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1.
To understand the origin and biogeochemistry of the organic matter in surface sediments of Lake Shihwa and Lake Hwaong, organic nitrogen, inorganic nitrogen, labile organic carbon, and residual organic carbon contents as well as stable isotope ratios for carbon and nitrogen were determined by KOBr-KOH treatment. Ratios of organic carbon to organic nitrogen (Corg/Norg) (mean = 24) were much higher than ratios of organic carbon to total nitrogen (Corg/Ntot) (mean=12), indicating the presence of significant amounts of inorganic nitrogen in the surface sediments of both lakes. Stable isotope ratios for organic nitrogen were, on average, 5.2‰ heavier than ratios of inorganic nitrogen in Lake Shihwa, but those same ratios were comparable in Lake Hwaong. This might be due to differences in the origin or the degree of degradation of sedimentary organic matter between the two lakes. In addition, stable isotope ratios for labile organic carbon were, on average, 1.4‰ heavier than those for residual organic carbon, reflecting the preferential oxidation of13C-enriched organic matter. The present study demonstrates that KOBr-KOH treatment of sedimentary organic matter can provide valuable information for understanding the origin and degradation state of organic matter in marine and brackish sediments. This also suggests that the ratio of Corg/Norg and stable isotope ratios for organic nitrogen can be used as indexes of the degree of degradation of organic matter.  相似文献   

2.
Surface sediment from the coastal bays of Gwangyang and Masan in South Korea were analyzed for their contents and isotopic values of organic carbon and total nitrogen. The sources and diagenetic alteration of organic matter were also assessed. Total organic carbon varied from 0.22% to 3.48% (average = 1.40%, n = 75), and C/N ratios varied from 2.4 to 15.2 (average = 8.79, n = 75). δ13Corg ranged from −19.92‰ to −25.86‰ (average = −21.21‰, n = 75), and δ15NTN ranged from 8.57‰ to 3.93‰ (average = 6.49‰, n = 75). Total organic carbon in both areas was associated with grain-size, with higher contents in finer grained sediment. The high carbon content observed in Masan Bay sediment correlated with its higher C/N ratio. δ13Corg and δ15NTN varied widely, attributable to various influences such as the input of terrestrial organic matter and diagenetic alteration. The depleted δ13Corg and higher δ15NTN observed in the sediment of Gwangyang Bay reflected terrestrial supply, implying that biogeochemical processes, i.e. bacterial degradation, were more active in Masan Bay sediment, which showed less depleted δ13Corg and higher δ15NTN than Gwangyang Bay sediment. δ15NTN was the more useful indicator of biogeochemical processes in the highly anoxic sediment. These results indicate that the δ13Corg and δ15NTN of sedimentary organic matter in coastal bays can indicate the source and degree of diagenetic alteration of sedimentary organic matter.  相似文献   

3.
Relationships between organic carbon, total nitrogen and organic nitrogen concentrations and variations in δ13Corg and δ15Norg are examined in surface sediments from the eastern central Arctic Ocean and the Yermak Plateau. Removing the organic matter from samples with KOBr/KOH and determining residual as well as total N shows that there is a significant amount of bound inorganic N in the samples, which causes TOC/Ntotal ratios to be low (4–10 depending on the organic content). TOC/Norg ratios are significantly higher (8–16). This correction of organic TOC/N ratios for the presence of soil-derived bound ammonium is especially important in samples with high illite concentrations, the clay mineral mainly responsible for ammonium adsorption. The isotopic composition of the organic N fraction was estimated by determining the isotopic composition of the total and inorganic nitrogen fractions and assuming mass-balance. A strong correlation between δ15Norg values of the sediments and the nitrate concentration of surface waters indicates different relative nitrate utilization rates of the phytoplankton in various regions of the Arctic Ocean. On the Yermak Plateau, low δ15Norg values correspond to high nitrate concentrations, whereas in the central Arctic Ocean high δ15Norg values are found beneath low nitrate waters. Sediment δ13Corg values are close to −23.0‰ in the Yermak Plateau region and approximately −21.4‰ in the central Arctic Ocean. Particulate organic matter collected from meltwater ponds and ice-cores are relatively enriched in 13C (δ13Corg=−15.3 to −20.6‰) most likely due to low CO2(aq) concentrations in these environments. A maximum terrestrial contribution of 30% of the organic matter to sediments in the central Arctic Ocean is derived, based on the carbon isotope data and various assumptions about the isotopic composition of the potential endmembers.  相似文献   

4.
The areas that we studied in the North Atlantic (53 and 60°N) and in the Labrador Sea in the summer were characterized by a wide variability of the concentrations of dissolved and particulate organic matter and its elemental composition both in the surface and in the deep waters. The concentrations of dissolved and particulate Corg varied within 69–360 μM and 0.7–25.6 μM, respectively; the Norg and Porg contents varied within 1.4–22.2 μM and 0.02–0.86 μM, respectively. The maximal concentrations were registered in the photic layer and in the zones of mixing between the waters of different genesis. The particulate matter contribution to the total organic matter (OM) content varied from 0.5 to 15.4%. The waters of the photic layer contained more particulate Corg than those of the near-bottom layer. The values of the C/N molar ratios from the surface to the bottom over the entire aquatic area surveyed varied 5-to 6-fold; at that, the values of the C/P molar ratios varied more than tenfold. In the most productive waters, the values of the C/N ratios were close to the Redfield ratios (6–10). The values of the C/P molar ratios varied from 160 in the photic layer to 4831 in the deep waters. The pronounced non-uniformity in the spatial distribution of the OM and its elemental composition is caused not only by the penetration of the waters of different origins but also by the changes in the microplankton metabolism under mixing of these waters.  相似文献   

5.
Origin of sedimentary organic matter in the north-western Adriatic Sea   总被引：1，自引：0，他引：1  
In order to evaluate the origin and the transformation of organic matter on the shallow shelf of the NW Adriatic Sea, organic carbon, total nitrogen and stable isotope ratios of organic carbon were analysed in riverine suspended matter and sediments as well as in marine suspended and sedimentary organic matter, in marine phytoplankton and zooplankton.The deposition of organic matter is influenced by fine sediment concentration. Surface sediments were characterised by highly variable biogeochemical conditions on the sea floor, whereas sub-surface sediments showed a more homogeneous hypoxic/anoxic environment.Low Corg/N ratio and high organic carbon and nitrogen concentrations in riverine suspended organic matter indicate an important contribution of freshwater phytoplankton within rivers, particularly during low flow regimes, which adds to the marine phyto- and zooplankton at shelf locations.In order to evaluate the importance of terrestrial, riverine and marine sources of OM in shelf sediments, a three end-member mixing model was applied to shelf surface sediments using 13C/12C values for organic matter and N/C ratios. The model showed an elevated contribution of terrestrial organic substances at intermediate depths (10–15 m), mostly corresponding to an area of coarser grain-size, whereas the riverine and marine organic fractions were mainly accumulating near the coast and offshore, respectively.  相似文献   

6.
Late Turonian, Coniacian and Santonian source rock samples from a recently drilled well (Tafaya Sondage No. 2; 2010) in the Tarfaya Basin were analyzed for quantity, quality, maturity and depositional environment of the organic matter (OM). To our knowledge such a thick sequence of organic matter-rich Turonian to Santonian source rocks was investigated in that great detail for the first time. Organic geochemical and organic petrological investigations were carried out on a large sample set from the 200 m thick sequence. In total 195 core samples were analyzed for total organic carbon (Corg), total inorganic carbon contents and total sulfur (TS) contents. Rock-Eval pyrolysis and vitrinite reflectance measurements were performed on 28 samples chosen on the basis of their Corg content. Non-aromatic hydrocarbons were analyzed on selected samples by way of gas chromatography–flame ionization detection (GC–FID) and GC–mass spectrometry (GC–MS). The organic matter-rich carbonates revealed a high source rock potential, representing type I kerogen and a good preservation of the organic matter, which is mainly of marine (phytoplankton) origin. HI values are high (400–900 mg/g Corg) and in a similar range as those described for more recent upwelling sediments along the continental slope of North Africa. TS/Corg ratios as well as pristane over phytane ratios indicate variable oxygen content during sediment deposition. All samples are clearly immature with respect to petroleum generation which is supported by maturity parameters such as vitrinite reflectance (0.3–0.4%), Tmax values (401–423 °C), production indices (S1/(S1 + S2) > 0.1) as well as maturity parameters based on ratios of specific steranes and hopanes.  相似文献   

7.
In addition to previously analyzed sediments of Cenomanian to Santonian age in the Tarfaya Sondage No. 2 well, this study presents the results of a stratigraphically younger interval of Santonian to Early Campanian age in the adjacent well Tarfaya Sondage No. 1. This interval is part of the oceanic anoxic event 3 (OAE3), which occurred mainly in the Atlantic realm. Due to known high quality source rocks related to OAEs (i.e. Cenomanian–Turonian), the investigated sample section was tested for the quality, quantity and kind of organic matter (OM), describing also the depositional environment. The study was carried out by means of (i) elemental analysis (Corg, CaCO3, TS), (ii) Rock–Eval pyrolysis, (iii) vitrinite reflectance measurements, (iv) gas chromatography-flame ionization detection (GC-FID) and (v) GC-mass spectrometry (GC–MS). Total content of organic carbon (Corg), values for the hydrogen index (HI) (mainly in the range 500–700 mg/g Corg) and S2 values (10–40 mg/g rock), support the assumption of a high petroleum generation potential in these Upper Cretaceous sediments. TS/Corg ratios as well as pristane/phytane ratios indicate variable oxygen contents during sediment deposition, representing a typical depositional setting for the Late Cretaceous and are in good agreement with previously analyzed data in the Tarfaya Basin. Phyto- and zoo-plankton were identified as marine sourced. All of the investigated Early Campanian and Santonian samples are immature with some tendencies to early maturation. These results are based on vitrinite reflectance (0.3–0.4% VRr), Tmax values (409–425 °C), production indices (PI; S1/(S1 + S2)< 0.1) and n-alkane ratios (i.e. carbon preference index). As the deposition of these sediments is time related to OAE3, the depositional environment was characterized by oxygen-deficiency or even anoxic bottom water conditions. This situation was favored during the Cretaceous greenhouse climate by limited oxygen solubility in the then warmer ocean water. Furthermore, local factors related to nutrient supply and primary bioproductivity led to the exceptionally thick, Upper Cretaceous organic matter-rich sedimentary sequence of the Tarfaya Basin.  相似文献   

8.
High-resolution geochemical, isotope and elemental data from core PC23A in the northern margin of the Aleutian Basin (Bering Sea) were used to reconstruct distinct paleoceanographic features of the last deglaciation (pre-Boreal[PB], Bølling-Allerød[BA], Younger Dryas[YD]). The PB and BA intervals are characterized by increased siliceous (diatom) and calcareous (coccolithophores and foraminifers) productivity represented by high biogenic opal and CaCO3 contents, respectively. The enhanced productivity can plausibly be attributed to an elevated sea-surface nutrient supply from increased melt-water input and enhanced Alaskan Stream injection under warm, restricted sea-ice conditions. High Corg/N ratios and low δ13C values of sediment organic matter during the PB and BA intervals reflect the contribution of terrestrial organic matters. The PB and BA intervals were also identified by laminated sediment layers of core PC23A, characterized by high Mo/Al and Cd/Al ratios, indicating that the bottom water condition remained anoxic. High δ15N values during the same period were attributed mainly to the increased nutrient utilization and subsequent denitrification of seawater nitrate. Part of high δ15N values may also be due to incorporation of inorganic nitrogen in the clay minerals. It is worthy of note that high total organic carbon (TOC) deposition occurred approximately 3,000 years before onset of the last deglaciation. Simultaneous high Corg/N ratios and low δ13C values clearly suggest that the high TOC content should be related to terrestrial organic carbon input. Low δ15N values during the high TOC interval also confirm the contribution of terrigenous organic matter. Although abundant calcareous phytoplankton production under cold, nutrient-poor conditions represented by Baex data was reported for high TOC deposition preceding the last deglaciation in an earlier study of the Okhotsk Sea, the main reason for the enhanced TOC deposition in the Bering Sea is an increased terrigenous input from the submerged continental shelves (Beringia) with a sea-level rise; this is further supported by Al enrichment of bulk sediments during the high TOC deposition.  相似文献   

9.
According to bioassay studies and high dissolved nutrient N/P ratios in the seawater column, phosphorus (P) is thought to control marine productivity in the northern Adriatic Sea. P in near-shore marine sediments of the Gulf of Trieste, the northernmost part of the Adriatic Sea, was investigated using pore water P distributions, and benthic P flux studies under oxic and anoxic conditions. The data show that P regeneration is up to three-fold more extensive in sediments overlain by oxygen-depleted waters and proceeds in parallel with Fe and Mn enhanced benthic fluxes. It appears from the incubation experiments that degradation of sedimentary organic matter is the main contribution to the flux of P at the sediment–water interface, while the release of phosphate adsorbed on the iron oxide surface is of minor importance.It appears that about 50% of P in the Gulf of Trieste is retained within in the sediments, probably bonded to clay minerals and carbonate grains or precipitated as fluoroapatite. In these sediments total P (Ptot) is preserved preferentially over organic C (Corg). P regenerated from surficial sediments contributes about 1/3 of the P that is assimilated by benthic microalgae. The phytoplankton P requirement should be entirely supplied from fresh-water sources. These results suggest that oxygen depletion in coastal areas caused by eutrophication enhances P regeneration from sediments, providing the additional P necessary for increased biological productivity. The development of anoxic bottom waters in coastal areas enhances the recycling of P, exacerbating the nutrient requirement in the area. A geochemical record of P burial in a longer sedimentary sequence revealed an increasing trend of Ptot and organic P (Porg) contents occurring approximately 50 years BP (after 1950), probably due to increasing use of inorganic fertilizers and detergents in the area.  相似文献   

10.
Sediments were sampled and oxygen profiles of the water column were determined in the Indian Ocean off west and south Indonesia in order to obtain information on the production, transformation, and accumulation of organic matter (OM). The stable carbon isotope composition (δ13Corg) in combination with C/N ratios depicts the almost exclusively marine origin of sedimentary organic matter in the entire study area. Maximum concentrations of organic carbon (Corg) and nitrogen (N) of 3.0% and 0.31%, respectively, were observed in the northern Mentawai Basin and in the Savu and Lombok basins. Minimum δ15N values of 3.7‰ were measured in the northern Mentawai Basin, whereas they varied around 5.4‰ at stations outside this region. Minimum bottom water oxygen concentrations of 1.1 mL L?1, corresponding to an oxygen saturation of 16.1%, indicate reduced ventilation of bottom water in the northern Mentawai Basin. This low bottom water oxygen reduces organic matter decomposition, which is demonstrated by the almost unaltered isotopic composition of nitrogen during early diagenesis. Maximum Corg accumulation rates (CARs) were measured in the Lombok (10.4 g C m?2 yr?1) and northern Mentawai basins (5.2 g C m?2 yr?1). Upwelling-induced high productivity is responsible for the high CAR off East Java, Lombok, and Savu Basins, while a better OM preservation caused by reduced ventilation contributes to the high CAR observed in the northern Mentawai Basin. The interplay between primary production, remineralisation, and organic carbon burial determines the regional heterogeneity. CAR in the Indian Ocean upwelling region off Indonesia is lower than in the Peru and Chile upwellings, but in the same order of magnitude as in the Arabian Sea, the Benguela, and Gulf of California upwellings, and corresponds to 0.1–7.1% of the global ocean carbon burial. This demonstrates the relevance of the Indian Ocean margin off Indonesia for the global OM burial.  相似文献   

11.
To examine the source and preservation of organic matter in the shelf sediments of the East China Sea (ECS), we measured bulk C/N and isotopes, organic biomarkers (n-alkanes and fatty acids) and compound-specific (fatty acids) stable carbon isotope ratios in three sediment cores collected from two sites near the Changjiang Estuary and one in the ECS shelf. Contrasting chemical and isotopic compositions of organic matter were observed between the estuarine and shelf sediments. The concentrations of total n-alkanes and fatty acids in the shelf surface sediments (0–2 cm) were 5–10 times higher than those in estuarine surface sediments but they all decreased rapidly to comparable levels below the surface layer. The compositions of n-alkanes in the estuarine sediments were dominated by C26-C33 long-chain n-alkanes with a strong odd-to-even carbon number predominance. In contrast, the composition of n-alkanes in the shelf sediment was dominated by nC15 to nC22 compounds. Long-chain (>C20) fatty acids (terrestrial biomarkers) accounted for a significantly higher fraction in the estuarine sediments compared to that in the shelf sediment, while short-chain (<C20) saturated and unsaturated fatty acids were more abundant in the shelf surface sediments than in the estuarine sediments. Stable carbon isotopic ratios of individual fatty acids showed a general positive shift from estuarine to shelf sediments, consistent with the variations in bulk δ 13CTOCTOC. These contrasts between the estuarine and shelf sediments indicate that terrestrial organic matter was mainly deposited within the Changjiang Estuary and inner shelf of ECS. Post-depositional diagenetic processes in the surface sediments rapidly altered the chemical compositions and control the preservation of organic matter in the region.  相似文献   

12.
Thus study is based on 31 box-core samples collected mainly from the mud-patches of the Galician and North-Portuguese shelf. Each of these cores, some decimetres in length, have been described, radiographied and sampled each centimetre for grain-size analysis and measurement of the particulate organic carbon (Corg) content. 210Pb excess profiles have been measured using gamma spectrometry, which, combined with the analysis of the vertical variations of the sedimentary facies, have allowed estimates of sedimentation rates. These rates were found to vary between 0.05 and 0.40 cm yr−1. Considering the latitudinal variation of sedimentation rates around the 100m contour, we note that the maximum rates occurred off the Douro estuary in the southern sector and also near the Galician rias to the north. The organic content (Corg) of sediments varied between 0.4 and 2%. Latitudinally Corg showed a decrease from the South to the North. These results coupled with the sedimentary map (see Dias, Gonzalez, Garcia & Diaz del Rio, 2001) have permitted us to establish the detrital mass budget and an inventory of Corg burial.  相似文献   

13.
Data on the contents and compositions of the hydrocarbons (HCs)—aliphatic (AHCs) and polycyclic aromatic (PAHs)—are provided in comparison with the contents of the total organic carbon (Corg), the lipids in the particulates, and the Corg in bottom sediments. Particular attention has been paid to the distribution of the HCs in the water area of the Kravtsov oil field. It has been established that the concentrations of AHCs in the water are governed by the content of particulates, and the elevated AHC concentrations are confined to the coastal areas. In the water area of platform D-6, the sandy bottom sediments were notable for the great variability of the HC concentrations, both laterally and from year to year. In the summer of 2010, the content of AHCs averaged 40 μg/g (19% in the Corg), and that of PAHs, 23 ng/g. Natural seepage from the sediment mass is considered to be a source of HCs along with oil contamination.  相似文献   

14.
Organic carbon fluxes through the sediment/water interface in the high-latitude North Atlantic were calculated from oxygen microprofiles. A wire-operated in situ oxygen bottom profiler was deployed, and oxygen profiles were also measured onboard (ex situ). Diffusive oxygen fluxes, obtained by fitting exponential functions to the oxygen profiles, were translated into organic carbon fluxes and organic carbon degradation rates. The mean Corg input to the abyssal plain sediments of the Norwegian and Greenland Seas was found to be 1.9 mg C m−2 d−1. Typical values at the seasonally ice-covered East Greenland continental margin are between 1.3 and 10.9 mg C m−2 d−1 (mean 3.7 mg C m−2 d−1), whereas fluxes on the East Greenland shelf are considerably higher, 9.1–22.5 mg C m−2 d−1. On the Norwegian continental slope Corg fluxes of 3.3–13.9 mg C m−2 d−1 (mean 6.5 mg C m−2 d−1) were found. Fluxes are considerably higher here compared to stations on the East Greenland slope at similar water depths. By repeated occupation of three sites off southern Norway in 1997 the temporal variability of diffusive O2 fluxes was found to be quite low. The seasonal signal of primary and export production from the upper water column appears to be strongly damped at the seafloor. Degradation rates of 0.004–1.1 mg C cm−3 a−1 at the sediment surface were calculated from the oxygen profiles. First-order degradation constants, obtained from Corg degradation rates and sediment organic carbon content, are in the range 0.03–0.6 a−1. Thus, the corresponding mean lifetime of organic carbon lies between 1.7 and 33.2 years, which also suggests that seasonal variations in Corg flux are small. The data presented here characterize the Norwegian and Greenland Seas as oligotrophic and relatively low organic carbon deep-sea environments.  相似文献   

15.
To establish the relative importance of terrigenous and marine organic matter in the southern Beaufort Sea, we measured the concentrations and the stable isotopic compositions of organic carbon and total nitrogen in sediments and in settling particles intercepted by sediment traps. The organic carbon content of surface sediment in the Chukchi and southern Beaufort Seas ranged from 0.6 to 1.6% dry wt., without a clear geographical pattern. The CORG:NTOT ratio ranged from 7.0 to 10.4 and did not vary significantly downcore at any one station. Values of δ13CORG and δ15NTOT in the sediment samples were strongly correlated, with the highest values, indicative of a more marine contribution, in the Amundsen Gulf. In contrast, the organic matter content, elemental (CORG:NTOT ratio) and isotopic (δ13CORG and δ15NTOT) composition of the settling particles was different from and much more variable than in the bottom sediments. The isotopic signature of organic matter in the Beaufort Sea is well constrained by three distinct end-members: a labile marine component produced in situ by planktonic organisms, a refractory marine component, the end product of respiration and diagenesis, and a refractory terrigenous component. A three-component mixing model explains the scatter observed in the stable isotope signatures of the sediment trap samples and accommodates an apparent two-component mixing model of the organic matter in sediments. The suspended matter in the water column contains organic matter varying from essentially labile and marine to mostly refractory and terrigenous. As it settles through the water column, the labile marine organic matter is degraded, and its original stable isotope signature changes towards the signature of the marine refractory component. This process continues in the bottom sediment with the result that the sedimentary organic matter becomes dominated by the refractory terrigenous and marine components.  相似文献   

16.
Elemental (TOC, TN, C/N) and stable carbon isotopic (δ13C) compositions and n-alkane (nC16–38) concentrations were measured for Spartina alterniflora, a C4 marsh grass, Typha latifolia, a C3 marsh grass, and three sediment cores collected from middle and upper estuarine sites from the Plum Island salt marshes. Our results indicated that the organic matter preserved in the sediments was highly affected by the marsh plants that dominated the sampling sites. δ13C values of organic matter preserved in the upper fresh water site sediment were more negative (−23.0±0.3‰) as affected by the C3 plants than the values of organic matter preserved in the sediments of middle (−18.9±0.8‰) and mud flat sites (−19.4±0.1‰) as influenced mainly by the C4 marsh plants. The distribution of n-alkanes measured in all sediments showed similar patterns as those determined in the marsh grasses S. alterniflora and T. latifolia, and nC21 to nC33 long-chain n-alkanes were the major compounds determined in all sediment samples. The strong odd-to-even carbon numbered n-alkane predominance was found in all three sediments and nC29 was the most abundant homologue in all samples measured. Both δ13C compositions of organic matter and n-alkane distributions in these sediments indicate that the marsh plants could contribute significant amount of organic matter preserved in Plum Island salt marsh sediments. This suggests that salt marshes play an important role in the cycling of nutrients and organic carbon in the estuary and adjacent coastal waters.  相似文献   

17.
Spatial distribution of the carbon and nitrogen content and their isotopic enrichment in suspended matter and sediments were measured in the Godavari estuary to identify the sources and transformation mechanism of organic matter. Significant variability in isotopic distribution was found over the entire length of the Godavari estuary, suggesting multiple sources of organic matter. The mean isotopic ratios (δ13Csed −25.1 ± 0.9, δ13Csus −24.9 ± 1, δ15Nsed 8.0 ± 2 and δ15Nsus 6.5 ± 0.9‰) and elemental concentrations (Csed 0.45 ± 0.2%, Csus 0.9 ± 0.7%, Nsed 0.07 ± 0.05% and Nsus 0.16 ± 0.1%) support a predominantly terrigenous source. Significant enrichment in the isotopic ratios of δ13C from the upper to lower estuary in both suspended (−27.5 and −24.3‰, respectively) and sedimentary (−26.2 and −24.9‰, respectively) phases indicates a decrease in the influence of terrigeneous material toward the mouth of the estuary. A significant positive relationship exists between the δ13C of suspended and sediment, which indicates that these two organic carbon pools are likely coupled in the form of a significant exchange between the two phases. A positive relationship exists between chlorophyll a and suspended organic matter, which may mean that a significant source of organic carbon is the in situ produced phytoplankton. But, applying a simple mixing model to our isotopes, data yielded about 46% as the contribution of the terrestrial source to suspended matter, which may support the excessive heterotrophic activity in the Godavari estuary reported earlier.  相似文献   

18.
Preservation of organic matter in estuarine and coastal areas is an important process in the global carbon cycle. This paper presents bulk δ13C and C/N of organic matter from source to sink in the Pearl River catchment, delta and estuary, and discusses the applicability of δ13C and C/N as indicators for sources of organic matter in deltaic and estuarine sediments. In addition to the 91 surface sediment samples, other materials collected in this study cover the main sources of organic material to estuarine sediment. These are: terrestrial organic matter (TOM), including plants and soil samples from the catchment; estuarine and marine suspended particulate organic carbon (POC) from both summer and winter. Results show that the average δ13C of estuarine surface sediment increases from −25.0 ± 1.3‰ in the freshwater environment to −21.0 ± 0.2‰ in the marine environment, with C/N decreasing from 15.2 ± 3.3 to 6.8 ± 0.2. In the source areas, C3 plants have lower δ13C than C4 plants (−29.0 ± 1.8‰ and −13.1 ± 0.5‰ respectively). δ13C increases from −28.3 ± 0.8‰ in the forest soil to around −24.1‰ in both riverbank soil and mangrove soil due to increasing proportion of C4 grasses. The δ13CPOC increases from −27.6 ± 0.8‰ in the freshwater areas to −22.4 ± 0.5‰ in the marine-brackish-water areas in winter, and ranges between −24.0‰ in freshwater areas and −25.4‰ in brackish-water areas in summer. Comparison of the δ13C and C/N between the sources and sink indicates a weakening TOM and freshwater POC input in the surface sedimentary organic matter seawards, and a strengthening contribution from the marine organic matter. Thus we suggest that bulk organic δ13C and C/N analysis can be used to indicate sources of sedimentary organic matter in estuarine environments. Organic carbon in surface sediments derived from anthropogenic sources such as human waste and organic pollutants from industrial and agricultural activities accounts for less than 10% of the total organic carbon (TOC). Although results also indicate elevated δ13C of sedimentary organic matter due to some agricultural products such as sugarcane, C3 plants are still the dominant vegetation type in this area, and the bulk organic δ13C and C/N is still an effective indicator for sources of organic matter in estuarine sediments.  相似文献   

19.
The sources and distribution of organic matter (OM) in surface waters and sediments from Winyah Bay (South Carolina, USA) were investigated using a variety of analytical techniques, including elemental, stable isotope and organic biomarker analyses. Several locations along the estuary salinity gradient were sampled during four different periods of contrasting river discharge and tidal range. The dissolved organic carbon (DOC) concentrations of surface waters ranged from 7 mg l−1 in the lower bay stations closest to the ocean to 20 mg l−1 in the river and upper bay samples. There was a general linear relationship between DOC concentrations and salinity in three of the four sampling periods. In contrast, particulate organic carbon (POC) concentrations were significantly lower (0.1–3 mg l−1) and showed no relationship with salinity. The high molecular weight dissolved OM (HMW DOM) isolated from selected water samples collected along the bay displayed atomic carbon:nitrogen ratios ([C/N]a) and stable carbon isotopic compositions of organic carbon (δ13COC) that ranged from 10 to 30 and from −28 to −25‰, respectively. Combined, such compositions indicate that in most HMW DOM samples, the majority of the OM originates from terrigenous sources, with smaller contributions from riverine and estuarine phytoplankton. In contrast, the [C/N]a ratios of particulate OM (POM) samples varied significantly among the collection periods, ranging from low values of 5 to high values of >20. Overall, the trends in [C/N]a ratios indicated that algal sources of POM were most important during the early and late summer, whereas terrigenous sources dominated in the winter and early spring.In Winyah Bay bottom sediments, the concentrations of the mineral-associated OM were positively correlated with sediment surface area. The [C/N]a ratios and δ13COC compositions of the bulk sedimentary OM ranged from 5 to 45 and from −28 to −23‰, respectively. These compositions were consistent with predominant contributions of terrigenous sources and lesser (but significant) inputs of freshwater, estuarine and marine phytoplankton. The highest terrigenous contents were found in sediments from the river and upper bay sites, with smaller contributions to the lower parts of the estuary. The yields of lignin-derived CuO oxidation products from Winyah Bay sediments indicated that the terrigenous OM in these samples was composed of variable mixtures of relatively fresh vascular plant detritus and moderately altered soil OM. Based on the lignin phenol compositions, most of this material appeared to be derived from angiosperm and gymnosperm vascular plant sources similar to those found in the upland coastal forests in this region. A few samples displayed lignin compositions that suggested a more significant contribution from marsh C3 grasses. However, there was no evidence of inputs of Spartina alterniflora (a C4 grass) remains from the salt marshes that surround the lower sections of Winyah Bay.  相似文献   

20.
Concurrent distributions of dissolved and suspended particulate organic carbon (DOC and POCsusp), nitrogen (DON and PONsusp) and phosphorus (DOP and POPsusp), and of suspended particulate inorganic phosphorus (PIPsusp), are presented for the open ocean water column. Samples were collected along a three-station transect from the upper continental slope to the abyssal plain in the eastern North Pacific and from a single station in the Southern Ocean. The elemental composition of surface sedimentary organic matter (SOM) was also measured at each location, and sinking particulate organic matter (POMsink) was measured with moored sediment traps over a 110-d period at the abyssal site in the eastern North Pacific only. In addition to elemental compositions, C : N, C : P and N : P ratios were also calculated. Surface and deep ocean concentrations of dissolved organic matter (DOM) and inorganic nutrients between the two sites displayed distinct differences, although suspended POM (POMsusp) concentrations were similar. Concentrations of DOM and POMsusp displayed unique C, N and P distributions, with POMsusp concentrations generally about 1–2 orders of magnitude less than the corresponding DOM concentrations. These differences were likely influenced by different biogeochemical factors: whereas the dissolved constituents may have been influenced more by the physical regime of the study site, suspended particulate matter may have been controlled to a greater extent by biological and chemical alteration. Up to 80% of total particulate P in POMsusp, POMsink and SOM consisted of PIP. For all organic matter pools measured, elemental ratios reveal that organic P is preferentially remineralized over organic C and organic N at both sites. Increases in C : P and N : P ratios with depth were also observed for DOM at both sites, suggesting that DOP is also preferentially degraded over C and N as a function of depth. A simple one-dimensional vertical eddy diffusion model was applied to estimate the contributions of dissolved and suspended particulate organic C, N and P fluxes from the upper mixed layer into the permanent thermocline. Estimated vertical DOM fluxes were 28–63% of the total organic matter fluxes; POMsusp and POMsink fluxes were 8–20 and 28–52% of the total.  相似文献   

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