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1.
The study addressed seasonal and interannual variations in the components of the trophic status (organic carbon, nitrogen and phosphorus; silica; suspended matter; and chlorophyll-a) and ionic composition (bicarbonates, sulfates, chlorides, calcium, magnesium, sodium, and potassium) in the headwater streams of the Angara River since the 1950s. The results show that the concentrations and seasonal variations of these components and long-term trends of their mean annual concentrations resulted from the interplay of biological, hydrological, and anthropogenic processes operating in Lake Baikal and reflect the current ecological state of the lake.  相似文献   

2.
The paper reviews data (acquired in 2007–2016) on aliphatic and polycyclic aromatic hydrocarbons in comparison with data on concentrations of lipids, Corg, and chlorophyll a in the water and bottom sediments the river–sea geochemical barrier (for the Northern Dvina, Ob, Yenisei, and Lena rivers). It was established that the concentrations of anthropogenic hydrocarbons decrease and these compounds precipitate like other organic compounds and particulate matter, where riverine and marine waters mix. Relatively pure water flows in the pelagic zones of seas. In spite of low temperatures in the Arctic, anthropogenic hydrocarbons transform so rapidly that natural compounds dominate in the water and bottom sediments: autochthonous in the seawater and allochthonous in the bottom sediments.  相似文献   

3.
The spatio-temporal variations in stable isotope signatures (??13C and ??15N) and C/N ratios of particulate organic matter (POM), and physicochemical parameters in a creek water column were examined in an estuarine mangrove ecosystem of Xuan Thuy National Park, Vietnam. The objective was to examine the factors influencing creek water properties, and the sources and exchange of POM in this important mangrove ecosystem. The diel and seasonal variations in water temperature, flow velocity, pH, dissolved oxygen, and salinity demonstrated that tidal level, season, and biological factors affected the creek water properties. Mangroves had relatively low ??15N and very low ??13C values, with respective average values of 1.5?±?0.9?? and ?28.1?±?1.4??. The low mangrove leaf ??15N indicated minor anthropogenic nitrogen loading to the mangrove forests. A significant positive correlation between POM?C??13C and salinity along the axis of Ba Lat Estuary, Red River, indicated that marine phytoplankton (??13C value, ?21.4?±?0.5??) was the predominant source of POM at the estuary mouth. Based on the co-variation of ??13C and C/N ratios, marine phytoplankton and mangrove detritus were predominant in POM of major creeks and small creeks, respectively. During the diurnal tidal cycle, the dynamics of POM were affected by sources of organic matter, tidal energy, and seasonal factors. The contribution of mangrove detritus to POM reached a maximum at the low tide and was enhanced during the rainy season, whereas marine phytoplankton contribution was highest at high tide.  相似文献   

4.
Molecular stratigraphic analyses using gas chromatograph-mass spectrometry have been performed in the upper section (S0, L1, S1) of the Yuanbo loess-paleosol sequences in northwest China, with a record extending from the last interglaciation through the present interglaciation. The CPI (Carbon Preference Index) values of both n-alkanols and n-alkan-2-ones display variations between loess deposits and paleosols, showing a correlation with the magnetic susceptibility record, an indicator of the East Asian summer monsoon. The observed variations in the indexes in relation to changes in lithology/paleoclimate are proposed to result from microbial degradation of higher plant lipids in the paleosols. The CPI values of n-alkanes, n-alkanols, and n-alkan-2-ones are negatively correlated with δ13C of bulk organic matter. The correlations suggest that the observed glacial-interglacial variations of δ13C data in the loess stratigraphy reflect the relative importance of the contribution of paleovegetation compared with microorganisms (including both the degradation and the addition of organic matter) and allochthonous loess/soil parent materials. It is thus necessary to evaluate the contributions of the latter two before the paleovegetation can be reconstructed based on the δ13C analysis of bulk organic matter in some loess-paleosol sequences of the Chinese Loess Plateau.  相似文献   

5.
The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the moun-tainous terrain.There is an increasing recognition of small mountain rivers(SMRs)to have a significant combined export of dissolved and particulate organic carbon to the global carbon flux.We analyzed flu-vial sediments from two SMRs and compared the results with two large mountain rivers(LMRs)in Nepal.We investigated the organic matter(OM),its compositional variability,and seasonal export using a suite of lipid biomarkers,namely n-alkanes,n-alkanoic acids,n-alkanols,and sterols.The SMRs indicated a similarity in lipid distribution and were affected by a strong seasonal variability.The LMRs showed a dis-tinct contrast in the distribution of lipids in suspended sediments.Bedload sediments in SMRs were derived from diverse sources with weak terrigenous dominance all-year-round compared to the sus-pended load.Functional lipids(n-alkanoic acids and n-alkanols)were the major constituents in SMR sed-iments,indicating better preservation.In contrast,n-alkane concentration dominated over other fractions in suspended sediments retrieved from LMRs.The biomarker trends differentiate SMRs from LMRs with lower transformed/degraded OM in SMRs.A common observation was the strong presence of even carbon compounds in short-chain n-alkanes in SMR bedload sediments and their predominance in suspended sediments in LMRs.Such an unusual trend is attributed to specific biomarker sources from the catchment and ongoing processes in fluvial systems.Topsoil colonized by fungal species under moist acidic condi-tions and autochthonous bacteria contributes to the organic matter pool in shallow SMRs.In LMRs,the contribution from thermally mature sedimentary hydrocarbons and the diagenetic reduction of n-alkanoic acids to n-alkanes are additional contributors to the allochthonous carbon pool.The differences in lipid concentrations,their distribution,seasonality,and the size of rivers suggest differential preserva-tion/degradation of the organic matter pool and their importance in contributing to the carbon budget.  相似文献   

6.
Most studies of soil organic matter are on humic substances although a substantial contribution of lipids is generally noted for soils. Moreover, soil lipids were shown to have a relatively high resistance to biodegradation. Thus, they could provide information on organic matter sources and diagenetic processes. Soil organic matter is highly heterogeneous and different dynamic pools are in evidenced. However the links between these pools and molecular structure have not yet been established. Soil lipids were investigated in three particle-size fractions of a forest soil. Lipids were shown to be preferentially located in the finest fraction. GC-MS analysis of free lipids has revealed different main sources depending on the particle-size fraction and differential degradation. Furthermore, the results obtained for the free lipids on the one hand, and the saponified lipids on the other hand, have indicated that different preservation mechanisms for lipids occur in this soil.  相似文献   

7.
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8.
人为土壤有机碳的分布特征及其固定意义   总被引：9，自引：0，他引：9       下载免费PDF全文
文章在分析不同类型的人为土壤形成过程及其特点的基础上研究了人为土壤有机碳含量、分布年龄与同位素组成特征。结果表明,人为土壤中有机碳的含量分布不同于起源土壤或者相应的非人为土壤,主要体现在有机碳含量降低的缓慢和不规则性以及有机碳含量的相对富集。通过计算证明人为土壤的有机碳密度高于相邻土壤或起源土壤。放射性碳测定表明人为土壤中的有机碳年龄较老,说明了有机碳在这些土壤中存在的相对稳定性。土壤有机碳的稳定同位素组成分析表明,土壤中深层的有机碳与现代有机碳来源不同,也表明了土壤中有机碳的稳定存在。文章还分析了人为土壤中有机碳富集和稳定的可能机制,包括物理、化学和生物学机制,认为就有机碳的固定而言,人为土壤是一种具有最佳管理方式的可持续利用的土壤资源  相似文献   

9.
River runoff and atmospheric fallout (dust and air particulate matter) are major input sources of natural and anthropogenic terrestrial organic and inorganic components to the Arabian seas. In this study, we report on the various lipid tracer compounds that might be transported to the Arabian Gulf by rivers, dust, and air particulate matter. These are based on geochemical analysis of sediment, dust, and particulate samples collected from Iraq, Kuwait, and Saudi Arabia. The samples were extracted with a dichloromethane/methanol mixture and analyzed by gas chromatography-mass spectrometry. The extractable organic compounds (lipids) in the samples include n-alkanes, n-alkanoic acids, n-alkanols, methyl n-alkanoates, steroids, triterpenoids, carbohydrates, and petroleum hydrocarbons. The steroids and triterpenoids were major components in river and wetland samples. The major sources of these lipids were from natural vegetation, microbial (plankton and bacteria) residues in the sediments, sand, and soils, with some contribution from anthropogenic sources. Accordingly, these sources could be major inputs to the Arabian seas besides the autochthonous marine products. Future studies of the organic and inorganic biogeochemistry on river, dust, and coastal areas are needed to characterize the various regional sources, transformation, and diagenetic processes of the organic matter en route to the marine environment.  相似文献   

10.
Activities of man in rivers and their watersheds have altered enormously the timing, magnitude, and nature of inputs of materials to estuaries. Despite an awareness of large-scale, long-term changes in river-estuarine watersheds, we do not fully understand the consequences to estuarine ecosystems of these activities. Deforestation, urbanization, and agriculturalization have changed the timing and nature of material inputs to estuaries. Conversion of land from forest to almost any other land use promotes overland flow of storm runoff; increases the timing, rate and magnitude of runoff; and increases sediment, organic matter, and inorganic nutrient export. It has been estimated that total organic carbon levels in rivers have increased by a factor of 3–5 over natural levels. Man’s activities have also changed the magnitude of particulate organic carbon relative to dissolved organic carbon export and the lability of the organic matter. Historically, rivers and streams had different features than they do today. Two of man’s activities that have had pronounced effects on the timing and quality of river water are channelization and damming. Agricultural drainage systems, channelized and deepened streams, and leveeing and prevention of overbank flooding have had the combined effect of increasing the amplitude and rate of storm runoff, increasing sediment load, increasing nutrient delivery downstream, and decreasing riparian wetland productivity. Dams on the other hand have altered natural discharge patterns and altered the downstream transfer of sediments, organic matter, and nutrients. Patterns of estuarine community metabolism are sensitive to variations, in the timing, magnitude, and quality of material inputs from watersheds. The autotrophic-heterotrophic nature of an estuary is determined by three primary factors: the ratio of inorganic to organic matter inputs, water residence time, and the overall lability of allochthonous organic matter inputs. A simulation model is used to explore the effects of man’s activities in watersheds on the spatial patterns of production and respiration in a generalized estuarine system. Examined are the effects of variations in the ratios of inorganic and organic nitrogen loading, the residence time of water in the estuary, the degradability of allochthonous organic matter, and the ratio of dissolved to particulate organic matter inputs. Simulations suggest that the autotrophic-heterotrophic balance in estuaries is more sensitive to variations in organic matter loading than inorganic nutrient loading. Water residence time and flocculation-sedimentation of organic matter are two physical factors that most effect simulated spatial patterns of metabolism in estuaries.  相似文献   

11.
For a better understanding of siliciclastic shelf environments, correlation between sequence stratigraphy and organic geochemistry is used. Our study is focused on the Cretaceous deposits of Marcoule (Gard, France), particularly on a close-packed siltites layer (200–400 m thick), which is well characterized as a marine flooding facies of a single trangressive–regressive cycle. During the Uppermost Albian and the Lower Cenomanian, the stratigraphic data indicate a change in the depositional environment from offshore to shoreface. Organic geochemistry is used in order to characterize origin and variability of the organic matter in relation to the stratigraphic data. The study is carried out on core samples from 2 drill holes (MAR 203 and MAR 501). Analyses of the aliphatic and aromatic hydrocarbons were performed using GC–MS and focused on biomarker distributions. The biomarkers indicate a contribution of mixed terrestrial and marine organic matter. The changes in molecular signatures are related to variations in the source of organic matter (marine versus terrestrial), preservation conditions (largely influenced by clay and early diagenesis), environmental oxidation-reduction and acidic conditions as well as bioturbation. Various environmental zones, characterized by different molecular signatures, can be distinguished. Resin derived biomarkers can be assigned to higher plant material input and may reflect the evolution and diversity of Gymnospermae versus Angiospermae during the transgressive/regressive cycle. The relative sea-level variations are clearly correlated with the nature and the preservation of the organic matter. For example, the Pr/Ph and Pr/n-C17 ratios as well as the regular steranes distributions underline the maximum flooding surface evidenced by other studies. We observe a good correlation between the organic data and sequence stratigraphy: changes in geochemical signatures reflect the 3rd order depositional cycles.  相似文献   

12.
Multidisciplinary analysis of the carbonaceous sediments of Warkalli Formation (Mio-Pliocene) from the Warkalli cliff section has been done to assess the source of organic matter, palaeodepositional settings and the hydrocarbon potential. The n-alkane distribution from n-C12 to n-C33 along with bimodal distribution indicates significant organic matter contribution from microbial activity and higher plants. The contribution from angiosperm source vegetation is indicated by the oleanane type of triterpenoids. The hopanes distribution indicates the immature stage of the organic matter, which is in agreement with the Tmax (av. 401 °C) and huminite reflectance (av. 0.28% Rr) values. The total organic carbon (TOC) contents vary between 0.8 and 6.72 wt. % in the studied sediments. Hydrogen index and oxygen index values range from 16 to106 mg HC/g TOC, and 113 to 344 mg CO2/g TOC, respectively. The maceral content is low, being dominated by the detrohuminite submaceral and the mineral matter accounts for 68 to 77% of the total composition. The phytoclast group (63–87%) is dominant with subordinate amorphous organic matter (4–35%). The study shows that the sediments were deposited in a marginal suboxic basin with intermittent variations. All the parameters unequivocally suggest that the studied sequence holds the potential to generate gaseous hydrocarbons.  相似文献   

13.
Eocene organic-rich sediments are widespread in the Amasya region of north-central Turkey and have been studied in outcrop. Detailed data from thick Eocene sediments (Derealan Formation) made it possible to construct an organic-facies framework using different zonations.

Organic matter is composed predominantly of autochthonous algal and amorphous material, with a minor contribution of allochthonous terrestrial material. Kerogen in the deposits is primarily Type I, as indicated by organic petrographic observations and Rock-Eval data. Total organic-carbon content (TOC) of this deposit decreases from over 54% in limestone and shale to less than 2% in the other deposits of the Derealan Formation. Tmax values vary between 441 ° and 456° C, confirming the increase in maturation trends indicated by vitrinite reflectance data.

Both organic petrographic and geochemical maturation parameters place the Eocene sediments of the Northern Gumushacikoy (Amasya) region within the B organic facies. According to the organic-carbon/sedimentation-rate relationship, the preservation of matter took place under anoxic conditions.  相似文献   

14.
Temporal and spatial changes in the sediment properties of a mangrove ecosystem (Cochin, southwest coast India) are presented. The region was freshwater dominated during monsoon (June–September) and seawater dominated during other two seasons. The system remained eutrophic due to the high inputs of organic matter (OM) during most part of the year. The organic-rich sediments accumulated high amount of carbohydrates (22% of OM) and proteins (11% of OM) during non-monsoon months as compared to coastal environments. Principal component analysis showed that the biochemical properties are uniformly influenced by seasonal and spatial variations. Higher concentrations of sediment protein over carbohydrate indicate an efficient mineralization leading to the non-availability of aged OM in the system. The dominance of these labile components is generally indicative of the eutrophic condition of the system.  相似文献   

15.
From June 2004 to December 2004, Lake Dianchi, which had large scale of cyanobacterial blooms was investigated in order to study P-fractionation in the suspended matter and the sediment. The investigation improves our understanding of phosphorus in Lake Dianchi and the relationship between phosphorus and cyanobacterial blooms. It contributes to the available literature on the behavior of P in hypertrophic lakes. The distribution of P-fractions in Lake Dianchi was not uniform from northwest to south, but was closely related to the trophic status of the whole lake. The concentrations of total phosphorus, labile P (NH4Cl-P), Organic P (NaOH-NRP) and loss on ignition in suspended matter were positively correlated with the strength of cyanobacterial blooms. Total phosphorus in suspended matter was relatively stable for almost half an year and closely related to Chl. a concentration. The main content of organic phosphorus is in the cyanobacterial blooms. The concentrations of phosphorus bound to metal oxides and carbonates (NaOH-SRP and HCl-P) in sediment were similar to NaOH-SRP and HCl-P in the corresponding suspended matter. The latter two forms of P in suspended matter were not affected by cyanobacterial blooms, indicating that the inorganic phosphorus is derived from the sediment after resuspension from the sediment due to wind and wave action. The contribution of the different P-fractions to TP in sediment and in suspended matter indicates that NH4Cl-P in the suspended matter is an important buffer for maintaining dissolved phosphorus in water.  相似文献   

16.
The sources impacting the water chemistry of the Nakdong River (NR) in South Korea were investigated in order to examine the pollution mechanism including the fate and transport of the contaminants and how much such sources may affect its main channel of water resource. Water samples were collected between 2007 and 2008 from 8 sites along a 510 km downstream transect of the NR, and chemical and isotopic compositions of the water samples were evaluated to identify natural and anthropogenic sources contributing to the water chemistry of the NR. The results showed that the major ion concentrations were mainly controlled by chemical weathering that occurred in the watershed, in which a silicate weathering is more dominant than a carbonate weathering. The 87Sr/86Sr ratios of the water samples were in a range from 0.71043 to 0.71520 within those of the Mesozoic volcanogenic sedimentary rocks long developed in the watershed, thereby supporting the fact that the water chemistry is governed by a chemical weathering. The δ34S values varied in a narrow range of 1.8–3.1‰, regardless of spatial and seasonal variations. Mass balance calculations indicated that the contributions of chemical weathering and anthropogenic sources during summer time increased along a downstream transect, from 67.3 ± 1.3 to 73.6 ± 0.5% and from 6.0 to 15.7%, respectively. In contrast, the contribution of chemical weathering during winter time decreased from 82.7 ± 0.8 to 72.5 ± 0.3%, while anthropogenic contribution increased up to 22.2%. These results indicated that the water chemistry of the NR was mainly caused by a chemical weathering, followed by anthropogenic inputs and rainwater. This study will provide baseline information for comparing the water quality issue before and after the implementation of the Four Rivers Restoration Project of South Korea.  相似文献   

17.
We investigated the influence of biological and physical seabed disturbance on the degradation of bulk organic matter and source specific lipid biomarker compounds by measuring downcore changes in bulk elemental composition, bulk stable isotopic (δ13C and δ15N) signatures, and lipid biomarker compounds in sediment cores collected from two sites in the York River, a subestuary of the Chesapeake Bay, USA. One site (LY) is influenced by biological mixing (bioturbation), restricted to the upper 15-20 cm, while the other site (POD) experiences intense, episodic physical mixing events that penetrate 50-100 cm into the sediment. We utilized a suite of auxiliary measurements to constrain the sources of organic matter, depositional environments, and general ages of the cores. Diagenetic modeling of total organic carbon and total nitrogen in sediments yielded higher apparent rate constants for POD than LY suggesting that the physical mixing regime promotes enhanced degradation of bulk organic matter. Apparent rate constants for select lipids representing distinct sources of organic matter were also higher at POD than LY for all but the most labile (i.e., diatom-derived fatty acids) biomarkers. Differences in stanol/stenol ratios also supported enhanced diagenesis of stenols at POD. The source-specific biomarkers, while useful in qualitatively identifying the sources of sedimentary organic matter, likely do not represent the full spectrum of its reactivity. However, based on our results, we hypothesize that the intense sediment disturbance at POD promotes degradation of more recalcitrant organic material, due to prolonged exposure to oxygen and other electron acceptors (e.g., NO3−, Mn and Fe oxides). In contrast, the degradation of more labile constituents is equally facilitated by biological and physical disturbance.  相似文献   

18.
The use of multiple stable isotopes in the study of trophic relationships in temperate estuaries has usually been limited to euhaline systems, in which phytoplankton, benthic microalgae, andSpartina alterniflora are major sources of organic matter for consumers. Within large estuaries such as Chesapeake Bay, however, many species of consumers are found in the upper mesohaline to oligohaline portions. These lower salinity wetlands have a greater abundance of macrophytes that use C3 photosynthesis to fix carbon, in addition toS. alterniflora, which fixes carbon via the C4 photosynthetic pathway. In a broad survey of the biota and sediments of a brackish tidal creek tributary to Chesapeake Bay, combined δ13C and δ34S measurements disclosed a balanced contribution to secondary production from phytoplankton, C3 macrophytes,Spartina sp., and benthic microalgae. Surface sediment δ13C suggested that the organic matter from C3 plants was derived both from allochthonous sources (terrestrial runoff) and from autochthonous production (marsh macrophytes). Unlike most estuarine systems studied to date, which are dominated by algae (phytoplankton and benthic microalgae) and C4 macrophytes, C3 plants are of greater importance in the diets of consumers in this low-salinity creek system.  相似文献   

19.
This study aims to compare the impact of oyster cultures on diagenetic processes and the phosphorus cycle in the sediments of the Aber Benoît and the Rivière d’Auray, estuary of Brittany, France. Our results showed clear evidence of the seasonal impact of oyster cultures on sediment characteristics (grain size and organic matter parameters) and the phosphorus cycle, especially in the Aber Benoît. At this site, seasonal variations in sulfide and Fe concentrations in pore waters, as well as Fe–P concentrations in the solid phase, highlighted a shift from a system governed by iron reduction (Reference) to a system governed by sulfate reduction (beneath oyster). This could be partly explained by the increase in labile organic matter (i.e., biodeposits) beneath oysters, whose mineralization by sulfate led to high sulfide concentrations in pore waters (up to 4,475 µmol l?1). In turn, sulfide caused an enhanced release of phosphate in the summer, as adsorption sites for phosphate decreased through the formation of iron–sulfide compounds (FeS and FeS2). In the Aber Benoît, dissolved Fe/PO4 ratios could be used as an indicator of phosphate release into oxic water. Low Fe/PO4 ratios in the summer indicated higher effluxes of phosphate toward the water column (up to 47 µmol m?2 h?1). At other periods, Fe/PO4 ratios higher than 2 mol/mol indicated very low phosphate fluxes. In contrast, in the Rivière d’Auray, the occurrence of macroalgae, stranding regularly all over the site, clearly masked the impact of oyster cultures on sediment properties and the phosphorus cycle and made the use of Fe/PO4 ratios more difficult in terms of indicators of phosphate release.  相似文献   

20.
Herein, lipid biomarker analysis is applied to surface sediments from the southeastern Niger Delta region for the quantitative determination of aliphatic lipids, steroids and triterpenoids in order to differentiate between natural (autochthonous vs. allochthonous) and anthropogenic organic matter (OM) inputs to this deltaic environment. This ecosystem, composed of the Cross, Great Kwa and Calabar Rivers, is receiving new attention due to increased human and industrial development activities and the potential effects of these activities impacting its environmental health. While the presence of low molecular weight n-alkanes (<C22) and the fossil biomarkers pristane and phytane in all samples, are indicative of a minor petroleum related input, the total extractable organic component of the surface sediments of these rivers remains predominantly of a natural origin as characterized by the variety and predominance of lipid classes that are mainly derived from the epicuticular waxes of vascular plants and include n-alkanes, n-alkanols, n-alkan-2-ones, n-alkanoic acids, steroids and triterpenoids. In addition, recent OM inputs from microorganisms are indicated by the presence of lower molecular weight n-alkanoic acids (Cmax = 16), while the major triterpenoids of the sediments, taraxerol and friedelin, and the major sterol, sitosterol, indicate recent OM inputs from vascular plants. Plankton-derived sterols, such as fucosterol and dinosterol, are also found in sediments from the Cross and Great Kwa Rivers and likely originate from autochthonous primary productivity. Furthermore, the coprosterols coprostanol and 24-ethylcoprostanol are present in most samples and indicate measurable anthropogenic contributions from domestic untreated sewage inputs and agricultural run-off, respectively. Of the three rivers studied, the Cross River system was excessively influenced by human and industrial development activities, including drivers such as urbanization and population center growth, land-use change to support agricultural production and animal husbandry, and petroleum exploration and production. These influences were found to be regionally specific as controlled by point sources of pollution based on the relative distributions measured and on the fact that the molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.  相似文献   

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