged from −1.70 µmol CO2 m−2 s−1 to −23.49 µmol CO2 m−2 s−1 and in the oilseed rape field they ranged from −1.40 µmol CO2 m−2 s−1 to −22.08 µmol CO2 m−2 s−1. In addition, the catch crop in the oilseed rape field contributed to the intensive absorption of CO2 after harvesting the main crop. [ABSTRACT FROM AUTHOR]

In the global carbon cycle, rivers are the main transport channel for terrestrial carbon sources into the ocean, and their CO2 fluxes at the water–air interface affect the carbon budget. As an important component of the carbon cycle in the terrestrial ecosystem, karst regions exhibit carbon source and sink effects due to their special environmental conditions. To elaborate the spatial and temporal distribution of CO2 fluxes at the water–air interface of karst rivers and the influencing factors, systematic monitoring of small karst rivers in southwest China was conducted between November and December 2019 and between June and July 2020, respectively. The results show that: (1) the water chemistry of Chiwuxi River belonged to the HCO3–Ca–Mg type, and Ca2+ and HCO3− temporally showed a larger concentration in the dry season than in the wet season. (2) CO2 partial pressure (pCO2) and CO2 fluxes showed a seasonal characteristic of higher values in the wet season than in the dry season. pCO2 ranged from 323.59 to 1380.38 μatm and CO2 fluxes ranged from −24.31 to 353.74 mmol (m2 d)−1. During the wet season, the Chiwuxi River showed a carbon source effect. During the dry season, the photosynthesis of aquatic plants reduced CO2 outgassing. (3) Isotopic compositions of dissolved inorganic carbon (δ13CDIC) showed a higher value in the dry season than in the wet season. The dissolved inorganic carbon mainly originated from soil CO2 and carbonate weathering. To improve the understanding of riverine carbon cycling, it is necessary to study CO2 fluxes at the water–air interface of small rivers in the karst region. Thus, this will help to reduce the uncertainty of CO2 fluxes in global rivers. [ABSTRACT FROM AUTHOR]

• Seasonal and inter-annual variations of NEE were examined. • The daily NEE shifts between PAR-dependent and NDVI-dependent with changes in SWC during the growing seasons. • SWC mainly controlled the inter-annual variability in annual NEE. Alpine ecosystems may be contribute to increasing atmospheric carbon dioxide (CO 2) concentrations under intensified climate change on the Tibetan Plateau (TP). The eddy covariance technique was used in this research to examine how net ecosystem CO 2 exchange (NEE) and its component fluxes, gross primary production (GPP), and ecosystem respiration (ER) varied over 10 years (from 2010 to 2019) in an alpine meadow on the eastern TP. This alpine meadow acted as a sink of CO 2 , with a mean of –92.5 ± 54.9 g C m–2 year–1 during the measurement period. The exponential ER response model is unsuitable for water stress conditions, potentially resulting in an overestimation of ER and GPP. The intra-annual variations of daily GPP and ER were more related to photosynthetic active radiation (PAR), soil temperature (Ts) and normalized difference vegetation index (NDVI), but the daily NEE during growing seasons shifts between PAR-dependent and NDVI-dependent with changes in soil water content (SWC). At monthly and seasonal scales, the sensitivity of GPP to NDVI and water conditions was higher than that of ER. The inter-annual variability in NEE was significantly related to the SWC. These findings are critical for understanding the response mechanism of carbon dynamics to the changing biotic and abiotic conditions in the TP. [ABSTRACT FROM AUTHOR]

Feeding ration is one of the most important factors that directly affect growth and physiology progress of sea cucumber Apostichopus japonicus. In present study, a 32-day experiment was carried out to investigate the effects of feeding ration (1%, 3%, and 7% of total body weight, named F1, F3 and F7, respectively) on growth performance, carbon allocation, energy budget and CO2 fluxes at water-air interface. Results showed the maximum specific growth rate was observed at F3, while F7 showed negative growth. And F3 exhibited the highest enzyme activities associated with respiration in respiratory tree and body wall. Carbon intake, nitrogen intake and energy intake were significantly affected by feeding ration, while energy allocation between F1 and F3 on growth and excretion were no significant difference, suggesting that increased feeding ration slightly increased the digestive burden. Compared to F1, food conversion efficiency and fecal energy of F3 were reduced, while respiration metabolizable energy was increased. Mean CO2 flux at water-air interface of F3 was significantly higher than that of F1 at noon and dusk, and mean CO2 flux of F7 was significantly lowest than other groups at all sample times. Our results revealed that feeding rations influence CO2 fluxes at water-air interface by altering physiological status, carbon content, and energy allocation for respiration metabolizable of sea cucumber. Our study provides a theoretical basis for promoting the development of efficient low-carbon aquaculture technology for sea cucumber and sustainable development of the industry.

Different functional groups of macrophytes vary in their impact on aquatic ecosystem structure and processes. The introduction of new species with different growth form, combined with a stochastic event, may have serious and irreversible consequences on lake functioning. Our goals were to document and explain physical, chemical, metabolic and biotic changes in the littoral zones of a volcanic lake before and following two coinciding events: invasion by a submersed macrophyte, Hydrilla verticillata (Hydrocharitaceae), followed by a rapid increase in the lake water level (>2.5 m). We recorded plant biomass, plant tissue C:N:P stoichiometry, macroinvertebrates, water characteristics data along transects through littoral zones, and measured gas emission in controlled mesocosms and in the lake. The native emergent species, Schoenoplectus californicus (Cyperaceae), was generally not able to survive such a rapid water level increase, and Hydrilla spread and formed dense mats further preventing Schoenoplectus regeneration. The impact of another introduced species, the free-floating Eichhornia crassipes (Pontederiaceae), was more localised, despite its much longer presence at the lake. Although the three species had comparable standing biomass, the two invader species had lower C:N:P ratios than Schoenoplectus, resulting in faster decomposition rates and indicating potential shifts in nutrient cycling within the ecosystem. The oxygen profile of the water column was altered by the non-native species in a significantly different manner: in Eichhornia, the saturation concentrations dropped down to 30%–50% of dissolved oxygen, while oxygen supersaturation was recorded in Hydrilla. Both Schoenoplectus and Eichhornia patches exhibited comparable carbon dioxide (CO2) fluxes, sequestering 230 and 300 mg CO2 m−2 hr−1, respectively, during the day and emitting 250 and 200 mg CO2 m−2 hr−1, respectively, during the night. Contrary to these two species, Hydrilla patches sequestered CO2 during the day (34 mg CO2 m−2 hr−1) and night (44 mg CO2 m−2 hr−1). The invasive species maintained a richer community of macroinvertebrates compared to several native species (excluding Schoenoplectus), both in taxa diversity and in numbers of individuals. When the results are considered in the regional context, an increase in nutrient supply could lead to the dominance of free-floating plants. We discussed management options more broadly considering the negative impacts of introduced species balanced against their beneficial effects, in the context of environmental changes.

Litter decomposition is an important source of carbon accumulation in the permafrost peatlands. Climate warming has led to shrub expansions and accelerated litter mixing with soils and fluctuations in the water table. However, little is known about how changes in the position of the litter will affect litter decomposition under climate warming. To reveal the mechanisms of response of the location of litter in the soil and climate warming to litter decomposition in permafrost peatlands. Here, we selected the evergreen shrub, Chamaedaphne calyculata, and the deciduous shrub, Vaccinium uliginosum, from the permafrost peatlands of the Greater Hing’an Mountains, China. The leaf litter was placed on the soil surface (no-mixing) and mixed with the soil (soil-litter mixing), and then it was incubated for 124 days at 15°C (control) and 20°C (warming). Our results showed that warming significantly increased the CO2 emission rates of C. calyculata and V. uliginosum by 19.9 and 17.4%, respectively. When compared to no-mixing, the CO2 emission rates were reduced (not significantly) by 1.5 (C. calyculata) and increased 13.6% (V. uliginosum) with soil-litter mixing. Interestingly, soil-litter mixing suppressed the positive effect of warming on the CO2 emission rates relative to no-mixing, and the suppressing effects in the V. uliginosum subplot were stronger than those in the C. calyculata subplot. Specifically, warming significantly increased the CO2 emissions of C. calyculata by 27.4% under no-mixing but the increase decreased to 13.1% under soil-litter mixing. Similarly, warming induced significant increases in the CO2 emissions of V. uliginosum, with an increase of 38.8% under no-mixing but non-significant increases (1.9%) were observed under soil-litter mixing. The combination of the enzyme activities of β-1,4-glucosidase, β-1,4-xylosidase and β-D-1,4-cellobiosidase and laccase and phenolics explained more than 60.0% of the variability in the CO2 emissions of C. calyculata and V. uliginosum, respectively. Our study highlights the importance of litter positions in mediating the responses of litter decomposition to climate warming and shrub expansions in the northern peatlands.

The carbon process of the alpine ecosystem is complex and sensitive in the face of continuous global warming. However, the long-term dynamics of carbon budget and its driving mechanism of alpine ecosystem remain unclear. Using the eddy covariance (EC) technique--a fast and direct method of measuring carbon dioxide (CO2) fluxes, we analyzed the dynamics of CO2 fluxes and their driving mechanism in an alpine wetland in the northeastern Qinghai-Tibet Plateau (QTP) during the growing season (May-September) from 2004-2016. The results show that the monthly gross primary productivity (GPP) and ecosystem respiration (Re) showed a unimodal pattern, and the monthly net ecosystem CO2 exchange (NEE) showed a V-shaped trend. With the alpine wetland ecosystem being a carbon sink during the growing season, that is, a reservoir that absorbs more atmospheric carbon than it releases, the annual NEE, GPP, and Re reached -67.5 ± 10.2, 473.4 ± 19.1, and 405.9 ± 8.9 gCm-2, respectively. At the monthly scale, the classification and regression tree (CART) analysis revealed air temperature (Ta) to be the main determinant of variations in the monthly NEE and GPP. Soil temperature (Ts) largely determined the changes in the monthly Re. The linear regression analysis confirmed that thermal conditions (Ta, Ts) were crucial determinants of the dynamics of monthly CO2 fluxes during the growing season. At the interannual scale, the variations of CO2 fluxes were affected mainly by precipitation and thermal conditions. The annual GPP and Re were positively correlated with Ta and Ts, and were negatively correlated with precipitation. However, hydrothermal conditions (Ta, Ts, and precipitation) had no significant effect on annual NEE. Our results indicated that climate warming would be beneficial to the improvement of GPP and Re in the alpine wetland, while the increase of precipitation can weaken this effect. [ABSTRACT FROM AUTHOR]

Understanding the CO2 flux over agricultural crop fields is critical because the temporal cycle is driven by both ecological environment and anthropogenic change. We analyzed the net ecosystem exchange of CO2 measured over a barley–rice double-cropping field using the eddy covariance method for 5 years. We conducted gap-filling based on u*-threshold criteria and partitioned the net ecosystem exchange into gross primary production and respiration. The relative importance analysis of solar radiation, temperature, soil heat flux, soil water content, and vapor deficit revealed that solar radiation and temperature were the dominant contributors to net ecosystem exchange. The annual variation in the net ecosystem exchange followed a bimodal pattern driven by CO2 uptake by both barley and rice, displaying two negative peaks in late April and mid-August. The elongation stages of the crops exhibited the highest flux. Gross primary production and respiration were closely related to solar radiation and nighttime temperature, respectively. The relative importance of the other environmental variables was affected by the cultivation season and irrigation water. In the period of rice cultivation, respiration was approximately 3 µmol m−2 s−1 higher during rice drainage than during the flooded period. The accumulated net ecosystem production was estimated to be 315 gC m−2 and 349 gC m−2 for the barley and rice growing periods, respectively, and 649 gC m−2 for the annual total. These values are comparable with the results of other studies on barley–rice double-cropping fields. [ABSTRACT FROM AUTHOR]

Arctic shelf seas receive greater quantities of river runoff than any other ocean region and are experiencing increased freshwater loads and associated terrestrial matter inputs since recent decades. Amplified terrestrial permafrost thaw and coastal erosion is exposing previously frozen organic matter, enhancing its mobilization and release to nearshore regions. Changing terrestrial dissolved organic matter (terr-DOM) loads and composition may alter shelf primary productivity and respiration, ultimately affecting net regional CO2 air–sea fluxes. However, the future evolution of Arctic Ocean climate feedbacks are highly dependent upon the biological degradability of terr-DOM in coastal waters, a factor often omitted in modelling studies. Here, we assess the sensitivity of CO2 air–sea fluxes from East Siberian Arctic Shelf (ESAS) waters to changing terr-DOM supply and degradability using a biogeochemical model explicitly accounting for bacteria dynamics and shifting terr-DOM composition. We find increasing terr-DOM loads and degradability trigger a series of biogeochemical and ecological processes shifting ESAS waters from a net sink to a net source of CO2, even after accounting for strengthening coastal productivity by additional land-derived nutrients. Our results suggest that future projected inputs of labile terr-DOM from peat and permafrost thaw may strongly increase the CO2 efflux from the Arctic shelf sea, causing currently unquantified positive feedback to climate change. [ABSTRACT FROM AUTHOR]

Assessment of consistency in seasonal variability of CO2 fluxes between GOSAT-IM, NASA-GEOS, and NOAA-CT databases was carried out over major biogeographic regions across the globe. A blended data product was composited through a linear least square error optimization procedure from the weighted mean of the three datasets. The blended-product is in closer agreement with GOSAT-IM followed by NOAA-CT and NASA-GEOS for most parts of the globe; however, the blended-product was found to be closer to NASA-GEOS for the Arabian Sea and India. Comparison with limited in-situ FLUXNET observations shows NASA-GEOS has a better agreement for India, and NOAA-CT is better for Europe, Africa, and the US. The mean climatology of these datasets exhibits spatially distinct and coherent patterns of positive and negative fluxes that characterize the source and sink of atmospheric CO2 across the globe. The tropical oceanic and terrestrial regions and the southern circumpolar oceans have been playing as the sources, whereas the temperate oceanic and terrestrial ecosystems and the Eurasian Boreal are the sinks. The seasonal cycles of the fluxes are intense over the northern temperate and boreal terrestrial and oceanic regions; wherein annual amplitudes dominate over the semi-annual amplitudes. The mean climatology varies in the range of −6 to 6 gC m−2 month−1 for oceans as well as continents; however, amplitudes of the seasonal cycle are one order higher for the continents (>20 gC m−2 month−1) than that of the oceans (<1 gC m−2 month−1). The tropical desert tracts, especially Sahara and Thar, and the equatorial oceans show minima in their climatological mean with the reduced seasonal cycle. All these data, however, depict a broad agreement in their seasonal cycle and mean climatology; they exhibit significant differences in their annual budgets, amplitude, and phases of annual and semi-annual harmonics. [ABSTRACT FROM AUTHOR]

Field-based quantification of soil greenhouse gas emissions from the Philippines' agriculture sector is missing for vegetable production systems, despite its substantial contribution to agricultural production. We quantified soil N2O emission, CH4 uptake, and CO2 efflux in vegetable farms and compared these to the secondary forest. Measurements were conducted for 13 months in 10 smallholder farms and nine forest plots on Andosol soil in Leyte, Philippines using static chambers. Soil N2O and CO2 emissions were higher, whereas CH4 uptake was lower in the vegetable farms than in the forest. Vegetable farms had annual fluxes of 12.7 ± 2.6 kg N2O-N ha−1 yr−1, −1.1 ± 0.2 kg CH4-C ha−1 yr−1, and 11.7 ± 0.7 Mg CO2-C ha−1 yr−1, whereas the forest had 0.10 ± 0.02 kg N2O-N ha ha−1 yr−1, −2.0 ± 0.2 kg CH4-C ha−1 yr−1, and 8.2 ± 0.7 Mg CO2-C ha−1 yr−1. Long-term high N fertilization rates in vegetable farms resulted in large soil mineral N levels, dominated by NO3– in the topsoil and down to 1-m depth, leading to high soil N2O emissions. Increased soil bulk density in the vegetable farms probably increased anaerobic microsites during the wet season and reduced CH4 diffusion from the atmosphere into the soil, resulting in decreased soil CH4 uptake. High soil CO2 emissions from the vegetable farms suggested decomposition of labile organic matter, possibly facilitated by plowing and large N fertilization rates. The global warming potential of these vegetable farms was 31 ± 2.7 Mg CO2-eq ha−1 yr−1 (100-year time frame). [ABSTRACT FROM AUTHOR]

The carbon process of the alpine ecosystem is complex and sensitive in the face of continuous global warming. However, the long-term dynamics of carbon budget and its driving mechanism of alpine ecosystem remain unclear. Using the eddy covariance (EC) technique—a fast and direct method of measuring carbon dioxide (CO2) fluxes, we analyzed the dynamics of CO2 fluxes and their driving mechanism in an alpine wetland in the northeastern Qinghai–Tibet Plateau (QTP) during the growing season (May–September) from 2004–2016. The results show that the monthly gross primary productivity (GPP) and ecosystem respiration (Re) showed a unimodal pattern, and the monthly net ecosystem CO2 exchange (NEE) showed a V-shaped trend. With the alpine wetland ecosystem being a carbon sink during the growing season, that is, a reservoir that absorbs more atmospheric carbon than it releases, the annual NEE, GPP, and Re reached −67.5 ± 10.2, 473.4 ± 19.1, and 405.9 ± 8.9 gCm-2, respectively. At the monthly scale, the classification and regression tree (CART) analysis revealed air temperature (Ta) to be the main determinant of variations in the monthly NEE and GPP. Soil temperature (Ts) largely determined the changes in the monthly Re. The linear regression analysis confirmed that thermal conditions (Ta, Ts) were crucial determinants of the dynamics of monthly CO2 fluxes during the growing season. At the interannual scale, the variations of CO2 fluxes were affected mainly by precipitation and thermal conditions. The annual GPP and Re were positively correlated with Ta and Ts, and were negatively correlated with precipitation. However, hydrothermal conditions (Ta, Ts, and precipitation) had no significant effect on annual NEE. Our results indicated that climate warming would be beneficial to the improvement of GPP and Re in the alpine wetland, while the increase of precipitation can weaken this effect.

Blue carbon ecosystems are recognized as carbon sinks and therefore for their potential for climate mitigation. While carbon stocks and burial rates have been quantified and estimated regionally and globally, there are still many knowledge gaps on carbon fluxes exchanged particularly at the interface vegetation-atmosphere. In this study we measured the atmospheric CO2 concentrations in a salt marsh located in the Patos Lagoon Estuary, southern Brazil. Eddy correlation techniques were applied to account for the CO2 exchange fluxes between the vegetation and the atmosphere. Our dataset refers to two sampling periods spanning from July up to November 2016 and from January to April 2017. By using time series analysis techniques including wavelet and cross-wavelet analysis, our results show the natural cycles of the CO2 exchanges variability and the relationship of these cycles with other environmental variables. We also present the amplitudes of the salt marsh-atmosphere CO2 fluxes’ diurnal cycle for both study periods and demonstrate that the CO2 fluxes are modulated by the passage of transient atmospheric systems and by the level variation of surrounding waters. During daytime, our site was as a CO2 sink. Fluxes were measured as -6.71 ± 5.55 μmol m-2 s-1 and -7.95 ± 6.44 μmol m-2 s-1 for the winter-spring and summer-fall periods, respectively. During nighttime, the CO2 fluxes were reversed and our site behaved as a CO2 source. Beside the seasonal changes in sunlight and air temperature, differences between the two periods were marked by the level of marsh inundation, winds and plant biomass (higher in summer). The net CO2 balance showed the predominance of the photosynthetic activity over community respiration, indicating the role of the salt marsh as a CO2 sink. When considering the yearly-averaged net fluxes integrated to the whole area of the Patos Lagoon Estuary marshes, the total CO2 sink was estimated as -87.6 Mg C yr-1. This paper is the first to measure and study the vegetation-atmosphere CO2 fluxes of a salt marsh environment of Brazil. The results will contribute to the knowledge on the global carbon budget and for marsh conservation and management plans, including climate change policies.

Research focusing on seagrass ecosystems as carbon storage has been conducted in various Indonesian waters. However, an essential aspect that remains unexplored is the simultaneous analysis of blue carbon storage in seagrass alongside carbon dioxide (CO2) flux values, particularly within Karimunjawa waters. This study aims to assess the organic carbon stock and sea–air CO2 flux in seagrass ecosystems in Karimunjawa. Our hypothesis posits that although seagrass ecosystems release CO2 into the water, their role as blue carbon ecosystems enables them to absorb and accumulate organic carbon within seagrass biomass and sediments. This investigation took place in Karimunjawa waters, encompassing both vegetated (seagrass meadows) and unvegetated (non-seagrass meadows) areas during August 2019, 2020, and 2022. Over this period, the organic carbon stock in seagrass and sediment displayed an increase, rising from 28.90 to 35.70 gCorg m−2 in 2019 and from 37.80 to 45.25 gCorg m−2 in 2022. Notably, the expanse of seagrass meadows in Karimunjawa dwindled by 328.33 ha from 2019 to 2022, resulting in a total carbon stock reduction of the seagrass meadows of 452.39 tC to 218.78 tC. Sediment emerges as a pivotal element in the storage of blue carbon in seagrass, with sedimentary organic carbon outweighing seagrass biomass in storage capacity. The conditions in Karimunjawa, including a high A:B ratio, low dry bulk density, and elevated water content, foster a favorable environment for sediment carbon absorption and storage, facilitated by the waters’ CO2 emission during the southeast monsoon season. Notably, our findings reveal that CO2 release within vegetated areas is lower compared to unvegetated areas. This outcome underscores how seagrass ecosystems can mitigate CO2 release through their adeptness at storing organic carbon within biomass and sediment. However, the presence of inorganic carbon in the form of calcium carbonate introduces a nuanced dynamic. This external source, stemming from allochthonous origins like mangroves, brown algae like Padina pavonica, and calcareous epiphytes, leads to an increase in sedimentary organic carbon stock of 53.2 ± 6.82 gCorg m−2. Moreover, it triggers the release of CO2 into the atmosphere, quantified at 83.4 ± 18.26 mmol CO2 m−2 d−1.

This modeling study intended to solve a part of the global scientific problem related to increased concentrations of carbon dioxide in the atmosphere via emissions from terrestrial ecosystems that, along with anthropogenic emissions, make notable contributions to the processes of climate change on the planet. The main stream of CO2 from natural terrestrial ecosystems is related to the activation of biological processes, such as the production/destruction of plant biomass. In this study, the Wetland-DNDC computer simulation model with a focus on nitrogen and carbon biogeochemical cycles was used to study the effect of hydrothermal conditions on greenhouse gas fluxes in West Siberian peatlands. The study was implemented on the site of the world’s largest pristine wetland/peatland system, the Great Vasyugan Mire (GVM). The study was carried out based on data from permanent measurements at meteo stations and our own in situ measurements of hydrological and thermal parameters on sites, which allowed for testing different scenarios of changes in environmental conditions (temperature, precipitation, groundwater level) together with a change in GHG fluxes. The study revealed the air temperature and the level of groundwater as the main drivers controlling CO2 fluxes. The study of different scenarios of change in annual air temperature revealed the threshold of change in the wetland/peatland ecosystem from carbon sink to carbon source to the atmosphere to happen with an increase in the average annual air temperature by 3 °C with reference to the average annual air temperature values in 2019. Also, we found that the wetland/peatland ecosystem turned to act as an active carbon sink with about 7 cm increase in annual groundwater level, compared with its base level of −21 cm.

Grassland ecosystems are an important component of global terrestrial ecosystems and play a crucial role in the global carbon cycle. Therefore, it is important to study the carbon dioxide (CO2) process in the Middle Tien Shan grassland ecosystem, which can be regarded as a typical representative of the mountain grasslands in Xinjiang. Eddy covariance (EC) and the global carbon fluxes dataset (GCFD) were utilized to continuously monitor the Middle Tien Shan grassland ecosystem in Xinjiang throughout the 2018 growing season. The findings revealed notable daily and monthly fluctuations in net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco). On a daily basis, there was net absorption of CO2 during the day and net emission during the night. The grassland acted as a carbon sink from 6:00 to 18:00 and as a carbon source for the remaining hours of the day. On a monthly scale, June and July served as carbon sinks, whereas the other months acted as carbon sources. The accumulated NEE, GPP, and Reco during the growing season were −329.49 g C m−2, 779.04 g C m−2, and 449.55 g C m−2, respectively. On the half-hourly and daily scales, soil temperature (Ts) was the main contributor to CO2 fluxes and had the greatest influence on the variations in CO2 fluxes. Additionally, air temperature (Ta) showed a strong correlation with CO2 fluxes. The grassland ecosystems exhibited the strongest CO2 uptake, reaching its peak at soil temperatures of 25 °C. Moreover, as the air temperatures rose above 15 °C, there was a gradual decrease in NEE, while CO2 uptake increased. The applicability of GCFD data is good in the grassland ecosystem of the Middle Tien Shan Mountains, with correlations of 0.59, 0.81, and 0.73 for NEE, GPP, and Reco, respectively, compared to field observations. In terms of remote sensing spatial distribution, the Middle Tien Shan grassland ecosystem exhibits a carbon sink phenomenon.

Growing and intensified mining activities in China have produced substantial quantities of carbonate-bearing tailings wastes. Rapid chemical weathering of these wastes, accompanied by active CO2 fluxes (CO2 absorption and degassing), have the potential to positively or negatively influence the emissions arising from the mining sector. However, few prior studies have examined these processes and effects. Herein, we present a systematic investigation of the chemical and mineral composition, hydro-geochemistry, and isotopes of four tailings ponds and filtrates in Panxi valley, Sichuan province, China. Our results reveal that significant rock–water interactions have occurred in carbonate-hosted tailings with active carbonate and silicate dissolution. The abundance of sulfuric acid in the dissolved load, derived from sulfide oxidation, provides a non-negligible portion of protons for chemical weathering. The influences on cationic weathering, therefore, were found to be carbonic–carbonate weathering > sulfide–carbonate weathering > sulfide–silicate weathering > mineral processing inputs > nature inputs > atmospheric inputs. Exoreic river basin tailings have the potential to fix atmospheric CO2 and provide a valuable strategy toward China's carbon neutrality goals. However, inland/arid area mining also has the potential to risk net CO2 degassing and hence encumber the mining industry's carbon performance. [ABSTRACT FROM AUTHOR]

The western Tropical Atlantic Ocean is a biogeochemically complex region due to the structure of the surface current system and the large freshwater input from the Amazon River coupled with the dynamics of precipitation. Such features make it difficult to understand the dynamics of the carbon cycle, leading to contrasting estimates in sea‐air CO2 exchanges in this region. Here, we demonstrate that these contrasting estimates occur because the western Tropical Atlantic Ocean can be split into three distinct sub‐regions in terms of the sea‐air CO2 exchanges. The sub‐region under the North Brazil Current domain acts as a weak annual CO2 source to the atmosphere, with low interannual variability. The sub‐region under the North Equatorial Current influence acts as an annual CO2 sink, with great temporal variability. The third sub‐region under the Amazon River plume influence shows greater interannual variability of CO2 exchanges, but it always acts as a net oceanic sink for CO2. Despite this large spatial variability, the entire region acts as a net annual CO2 sink of −1.6 ± 1.0 mmol m−2 day−1. Importantly, the Amazon River plume waters drive 87% of the CO2 uptake in the western Tropical Atlantic Ocean. In addition, we found a significant increasing trend in sea surface CO2 partial pressure in the North Brazil Current and North Equatorial Current waters. Such trends are more pronounced than the increase in atmospheric CO2 partial pressure, revealing the sensitivity of carbon dynamics in these sub‐regions to global climate change. Key Points: Sea‐air CO2 release (uptake) shown in the North Brazil Current (North Equatorial Current) domainStrong CO2 uptake under the Amazon River plume influence, which accounts for 87% of the CO2 uptake by the western Tropical Atlantic OceanIncreasing trend of sea surface CO2 partial pressure in the North Brazil Current and the North Equatorial Current waters [ABSTRACT FROM AUTHOR]

Climate extremes and anomalies modify the CO2 ecosystem–atmosphere exchange of the boreal forests and consequently alter the terrestrial carbon stocks and the atmospheric greenhouse gas concentrations. The effects of the anomalous weather conditions on the CO2 net ecosystem exchange (NEE), total ecosystem respiration (TER), and gross primary production (GPP) of the typical southern taiga nemorose spruce forest were analyzed using continuous eddy covariance flux measurements in the 2015–2020 period. The forest was found to be a source of atmospheric CO2 in 2016, 2017, 2019, and 2020 (the mean annual GPP/TER ratio was between 0.87 and 0.97). In 2018, the forest was found to act as a CO2 sink (GPP/TER = 1.47) when a positive temperature anomaly in the growing season was accompanied by a negative precipitation anomaly and increased global radiation. The early start of the CO2 uptake in the anomalously warm winter of 2019/2020 did not result in an increase in the annual GPP/TER ratio (0.90). The comparison of the flux data obtained from the nemorose spruce forest on the well-drained soils with the data obtained from paludified spruce forest in the same landscape showed that the mean annual GPP/TER ratio of the sites alternatively responded to the mentioned anomalies. This study suggests that a variety of soil moisture regimes across the southern taiga spruce forests provide a non-uniformity in the response reactions of the CO2 ecosystem–atmosphere exchange on the climate anomalies. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) fluxes and evapotranspiration (ET) during the non-growing season can contribute significantly to the annual carbon and water budgets of agroecosystems. Comparative studies of vegetation phenology and the dynamics of CO2 fluxes and ET during the dormant season of native tallgrass prairies from different landscape positions under the same climatic regime are scarce. Thus, this study compared the dynamics of satellite-derived vegetation phenology (as captured by the enhanced vegetation index (EVI) and the normalized difference vegetation index (NDVI)) and eddy covariance (EC)-measured CO2 fluxes and ET in six differently managed native tallgrass prairie pastures during dormant seasons (November through March). During December–February, vegetation phenology (EVI and NDVI) and the dynamics of eddy fluxes were comparable across all pastures in most years. Large discrepancies in fluxes were observed during March (the time of the initiation of growth of dominant warm-season grasses) across years and pastures due to the influence of weather conditions and management practices. The results illustrated the interactive effects between prescribed spring burns and rainfall on vegetation phenology (i.e., positive and negative impacts of prescribed spring burns under non-drought and drought conditions, respectively). The EVI better tracked the phenology of tallgrass prairie during the dormant season than did NDVI. Similar EVI and NDVI values for the periods when flux magnitudes were different among pastures and years, most likely due to the satellite sensors' inability to fully observe the presence of some cool-season C3 species under residues, necessitated a multi-level validation approach of using ground-truth observations of species composition, EC measurements, PhenoCam (digital) images, and finer-resolution satellite data to further validate the vegetation phenology derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) during dormant seasons. This study provides novel insights into the dynamics of vegetation phenology, CO2 fluxes, and ET of tallgrass prairie during the dormant season in the U.S. Southern Great Plains. [ABSTRACT FROM AUTHOR]

Continuous long-term eddy covariance (EC) measurements of CO2 fluxes (NEE) in a variety of terrestrial ecosystems are critical for investigating the impacts of climate change on ecosystem carbon cycling. However, due to a number of issues, approximately 30–60% of annual flux data obtained at EC flux sites around the world are reported as gaps. Given that the annual total NEE is mostly determined by variations in the NEE data with time scales longer than one day, we propose a novel framework to perform gap filling in NEE data based on machine learning (ML) and time series decomposition (TSD). The novel framework combines the advantages of ML models in predicting NEE with meteorological and environmental inputs and TSD methods in extracting the dominant varying trends in NEE time series. Using the NEE data from 25 AmeriFlux sites, the performance of the proposed framework is evaluated under four different artificial scenarios with gap lengths ranging in length from one hour to two months. The combined approach incorporating random forest and moving average (MA-RF) is observed to exhibit better performance than other approaches at filling NEE gaps in scenarios with different gap lengths. For the scenario with a gap length of seven days, the MA-RF improves the R2 by 34% and reduces the root mean square error (RMSE) by 55%, respectively, compared to a traditional RF-based model. The improved performance of MA-RF is most likely due to the reduction in data variability and complexity of the variations in the extracted low-frequency NEE data. Our results indicate that the proposed MA-RF framework can provide improved gap filling for NEE time series. Such improved continuous NEE data can enhance the accuracy of estimations regarding the ecosystem carbon budget.

Desert ecosystem CO2 exchange may play an important role in global carbon cycling. However, it is still not clear how the CO2 fluxes of shrub-dominated desert ecosystems respond to precipitation changes. We performed a 10-year long-term rain addition experiment in a Nitraria tangutorum desert ecosystem in northwestern China. In the growing seasons of 2016 and 2017, with three rain addition treatments (natural precipitation +0%, +50%, and +100% of annual average precipitation), gross ecosystem photosynthesis (GEP), ecosystem respiration (ER), and net ecosystem CO2 exchange (NEE) were measured. The GEP responded nonlinearly and the ER linearly to rain addition. The NEE presented a nonlinear response along the rain addition gradient, with a saturation threshold by rain addition between +50% and +100%. The growing season mean NEE ranged from −2.25 to −5.38 μmol CO2 m−2 s−1, showing net CO2 uptake effect, with significant enhancement (more negative) under the rain addition treatments. Although natural rainfall fluctuated greatly in the growing seasons of 2016 and 2017, reaching 134.8% and 44.0% of the historical average, the NEE values remained stable. Our findings highlight that growing season CO2 sequestration in desert ecosystems will increase against the background of increasing precipitation levels. The different responses of GEP and ER of desert ecosystems under changing precipitation regimes should be considered in global change models.

The interaction of warming and soil texture on responsiveness of the key soil processes i.e. organic carbon (C) fractions, soil microbes, extracellular enzymes and CO2 emissions remains largely unknown. Global warming raises the relevant question of how different soil processes will respond in near future, and what will be the likely regulatory role of texture? To bridge this gap, this work applied the laboratory incubation method to investigate the effects of temperature changes (10-50 °C) on dynamics of labile, recalcitrant and stable C fractions, soil microbes, microbial biomass, activities of extracellular enzymes and CO2 emissions in sandy and clayey textured soils. The role of texture (sandy and clayey) in the mitigation of temperature effect was also investigated. The results revealed that the temperature sensitivity of C fractions and extracellular enzymes was in the order recalcitrant C fractions > stable C fractions > labile C fractions and oxidative enzymes > hydrolytic enzymes. While temperature sensitivity of soil microbes and biomass was in the order bacteria > actinomycetes > fungi - microbial biomass C (MBC) > microbial biomass N (MBN) > microbial biomass N (MBP). Conversely, the temperature effect and sensitivity of all key soil processes including CO2 emissions were significantly (P < 0.05) higher in sandy than clayey textured soil. Results confirmed that under the scenario of global warming and climate change, soils which are sandy in nature are more susceptible to temperature increase and prone to become the CO2-C sources. It was revealed that clayey texture played an important role in mitigating and easing off the undue temperature influence, hence, the sensitivity of key soil processes. [ABSTRACT FROM AUTHOR]

Environmental conditions influence forest ecosystems and consequently, its productivity. Thus, the quantification of forest CO2 exchange is a critical requirement to estimate the CO2 balance of forests on a local and regional scale. Besides interpreting the annual CO2 exchange corresponding to environmental conditions over the studied years (2015–2020) at the floodplain forest in Lanžhot, Czech Republic (48.6815483 N, 16.9463317 E), the influence of below-above canopy air mass decoupling on above canopy derived CO2 exchange is the focus of this study. For this purpose, we applied the eddy covariance (EC) method above and below the forest canopy, assessing different single- and two-level flux filtering strategies. We focused on one example year (2019) of concurrent below and above canopy EC measurements. We hypothesized that conventional single-level EC flux filtering strategies such as the friction velocity (u*) filtering approach might not be sufficient to fully capture the forest CO2 exchange at the studied ecosystem. Results suggest that decoupling occurs regularly, but the implication on the above canopy derived EC CO2 fluxes appears to be negligible on an annual scale. We attribute this to the open canopy and flat EC tower surrounding terrain which inhibits horizontal removal of below-canopy respired CO2. [ABSTRACT FROM AUTHOR]

The interaction of warming and soil texture on responsiveness of the key soil processes i.e. organic carbon (C) fractions, soil microbes, extracellular enzymes and CO2 emissions remains largely unknown. Global warming raises the relevant question of how different soil processes will respond in near future, and what will be the likely regulatory role of texture? To bridge this gap, this work applied the laboratory incubation method to investigate the effects of temperature changes (10–50 °C) on dynamics of labile, recalcitrant and stable C fractions, soil microbes, microbial biomass, activities of extracellular enzymes and CO2 emissions in sandy and clayey textured soils. The role of texture (sandy and clayey) in the mitigation of temperature effect was also investigated. The results revealed that the temperature sensitivity of C fractions and extracellular enzymes was in the order recalcitrant C fractions > stable C fractions > labile C fractions and oxidative enzymes > hydrolytic enzymes. While temperature sensitivity of soil microbes and biomass was in the order bacteria > actinomycetes > fungi ≈ microbial biomass C (MBC) > microbial biomass N (MBN) > microbial biomass N (MBP). Conversely, the temperature effect and sensitivity of all key soil processes including CO2 emissions were significantly (P < 0.05) higher in sandy than clayey textured soil. Results confirmed that under the scenario of global warming and climate change, soils which are sandy in nature are more susceptible to temperature increase and prone to become the CO2-C sources. It was revealed that clayey texture played an important role in mitigating and easing off the undue temperature influence, hence, the sensitivity of key soil processes.

Abstract Among the regions of the Southern Ocean, the northern Antarctic Peninsula (NAP) has emerged as a hotspot of climate change investigation. Nonetheless, studies have indicated issues and knowledge gaps that must be addressed to expand the understanding of the carbonate system in the region. Therefore, we focused on identifying current knowledge about sea-air CO2 fluxes (FCO2), anthropogenic carbon (Cant) and ocean acidification along NAP and provide a better comprehension of the key physical processes controlling the carbonate system. Regarding physical dynamics, we discuss the role of water masses formation, climate modes, upwelling and intrusions of Circumpolar Deep Water, and mesoscale processes. For FCO2, we show that the summer season corresponds to a strong sink in coastal areas, leading to CO2 uptake that is greater than or equal to that of the open ocean. We highlight that the prevalence of summer studies prevents comprehending processes occurring throughout the year and the net annual CO2 balance in the region. Thus, temporal investigations are necessary to determine natural environmental fluctuations and to distinguish natural variability from anthropogenically driven changes. We emphasize the importance of more studies regarding Cant uptake rate, accumulation, and export to global oceans.

This study presents high-resolution data on diel variations of carbonate chemistry in a semi-arid estuary (Jaguaribe River) in NE Brazil, which has witnessed decreasing annual rainfall and freshwater inputs due to climate change and river damming. In addition, the estuary has been suffering with increasing discharges from shrimp farm and urban effluents. We monitored surface water and atmospheric CO2 partial pressure (pCO2), temperature, salinity, and wind speed with continuous real-time measurements during two eulerian surveys in October 2017 (33 h) and September 2018 (44 h), during spring tides in the dry season. Additionally, pH, total alkalinity (TA), dissolved inorganic carbon (DIC), carbonate (CO32–), and saturation state of calcite (Ωcal) and aragonite (Ωara) were monitored hourly. Higher salinity (>38) during ebb tides confirmed the hypersalinity and negative estuarine circulation. TA and DIC concentrations in the estuary were higher than in the adjacent coastal ocean due to evaporation, showing positive correlation with salinity and negative correlation with tidal height. Measured TA and DIC concentrations were slightly higher than those calculated by the conservative evaporation model, suggesting their production in the estuary by aerobic and anaerobic processes. CO32–, Ωcal, and Ωara showed a clear semi-diurnal (tidal-driven) and diel (24 h; biological-driven) patterns: lowest values occurred at flood tide during night-time (respectively, 185 μmol kg–1, 4.3 and 2.8), whereas highest occurred during ebb tide and daytime (respectively, 251 μmol kg–1, 5.7 and 3.8). DIC/TA ratios were higher at night-time supporting a diel control (linked to solar irradiance) of the carbonate buffering capacity. pCO2 was oversaturated comparing to the atmosphere (512–860 μatm) and the estuary was a source of CO2, with fluxes ranging from 2.2 to 200.0 mmol C m–2 d–1 (51.9 ± 26.7 mmol C m–2 d–1), which are higher than emissions normally found in low-inflow, marine-dominated estuaries. The diel variability of DIC indicated a net heterotrophic metabolism averaging −5.17 ± 7.39 mmol C m–2 h–1. Eutrophication amplifies the diel variability of the CO2 system generating large differences between daytime and night-time. The results highlight the importance of considering diel variability when estimating CO2 fluxes and carbonate chemistry in eutrophic, semi-arid, and tidally dominated estuaries under rapid environmental changes, and may represent future conditions in estuaries worldwide experiencing warming, increasing aridity and eutrophication.

The Gulf of California (GC) features many oceanographic processes. It communicates with the Pacific Ocean via a surface water outflow (0-200 m) with relatively low dissolved inorganic carbon (DIC) values and a water inflow (200-600 m) with high DIC values. Data on the marine carbon system in the GC are scarce and most have been taken from the Midriff Islands region, in the central part of the gulf. We explored possible forcing agents that control the ocean-atmosphere CO2 flux (fCO2) variability in 5 coastal zones of the GC. We carried out 6 oceanographic cruises in 5 regions: off northern Sinaloa in September 2016 (NAV2016) and in March 2017 (NAV2017), in the Guaymas Basin (central gulf) in September 2016 (GUA2016), in Concepción Bay (Baja California Sur) in July 2017 (BC2017), in Mulegé (Baja California Sur) in July 2017 (MUL2017), and off Mazatlán (southern gulf) in July 2017 (MAZ2017). We measured temperature, salinity, DIC, and total alkalinity and calculated the surface water partial pressure of CO2 and fCO2. We also used sea surface height anomaly with geostrophic flow, sea surface temperature, and chlorophyll concentration data from satellite imagery to generate composites for the sampling days. The lowest temperature, highest DIC, and negative fCO2 were registered in NAV2017. NAV2016, GUA2016, and BC2017 showed the highest temperatures; and MUL2017 and MAZ2017, intermediate temperatures. The most contrasting fCO2 values occurred in GUA2017 (0.56 ± 0.46 mmol C·m-2·d-1) and MAZ2017 (-2.26 ± 1.85 mmol C·m-2·d-1). In general, fCO2 is determined by the oceanographic conditions of each study area. [ABSTRACT FROM AUTHOR]