The Stable Carbon Isotopic Compositions of n-Alkanes in Sediments of the Bohai and North Yellow Seas: Implications for Sources of Sedimentary Organic Matter

Stable carbon isotopic compositions of n-alkanes in surface sediments of the Bohai and North Yellow Seas were investigated to elucidate sources of sedimentary organic matter in these seas. The long-chain n-alkanes in surface sediments are predominantly long-chain C27, C29, and C31 types, with obvious odd carbon predominance. The δ13 C values of long-chain n-C27, n-C29, and n-C31 alkanes are-30.8% ± 0.5‰,-31.9% ± 0.6‰, and-32.1% ± 1.0‰, respectively, within the range of n-alkanes of C3 terrestrial higher plants. This suggests that sedimentary n-alkanes are derived mainly from terrestrial higher plants. Compound-specific carbon isotopic analysis of long-chain n-alkanes indicates that C3 terrestrial higher plants predominate(64%–79%), with angiosperms being the main contributors. The n-alkane δ13 C values indicate that mid-chain n-alkanes in sediments are derived mainly from aquatic emergent macrophytes, with significant petroleum pollution and bacterial degradation sources for short-chain n-alkanes.

Carbon and nitrogen isotopes analysis and sources of organic matter in surface sediments from the Sanggou Bay and its adjacent areas, China

Naturally existing stable carbon and nitrogen isotopes are important in the study of sedimentary organic matter sources. To identify the sources of sedimentary organic matter in Sanggou Bay and its adjacent areas, which is characterized by high-density shellfish and seaweed aquaculture, the grain size, organic carbon （OC）, total nitrogen （TN）, carbon and nitrogen isotopic composition （δ13C andδ15N） of organic matter in the surface sediment were determined. The results showed that, in August, sedimentary OC and TN ranged from 0.17% to 0.76% and 0.04% to 0.14%, respectively. In November, OC and TN ranged from 0.23% to 0.87% and 0.05% to 0.14%, respectively. There was a significant positive correlation between OC and TN （R=0.98, P＆lt;0.0001）, indicating that OC and TN were homologous. In August, theδ13C andδ15N of organic matter varied from -23.06‰ to -21.59‰ and 5.10‰ to 6.31‰, respectively. In November,δ13C andδ15N ranged from -22.87‰ to -21.34‰ and 5.13‰ to 7.31‰, respectively. This study found that the major sources of sedimentary organic matter were marine shellfish biodeposition, seaweed farming, and soil organic matter. Using a three-end-member mixed model, we estimated that the dominant source of sedimentary organic matter was shellfish biodeposition, with an average contribution rate of 65.53% in August and 43.00% in November. Thus, shellfish farming had a significant influence on the coastal carbon cycle.

Organic carbon and nitrogen isotopes in surface sediments from the western Arctic Ocean and their implications for sedimentary environments

Surface sediments from the Chukchi Sea and adjacent arctic deep sea were investigated for organic carbon and nitrogen isotopes （in δ13Corg and δ15Norg） as well as biogeni＇c silica （BSiO2）. δ13Corg and δ15Norg values of surface sediments in the study area fall between the end-member values of marine and terrestrial organic matter from the surrounding lands and seas, their variations reflect the changes of marine productivity and terrestrial supply in the study area. BSiO2 shows a similar distribution pattern with δ13Corg and δ15Norg, and can be used as an indicator of marine productivity. In the central-west Chukchi Sea and the Chukchi Rise, sediments have higher δ13Corg, δ15Norg and BSiO2 values, indicating the region has high marine productivity influenced by the nutrient-rich branches of the Pacific waters. In the coastal zone off northwestern Alaska, δ13Corg and δ15Norg values become lighter, indicating a weakening marine productivity and an increasing terrigenous supply due to the effects of the least nutrient-rich branch of the Pacific waters. In the north and the northeast of the study area （including the Chukchi Plateau, the Canada Basin and the Beaufort shelf）, δ13Corg, δ15Norg and BSiO2 have the lowest values, and the terrigenous organic matter becomes dominant in surface sediments because this region has the longest ice-covered duration, the least nutrient-rich seawater and the increasing supply of terrestrial materials from the Mackenzie River and the northern Alaska under the action of the clockwise Beaufort gyre. Because the subarctic Pacific waters are continuously discharged into the central basin of the Arctic Ocean through the study area, the nutrient pool in the Chukchi Sea can be considered as a typical open system, the ratio of δ15Norg to BSiO2 content show some tracers that the level of nutrient utilization is contrary to nutrient supply and marine productivity formed in seawater.

Organic Carbon Isotope Geochemistry of the Neoproterozoic Doushantuo Formation,South China

The Neoproterozoic Doushantuo Formation on the Yangtze Platform, South China, documents a sedimentary succession with different sedimentary facies from carbonate platform to slope and to deep sea basin, and hosts one of the world-class phosphorite deposits. In these strata, exquisitely preserved fossils have been discovered： the Weng＇an biota. This study presents carbon isotope geochemistry which is associated paired carbonate and organic matter from the Weng＇an section of a carbonate platform （shelf of the Yangtze Platform, Guizhou Province） from the Songtao section and Nanming section of a transition belt （slope of the Yangtze Platform, Guizhou Province） and from the Yanwutan section （basin area of the Yangtze Platform, Hunan Province）. Environmental variations and bio-events on the Yangtze Platform during the Late Neoproterozoic and their causal relationship are discussed. Negative carbon isotope values for carbonate and organic carbon （mean δ^13Corg = -35.0‰） from the uppermost Nantuo Formation are followed by an overall increase in δ^13C up-section. Carbon isotope values vary between -9.9‰ and 3.6‰ for carbonate and between -35.6‰ and -21.5‰ for organic carbon, respectively. Heavier δ^13Ccarb values suggest an increase in organic carbon burial, possibly related to increasing productivity （such as the Weng＇an biota）. The δ^13C values of the sediments from the Doushantuo Formation decreased from the platform via the slope to basin, reflecting a reduced environment with minor dissolved inorganic carbon possibly due to a lower primary productivity. It is deduced that the classical upwelling process, the stratification structure and the hydrothermal eruption are principally important mechanisms to interpret the carbon isotopic compositions of the sediments from the Doushantuo Formation.

Sources of particulate organic matter in the Chukchi and Siberian shelves: clues from carbon and nitrogen isotopes

The stable isotopic composition(δ13C andδ15N)and carbon/nitrogen ratio(C/N)of particulate organic matter(POM)in the Chukchi and East Siberian shelves from July to September,2016 were measured to evaluate the spatial variability and origin of POM.Theδ13CPOC values were in the range of−29.5‰to−17.5‰with an average of−25.9‰±2.0‰,and theδ15NPN values ranged from 3.9‰to 13.1‰with an average of 8.0‰±1.6‰.The C/N ratios in the East Siberian shelf were generally higher than those in the Chukchi shelf,while theδ13C andδ15N values were just the opposite.Abnormally low C/N ratios(<4),lowδ13CPOC(almost−28‰)and highδ15NPN(>10‰)values were observed in the Wrangel Island polynya,which was attributed to the early bloom of small phytoplankton.The contributions of terrestrial POM,bloom-produced POM and non-bloom marine POM were estimated using a three end-member mixing model.The spatial distribution of terrestrial POM showed a high fraction in the East Siberian shelf and decreased eastward,indicating the influence of Russian rivers.The distribution of non-bloom marine POM showed a high fraction in the Chukchi shelf with the highest fraction occurring in the Bering Strait and decreased westward,suggesting the stimulation of biological production by the Pacific inflow in the Chukchi shelf.The fractions of bloom-produced POM were highest in the winter polynya and gradually decreased toward the periphery.A negative relationship between the bloom-produced POM and the sea ice meltwater inventory was observed,indicating that the net sea ice loss promotes early bloom in the polynya.Given the high fraction of bloom-produced POM,the early bloom of phytoplankton in the polynyas may play an important role on marine production and POM export in the Arctic shelves.

Organic carbon isotope and pollen evidence for mangrove development and response to human activity in Guangxi(Southwest China) over the last 140 years

Mangrove degradation must reduce carbon sequestration in recent years, thereby aggravating global warming.Thus, short-term impacts of human activity on mangrove ecosystems are cause for concern from local governments and scientists. Mangroves sediments can provide detailed records of mangrove species variation in the last one hundred years, based on detailed 210 Pb data. The study traced the history of mangrove development and its response to environmental change over the last 140 years in two mangrove swamps of Guangxi, Southwest China. Average sedimentation rates were calculated to be 0.48 cm/a and 0.56 cm/a in the Yingluo Bay and the Maowei Sea, respectively. Chemical indicators（δ13Corg and C：N） were utilized to trace the contribution of mangrove-derived organic matter（MOM） using a ternary mixing model. Simultaneous use of mangrove pollen can help to supplement some of these limitations in diagenetic/overlap of isotopic signatures. We found that vertical distribution of MOM was consistent with mangrove pollen, which could provide similar information for tracing mangrove ecosystems. Therefore, mangrove development was reconstructed and divided into three stages： flourishing, degradation and re-flourishing/re-degradation period. The significant degradation, found in the period of 1968–1998 and 1907–2007 in the Yingluo Bay and the Maowei Sea, respectively, corresponding to a rapid increase of reclamation area and seawall length, rather than climate change as recorded in the region.

Study the Changes in Soil Organic Carbon of Rice-Maize Cropping System in the Top Layer of Alluvisol Soil in Dan Phuong: A Study of C-13 Stable Isotope Composition (<i>&delta;</i>¹³C)

In this study, the experiments on field were conducted to examine the change in the content of soil organic carbon (SOC), its C-13 stable isotope composition (δ 13C) and some main physical, chemical parameters (soil moisture, pH, soil density, content of humic, fulvic, total N, total P, total K) in alluvial soil of Dan Phuong region—Vietnam at a depth of 0 - 30 cm when we changed the regime from 2 maize -1 rice crop to 2 rice - 1 maize crop per 1 year. In addition to analyzing the main parameters in soil, C content and its δ 13C value in parts of rice and maize (root, stem and leaf) were also analyzed to assess the contribution of plant residues on soil organic carbon content after harvest. The experiment was carried out in 2016-2017 on the field with the traditional farming method of local farmers along with the tropical monsoon weather conditions of the North-Vietnam. The results showed that SOC had positive correlation with total N, total P parameters and negative correlation with δ 13C values of soil samples at two layers (0 - 15 cm and 15 - 30 cm). The average of total dry biomass (stem, stump + roots and leaf parts) per 1 rice and 1 maize crop was 10.64 Mg/ha and 9.09 Mg/ha, respectively. The average of δ 13C value of rice (C3 plant) was -29.78‰ and its value of maize (C4 plant) was -12.61‰. The new plant (rice) contributes to the total soil organic carbon content from 11.31% to 44.14% at the 0 - 15 cm layer and from 6.55% to 11.31% at the 15 - 30 cm layer in one-year experiment period.

Organic carbon content and carbon isotope variations across the Permo-Triassic boundary in the Gartnerkofel-1borehole, Carnic Alps, Austria

The Gartnerkofel borehole is one of the most thoroughly studied and described Permo-Triassic sections in the world. Detailed bulk organic carbon isotope studies show a negative base shift from-24% to-28% in the Latest Permian which latter value persists into the Earliest Triassic after which it decreases slightly to-26%. Two strongly negative peaks of [-38% in the Latest Permian and a lesser peak of-31% in the Early Triassic are too negative to be due to a greater proportion of more negative organic matter and must be due to very negative methane effects. The overall change to more negative values across the Bulla/Tesero boundary fits the relative rise in sea level for this transition based on the facies changes. A positive shift in organic carbon isotope values at the Late Permian Event Horizon may be due to an increase in land-derived organic detritus at this level—a feature shown by allTethyan Permo-Triassic boundary sections though these other sections do not have the same values. Carbonate carbon isotope trends are similar in all sections dropping by2–3 units across the Permo-Triassic boundary. Gartnerkofel carbonate oxygen values are surprisingly, considering the ubiquitous dolomitization, compatible with values elsewhere and indicate reasonable tropical temperatures of 60 °C in the Latest Permian sabkhas to 20–40 °C in the overlying marine transition beds. Increased landderived input at the Late Permian Event Horizon may be due to offshore transport by tsunamis whose deposits have been recognized in India at this level.

The Chang 7 member of the upper Triassic in the southwest Ordos Basin:Carbon isotope studay of dispersed organic matter and its paleoclimate significance

The carbon isotope δ 13C value of dispersed organic matter in the Upper Triassic sediments in the Ordos basin is （-24.5 to -26.6） ×10^-3 with the carbon being derived from C3-1ike pleustons. The paleoclimate of the Late Triassic, especially during the deposition of the Chang 7 member, was characterized by a hot and humid climate. It underwent four small climate cycles from humid and warm to humid and hot.

Stable Carbon Isotope and Long-Chain Alkane Compositions of the Major Plants and Sediment Organic Matter in the Yellow River Estuarine Wetlands

Elemental(TOC,TN,C/N)and stable carbon isotopic(δ^13C)compositions and long-chain alkane(n C16-38)concentrations were measured for eight major plants and a sediment core collected from the Yellow River estuarine wetlands.Our results indicate that both C3(-25.4‰to-29.6‰)and C4(-14.2‰to-15.0‰)plants are growing in the wetlands and C3 plants are the predominant species.The biomass of the wetland plants had similar organic carbon(35.5-45.8%)but very different organic nitrogen(0.35-4.15%)contents.Both C3 and C4 plants all contained long-chain alkanes with strong odd-to-even carbon numbered chain predominance.Phragmites australis,a dominant C3 plant contained mainly n C29 and n C31 homologues.Aeluropus littoralis,an abundant C4 plant were concentrated with n C27 and n C29 homologues.Organic matter preserved in the Yellow River estuarine sediments showed strong terrestrial signals(C/N=11-16,δ^13C=-22.0‰to-24.3‰).The distribution of long-chain n-alkanes in sediments also showed strong odd-to-even carbon chain predominance with n C29 and n C31 being the most abundant homologues.These results suggest that organic matter preserved in the Yellow River estuarine sediments were influenced by the wetland-derived organic matter,mainly C3 plants.The Yellow River estuarine wetland plants could play important role affecting both the carbon and nutrient cycling in the estuary and adjacent coastal waters.

Application o f 210 Pb, Carbon and Nitrogen Isotope in Tracing of Changes and Burial Effect of Endogenous and Terrigenous Organic Matter in the Bering Sea over the Past 100 Years

By using the multi-tube sediment samples collected from NB01 station in the Bering Sea during the period of the fourth Chinese Arctic research expedition in 2010,as well as the dating technique of radioisotope ^(210)Pb in sedimentary strata,based on the exponential decay trend of ^(210)Pb exwith the column sample depth,relative stable modern sedimentary environment in the investigation area was reflected. The results show that the deposition rate of modern marine sediment S was 0. 27 cm/a,and correlation coefficient R was 0. 96( n = 17),while time span was 107 a(1903-2010). Meanwhile,carbon,nitrogen and isotopes were used to trace the sources of materials in the Bering Sea. It is found that the content of organic carbon and nitrogen in the column samples from NB01 station in the Bering Sea was 1. 18%-1. 80% and 0. 16%-0. 28% respectively,and C/N ratio ranged from 5. 13 to 8. 31. Total organic carbon( TOC) and total organic nitrogen( TON) were preserved well in sedimentary strata and had good consistency,showing that sources of organic matter were consistent. Moreover,their changes positively correlated with^(210)Pb. Organic carbon isotope( δ13 C) ranged from-22. 45‰ to-21. 82‰,and its changing trend was similar to that of C/N ratio; organic nitrogen isotope(δ15 N) varied from 7. 53‰ to 8. 54‰,indicating that organic matter was mainly from remaining marine organisms after being decomposed,into which a certain quantity of terrigenous materials were mixed. In the 100 years,the overall trend of terrigenous materials became increasingly obvious,showing that the input and burial of organic carbon from seas and land in the Bering Sea were changing. According to the burial rate of surface sediment and content of organic carbon,the apparent burial flux of sedimentary organic carbon in the column sample from NB01 station in the Bering Sea was estimated,about 1 450 mmol C/( m^2·a). It is suggested that the high burial flux of sedimentary organic carbon in the regions was mainly related to the high primary productivity of the water body,the high output efficiency of organic carbon in the photic zone,favorable preservation and metabolic mechanism of organic matter,and high deposition rate.

Paleoclimatic Change Inferred from Carbon Isotope Composition of Organic Matter in Sediments of Dabusu Lake, Jilin Province, China

Study on the organic compounds and stable isotope composition of a sediment section in Dabusu Lake revealed that the organic materials in the sediments came mainly from terrestrial plants brought into the lake by runoff. The δ 13 C of the organic materials had high values during warm-dry climatic stages and decreased in cold-wet stages. Analysis of data on carbonate content and 14 C age showed that the lake basin had experienced several wet-cold and warm-dry climatic cycles since 15000 a BP. Since 6700 a BP, the climate reached a relatively stable warm-dry stage, so that the lake water was gradually condensed and finally a saline lake was formed.

Organic Carbon Isotopic Evolution during the Ediacaran-Cambrian Transition Interval in Eastern Guizhou,South China: Paleoenvironmental and Stratigraphic Implications

Secular variations of carbon isotopic composition of organic carbon can be used in the study of global environmental variation, the carbon cycle, stratigraphic delimitation, and biological evolution, etc. Organic carbon isotopic analysis of the Nangao and Zhalagou sections in eastern Gnizhou reveals a negative excursion near the Precambrian-Cambrian boundary that correlates with a distinct carbonate carbon isotopic negative excursion at this boundary globally. Our results also demonstrate that several alternating positive and negative shifts occur in the Meishucunian, and an obvious negative anomaly appears at the boundary between the Meishucunian and Qiongzhusian. The isotope values are stable in the middle and lower parts but became more positive in the upper part of the Qiongzhusian. Evolution of organic carbon isotopes from the two sections in the deepwater facies can be well correlated with that of the carbonate carbon isotopes from the section in the shallow water facies. Integrated with other stratigraphic tools, we can precisely establish a lower Cambrian stratigraphic framework from shallow sheff to deep basin of the Yangtze Platform.

Spatial distributions of organic carbon and nitrogen and their isotopic compositions in sediments of the Changjiang Estuary and its adjacent sea area

The spatial distribution patterns of total organic carbon and total nitrogen show significant correlations with currents of the East China Sea Shelf. Corresponding to distributions of these currents, the study area could be divided into four different parts. Total organic carbon, total nitrogen, and organic carbon and nitrogen stable isotopes in sediments show linear correlations with mean grain size, respectively, thus ＂grain size effect＂ is an important factor that influences their distributions. C/N ratios can reflect source information of organic matter to a certain degree. In contrast, nitrogen stable isotope shows different spatial distribution patterns with C/N and organic carbon stable isotope, according to their relationships and regional distributions. The highest contribution （up to 50%） of terrestrial organic carbon appears near the Changjiang Estuary with isolines projecting towards northeast, indicating the influence of the Changjiang dilution water. Terrestrial particulate organic matter suffers from effects of diagenesis, benthos and incessant inputting of dead organic matter of plankton, after depositing in seabed. Therefore, the contribution of terrestrial organic carbon to particulate organic matter is obviously greater than that to organic matter in sediments in the same place.

Stable carbon isotopic composition of soil organic matter in the karst areas of Southwest China

This study dealt with the distribution characteristics of soil organic carbon (SOC) and the variation of stable carbon isotopic composition (δ13C values) with depth in six soil profiles, including two soil types and three vegetation forms in the karst areas of Southwest China. The δ13C values of plant-dominant species, leaf litter and soils were measured using the sealed-tube high-temperature combustion method. Soil organic carbon contents of the limestone soil profiles are all above 11.4 g/kg, with the highest value of 71.1 g/kg in the surface soil. However, the contents vary between 2.9 g/kg and 46.0 g/kg in three yellow soil profiles. The difference between the maximum and minimum δ13C values of soil organic matter (SOM) changes from 2.2‰ to 2.9‰ for the three yellow soil profiles. But it changes from 0.8‰ to 1.6‰ for the limestone soil profiles. The contrast research indicated that there existed significant difference in vertical patterns of organic carbon and δ13C values of SOM between yellow soil and limestone soil. This difference may reflect site-specific factors, such as soil type, vegetation form, soil pH value, and clay content, etc., which control the contents of different organic components comprising SOM and soil carbon turnover rates in the profiles. The vertical variation patterns of stable carbon isotope in SOM have a distinct regional character in the karst areas.

Distribution of organic carbon in sediments and its influences on adjacent sea area in the turbidity maximum of Changjiang Estuary in China

Distributions and sources of total organic carbon （TOC）in seabed sediments and their implications for hydrodynamics are analyzed, in the turbidity maximum of the Changjiang Estuary. Ecology ecoenvironmental effects of estuary water on the continuously increasing terrigenous organic carbon from the Changjiang River are also explored through variations of organic carbon content and water quality indicators. Results show that, hydrodynamics exert important influences on distributions of organic carbon in the tur- bidity maximum of Changjiang Estuary. For their redistribution effect of terrigenous organic carbon within the moving layer in the whole region, variations from land to sea are not indicated by surficial and vertical average values of TOC and total nitrogen （TN） contents in core sediment, as well as organic stable carbon isotopes in surface sediments. However, on the long-time scale, the trend of terrigenous organic carbon decreasing from land to sea is still displayed by variations of stable carbon isotopic average values becoming heavier from land to sea. Previous studies have shown that high content of Chl a cannot appear in the Changjiang Estuary in despite of adequate nourishment supply, because photosynthesis of phytoplankton is constrained by high suspended sediment concentration（SSC）. However, an area with a high content of Chl a occurs, which may be caused by resuspended benthic algae with bottom fine grain-size sediments. Tremendous pressures are imposed on the environment of Changjiang Estuary, because of uhrophication trends and special hydrodynamics. Phytoplankton bloom area tends to extend from the outer sea to the mouth of Changjiang River.

The Original Organism Assemblages and Kerogen Carbon Isotopic Compositions of the Early Paleozoic Source Rocks in the Tarim Basin, China

Original organisms are the biological precursors of organic matter in source rocks. Original organisms in source rocks are informative for oil-source rock correlation and hydrocarbon potential evaluation, especially for source rocks which have high-over level of thermal maturity. Systematic identification of original organism assemblages of the Lower Paleozoic potential source rocks and detailed carbon isotopic composition of kerogen analyses were conducted for four outcrop sections in the Tarim basin. Results indicated that the original organism assemblages of the lower part of the Lower Cambrian were composed mainly of benthic algae, whereas those of the Upper Cambrian and the Ordovician were characterized by planktonic algae. Kerogen carbon isotopic data demonstrated that the δ13 Ckerogen values of source rocks dominated by benthic algae are lower than-34‰, whereas the δ13 Ckerogen values of source rocks dominated by planktonic algae are higher than-30‰ in general. We tentatively suggested that the carbon species those are utilized by algae and the carbon isotopic fractionation during photosynthesis are the major controls for the δ13 Ckerogen values in the Lower Paleozoic source rocks in the Tarim basin. Correlating the δ13 C values of oils exploited in the Tarim basin, the original organism assemblages, and δ13 Ckerogen values of source rocks, it implied that the Lower Paleozoic oils exploited in the Tarim basin should be sourced from the source rocks with original organism assemblages dominated by planktonic algae, and the hydrocarbon sourced from the Cambrian benthic algae should be of great exploration potential in future. Original organism assemblages in source rocks can provide important clues for oil-source rocks correlation, especially for the source rocks with high thermal maturity.

Distribution and Sources of Organic Matter in Surface Sediments of the Karachi Coast,Pakistan

Under the steadily intensifying human activities in coastal areas,it is crucial to distinguish the sources of organic matter(OM)in sediments for better understanding of the environmental change.In this study,25 surface sediments collected along the harbor and creeks areas off Karachi coast were used for total organic carbon(TOC),total nitrogen(TN),stable carbon(δ^(13)C)and nitrogen(δ^(15)N)isotopic compositions,phytoplankton biomarkers(brassicasterol,dinosterol and cholesterol)and glycerol dialkyl glycerol tetraethers(GDGTs)analyses,to trace the distribution of OM and identify its sources.TOC,TN,δ^(13)C,and δ^(15)N are in the range of 0.04% to 5.28%,0.01% to 0.57%,-17.55‰ to -26.31‰,and 2.83‰ to 6.04‰,respectively.C/N values range from 4.24 to 21.04.The δ^(13)C,δ^(15)N,C/N,BIT(Branched Isoprenoid Tetraether)index together with phytoplankton biomarkers show both marine and terrestrial OM input to the creeks and Harbor stations.In contrast,the stations from Western Coast indicate a marine source predominance.A clearly impact of human activities is seen from sediments near river mouths.

Terrestrial dissolved organic carbon consumption by heterotrophic bacterioplankton in the Huanghe River estuary during water and sediment regulation

Nearly 20%–50% of the annual terrestrial dissolved organic carbon(DOC)from the Huanghe(Yellow)River was transported to the estuary during the 5-14d of water and sediment regulation.The concentration of DOC increased sharply during the period of water and sediment regulation,which may promote the terrestrial DOC consumption by heterotrophic bacterioplankton.Water and sediment regulation provides an ideal condition for the study of terrestrial DOC consumption by heterotrophic bacterioplankton when terrestrial DOC increases sharply in rainy season,which may help to seek the fates of terrestrial DOC in the estuaries and coasts.In this study,the concentration and stable isotope of DOC,the biomass,growth,and respiration of heterotrophic bacterioplankton were determined.By the study,we found both average percent contribution of terrestrial DOC to the DOC pool and Contribution of terrestrial DOC to the carbon composition of heterotrophic bacterioplankton decreased as distance from the river mouth increased off shore,which was deceased from(39.2±4.0)%,(37.5±4.3)%to(30.3±3.9)%,(28.2±3.9)%respectively.255-484μg C/(L·d)terrestrial DOC was consumed by heterotrophic bacterioplankton.And 29%-45%terrestrial DOC consumed by heterotrophic bacterioplankton releasing as CO2 by respiration.Comparing with tropical estuary,terrestrial DOC consumed by heterotrophic bacterioplankton was lower in temperate estuary(this study).Temperature may limit the consumption of terrestrial DOC by heterotrophic bacterioplankton.

Variation characteristics of CO_(2) in a newly-excavated soil profile,Chinese Loess Plateau:Excavation-induced ancient soil organic carbon decomposition

Soils of the Chinese Loess Plateau(CLP)contain substantial amounts of soil inorganic carbon(SIC),as well as recent and ancient soil organic carbon(SOC).With the advent of the Anthropocene,human perturbation,including excavation,has increased soil CO_(2) emission from the huge loess carbon pool.This study aims to determine the potential of loess CO_(2) emission induced by excavation.Soil CO_(2) were continuously monitored for seven years on a newly-excavated profile in the central CLP and the stable C isotope compositions of soil CO_(2) and SOC were used to identify their sources.The results showed that the soil CO_(2) concentrations ranged from 830μL·L^(-1) to 11190μL·L^(-1) with an annually reducing trend after excavation,indicating that the human excavation can induce CO_(2) production in loess profile.Theδ^(13) C of CO_(2) ranged from–21.27‰to–19.22‰(mean:–20.11‰),with positive deviation from top to bottom.The range of δ^(13)CSOC was–24.0‰to–21.1‰with an average of–23.1‰.Theδ^(13) C-CO_(2) in this study has a positive relationship with the reversed CO_(2) concentration,and it is calculated that 80.22%of the soil CO_(2) in this profile is from the microbial decomposition of SOC and 19.78%from the degasification during carbonate precipitation.We conclude that the human excavation can significantly enhance the decomposition of the ancient OC in loess during the first two years after perturbation,producing and releasing soil CO_(2) to atmosphere.