Sediment Organic Carbon Content Research Articles

Distribution and Genesis of Organic Carbon Storage on the Northern Shelf of the South China Sea.

The sediments distributed in the marginal seas of the continental shelf are important burial materials for global organic carbon (OC). There have been many estimates of the global continental shelf OC reserves, but due to the limited acquisition of measured data, the estimated results have great uncertainty. The vast continental shelf in the northern part of the South China Sea (SCS) provides a good place for the storage of OC. Based on a large amount of sediment OC data obtained from the northern coast of the SCS, the OC storage in the surface sediment (0~10 cm) in the study area (approximately 8.63 × 104 km2) was accurately calculated as 51 Tg. The study area covers different regions, such as estuaries, open seas, strait areas and upwelling development areas, and the OC content of each area is quite different. According to provenance analysis, the source of OC in sediments is mainly from the input of Pearl River runoff. The OC content is significantly higher and less affected by sediment particle size in the Pearl River Estuary and the surrounding areas; meanwhile, the OC content gradually decreases with the distance from the Pearl River Estuary. Far from the western Pearl River Estuary, the sediment OC content is mainly controlled by the particle size of the sediments and is significantly correlated with silt and clay content. The deposition rate is also an important factor affecting the burial of OC, for the high deposition rates correspond to the high levels of OC in the nearshore estuarine areas, as well as the low deposition rate region having low OC content in the sediments even though it has a high productivity of OC, such in as the upwelling sea area on the eastern side of Hainan.

Understanding how nutrient limitation and plant traits influence carbon in mangrove‐seagrass coastal ecosystems

AbstractMangrove forests and seagrass meadows provide critical ecosystem services, including the accumulation of “blue carbon.” Plants' functional traits could influence this blue carbon accumulation. To test for interactions among functional traits and blue carbon accumulation, we conducted a study in connected mangrove‐seagrass coastal ecosystems in southeast Florida (USA). We quantified how plants' above‐ground traits correlated with sediment nutrient content, and how changes in traits along inland‐to‐coastal gradients influenced inorganic and organic carbon storage potential. Physical traits of Thalassia testudinum were higher at sites with higher sediment phosphorus (SP) and nitrogen (SN) concentrations. Sediment organic carbon concentrations were positively correlated to T. testudinum physical traits. Root density, pneumatophore abundance, specific leaf area, leaf toughness, leaf nitrogen, and phosphorus content were positively correlated with SN concentrations in the mangrove forest coastal fringe. Mangrove leaf thickness and root complexity index were negatively correlated with SP concentrations in the coastal fringe. Our results also indicate that seagrass above‐ground traits and blue carbon were strongly correlated in areas with higher sediment nutrient concentrations. Moreover, mangrove root complexity is coupled with phosphorus limitation, whereby highly complex root systems develop with decreasing phosphorus concentrations. Distinct functional traits of plants drive variation in carbon retention capacity even in interconnected ecosystems.

Analisis Karbon dalam Sedimen pada Ekosistem Lamun di Teluk Gilimanuk, Bali


 
 
 
 The increased CO2 emissions in the atmosphere have caused several environmental changes. Therefore, a larger CO2 absorption capacity is required. Seagrass can absorb carbon relatively fast and able to store it. Seagrass beds can trap sediment, so the absorption of organic carbon from the sediment by seagrass can be influenced by the size of the substrate. It has been found that the larger the substrate grain, the lower the ability of plants to absorb the organic matter. This study aimed to determine the seagrass density and cover as well as carbon storage in seagrass bed sediments. The variable measured was Sediment-Organic Carbon Content (S-OCC) and Sediment-Organic Carbon Stock (S-OCS) of seagrass ecosystems in Gilimanuk Bay. Employing purposive sampling, 20 sampling points were selected randomly where seagrass beds were present. The data were obtained using a 1×1m quadrant transect. The carbon content of the sediment was calculated by the Loss of Ignition (LOI) method by removing organic matter at a temperature of 600? in a furnace. This study found four seagrass species: Enhalus acoroides, Cymodocea rotundata, Cymodocea serrulate, and Halophila ovalis. The average density of seagrasses in this habitat ranged from 17 – 179 #/m2, with seagrass cover values ranging from 25 to 100%. The sediment carbon content, measured as carbon stock, on seagrass ecosystems at Gilimanuk Bay was 0.21% - 5.51% for S-OCC and 0.002 – 0.059 g Corg cm-3 for S-OCS. Total S-OCS in Gilimanuk Bay was 11165.84 Mg g Corg.
 
 
 

Eutrophication reduced the release of dissolved organic carbon from tropical seagrass roots through exudation and decomposition

Seagrass bed ecosystem is one of the most effective carbon capture and storage systems on earth. Seagrass roots are the key link of carbon flow between leaf-root-sediment, and the release of dissolved organic carbon (DOC) from seagrass roots through exudation and decomposition are vital sources to the sediment organic carbon (SOC) in the seagrass beds. Unfortunately, human-induced eutrophication may change the release process of DOC from seagrass roots, thereby affecting the sediment carbon storage capacity. However, little is known about the effect of nutrient enrichment on the release of DOC from seagrass roots, hindering the development of seagrass underground ecology. Therefore, we selected Thalassia hemprichii, the tropical dominant seagrass species, as the research object, and made a comparison of the release of DOC from roots through exudation and decomposition under different nitrate treatments. We found that under control, 10 μmol L−1, 20 μmol L−1 and 40 μmol L−1 nitrate treatments, soluble sugar of T. hemprichii roots were 71.37 ± 3.43 mg g−1, 67.03 ± 5.33 mg g−1, 49.14 ± 3.48 mg g−1, and 18.51 ± 2.09 mg g−1, respectively, while the corresponding root DOC exudation rates were 7.00 ± 0.97 mg g DW root−1 h−1, 5.11 ± 0.42 mg g DW root−1 h−1, 4.08 ± 0.23 mg g DW root−1 h−1, and 3.78 ± 0.74 mg g DW root−1 h−1, respectively. There was a significant positive correlation between root soluble sugar and DOC exudation rate. DOC concentration of sediment porewater and SOC content also decreased under nitrate enrichment (though not significantly), which were both significantly positively correlated with the rate of root exuded DOC. Meanwhile, nitrate enrichment also reduced the release rate of DOC from seagrass roots during initial decomposition, and the release flux of DOC from decomposition. Therefore, nutrient enrichment could decrease nonstructural carbohydrates of seagrass roots, reducing the rate of root exuded DOC, thereby lowered SOC, as well as the DOC release from seagrass root decomposition. In order to increase the release of DOC from seagrass roots and improve the carbon sequestration capacity of seagrass beds, effective measures should be taken to control the coastal nutrients input into seagrass beds.

Avermectin Toxicity to Benthic Invertebrates is Modified by Sediment Organic Carbon and Chemical Residence Time.

Chemicals used in sea lice management strategies in salmonid aquaculture include the avermectin class of compounds that can accumulate and persist in the sediments underneath salmon farms and directly impact nontarget benthic fauna. The effects of sediment organic carbon content and chemical residence time (CRT) on the lethal and sublethal toxicity of emamectin benzoate (EB; formulation: Slice®) and ivermectin (purified) and a combination of both were examined in two benthic invertebrates, the amphipod Eohaustorius estuarius and the polychaete Neanthes virens. In both species, increased sediment organic carbon content significantly reduced lethal toxicity, a modulation that was more pronounced for ivermectin and combination exposures. At a CRT of 4 months, lethal toxicity was reduced in E. estuarius but was unaffected in N. virens. Sublethal toxicity in N. virens (burrowing behavior) was modulated by sediment organic carbon and CRT in a similar manner to the trend in lethal toxicity. Inconsistencies in behavior (phototaxis) in E. estuarius made conclusions regarding toxicity modification by sediment organic carbon or CRT inconclusive. Our results indicate that environmental factors including sediment organic carbon content and the time compounds reside in sediments are important modifiers of chemotherapeutant toxicity in nontarget benthic species and should be considered when regulatory decisions regarding their use are made.Environ Toxicol Chem 2022;41:1918-1936. © 2022 SETAC.

Contamination of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in sediment of the Cau River, Vietnam.

Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are recognized as emerging environmental pollutants because of their high persistence in various environmental matrices and toxic effects on humans and animals. In Vietnam, PFOA and PFOS have been detected in surface water and sediment in recent studies. The objectives of this study were to evaluate the spatial and vertical distribution, determine the factors affecting the sorption onto sediment, and assess the environmental risk of PFOS and PFOA in the sediment of the Cau River. The average concentrations of PFOS and PFOA in the surface sediment were 2.66ng/g and 0.84ng/g, respectively. The highest concentrations were recorded in the areas receiving wastewater from domestic and industrial activities. According to the depth, the contents of target chemicals in the surface sediments (0-5cm) were lower than those in the second layer (5-10cm). The remaining layers have decreasing concentration as the depth of the sediment increases. The water-sediment distribution coefficient was relatively different for PFOS and PFOA with log Kd values ranging from 1.31 to 1.86 and from 0.08 to 1.31, respectively. This study also demonstrated that the level of PFOS and PFOA in sediment is significantly correlated with total organic carbon content of sediment. No apparent relation was found between PFOS, PFOA concentration in sediment, and particle size distribution. Risk quotients of the two compounds were below 0.01, indicating that the environmental risk in the sediment is negligible at present. The results of this study provide an overview of PFOS and PFOA contamination in sediment in the Cau River, Vietnam.

Mangrove sediment organic carbon storage and sources in relation to forest age and position along a deltaic salinity gradient

Abstract. Mangroves are widely recognised as key ecosystems for climate change mitigation as they capture and store significant amounts of sediment organic carbon (SOC). Yet, there is incomplete knowledge on how sources of SOC and their differential preservation vary between mangrove sites in relation to environmental gradients. To address this, sediment depth profiles were sampled from mangrove sites ranging from river-dominated to marine-dominated sites and including old and young mangrove sites in the Guayas delta (Ecuador). The stable carbon isotope ratios (δ13C) and the elemental composition (OC %, C : N) of sediment profiles, local vegetation (i.e. autochthonous carbon) and externally supplied suspended particulate matter (i.e. allochthonous carbon) were obtained to assess variations in the amount and sources of SOC at different locations throughout the delta. In general, across all sites, we found that increasing SOC contents and stocks are associated with decreasing δ13C and increasing C : N ratios, indicating that SOC stocks and sources are intrinsically related. The SOC stocks (down to 0.64 m depth profiles) are significantly lower in young mangrove sites (46–55 Mg C ha−1) than in old sites (78–92 Mg C ha−1). The SOC in the young mangrove sites is mainly of allochthonous origin (estimated on average at 79 %), whereas in the old sites there is a slight dominance of autochthonous OC (on average 59 %). Moreover, from river- to marine-dominated sites, a pattern was found of increasing SOC stocks and increasing autochthonous SOC contribution. These observed differences along the two studied gradients are hypothesised to be mainly driven by (1) expected higher sedimentation rates in the river-dominated and lower-elevation younger sites, thereby `diluting' the SOC content and decreasing the relative autochthonous contribution, and (2) potential differences in preservation of the different SOC sources. Our finding of high contributions of allochthonous SOC, especially in young mangroves, implies that this carbon is not originating from CO2 sequestration by the mangrove ecosystem itself but is externally supplied from other terrestrial, marine or estuarine ecosystems. We argue that accounting for lower SOC stocks and higher contribution of allochthonous SOC in young and river-dominated mangrove sites, as compared to old and marine-dominated sites, is particularly relevant for designing and valuing nature-based climate mitigation programmes based on mangrove reforestation.

清澜港红树林湿地典型群落类型沉积物活性有机碳组分分布特征

PDF HTML阅读 XML下载 导出引用 引用提醒 清澜港红树林湿地典型群落类型沉积物活性有机碳组分分布特征 DOI: 10.5846/stxb202105081203 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 省属科研院所技术创新专项项目（jscx202023）；海南省科研院所技术创新专项基础性科研工作（jcxk202003） Distribution characteristics of active organic carbon components in sediments of typical community types of mangrove wetland in Qinglan Port Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:滩涂海岸红树林生态系统通常具有较高的土壤养分，尤其是沉积物有机碳含量。海南岛红树林种类丰富且生长较好，通过对红树林沉积物有机碳组分的基础研究有利于提高对红树林湿地固碳能力的评估精度，加深对海洋蓝碳的认识。以清澜港红树林5种典型群落类型为对象，比较分析表层土壤（0-10 cm）总有机碳（TOC）、微生物生物量碳（MBC）、易氧化有机碳（EOC）、可溶性有机碳（DOC）含量差异及其与土壤因子之间的相关性。结果表明：（1）不同群落类型间，土壤TOC、MBC、DOC和EOC含量均值分别为66.76 g/kg、177.08 mg/kg、25.49 mg/kg和2.34 g/kg。对比发现，土壤TOC在角果木群落中含量最高，但各群落间无显著差异；土壤MBC在不同群落间存在显著差异，其中角果木群落和杯萼海桑群落显著高于榄李群落；土壤DOC在不同群落间存在显著差异，其中海莲群落和角果木群落显著高于其余群落；土壤EOC在不同群落间存在显著差异，其中角果木群落显著高于海莲群落和正红树群落。（2）活性有机碳各个组分占总有机碳的比例均值大小依次为EOC>MBC>DOC。土壤EOC、MBC、DOC的分配比例分别介于3.23%-4.02%、0.22%-0.36%、0.02%-0.08%之间。（3）冗余分析表明，土壤TN对土壤有机碳组分含量的单独解释率最高。土壤pH在土壤的单独解释率最低，其对土壤有机碳组分含量影响较小。（4）土壤TOC、MBC、DOC、EOC与土壤TN、含水量（SWC）呈极显著正相关。综上所述，潮位以及不同群系类型引起的土壤理化性质共同影响着土壤活性有机碳组分的浓度。 Abstract:Mangrove ecosystems in tidal flats usually contain a large proportion of soil nutrients, especially organic carbon content in sediments. The basic research on organic carbon components of the sediments in the large variety of luxuriant mangrove forests in Hainan Island can help more accurately evaluate the carbon sequestration capacity of mangrove wetlands and improve the knowledge about marine blue carbon. This paper comparatively analyzes the different contents of total organic carbon (TOC), microbial biomass carbon (MBC), easily oxidized organic carbon (EOC), and dissolved organic carbon (DOC) in the topsoil (0-10 cm) in five typical populations of mangrove in Qinglan Port and their correlation with soil factors. The result shows that (1) the average contents of TOC, MBC, DOC and EOC in the surface soils in different populations of mangrove are 66.76 g/kg, 177.08 mg/kg, 25.49 mg/kg, and 2.34 g/kg, respectively. According to the comparative analysis, the content of TOC is the highest in the soil in the Ceriops tagal community, but it is not significantly different among all the communities;The content of MBC in the soil is significantly different among all flora communities, where the content of MBC in the soil in Ceriops tagal community and Sonneratia alba community is much higher than that in Lumnitzera racemosa community. The content of DOC in the soil in all communities is significantly different, where the content of DOC in the soil in Bruguiera sexangula community and Ceriops tagal community is much higher than that in other communities. The content of EOC in the soil in all communities is significantly different, where the content of EOC in the soil in Ceriops tagal community is much higher than that in Bruguiera sexangula community and Rhizophora Apiculata community. (2) The average ratio of active organic carbon components to total organic carbon in MBC is higher than in DOC, and that in EOC is the highest. The distribution ratios of EOC, MBC and DOC in soil are between 3.23% and 4.02%, 0.22% and 0.36%, and 0.02% and 0.08% respectively. (3) Redundancy analysis shows that total nitrogen (TN) in soil is more justified to exclusively prove organic carbon components in the soil. Soil pH is less justified to exclusively prove the organic carbon component in the soil. (4) TOC, MBC, DOC and EOC in soil are positively correlated with soil TN and soil water content (SWC). In conclusion, tidal level soil physical and chemical properties caused by different biotic communities jointly affect the concentration of soil active organic carbon components. 参考文献 相似文献 引证文献

Condition of macroinvertebrate communities in the Buffalo River Area of Concern following sediment remediation

The lower 10 km of the Buffalo River, a tributary to Lake Erie, was designated as an Area of Concern (AOC) in 1987 through the Great Lakes Water Quality Agreement because sediment contamination and habitat alteration from past industrialization caused several Beneficial Use Impairments (BUIs). Extensive remediation efforts conducted between 2011 and 2015 removed approximately 688,100 cubic meters of contaminated sediment from the Buffalo River AOC, and subsequent chemical analysis of sediments indicated that most remedial goals had been achieved. Benthic macroinvertebrate communities and sediment toxicity were evaluated in the AOC and an upstream reference area in 2017 and 2020 to determine whether remediation has improved benthic conditions sufficiently that the benthos BUI designation can be removed. Community condition was characterized using the New York State multi-metric index of biological integrity and bed sediments were used for 10-day toxicity tests with Chironomus dilutus and Hyalella azteca. Macroinvertebrate communities were classified as moderately to slightly impacted at most AOC sites compared to slightly impacted at most reference sites, but toxicity tests did not identify any evidence of toxicity in sediments from the AOC. A linear mixed effects model indicated that total organic carbon concentration in sediments, distance upstream from the river mouth, and the relative dominance of zebra mussels Dreissena polymorpha were the primary predictors of macroinvertebrate community condition. These findings are consistent with those from other AOCs in New York which indicate that contemporary benthic communities are generally shaped by legacy habitat alterations rather than AOC-specific sediment contamination and toxicity.

Increasing sulfate concentration and sedimentary decaying cyanobacteria co-affect organic carbon mineralization in eutrophic lake sediments

Sulfate (SO42−) concentrations in eutrophic lakes are continuously increasing; however, the effect of increasing SO42− concentrations on organic carbon mineralization, especially the greenhouse gas emissions of sediments, remains unclear. Here, we constructed a series of microcosms with initial SO42− concentrations of 0, 30, 60, 90, 120, 150, and 180 mg/L to study the effects of increased SO42− concentrations, coupled with cyanobacterial blooms, on organic carbon mineralization in Lake Taihu. Cyanobacterial blooms promoted sulfate reduction and released a large amount of inorganic carbon. The SO42− concentrations in cyanobacteria treatments significantly decreased and eventually reached close to 0. As the initial SO42− concentration increased, the sulfate reduction rates significantly increased, with maximum values of 9.39, 9.44, 28.02, 30.89, 39.68, and 54.28 mg/L∙d for 30, 60, 90, 120, 150, and 180 mg/L SO42−, respectively. The total organic carbon content in sediments (51.16–52.70 g/kg) decreased with the initial SO42− concentration (R2 = 0.97), and the total inorganic carbon content in overlying water (159.97–182.73 mg/L) showed the opposite pattern (R2 = 0.91). The initial SO42− concentration was positively correlated with carbon dioxide (CO2) emissions (R2 = 0.68) and negatively correlated with methane (CH4) emissions (R2 = 0.96). The highest CO2 concentration and lowest CH4 concentration in the 180 mg/L SO42− treatment were 1688.78 and 1903 μmol/L, respectively. These biogeochemical processes were related to competition for organic carbon sources between sulfate reduction bacteria (SRB) and methane production archaea (MPA) in sediments. The abundance of SRB was positively correlated with the initial SO42− concentration and ranged from 6.65 × 107 to 2.98 × 108 copies/g; the abundance of MPA showed the opposite pattern and ranged from 1.99 × 108 to 3.35 × 108copies/g. These findings enhance our understanding of the effect of increasing SO42− concentrations on organic carbon mineralization and could enhance the accuracy of assessments of greenhouse gas emissions in eutrophic lakes.

Organic carbon composition and microbial transformation of seagrass meadow and its responses to eutrophication

<p indent="0mm">Carbon neutrality is an important concept in global climate change governance. Seagrass beds rank among the most productive autotrophic ecosystems on the planet, and are receiving increasing attention as globally-significant hotspots of organic carbon (“blue carbon”) sequestration. The blue carbon stored in seagrass beds has important implications for climate change mitigation. The protection of seagrass beds will also protect their organic carbon sequestration potential, consequently helping to achieve the goal of carbon neutrality. Unfortunately, about 29% of the world’s seagrass beds have been destroyed, with a loss rate of 7% a⁻¹ since 1990, mostly due to eutrophication. The organic carbon sequestration potential of seagrass beds could be influenced by the subsequent changes in organic carbon composition, and microbial transformation processes. We systematically reviewed the relevant local and international research to summarize the composition and microbial transformation of organic carbon and its responses to eutrophication. Organic carbon is present in various forms in seagrass beds, and can be roughly divided into primary producer living biomass carbon, litter organic carbon, water organic carbon, and sediment organic carbon according to its storage area. Organic carbon can also be divided into labile organic carbon (LOC), which is susceptible to microbial decomposition, and recalcitrant organic carbon (ROC), which is resistant to microbial decomposition. The total ROC (cellulose and lignin) content in seagrass is present in the range of <sc>153−561 mg/g,</sc> and accounts for more than 28.7% of the organic carbon in the seagrass plants. The ROC content of seagrass plants is affected by the species, morphology, tissue and organ types, and climatic zones. In the water column, color dissolved organic matter (CDOM) and neutral sugars are indicators of LOC, while the lignin phenol and humic-like fractions of fluorescent dissolved organic matter (FDOM) are potential tracers of ROC. The DOM in water can be divided into dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and dissolved organic phosphorus (DOP). The DOC/DON and DOC/DOP ratios are used to reflect DOC lability and microbial bioavailability, with high DON and DOP concentrations indicating high DOC lability. In sediments, extractable organic carbon and microbial biomass carbon are important indicators of LOC, while aromatic hydrocarbons and alkanes are indicative of recalcitrant components. There are significant differences in the sediment organic carbon contents of temperate and tropical regions. Microorganisms play a vital role in the transformation of organic carbon. There are geographic differences in microbial composition, which are mainly influenced by the available habitats and climate zones, but there are no differences between seagrass species within a fine-scale seagrass bed. Different microorganisms have different decomposition capacities. <italic>R</italic>-strategist microbes, including Clostridiales<italic> </italic>and<italic> </italic>Gammaproteobacteria, are able to rapidly decompose LOC, while <italic>k</italic>-strategists, such as Verrucomicrobiae<italic> </italic>and Anaerolinae, can break down the more recalcitrant compounds. There is a succession of <italic>r</italic>- to <italic>k</italic>-strategists microbes during the decomposition of fresh organic matter (including fresh seagrass litter, DOC, and SOC). Eutrophication may lead to the transformation of the community structure of primary producers in seagrass beds from seagrass to macroalgae, which will increase the input of labile carbon. This consequently causes an increase in LOC in the plant biomass, water column, and sediments, but a decrease in ROC. The nutrient loading can affect the microbial community structure and enzyme activity, which will affect the microbial transformation of organic carbon. Furthermore, nutrient and LOC inputs may induce a “priming effect” that promotes the remineralization of stored organic carbon. Several future research directions for determining the transformation of seagrass beds and their organic carbon were proposed. (1) Extensive studies of the organic carbon components (LOC and ROC) in seagrass beds are required. (2) There is a need to better understand the composition, function, and gene expression of microbial communities in seagrass beds. (3) The eutrophication mechanisms in microbial communities and the related extracellular enzyme activities need to be determined. (4) The response of the organic matter decomposition process to nutrient loading and the interaction of nutrients and algae need to be studied. There is also a need to strengthen local research on the carbon storage potential of seagrass beds to mitigate global climate change and provide theoretical support for achieving carbon neutrality.

Measuring pollution based on total petroleum hydrocarbons and total organic carbon in Tigris River, Maysan Province, Southern Iraq

In the current study, the concentrations of total petroleum hydrocarbons (TPHs) in water and total organic carbon content in sediments were measured. A number of environmental factors, including water temperature, dissolved oxygen, pH, electrical conductivity, nitrates, and phosphates, have also been measured in the Tigris River deposits and in three selected stations on its course in Maysan Province in southern Iraq during the months of November, 2014, December, 2014, and January, 2015. The highest temperature, 25 °C, was recorded at Ali Al Gharbi District Station (St1) in November, while the lowest temperature, 15°C, was recorded at Al-Amara District Station (St2) in January. Moreover, the highest value of dissolved oxygen, 9.1 mg L-1, was recorded in St1 in January, while the lowest value, 7.5 mg L-1, was recorded at the same station in December. All pH values were within the baseline trend for the duration of the study, with the highest level, 7.8, recorded at St2 in November, while the lowest level, 7.05, at Al Majar Al-Kabir District Station (St3) in the same month. The highest value for electrical conductivity was 2416 μs cm-1 at Al-Amara District Station in November, while the lowest value was 2000 μs cm-1 at the same station in December. The highest concentration of nitrate ion, 6.25 mg L-1, was recorded at St2 in November, while the lowest value, 3.8 mg L-1,at St1 in December. Moreover, the highest phosphate value, 0.59 mg L-1, was recorded at St2 in January, while the lowest, 0.049 mg L-1, at St3 in November. The highest rate of total organic carbon content was 2.15%, recorded at St2 in November, while the lowest, 1.7%, at St1 in the same month. The highest concentration of TPHs in the water was 5.22, recorded at St2 in January, while the lowest, 2.85, at St1 in November. The present study concluded that St2 was heavily contaminated with organic matter. This station had the highest concentration of total petroleum hydrocarbons, which is mainly due to the increased population density beside the station, leading to increased human activities and the introduction of various wastes. These wastes contain nutrients and organic compounds, such as compounds containing petroleum derivatives, discharging to the water and sediment. Furthermore, there was a positive correlation between the organic carbon rate (%) and the concentration of petroleum hydrocarbons.

Chronological records of sediment organic carbon at an entrance of Dongting Lake: Response to historical meteorological events

Lake sediments are the products of soil erosion and are strongly influenced by climate variability, particularly extreme meteorological events. Sediment organic carbon (SOC) can reflect environmental changes that affect sediment transport. However, the response of SOC chronological records to major meteorological events is relatively unknown. This study explored the chronological regularity of SOC and verified its variations using major historical meteorological events. Based on three sediment profiles with a depth of 230 cm at the Yuan River entrance to the West Dongting Lake (Hanshou entrance), the SOC chronology was reconstructed by employing the sedimentation rates calculated by 137Cs and 210Pb. The sedimentary environment then was interpreted via comparisons and quantitative analysis. The grain distribution and the S-shaped distribution of SOC reflected the general deposition regularity of organic carbon in lake sediments, which gradually stabilized with depth. The average sedimentation rates based on 137Cs and 210Pb were 1.310 and 1.319 cm a−1, respectively. Accordingly, SOC records covered the past 76 years via dating (0–100 cm), during which the SOC content first increased and subsequently stabilized. By comparing the data with the occurrence of 11 major historical meteorological events, we found that SOC generally increased after these events. Moreover, the frequent occurrence of meteorological events stabilized the SOC content. Severe floods had a greater impact on SOC content than severe droughts, causing SOC to change by up to 20.24% and 8.77%, respectively. Our findings suggest that major historical meteorological events can verify SOC chronological records, thereby highlighting their significant impacts on organic carbon variations in sediments.

Fine-scale spatial variability in organic carbon in a temperate mangrove forest: Implications for estimating carbon stocks in blue carbon ecosystems

Mangrove ecosystems have the potential to store large amounts of carbon but detailed studies on the fine scale spatial variability of biomass components and sediment organic carbon (SOC) and their relationships are lacking. Here we investigated the fine-scale spatial variation of SOC, aboveground and belowground biomass using systematic grid sampling in a temperate Avicennia marina ((Forssk.) Vierh) forest in Australia. We estimated aboveground biomass in a 9 × 9 sampling grid within a 0.16 ha plot and measured SOC, fine root biomass and necromass down to 1 m at 81 sampling points in an A. marina forest in Western Port Bay near Melbourne, Australia. We detected large differences in all measured carbon pools. SOC increased from low to high intertidal position but showed no consistent trend with depth. Aboveground biomass carbon was highly variable (mean 84 ± 56 Mg C ha−1), and showed no consistent trends with intertidal position. The average total organic carbon stock at the study site was 207 ± 80 Mg C ha−1. Aboveground biomass contributed 41% and coarse roots around 6% to the total carbon content of the forest. The bulk of organic carbon in the ecosystem was SOC (53%) and necromass was an important contributor to SOC. Aboveground biomass was a poor predictor of all belowground carbon pools. Our data indicate that 43 sediment cores would be required to determine mean SOC content at the level required by international carbon accounting standards. The high spatial variability of all carbon stocks in the system indicates that current sampling strategies for SOC need to be revised in order to improve predictions of the amount of carbon stored in blue carbon ecosystems.

Activity and structure of methanogenic microbial communities in sediments of cascade hydropower reservoirs, Southwest China

Freshwater reservoirs are an important source of the greenhouse gas methane (CH4). However, little is known about the activity and structure of microbial communities involved in methanogenic decomposition of sediment organic matter (SOM) in cascade hydropower reservoirs. In this study, we targeted on sediments of three cascade reservoirs in Wujiang River, Southwest China. Our results showed that the content of sediment organic carbon (SOC) was between 3% and 11%, and it's positively correlated with both C/N ratio and recalcitrant organic carbon content of SOM. Meanwhile, SOC content was positively correlated with CH4 production rates but had no significant correlation with total CO2 production rates of the sediments, when rates were normalized to sediment volume. Resultantly, the sediment anaerobic decomposition rates hardly significantly increase along with the SOC content. These results suggested that the terrestrial organic matter accumulated after damming stimulated CH4 production from the reservoir sediments even though its decomposition rate was limited. Meantime, high throughput sequencing of 16S rRNA genes indicated that not only the hydrogenotrophic and acetoclastic, but also the methylotrophic methanogens (Methanomassiliicoccus) are abundant in the reservoir sediments. Moreover, metagenomic sequencing also suggested that methylotrophic methanogenesis are potentially important in the sediment of cascade reservoirs. Finally, the hydraulic residence time of the reservoir could be the key controlling factor of the structures of bacterial and archaeal communities as well as the CH4 production rates of the reservoir sediments.

Changes in Sediment Organic Carbon Accumulation under Conditions of Historical Sea-Level Rise, Southeast Saline Everglades, Florida, USA

Mangroves can store more sediment organic carbon (SOC) than freshwater and salt marshes. Understanding how mangroves have responded to historical sea-level rise (SLR) is fundamental to assessing their resilience and capacity to store carbon as SLR accelerates. We quantified landscape-level temporal and spatial trends in historical coastal wetland sediment accumulation and associated SOC content (i.e., storage) along coastal-to-inland gradients in Southeast Florida. The observed trends were transgressive and attributed to the historical rise in sea level. Our results indicate an overall significant increase in the SOC content of the historic wetland sediment succession caused by the vertical accumulation and landward migration of carbon-rich mangrove-dominated plant communities (mean = 0.08 g cm−3) into and over carbon-poor wet prairie plant communities (mean = 0.02 g cm−3). The observed historical increase in SOC is predicted to diminish over time as the difference between rates of SLR and vertical sediment accumulation increases and because the landward migration of mangrove-dominated plant communities is now obstructed by a shore-parallel flood-control levee. These results are likely to unfold in other low-latitude coastal wetlands where they are sandwiched between rising seas and an urbanized landscape.

Effects of marine pollution, climate, and tidal range on biomass and sediment organic carbon in Chinese mangrove forests

Mangroves are among the most important carbon reservoirs for atmospheric CO2. Nonetheless, how the biomass and sediment organic carbon (SOC) of mangrove forests are affected by marine pollution, in addition to climate and tidal range, on a regional scale is unknown. This study aimed to assess how spatial patterns of biomass and SOC could be influenced by the climate, tidal range, and marine pollution in China’s mangrove forests. The result showed that aboveground biomass (AGB), surface SOC content (SOCC), and SOC density (SOCD) showed clear latitudinal change patterns on a regional scale and decreased in a non-linear manner with increasing latitude. Correlation analysis and principal component analysis (PCA) indicated that latitudinal variation in AGB, SOCC, and SOCD was mainly regulated by temperature-related indicators. However, AGB, SOCC, and SOCD were not found to be correlated to annual precipitation. Besides, the tidal range was found to be negatively correlated to biomass and SOC content/stock. Tidal range is one important abiotic predictor used to understand the latitudinal patterns of mangrove biomass and SOC dynamics. Correlation analysis and PCA revealed that mangrove biomass and SOC content/stock were negatively affected by heavy metal pollution, and they were disproportionately negatively correlated to marine heavy metal concentrations in the coastlines neighboring mangrove forests. Environmentally-sound technology should be adapted to prevent, control, and remediate heavy metal pollution to increase carbon storage in China’s mangrove forests. Mangrove biomass and SOC content/stock were also found to be negatively related to the suspended solid concentration in the coastlines neighboring mangrove forests. In contrast, vegetation biomass was found to be positively correlated to ammonia nitrogen content. However, biomass was found to be not correlated to nitrate-nitrogen, nitrites-nitrogen, inorganic forms of nitrogen, and non-ionic ammonia. Additional studies are needed to confirm the mechanisms by which different forms of nitrogen enrichment affect biomass storage.

Insight into the adsorption mechanisms of ionizable imidazolinone herbicides in sediments: Kinetics, adsorption model, and influencing factors

To reveal the adsorption mechanisms of imazamox, imazapic, and imazethapyr on sediment and batch experiments were carried out in this study. The adsorption kinetics of three imidazolinone herbicides on sediment were accurately described by the pseudo-second-order kinetic model(R2 > 0.9004). The values of adsorption capacity (Qe.cal) were ranged from 0.0183 to 0.0859 mg kg−1 for three herbicides. Adsorption equilibrium was reached within 24 h for three herbicides on sediment, and well fitted by the Freundlich model(R2 > 0.9561). The KF of values for adsorption obtained sediment samples were ranged from 0.2501 to 1.322 L1/n mg1-1/n kg−1for three herbicides. These results indicated that intraparticle diffusion and external mass transport were the main rate controlling steps of the adsorption of herbicides on sediment and that the chemical adsorption was dominant during the adsorption processes. The calculated hysteresis coefficient H were 0.9422,0.7877 and 0.744 for imazmox, imazapic and imazethapyr in raw sediment, respectively, indicating that there is a hysteresis in desorption. The influences of solution pH and sediment organic carbon content on the imidazolinone herbicide adsorption behaviors were also examined. Which shown that the adsorption process for herbicides was highly pH-dependent and adsorption efficiency was closely related to the organic matter content of the sediment, suggesting that electrostatic interactions played crucial roles in the adsorption behavior between sediment and imidazolinone herbicides, and the herbicides were mostly absorbed by the amorphous materials of sediment. These research findings are important for assessing the fate and transport of imidazolinone herbicides in water–sediment systems.

Integrated analysis of petroleum biomarkers and polycyclic aromatic compounds in lake sediment cores from an oil sands region.

We examined polycyclic aromatic compounds (PACs) and petroleum biomarkers (steranes, hopanes, and terpanes) in radiometrically-dated lake sediment cores from the Athabasca oil sands region (AOSR) and the Peace-Athabasca Delta (PAD) region in Alberta (Canada) to determine whether contributions from petroleum hydrocarbons have changed over time. Two floodplain lakes in the PAD (PAD 30, PAD 31) recorded increased flux of alkylated PACs and increased petrogenic (petroleum-derived) hydrocarbons after ∼1980, coincident with a decline of sediment organic carbon content and a rise of bulk sedimentation rate, likely due to increased Athabasca River flow. A large expansion of upstream oilsands mining, upgrading, and refining may also have contributed to the observed shift to more petrogenic hydrocarbons to sediments since the 1980s. Alkylated PAC flux increased in the floodplain lake analyzed within the AOSR (Saline Lake) since the 1970s-1980s, coincident with a sharp rise in sediment organic carbon content and increased contributions of petrogenic hydrocarbons. These changes identify increased supply of petrogenic PACs occurred as Athabasca River floodwaters waned, and may implicate aerial contributions of petrogenic hydrocarbons from oilsands activity. PACs and petroleum biomarkers (steranes, hopanes, and terpanes) in sediment cores from Saline Lake, PAD 30 and PAD 31 revealed a predominance of petrogenic hydrocarbons in these lakes. In contrast, we recorded minimal petrogenic hydrocarbons in the reference lakes outside the surface minable area of the AOSR and PAD (Mariana Lake and BM11), though we noted slight increases in petrogenic contributions to modern (2010-2016) sediments. We show how a combined analysis of PACs and petroleum biomarkers in sediments is useful to quantify petrogenic contributions to lakes with added confidence and highlight the potential for petroleum biomarkers in lake sediment cores as a novel and effective method to track petroleum hydrocarbons in lake sediment.

Assessing the role of the “estuarine filter” for emerging contaminants: pharmaceuticals, perfluoroalkyl compounds and plasticisers in sediment cores from two contrasting systems in the southern U.K.

The environmental occurrence, fate and ecotoxicity of emerging contaminants (ECs) has been the subject of increasing research, policy and public concern over the past two decades. While a wide range of publications have examined the environmental persistence and sediment/soil interactions of ECs following their discharge into aquatic environments, the extent to which ECs are sequestered in estuarine sediments, and the impact of this on their environmental persistence and supply to the ocean, in comparison remains unclear. This Article examines the environmental concentrations of seven, relatively water-soluble and environmentally mobile, ECs (including pharmaceuticals, perfluoroalkyl compounds, and plasticisers) in dated intertidal saltmarsh cores from two contrasting estuarine sites in the southern U.K. (one heavily urbanised/industrial, the other non-urbanised). Mean sediment EC concentrations are similar in both estuarine systems (in the range 0.1 (acetaminophen) to 17 (4-hydroxyacetophenone) ng/g dry weight). Despite their variable reported Log Kow values (from ca. 0.5 to > 7), the ECs are all apparently mobile in the marsh systems studied, and where subsurface concentration maxima are present these most likely relate to local flushing or diffusive processes and cannot be clearly linked to likely input trends or changes in sediment geochemistry (including sedimentary organic carbon content). The “estuarine filter” here, at least with respect to intertidal saltmarsh sediments, shows reduced potential to sequester the seven ECs examined and mediate their supply to coastal and shelf environments.