Contribution Of Organic Carbon Research Articles

Source characteristics and quantitative estimates of organic carbon composition in the intertidal zones of Jiaozhou Bay, China

The Jiaozhou Bay (JZB) intertidal zone is a significant carbon reservoir that plays a crucial role in transporting and accumulating organic matter; however, quantitative studies of organic matter sources are scarce. In this study, we present bulk parameters of total organic carbon (TOC), TOC/TN, δ13C, and biomarker contents in 36 surface sediment samples from the JZB intertidal zones to quantify the contribution of organic carbon (OC) derived from terrestrial/marine sources, such as C3 plants, C4 plants, estuarine productivity, sewage outlets, and marine productivity. The results demonstrated that a two-end-member model based on the traditional indicators of TOC/TN or δ13C is not appropriate for quantifying the OC source. The presence of C3 plants, C4 plants, and sewage outlets in the JZB intertidal zone could lead to errors in determining OC contribution when solely using TOC/TN or δ13C. A classical mixing diagram (three-end-member model) utilizing TOC/TN and δ13C values revealed that OC contribution was dominated by marine productivity throughout the intertidal zone. In the west, the average OC contribution from marine productivity, estuarine productivity, and C4 plants was 73.8 %, 14.2 %, and 12.0 %, respectively. In the east, the average OC contribution from marine productivity, estuarine productivity, and sewage outlets was 57.6 %, 24.9 %, and 17.4 %, respectively. The higher OC contribution from marine productivity in the west was attributed to the occurrence of Spartina alterniflora, while the OC contribution from estuarine productivity in the east was primarily due to the presence of more rivers flowing into the JZB compared to the west. By combining biomarkers and OC contents, a significant positive relationship verified the suitability of the end-member values selected for the three-end-member mixing model in the west and east intertidal zones of JZB. This finding was further supported by principal component analysis (PCA) analyses of these proxies. This study demonstrated that OC sources in intertidal zones varied among contrasting coastal environmental conditions and addressed the knowledge gap regarding biogeochemical cycles and ecological protection in the JZB intertidal zones.

Isotopic and molecular analyses of n-alkanes in a temporal study of coastal sediment contributions to organic carbon degradation induced by algal bloom and terrestrial runoff.

The priming effect (PE) refers to the enhanced remineralization of recalcitrant organic carbon (OC) driven by the respiration of labile OC, potentially increasing CO2 fluxes from aquatic ecosystems. Patterns of PE induced by marine and terrestrial OC inputs can be explored through sedimentary contributions to the degraded OC pool. In this study, coastal sediments (δ13Cbulk=-25.26±0.06‰, 1.63±0.07% OC) were spiked with isotopically distinct marine and terrestrial OC sources (Nannochloropis phytoplankton, δ13C=-43.18±0.31‰; and C4 corn leaves, δ13C=-13.90±0.09‰). Source contributions to respired OC were investigated using n-alkane concentration profiles and stable carbon isotopes (C15-C30) across 30 microcosms. Elevated concentrations of 13C-enriched high molecular weight n-alkanes (e.g., δ13CC29=-26.3±0.5‰) were observed in corn leaf amendments, whereas the phytoplankton spike exhibited a higher abundance of 13C-depleted low molecular weight n-alkanes (e.g., δ13CC17=-46.8±0.4‰). Mixing models indicate the sedimentary OC contribution to the degraded biomarkers, for which an increasing trend suggests a PE. Phytoplankton-amended microcosms showed a sediment OC contribution of 10.3±1.5% to the degradation of the C17 n-alkane. The corn leaf spike resulted in consistently higher contributions of 30.4±3.6% for the lost C29 n-alkane, documenting the effect of carbohydrate rich organic matter on sedimentary OC remineralization. A synergistic interaction emerged when sediments received a mix of marine and terrestrial OC, exhibiting contributions to n-alkane loss of 48.3±5.3% for C17, and 35.2±5.2% for C29. Following biochemical fractionation that leads to the selective breakdown of certain biochemical structures, our data indicate greater sedimentary degradation during induced terrestrial runoff compared to an algal bloom, providing a quantitative measure of OC remineralization.

Pigments in Cores of Bottom Sediment as Indicators of the Trophic Status Dynamics in the Benthal of a Large Reservoir

New data on the dynamics of pigment characteristics for different silts in the basin-valley Rybinsk Reservoir, the largest source of fresh water on the Upper Volga, are presented. The concept of eutrophication of the reservoir under modern climate warming is supplemented. The content of pigments in bottom sediment cores taken after 10 years (in 2009 and 2019) was compared. According to the latest survey, the average content of chlorophyll a with pheopigments in cores at the stations is characterized by higher values, and the carotenoid/chlorophyll ratio (index Е 480 /Е 665 ) is lower than according to the first survey. The relationship between the index Е 480 /Е 665 and the total content of chlorophyll a and pheopigments in cores from most stations is negative, as in phytoplankton. In the total array of studied sediment samples, the contribution of pigment concentrations (chlorophyll a + pheopigments) belonging to the hypertrophic category is increased. The average content of sedimentary pigments in lake-like areas increased compared to riverine areas. The dynamics of pigments is clearly expressed in cores of gray clayey silt and smoothed in peat–originated silt. Over the period from 2009 to 2019, the average contribution of autochthonous organic carbon, estimated from the sum of chlorophyll and pheopigments, increased from 7.7% to 12.3% of total organic carbon in cores. The trends of the pigment concentrations in cores indicate an increase in the trophic state of benthal to date. The significance of the pigment characteristics of bottom sediments for monitoring the benthal productivity over the entire period of reservoir operation is discussed.

Effects of Straw Management and Nitrogen Application Rate on Soil's Physicochemical Properties and Rice Yield in Saline-Sodic Paddy Fields.

Straw return plays a vital role in crop yield and sustainable agriculture. Extensive research has focused on the potential to enhance soil fertility and crop yield through straw return. However, the potential impacts of straw return on saline-sodic soils have been relatively neglected due to the unfavorable characteristics of saline-sodic soils, such as high salinity, poor structure, and low nutrient contents, which are not conducive to crop growth. Therefore, a two-year field experiment was conducted to assess the effects of straw management (retention or removal) with nitrogen fertilizers (0, 90, 180, 270, and 360 kg N ha-1) on soil aggregates, soil chemical properties, and rice yields in saline-sodic soil. The results showed that straw return with nitrogen fertilization significantly decreased the soil exchange sodium percentage (ESP) and the percentage and organic carbon contribution of silty clay particles and also significantly increased the soil aggregate stability, organic matter (SOM), and percentage and organic carbon contribution of macroaggregates. However, there was no significant difference between 270 kg N ha-1 and 360 kg N ha-1 for all soil indicators under straw return. Straw return significantly increased rice grain yield by 5.77% (two-year average) compared to straw removal. The highest grain yield of 8.01 t ha-1 (two-year average) was obtained from straw return combined with 270 kg N ha-1. However, since this experiment was conducted for only two years, the positive effects of long-term straw return on soil and rice yield could have been greater. Therefore, the application of 270 kg N ha-1 in the early stages of straw return is a promising management practice for improving saline-sodic soils and increasing rice yields.

Contribution of Organic Carbon, Moisture Content, Microbial Biomass-Carbon, and Basal Soil Respiration Affecting Microbial Population in Chronosequence Manganese Mine Spoil

The research was carried out to determine the potential effect of microbiota, organic carbon, percentage of moisture content, and microbial biomass concentration as an evaluator of variation in basal soil respiration rate. Relative distribution and composition of the microbial population were estimated from six different chronosequence manganese mine spoil (MBO0, MBO2, MBO4, MBO6, MBO8, MBO10) and forest soil (FS). The variation was seen in moisture content (6.494±0.210-11.535±0.072)%, organic carbon (0.126±0.001- 3.469± 0.099)%, MB-C (5.519±1.371- 646.969± 11.428) μg.g-1 of soil. A positive correlation was shown between OC with MB-C (r = 0.938; p< 0.01) and moisture content (MC) (r = 0.962; p< 0.01). Variation in the basal soil respiration (BSR) and microbial metabolic quotients (MMQ) was shown to range between 0.352 ± 0.007- 0.958 ±0.014μg CO2-C.g-1 and 6.5× 10-3 - 1.481×10-3 μg CO2-C.g-1 microbial-C.h-1 with BSR: OC from (2.793-0.276)% respectively. This result shows that there is a gradual increase in OC, MC, MB-C, and BSR across seven different sites due to progressive enhancement in soil fertility that leads to the initialization of succession. Stepwise multiple regression analysis further confirms the degree of variability added by microbial biomass C, moisture content, organic carbon, and microbial population on basal soil respiration in microbes. Principal component analysis enables the differentiation of seven different soil profiles into independent clusters based on cumulative variance given by physico-chemical and microbial attributes that indicate the level of degradation of land and act as an index to restore soil fertility.

Formation of an Active Giant Nonsulfide Zinc System, Jinding, China: Relationships Among Tectonics, Climate, and Supergene Metal Remobilization

Abstract The oxidized portion of the giant Jinding Zn-Pb deposit, Yunnan, China, accounts for about 40% of the original metal resource, indicating a nonsulfide zinc component of 80 to 90 million tonnes (Mt), making it among the largest nonsulfide zinc concentrations known. The presence of the Jinding deposit within a rugged topographic upland undergoing active weathering and erosion suggests that the nonsulfide zinc supergene system was active at the time of discovery. The ore-bearing strata cropped out at ~2800 m elevation, and strong oxidation effects are present to at least 200 m below the premining surface. The exhumation of the late Oligocene Jinding primary ores and exposure to groundwater modification may have been initiated by late Miocene uplift that coincides with the onset of the Southeast Asia monsoonal climate. The abundance of calcium carbonate in the Jinding host strata and primary ore results in the preserved nonsulfide zinc ores being dominated by smithsonite crusts of a variety of compositions, along with a diverse assemblage of supergene Zn-Pb and other minerals reflecting the primary ore composition. Complex microstratigraphic banding in smithsonite at scales of ≤20 µm is revealed by luminescent microscopy, likely recording groundwater-related annual precipitation events. Jinding smithsonites from the Beichang and Jaiyashan ore zones have δ18OV-SMOW values (in which V-SMOW = Vienna-standard mean ocean water) that vary between 18.6 and 21.5‰, which are unusually low compared with most supergene smithsonites. These values are consistent with the cold conditions of the Jinding area (11°C mean annual temperature) and are compatible with local cold springs and travertines. The δ13CV-PDB values (in which V-PDB = Vienna-Pee Dee Belemnite) of the Jinding smithsonites range between –10.1 and –3.6‰ and are distinct from calcites formed by local hot springs and from low-18O smithsonites from other nonsulfide zinc deposits. The light carbon isotope composition of Jinding smithsonites suggests a major contribution of organic carbon and only minor, if any, contributions from local Triassic marine limestone and atmospheric CO2. The 13C-depleted carbon likely was derived from soils with C3 plant-dominated organic matter, from oxidation of hydrocarbons in the primary ore, or from dissolution of isotopically light sandstone cements or ore calcites. Reaction path models show that the reaction of descending, cool, oxidizing, meteorically derived groundwater with calcite, CO2, and primary sulfide minerals can account for much of the observed supergene mineral assemblage. The Jinding nonsulfide zinc mineralization reflects the interrelationships among tectonic, climatic, and groundwater processes in high elevation and/or latitude settings, notably related to cold groundwater. Although the preservation of thick nonsulfide zinc concentrations was impeded by the dynamic regional tectonic and climatic conditions that resulted in high precipitation and erosion rates, the size of the primary ore zone and focused groundwater transport resulted in the development of a giant nonsulfide zinc mineralization system.

A global assessment of mangrove soil organic carbon sources and implications for blue carbon credit.

Mangroves can retain both autochthonous and allochthonous marine and/or terrestrial organic carbon (OC) in sediments. Accurate quantification of these OC sources is essential for the proper allocation of blue C credits. Here, we conduct a global-scale analysis of sediments autochthonous and allochthonous OC contributions in estuarine and marine mangroves using stable isotopes. Globally, mangrove-derived autochthonous OC was the main contributor to estuarine and marine mangrove top-meter soil organic carbon (SOC) (49% and 62%, respectively). Less marine allochthonous OC (21%) was deposited than terrestrial allochthonous OC (30%) in estuarine mangrove sediments. Estuarine mangroves accumulated more SOC in sediments than marine mangroves (282 ± 8.1 Mg C ha-1 and 250 ± 5.0 Mg C ha-1, respectively), primarily due to the additional terrestrial OC inputs. Globally, marine mangroves held 67% of the total mangrove SOC, reaching 3025 ± 345 Tg C, while 1502 ± 154 Tg C was stored in estuarine mangrove sediments. The findings emphasize the substantial influence of coastal environmental settings on OC contributions, underlining the necessity of accurate OC source quantification for the effective allocation of blue carbon credits.

Stark seasonal contrast of fine aerosol levels, composition, formation mechanism, and characteristics in a polluted megacity.

In this study, we investigated the temporal variation of organic and inorganic aerosol with its optical properties in Mumbai (India), an urban coastal region. Mean PM2.5concentrations during the sampling period were 175μg/m3 (winter) and 90μg/m3 (summer). During winter, the average concentrations of organic (OC), elemental (EC), and water-soluble organic carbon (WSOC) were three times higher than in summer. Secondary organic carbon (SOC) contribution in OC was higher in summer (78%) than in winter (53%), and strong solar radiation in summer likely caused this outcome. Aerosols were slightly acidic in both seasons, with an average pH of 5.7 (winter) and 6.0 (summer). A correlation was observed between SOC and the acidity of particles in summer (R2 = 0.6), indicating some amount of acid-catalysed SOC formation. In both seasons, the sulphate oxidation ratio (SOR) was higher than the nitrate oxidation ratio (NOR), which may reflect a preference for SO2 oxidation over NO2 or the difference in partitioning ammonium nitrate into ammonium sulphate under high RH. The dominant mechanism of SOC formation (gas vs aqueous phase oxidation) also showed seasonal variation. In winter, a relatively steep reduced major axis (RMA) slope of O3/CO suggests gas phase oxidation was the dominant mechanism of SOC production. Winter has more BrC fraction than summer, indicating higher absorbing aerosols, though the efficiency of absorbing the light was higher in summer. To assess the radiative forcing of PM2.5 on a local scale, an effective carbon ratio (ECR) was computed. The findings pointed to a local radiative heating impact caused by PM2.5. The spectral slope ratio and MAE at 250 to 300nm ratio (E2/E3) revealed a higher abundance of high molecular weight species in WSOC during summer than in winter.

ENSO modulates soil organic carbon retention and deposition in the East China Sea

Accurately quantifying the contribution of terrestrial soil organic carbon (SOC) in marine environment is still a challenge. Moreover, reassessing the effect of climate change on SOC variability is necessary, with the increasing variability of El Niño under greenhouse warming. Here, we present new insights from bacterial 3-hydroxy fatty acids (3-OH-FAs) by systematically analyzing the distributions of 3-OH-FA in soils, lake/river sediments and marine sediments, and propose a novel proxy (RIA, the ratio of odd carbon number iso to anteiso 3-OH-FAs) to quantificationally evaluate the contribution of OC from different components. The reliability of the RIA proxy is tested by using a three end-member model and Monte Carlo simulations along a transect from the Yangtze River estuary to the ECS shelf. Then the RIA proxy is applied to a core in the East China Sea covering the past 700 years, and the results reveal that El Niño (La Niña) induced more (less) precipitation and increased (decreased) SOC deposition. This study provides a novel approach for quantifying terrigenous OC inputs and burial in marginal seas and shows the impact of El Niño-Southern Oscillation (ENSO) modes on SOC loss and burial in marginal seas under global warming.

Fate of soil organic carbon in estuarine mangroves: Evidences from stable isotopes and lignin biomarkers

Coastal wetlands are increasingly recognized for their role in climate change mitigation, particularly through the sequestration of soil organic carbon (SOC). Despite widespread acknowledgement of their importance, the variation in organic carbon (OC) sources among different estuarine mangrove wetlands, and how these sources interact with environmental factors, is not fully elucidated. This research focuses on the role of estuarine mangrove wetlands in climate change mitigation through SOC sequestration. It explores the distribution, sources, and decomposition of SOC in a wetland with four mangrove communities along a tidal gradient. These include a tidal flat, a Sonneratia apetala forest, a mixed S. apetala and Kandelia obovata forest, and a K. obovata forest. The study employs biogenic element analysis (C, N, lignin phenols) and natural stable carbon isotope ratios (δ13C and δ15N) to assess SOC. Key findings show a decrease in SOC and total nitrogen (TN) from the upstream K. obovata forest to the downstream tidal flat. A stable isotope mixing model reveals a diminishing mangrove-derived OC contribution in topsoil (0–40 cm), estimated at 62 % in the K. obovata forest, 45 % in the central region, and 24 % in tidal flats. Soil profiles suggest microbial decomposition as the main isotope fractionation mechanism, with lignin analysis indicating woody angiosperms as the primary OC source. These findings enhance understanding of OC origins and decomposition in coastal wetlands and inform “blue carbon” management, highlighting the terrestrial-estuary continuum's significance.

Transforming air pollution management in India with AI and machine learning technologies

A comprehensive approach is essential in India's ongoing battle against air pollution, combining technological advancements, regulatory reinforcement, and widespread societal engagement. Bridging technological gaps involves deploying sophisticated pollution control technologies and addressing the rural–urban disparity through innovative solutions. The review found that integrating Artificial Intelligence and Machine Learning (AI&ML) in air quality forecasting demonstrates promising results with a remarkable model efficiency. In this study, initially, we compute the PM2.5 concentration over India using a surface mass concentration of 5 key aerosols such as black carbon (BC), dust (DU), organic carbon (OC), sea salt (SS) and sulphates (SU), respectively. The study identifies several regions highly vulnerable to PM2.5 pollution due to specific sources. The Indo-Gangetic Plains are notably impacted by high concentrations of BC, OC, and SU resulting from anthropogenic activities. Western India experiences higher DU concentrations due to its proximity to the Sahara Desert. Additionally, certain areas in northeast India show significant contributions of OC from biogenic activities. Moreover, an AI&ML model based on convolutional autoencoder architecture underwent rigorous training, testing, and validation to forecast PM2.5 concentrations across India. The results reveal its exceptional precision in PM2.5 prediction, as demonstrated by model evaluation metrics, including a Structural Similarity Index exceeding 0.60, Peak Signal-to-Noise Ratio ranging from 28–30 dB and Mean Square Error below 10 μg/m3. However, regulatory challenges persist, necessitating robust frameworks and consistent enforcement mechanisms, as evidenced by the complexities in predicting PM2.5 concentrations. Implementing tailored regional pollution control strategies, integrating AI&ML technologies, strengthening regulatory frameworks, promoting sustainable practices, and encouraging international collaboration are essential policy measures to mitigate air pollution in India.

Thinning shelter forest reduced the soil priming effect and soil microbial respiration by altering the contribution of soil organic carbon from different sources

Thinning affects the understorey microclimate and the material input into the shelter forest soil, and it alters the contribution of the plant-derived and microbial-derived carbon (C). This difference effects the utilization of C by soil microbes and ultimately soil C emission. There is still no adequate characterization for the contribution of plant-derived and microbial-derived C to soil organic C (SOC) under thinning. Moreover, how this difference affects microbially driven C emissions (soil microbial respiration, SMR) and the contribution to the soil priming effect in this process are still unknown. The contribution of plant-derived and microbial-derived C to SOC were quantified by comparing lignin phenols and amino sugars under thinning and control treatments. Meanwhile, a 30-day indoor cultivation experiment was conducted. Soil priming effect and SMR were tested by adding 13C-labelled glucose to the soil of the thinning and control treatments. The purpose was to investigate the contribution of C from different sources to SOC, as well as its influence mechanism on soil priming effect and SMR.The results indicate that thinning significantly increased the fungal-derived (10.19 and 7.34 g kg−1) and microbial-derived C (11.05 and 8.19 g kg−1) of Quercus acutissima Carruth (QAC) and Pinus thunbergii Parl (PTP). However, the bacterial-derived C (0.86 and 0.85 g kg−1) decreased. Compared to the control treatment, the plant-derived, fungal-derived and microbial-derived C increased by 6.6 % and 1.1 %, 17.9 % and 12.2 %, and 16.6 % and 10.1 %, respectively, while bacterial-derived C decreased by 1.3 % and 2.1 %. Thinning reduced the soil priming effect of QAC by lowering the pH and increasing F/B and fungal-derived C. At the same time, this phenomenon was not evident in PTP, mainly attributed to the content of SOC and vanillyl and syringyl monomers. Thinning reduced the SMR, which was mainly related to the suppression of soil priming effect. In summary, this study has demonstrated that thinning reduced the soil priming effect and SMR of shelter forests by altering the contribution of plant-derived and microbial-derived C to SOC.

Precipitation patterns impact soil aggregates and organic carbon of an alpine wetland on the Qinghai-Tibetan Plateau

Global climate change is predicted to influence both precipitation amount and frequency in many regions. However, little is known about how precipitation changes affect soil aggregates and soil organic carbon (SOC) in alpine wetlands. Plots of an alpine wetland on the Qinghai-Tibetan Plateau were subjected to two precipitation frequencies (high vs. low, i.e., 1 and 3 times of nature rainfall intervals) crossed with two precipitation amounts (high vs. low, i.e., 100 % and 70 % of the amount of natural rainfall). Two years later, we investigated changes of soil aggregates (silt + clay, < 53 μm; microaggregates, 53∼250 μm; and macroaggregates, >250 μm) and SOC in three soil depths, i.e., 0–15 cm, 15–30 cm and 30–50 cm. Averaged across the three soil depths, the content of SOC and dissolved organic carbon (DOC) in the simulated natural precipitation (high amount, high frequency treatment) were 127.22 g kg−1 and 0.19 g kg−1, respectively. Reducing precipitation amount or frequency led to a 19.6 %-26.2 % increase in SOC, and 28.7 %-44.4 % increase in DOC. Microbial biomass carbon in natural precipitation was 1.33 g kg−1 across the three soil depths, and its response to precipitation varied with soil depths. The fraction of macroaggregates in the 0–15 cm soil depth was 63.5 % in the simulated natural precipitation treatment, and decreased by 18.6 %–21.9 % in response to reduced precipitation amount or frequency. Aggregate fractions in the 15–30 cm soil depth did not respond significantly to the changes of precipitation patterns. Reducing precipitation frequency or amount decreased the contribution of macroaggregate-associated organic carbon to SOC compared to the simulated natural precipitation, but increased the contribution of microaggregate-associated organic carbon, especially in the 0–15 cm soil depth. Structural equation models revealed that SOC was regulated by soil aggregate composition and microbial biomass carbon. The buffering of the surface soil weakened the effects of precipitation changes on aggregates and aggregate-associated organic carbon in the deep soil. These results suggest that reducing precipitation frequency or amount can decrease the fraction of macroaggregates in the surface soil, and weaken the physical protection of macroaggregates for SOC. Thus, changes in precipitation patterns may have a significant impact on SOC storage and stability in alpine wetlands through their influence on soil aggregate composition.

UV light absorption at 370 nm by mineral dust, organic carbon, and elemental carbon in the Himalayas and Tibetan Plateau

The mass and light absorption contributions of organic carbon (OC), elemental carbon (EC), and mineral dust influence glacial melting and potentially contribute to climate change over the high Himalayas and Tibetan Plateau (HTP). Plateau-scale investigations of these components and their respective light absorption are limited due to the high altitude. In this study, we combined the analysis of major light-absorbing substances and their corresponding multiwavelength absorption to determine their specific contributions firstly. We investigated the spatial variations of total suspended particle (TSP) mass across the HTP, noting high contributions from dust, carbonaceous components, and secondary inorganic aerosols (SNA, including sulfate, nitrate, and ammonium). Enhanced levels of primary and secondary OC and SNA were observed in the marginal areas of the HTP, associated with high relative humidity (RH) and OX levels (O3+NO2). EC was the primary contributor to light absorption, accounting for approximately 68%, 46%, and 64% in Ngari, Qinghai Lake, and Beiluhe, respectively. We found higher light-absorbing contributions from carbonaceous aerosols in the marginal areas compared to the central HTP site, particularly during the heating seasons (∼90%). Fugitive dust significantly contributed to TSP mass but not to light absorption. The concurrent constraints on the mass and optical properties of OC, EC, and dust in this study can help reduce uncertainties in climate models specific to the HTP.

Spatio-temporal dynamics of the carbonate system during macroalgae farming season in a semi-closed bay in southeast China

Ocean Negative Carbon Emission (ONCE) involves utilizing natural marine chemistry and biology, along with mariculture, to achieve carbon sink goals. Growing awareness of the interplay between aquaculture and the coastal carbonate system has drawn researchers’ attention amid ring CO2 concentrations and the negative impacts of aquaculture on the environment. In this study, twelve sites representing different maricultural types were selected, including macroalgae, shellfish, fish, and non-farming areas. The environmental factors, dissolved inorganic carbon (DIC), total alkalinity (TA), and pCO2, were measured monthly during kelp farming periods. Nitrate is a major component of total nitrogen, and the NO3-N concentration in the macroalgal culture zone was lower than others, indicating effective nitrogen removal by macroalgae aquaculture. TA and DIC in non-farmed areas demonstrated larger variation ranges than in farming areas, probably due to the effects of precipitation on salinity. Aquaculture activities effectively maintained TA and DIC, with macroalgae cultivation playing an important role in TA stability, potentially resisting acidification. The pCO2sea-air of macroalgae culture areas in spring was slightly negative, suggesting carbon sink potential. However, further research is needed to assess the full extent of this “fourth type” of blue carbon, including accurate carbon footprint calculation and the contributions of particulate organic carbon and recalcitrant dissolved organic carbon. This study provided insight into the comprehensive contribution of different aquaculture types to the fishery environment and carbonate system, which can help guide aquaculture management and facilitate the carbon-neutral transition of aquaculture.

How does exotic Spartina alterniflora affect the contribution of iron-bound organic carbon to soil organic carbon in salt marshes?

Iron-bound organic carbon (OC-FeR) is important for the stability of soil organic carbon (SOC) in salt marshes, and the Spartina alterniflora invasion reshaped local salt marshes and changed the SOC pool. To evaluate the effects of S. alterniflora invasion on the contribution of OC-FeR to SOC, we determined the OC-FeR content and soil characteristics in the 0–50 cm soil profile along the vegetation sequence, including mudflats (MF), S. alterniflora marshes established in 2003 (SA03) and 1989 (SA89), the ecotone of S. alterniflora and Phragmites australis (SE), S. salsa marsh (SS), and P. australis marsh (PA). The SOC content was 6.55–17.5 mg g−1 in the S. alterniflora marshes. Reactive iron oxides (Fed, Feo, Fep) accumulated significantly in the S. alterniflora and P. australis salt marshes. PA and S. alterniflora marshes had higher DOC contents of 0.28–0.77 mg g−1. The OC-FeR content in the 0–50 cm soil profile in these ecosystems ranged from 0.3 to 3.29 mg g−1, with a contribution to the SOC content (fOC-FeR) of approximately 11 %, which was highest in SA03 (16.3 % ~ 18.8 %), followed by SA89, SE, and PA. In addition, the molar ratios of OC-FeR to Fed were <1, indicating that the iron oxides were associated with SOC through sorption more than coprecipitation. According to the structural equation model, SOC, DOC and iron oxides were the direct driving factors of OC-FeR formation, while the vegetation zone indirectly functioned by regulating organic C inputs, iron oxide formation, and pH. This study suggested that S. alterniflora invasion promotes iron-bound organic carbon accumulation by increasing organic C inputs and regulating iron oxide formation in salt marshes, but such promotion will degenerate with development duration.

Soil quality: an indicator of recovery in a nature reserve in the Colombian Andes

Soils provide essential ecosystem services for the existence of ecosystems and biodiversity. It is crucial to understand their quality through the evaluation of ecological processes. However, only some studies estimate the effectiveness of ecosystem restoration based on evaluating soil quality (SQ) indicators. This research evaluated the five most common land-use scenarios in Andean ecosystems within the Natural Reserve of the Civil Society (RNSC) “La Montaña Mágica” under natural forest, coffee plantation, badlands, and active and passive restoration. The main objective was to analyze the physical, chemical, and biological characteristics concerning land use, establish the baseline for SQ indicators in different land use activities, and determine the status of restoration systems for other land uses in the study site. ANOVA and Dunnett's test evaluated SQ parameters. In passive and active restoration, soil bulk density, porosity, and the number of individuals and families of macroinvertebrates were improved. The latter presented low pH and aluminum values but increased potassium compared to other soil uses. The restoration strategies favored changes in SQ indicators due to the contribution of organic carbon, a developed root system, and the recirculation of nutrients in the edaphic system. This study provided information on changes in SQ with soil usage as a practical tool to evaluate ecological restoration methods in natural areas of the eastern Colombian Andes.

Contribution of aged organic carbon to suspended particulate organic carbon in the western equatorial Indian Ocean

We investigated dual carbon isotopes within the vertical water column at sites 67-1 and 67-2 of the western equatorial Indian Ocean to determine the source and age of particulate organic carbon (POC) and thus evaluated the contributions of modern and fossil (aged) POC. The concentration of POC ranged from 7 to 47.3 μgC L−1, δ13CPOC values ranged from –31.8 to –24.4‰, and Δ14CPOC values ranged from –548 to –111‰. Higher values of δ13CPOC and Δ14CPOC near the surface indicated an influence of autochthonous POC, whereas decreasing trends toward the bottom suggested a contribution of aged OC sources to the total POC pool. The contribution of fossil POC was lower near the surface, accounting for only 12% and 6% of the total POC at sites 67-1 and 67-2, respectively; however, in the deeper layers below 1,000 m, the contribution of fossil POC increased to 52% and 44% of the total POC at the two sites. Mechanisms for the increased contributions of fossil OC within deeper POC include the inflow of aged OC from sediments resuspended near slopes, the adsorption of old dissolved organic carbon in deep water masses, and the impact of aged OC that may originate from hydrothermal sources. This study highlights the importance of aged OC in the carbon cycle of the equatorial Indian Ocean.

Sources and high burial efficiency of fossil organic carbon in small bays and implication for coastal carbon cycle

Coastal seas receive and store large amounts of organic carbon (OC) from land and ocean, thereby playing a crucial role in the global carbon cycle. Understanding factors that influencing OC sources and burial efficiencies in coastal areas have been challenging. We selected the Jiaozhou Bay (JZB) and its surrounding rivers heavily affected by human activities as a case study small bay. We presented bulk parameters of grain size, sediment surface area (SSA), TOC content and carbon isotopes (δ13Corg and Δ14Corg), terrestrial biomarkers (∑C27 + C29 + C31n-alkanes) and marine biomarkers (brassicasterol and dinosterol) in surface sediments and suspended particulates. Our results showed low TOC and biomarker contents in the Dagu River Estuary from the west of the JZB associated with coarse sediments and lower SSA. To estimate the OC proportions, we applied a three-end member mixing model based on TOC δ13Corg and biomarker ratios and obtained the OC contribution from phytoplankton (average 52 %), soil (average 34 %) and wetlands (average 14 %). A transect from east to west of the JZB was selected to further assess the OC age composition based on radiocarbon isotopic (14C) measurements for a new perspective. The lower Δ14Corg values in the east revealed fossil OC contributions from human activities, such as petroleum pollutant inputs from sewage outlets. Based on a dual‑carbon isotope (δ13Corg and Δ14Corg) mass balance mixing model, the OC contributions were 40 %, 34 %, 14 %, 12 % from fossil carbon, phytoplankton, wetlands and soil, respectively. The very high burial efficiency of fossil OC in JZB (111 ± 19 %) indicated that small bays such as the JZB could be an important sedimentary carbon sink.

Water column organic carbon composition as driver for water-sediment fluxes of hazardous pollutants in a coastal environment

The environmental fate of hazardous hydrophobic pollutants in the marine environment is strongly influenced by organic carbon (OC) cycling. As an example, the seasonality in primary production impacts both water column OC quantity and quality, which may influence pollutant mass transport from the water column to the sediment. This study aims to better understand the role of water column OC variability for the fate of pollutants in a near-coastal area. We conducted an in situ sampling campaign in the coastal Baltic Proper during two seasons, summer and autumn. We used polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) as model compounds, as they represent a wide range in physicochemical properties and are ubiquitous in the environment. Freely dissolved, and OC-bound concentrations were studied in the water column and surface sediment. We found stronger sorption of pollutants to suspended particulate matter (SPM) during the summer compared to the autumn (average 0.6 and 0.9 log unit higher particle-water partition coefficients during summer for PAHs and PCBs). Our data suggest that stronger sorption mirrors a compositional change of the OC towards higher contribution of labile OC during the summer, characterized by two times higher fatty acid and 24% higher dicarboxylic acids in SPM during summer. High concentrations of OC in the water column during the autumn resulted in increased SPM-mediated sinking fluxes of pollutants. Our results suggest that future changes in primary production are prone to influence the bioavailability and mobility of pollutants in costal zones, potentially affecting the residence time of these hazardous substances in the circulating marine environment.