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1.
The soluble organic matters were extracted from marine sediments in the sea area of Southern Ocean by using organic solvents. The hydrocarbon and carboxylic acid fractions were separated with the thin layer chromatography. The organic compounds of 170(H), 21α(H)- bishomomoretene, cholest - 5 - ene, 24 - methyl - cholestene, 24 - ethylcholestene, hop-17(21)-ene, neohop - 13(18)-ene, fern-8-ene, fern-7-ene, 170(H), 210 (H) - hop - 22(29)-ene (diplotene), steranes, β, β-hopanes C29 -C31 and unsaturated carboxylic acids C18:2Δ9.12 , C18:1Δ9,C18:1Δ11 , have been identi-fied in the hydrocarbon and carboxylic acid fractions by means of gas chromatography and gas chromatography - mass spec-trometry - data system. The distributions of 3, a - bishomomoretene, β,β- hopene and β,β- hopane are characteristic of immature organic matter. The sterane, C29 20S/20R epimer ratio 0. 6 indicate that the organic matter had experienced a thermal evolution in the early sedimentation. The unsaturated fatty acids espec  相似文献   

2.
The Yanshiping section, which includes the Quemo Co, Buqu, Xiali, Suowa and Xueshan Formations (Yanshiping Group) exposes organic-rich Middle to Late Jurassic deposits in the Qiangtang Basin of northern Tibet. The biostratigraphic data, from bivalves, brachiopods as well as dinoflagellate cysts, define a Bajocian to Tithonian age. This study focuses on the biomarkers present in these mudstones and limestones to determine the sources, thermal maturity and depositional environment of the organic matter. Most samples show a clear dominance of short-chain (C15–C20) n-alkanes with a maximum at C19 or C19 with a secondary maximum at C23 except for the sample BP01(22)S1 where the predominant range is C22 to C26 with a maximum at C24, significant CPI and odd-to-even predominance. The hopanoids and steroids suggest that the sources of organic matter were dominated by phytoplankton, especially algae, as the primary source. Furthermore, the Pr/Ph, Pr/nC17 and Ph/nC18, with relatively low values plus high abundance of 17α(H)-hopanes, support deposition in dysoxic to reducing, relatively shallow-water depositional settings, and the presence of gammacerane indicates normal marine salinity and/or water-column stratification. All samples are fairly mature with respect to petroleum generation, a conclusion supported by maturity parameters such as C31 22S/(22S + 22R) hopanes and C29 ααα20S/(20S + 20R) steranes.  相似文献   

3.
Bicyclic Sesquiterpanes (BSs) are ubiquitous components of crude oils and ancient sediments. BSs in crude oils and diesel oil were identified and characterized, the effects of moderate weathering on BS distributions were discussed, and a methodology using diagnostic indices of BSs was developed for oil correlation and differentiation. The results showed that crude oils and oil products had different abundances and distributions of BSs and, consequently, resulted in different diagnostic ratios. The selected diagnostic ratio indices of BSs, such as BS4/BS5 (ratio of 4,4,8,9,9-pentamethyl-decahydronaphthalene to 8β (H)-drimane), BS6/BS5 (ratio of 4,4,9,9,10-pentamethyl-decahydronaphthalene to 8β (H)-drimane), BS8/BS9 (ratio of the second peak to the third peak of C 16 sequiterpane), and BS8/BS10 (ratio of C 16 sequiterpane to 8β (H)-homodrimane), still maintained better stabilities (%RSD < 5%) after weathering for 30 d. The longer weathering process (150 d) had some effect on such ratios (5% < %RSD < 10%). The facts of the uniqueness, abundance in petroleum, and chemical stability of BSs enable them to be suitable as an effective diagnostic means for identifying spilled oil with moderate weathering, particularly for lighter refined product samples that are difficult to identify by current techniques.  相似文献   

4.
The Triassic Yanchang Formation is the main source rocks for Mesozoic oil in Ordos Basin. The formation includes 10 oil-bearing beds (Ch 1–Ch 10), that each can be further divided into two to three intervals. Abundant C12–C14 and C15–C16 bicyclic alkanes have been detected in the formation in the Xifeng oilfield, Ordos Basin. The C12–C14 group is dominated by C12 and C13, and the C15–C16 group contains abundant C15. The groups show three distribution patterns: A) the C12–C14 group is the major component in the non-source rocks of the Ch 7-1 and Ch 8-1 intervals; B) both groups are abundant and are common in source rocks of the Ch 7-3 interval; and C) the C15–C16 group is the major component in source rocks of the Ch 7-3 interval and also in sediments that contain type Ⅰ or partial sapropel type Ⅱ1 organic matter (OM) in the Ch 7-2 and Ch 8-1 intervals. Although thermal maturities of the source rocks in the Ch 7 section are similar, they show significant differences with respect to the drimane isomerisation index, which indicates that the drimane rearrangement is controlled by thermal evolution of the sediments, but may also be closely related to the depositional environment. This study determined that reducing environments are more conducive to preservation of drimane than oxic environments. The drimane isomerisation index and the value of the hopane parameter Tm/Ts are positively correlated. The parameter Tm/Ts varies over a wide range within the sequence, and the large variations may be a result of terrigenous OM input by turbidity currents and/or gravity flows, mixed with the autochthonous sediments. Abundant homodrimane in both source rocks may reflect reducing environments in deep lakes and major input of higher plant OM. Organic-rich shale and oil shale in the Ch 7-3 interval of the Yanchang Formation are the primary sources of oil in reservoirs in the Xifeng area. The crude oil is rich in bicyclic alkanes that are dominated by C15–C16 as source rocks with pattern C for bicyclic alkanes, which indicates an origin mainly from the Ch 7-3 interval. The main peaks in all of the crude oils are associated with 8β(H)-drimane and lower abundance of rearranged drimane. However, most of the source rocks have a main peak associated with 8β(H)-homodrimane or rearranged drimane. Weak microbial action, selective degradation and water washing may be the cause of the significant difference in bicyclic sesquiterpane composition between the crude oil and the source rocks. The result suggests that oil-source correlations based on the bicyclic sesquiterpanes are questionable.  相似文献   

5.
A great deal is known about the genetic relationships between biomarkers and their biogenic precursors in organic rich rocks. The same is true of the way in which biomarker compound ratios change during maturation. On the other hand, very little is known about whether a crude oil can fully retain its inherent compositional ancestry during expulsion from a source rock. Thanks to shales being characterized in great detail for their unconventional resource potential, new information is gradually coming to light. Here we report on observations in biomarker geochemistry of a thermally mature core of the Barnett Shale, in which organofacies and maturity are essentially the same, but where intraformational sources and reservoirs have already been reported.Our results indicate that most biomarkers are not fractionated as the primary migration of petroleum within source rocks takes place. The 20S/(20S + 20R) ratio of C27 steranes is uniform in the whole source-rock sequence, while the 20S/(20S + 20R) ratio of C29 steranes shows indistinctly high values in the reservoir unit. The 20S/(20S + 20R) ratio of diasteranes and the 22S/(22S + 22R) ratio of C31 17α-hopanes do not appear to have been fractionated, which may be a result of the thermal isomerization reactions predominating over and masking out the possible fractionation effects. Diasteranes/steranes ratios do not exhibit features that suggest an association with fractionation, but rather are broadly correlated with lithology. However, compared to the diasteranes/steranes ratios, the Ts/(Ts + Tm) ratio is much more sensitive to changes in mineral compositions. Variations in the Ts/(Ts + Tm) ratio show a positive correlation (R2 = 0.73) with mixed-layer illite-smectite content. Fractionation in the Ts/(Ts + Tm) ratio, if it has so occurred, may be subsequently overprinted by in-situ clay-catalyzed reactions.  相似文献   

6.
The Pearl River Mouth Basin in the South China Sea has accumulated >2 km of Eocene sediments in its deep basin, and has become the exploration focus due to the recent discoveries of the HZ25-7 oil field in the Eocene Wenchang (E2w) Formation. In this study, the geochemical characteristics of potential source rocks and petroleum in the HZ25-7 oil field are investigated and the possible origins and accumulation models developed. The analytical results reveal two sets of potential source rocks, E2w and Enping (E2e) formations developed in the study area. The semi-deep-to-deep lacustrine E2w source rocks are characterized by relatively low C29 steranes, low C19/C23 tricyclic terpane (<0.6), low C24 tetracyclic terpane/C30 hopane (<0.1), low trans-trans-trans-bicadinane (T)/C30 hopane (most <2.0), and high C30 4-methyl sterane/ΣC29 sterane (>0.2) ratios. In contrast, the shallow lacustrine and deltaic swamp-plain E2e source rocks are characterized by relatively high C29 steranes, high C19/C23 tricyclic terpane (>0.6), high C24 tetracyclic terpane/C30 hopane (>0.1), variable yet overall high T/C30 hopane, and low C30 4-methyl sterane/ΣC29 sterane (<0.2) ratios. The relatively low C19/C23 tricyclic terpane ratios (mean value: 0.39), low C24 tetracyclic terpane/C30 hopane ratios (mean value: 0.07), high C30 4-methyl sterane/ΣC29 sterane ratios (mean value: 1.14), and relatively high C27 regular sterane content of petroleum in the HZ25-7 oil field indicate that the petroleum most likely originated from the E2w Formation mudstone in the Huizhou Depression. One stage of continuous charging is identified in the HZ25-7 oil field; oil injection is from 16 Ma to present and peak filling occurs after 12 Ma. Thin sandstone beds with relatively good connectivity and physical properties (porosity and permeability) in the E2w Formation are favorable conduits for the lateral migration of petroleum. This petroleum accumulation pattern implies that the E2w Formation on the western and southern margins of the Huizhou Depression are favorable for petroleum accumulation because they are located in a migration pathway. Thus exploration should focus in these areas in the future.  相似文献   

7.
We used a research submersible to obtain 33 sediment samples from chemosynthetic communities at 541–650 m water depths in the Green Canyon (GC) area of the Gulf of Mexico slope. Sediment samples from beneath an isolated mat of H2S-oxidizing bacteria at GC 234 contain oil (mean = 5650 ppm) and C1–C5 hydrocarbons (mean = 12,979 ppm) that are altered by bacterial oxidation. Control cores away from the mat contain lower concentrations of oil (mean = 2966 ppm) and C1–C5 hydrocarbons (mean = 83.6 ppm). Bacterial oxidation of hydrocarbons depletes O2 in sediments and triggers bacterial sulfate reduction to produce the H2S required by the mats. Sediment samples from GC 185 (Bush Hill) contain high concentrations of oil (mean = 24,775 ppm) and C1–C5 hydrocarbons (mean = 11,037 ppm) that are altered by bacterial oxidation. Tube worm communities requiring H2S occur at GC 185 where the sea floor has been greatly modified since the Pleistocene by accumulation of oil, thermogenic gas hydrates, and authigenic carbonate rock. Venting to the water column is suppressed by this sea-floor modification, enhancing bacterial activity in sediments. Sediments from an area with vesicomyid clams (GC 272) contain lower concentrations of oil altered by bacterial oxidation (mean = 1716 ppm) but C1–C5 concentrations are high (mean = 28,766 ppm). In contrast to other sampling areas, a sediment associated with the methanotrophic Seep Mytilid I (GC 233) is characterized by low concentration of oil (82 ppm) but biogenic methane (C1) is present (8829 ppm).  相似文献   

8.
The occurrence of widely distributed acyclic isoprenoid hydrocarbons (C2O, C25 and C30) with highly branched structures, in sediments and biota is reviewed. The compounds occur as alkanes and alkenes with from one to at least four double bonds in young aquatic (both marine and lacustrine) sediments from many parts of the globe (e.g. Peru, Antarctica, Gulf of Suez, North Sea, Atlantic) sometimes in high concentrations (e.g. 40 μg g−1 sediment) relative to other hydrocarbons. However, the compounds rapidly disappear in older sediments, possibly due to biodegradation and reaction with sedimentary sulphur. These and other factors are discussed.The sources of this fascinating group of hydrocarbons remain largely unknown, though evidence points to algae (possibly diatoms) as one possibility. The recent identification of related sulphur-containing compounds in a crude oil promises to extend the number of reports of these compounds still further, and to increase their importance as environmental biological markers.  相似文献   

9.
We conducted an in situ feeding experiment using 13C-labeled unicellular algae in Sagami Bay, Japan (water depth, 1450 m), in order to understand the fate of lipid compounds in phytodetritus at the deep-sea floor. We examined the incorporation of excess 13C into lipid compounds extracted from bulk sediments and benthic foraminiferal cells. 13C-enriched fatty acids derived from 13C-labeled algae were exponentially degraded during 6 days of incubation in the sediment. Subsequent enrichments in 13C in sedimentary n-C15, anteiso-C17, and C17 fatty acids indicated the microbial degradation of algal material and production of bacterial biomass in the sediment. We observed the incorporation of 13C-labeled algal phytol and fatty acids into foraminiferal cells. The compositions of 13C-labeled algal lipids in foraminiferal cells were different from those in the bulk sediments, indicating that foraminiferal feeding and digestion influenced the lipid distribution in the sediments. Furthermore, some sterols in Globobulimina affinis (e.g., 24-ethylcholesta-5,22-dien-3β-ol, 24-ethylcholest-5-en-3β-ol, and 23,24-dimethylcholesta-5,22E-dien-3β-ol) were newly produced via the modification of dietary algal sterols within 4–6 days. In addition to the effects of bacteria, feeding by benthic foraminifera can result in a significant reorganization of the composition of organic matter and influence benthic food webs and carbon cycling at the deep-sea floor.  相似文献   

10.
Comparative studies of the composition and distribution of the dispersed organic matter (DOM) were performed for the bottom sediments from active areas of the Ashadze hydrothermal field (the Mid-Atlantic Ridge, 13° N) and for background sediments from the area treated (sampled during the cruises of R/V Professor Logachev in 2003 and 2007). The content of hydrocarbons (HCs) in the hydrothermal samples is about 20 times as high as the background values. The HCs composition includes both low-transformed (isoprenoids, hopenes, ββ-hopanes, and ααα27R-steranes) and geologically mature chemofossils (C16-C35 n-alkanes, geohopanes, moretanes, and polyaromatic hydrocarbons). The polyaromatic hydrocarbons (PAHs) are mainly represented by phenanthrene and its alkyl homologues, i.e., by possible products of the diagenetic transformation of biogenic precursors. The results obtained point to the mixed genesis of the hydrothermal DOM, which is caused first by the diversity of the biota composition in the considered region, as well as by the specificity of the processes of the DOM’s maturing under the extreme environmental conditions.  相似文献   

11.
Woei-Lih Jeng   《Marine Chemistry》2006,102(3-4):242-251
The n-alkane average chain length (ACL) is the weight-averaged number of carbon atoms of the higher plant C25–C33 n-alkanes. The abundance of individual n-alkanes from higher plant sources generally increases with increasing carbon number in coastal marine sediments around Taiwan, but this trend is reversed for petrogenic hydrocarbons. The ACL would potentially be lowered if petrogenic hydrocarbons were added to sediments containing biogenic hydrocarbons alone. To test this idea, a marine environment off southwestern Taiwan known to contain both biogenic and petrogenic hydrocarbons and two nearby rivers were selected for investigating possible difference in ACL values between their sediments. The average CPI of C25–C33 n-alkanes was 4.08 ± 2.04 (range 1.90–8.96, n = 15) for the river sediments and 1.70 ± 0.16 (range 1.43–1.97, n = 15) for the marine sediments. The ACL of C25–C33 n-alkanes for river sediments ranged from 29.2 to 30.5 (average 29.9 ± 0.4), and for marine sediments from 28.4 to 29.3 (average 28.9 ± 0.3). The ACL difference between marine and river sediments was significant (Student's t test at 99% confidence) although it appeared small. It is suggested that the ACL can be an additional indicator for detection of petrogenic hydrocarbons in coastal marine sediments.  相似文献   

12.
Coupling between degraded benthic habitats and populations of epibenthic and pelagic organisms is evident around major sewage outfalls in the Southern California Bight. The distribution of bottom-feeding fishes appears to be affected, but sampling has not been intensive enough to rigorously define patterns for more than a few species. Some evidence suggests that changes in fish abundance may be related to changes in the distribution and abundance of benthic prey; those species (e.g. Dover sole) that can adapt their diets to take advantage of dense populations of opportunistic polychaetes may be found in large numbers around outfalls. Some benthic crustacean feeders are at a disadvantage. Sewage effluent is an allochthnous source of organic matter to the food web and Dover sole and ridgeback shrimp both show shifts in stable isotope ratios consistent with the thesis that sewage-derived organic matter in sediments is trophically transferred to epibenthic organisms. Constructing a carbon budget based on the δ13C shifts in these species from area of a major outfall relative to a distant control station suggests that there is an in situ source of isotopically very light carbon in outfall sediments, perhaps from CO2 fixation by chemoautotrophs and biological methane oxidation. Benthic-pelagic coupling is also evident in the accumulation of chlorinated hydrocarbons by fish and other organisms. At the two major Los Angeles area outfalls log-transformed liver-to-sediment concentration ratios of chlorinated benzenes, which are accumulated to moderate levels in fish, show a linear relationship to the log of Kow (the octanol-to-water partioning coefficient) of these compounds. Chlorinated hydrocarbons with greater lipid solubility, e.g. PCBs and p,p-DDE, are concentrated to very high levels. Studies of food webs using Cs/K as a measure of trophic level suggest that trophic-step magnification is concentrating these compounds in higher trophic levels.  相似文献   

13.
Two models, a spectral refraction model (Longuet-Higgins) and a parabolic equation method (PEM) refraction-diffraction model (Kirby), are used to simulate the propagation of surface gravity waves across the Southern California Bight. The Bight contains numerous offshore islands and shoals and is significantly larger (≈ 300 km by 300 km) than regions typically studied with these models. The effects of complex bathymetry on the transformation of incident wave directional spectra, S0(f,θ0), which are very narrow in both frequency and direction are difficult to model accurately. As S0(f,θ0) becomes broader in both dimensions, agreement between the models improves and the spectra predicted at coastal sites become less sensitive to errors in the bathymetry grid, to tidal changes in the mean water depth, and to uncertainty in S0(f,θ0) itself. The smoothing associated with even relatively narrow (0.01 Hz-5° bandwidth) S0(f,θ0) is usually sufficient to bring the model predictions of shallow water energy into at least qualitative agreement. However, neither model is accurate at highly sheltered sites. The importance of diffraction degrades the predictions of the refraction model, and a positive bias [O (10%) of the deep ocean energy] in the refraction-diffraction model estimates, believed to stem from numerical “noise” (Kirby), may be comparable to the low wave energy. The best agreement between the predicted spectra generally occurs at moderately exposed locations in deeper waters within the Bight, away from shallow water diffractive effects and in the far-field of the islands. In these cases, the differences between the models are small, comparable to the errors caused by tidal fluctuations in water depth as waves propagate across the Bight. The accuracy of predicted energies at these sites is likely to be limited by the uncertainty in specifying S0(f,θ0).  相似文献   

14.
Seismic data from a 186 km-long refraction profile in the Santa Barbara Channel have been interpreted using several velocity inversion techniques. Data were obtained during two cruises in 1978 and 1979. Seismic arrivals from fifty explosions of between 1 and 300 lbs. of TNT were recorded by two ocean bottom seismometers, four permanent ocean bottom stations (University of Southern California), and much of the United States Geological Survey/California Institute of Technology southern California seismic network. Travel-time inversion gives a V p of 6.3 km sec-1 at 7.2 km depth above 7.2 km sec-1 at 14.4 km depth at the western end of the channel. At the eastern end, solutions suggest three sediment refractors overlying V p of 6.4 km sec-1 at 7.3 km depth, above 7.0 km sec-1 at 11.6 km depth, above mantle arrivals with V p of 8.3 km sec-1 at 21.8 km depth. The velocity structure determined by these methods suggests that the channel has a sedimentary fill of from 4 to 7 km and a layer of mafic plus ultramafic rock 14 to 17 km thick. The greatest thicknesses of sediments are restricted to east of Point Conception. The velocity data also suggest that the Franciscan formation may not be present beneath the channel. Rather, the crust here may represent a thickened portion of the Coast Range ophiolite.  相似文献   

15.
本文建立了半透膜渗透装置(semi-permeable membrane device,SPMD)富集-超声萃取-凝胶渗透色谱净化-气相色谱法测定沉积物间隙水中多氯联苯(PCBs)的方法。比较了有机溶剂透析法与超声萃取法从膜袋内提取PCBs的回收率,发现超声萃取法在节省时间和溶剂方面有明显优势。应用凝胶渗透色谱分离与净化SPMD提取物,收集11—17min的流出液能达到最佳分离效果。基于此方法测定了大连湾沉积物间隙水中自由溶解态PCBs的含量(C_(W-SPMD)),同时又分析了沉积物中PCBs的总量(C_(SED))、间隙水中PCBs的含量(有机碳含量校正法,C_(W-SED))和间隙水中PCBs的总含量(离心法,C_(PW))。结果表明,C_(PW)值显著高于C_(W-SED)和C_(W-SPMD)值。因此,考虑到生物可利用性,无论采用沉积物中或者间隙水中的PCBs总量进行污染物生态风险评价均会造成风险被高估,建议采用间隙水中可溶解态含量。  相似文献   

16.
This study examined the fate of Prudhoe Bay crude oil in nearshore sediments of the Beaufort Sea, in situ, with emphasis on the rôle of microorganisms in the weathering process. The results indicate that oil is degraded in Arctic sediments very slowly; only after 1 year's exposure was biodegradation evident. Several factors probably contributed to the slow rate of microbial weathering, including: limited populations of hydrocarbon utilising microorganisms; localised high oil concentrations; low temperatures; limiting nutrient concentrations (unfavourable C:N and C:P ratios); low oxygen tensions and limited circulation of interstitial waters in fine-grained sediments. Abiotic weathering of the oil was also slow, with limited loss of low molecular weight aliphatic and aromatic hydrocarbons during 2 years' exposure. Significant features of the overall weathering process were: lack of initial loss of low molecular weight compounds; aliphatic compounds were not preferentially degraded over aromatic compounds and C17, and lower molecular weight normal alkanes were preferentially degraded over higher molecular weight alkanes. The results of this study indicate that hydrocarbons will persist relatively unaltered for several years if Beaufort Sea sediments are contaminated with petroleum.  相似文献   

17.
The paper presents research results on the concentrations and compositions of aliphatic and polycyclic aromatic hydrocarbons in the surface layer of bottom sediments in the Northwestern Caspian Sea (2014) and compares them to data for sediments of the Middle and Southern Caspian (2012–2013). The seepage of hydrocarbons out of the sediment mass, resulting in abnormally high concentrations of aliphatic hydrocarbons per dry weight (up to 468 μg/g), as well as within the Corg composition (up to 35.2%), is considered the main source of hydrocarbons in sediments in the surveyed area of the Northern Caspian. This is also confirmed by the absence of any correlation between the hydrocarbon and Corg distributions, as well as by the transformed oil composition of high-molecular alkanes. The distribution of markers within polycyclic aromatic hydrocarbons points to a mixed genesis—petrogenic and pyrogenic—with prevalence of the latter. Unlike the shallow-water northern part of the Caspian Sea, the content and composition of hydrocarbons in deep-seated sediments are affected by facial conditions of sedimentation and by matter exchange at the water–bottom interface. Therefore, despite high Corg concentrations (up to 9.9%), sediments in deep-water depressions are characterized by a quite low concentration of aliphatic hydrocarbons (52 μg/g on average; 0.2% of Corg) with prevailing natural allochthonous alkanes.  相似文献   

18.
The alkaline aluminate waste, of which 1000–2000 tonnes are dumped a few times a year off the Belgian coast in the Southern Bight of the North Sea, contains 5·4% NaCl, 1·8% dissolved Al and 7·4% NaOH, in addition to traces of heavy metals and some aniline- and phenol-derivatives. The pH rises locally to 8-5 and the total Al-concentration reaches 120niglitre−1(corresponding to an initial waste dilution factor of only 150) in the 10-m wide track just beyond the discharging barge, but these decay quickly to pH 8·1 and 1 mg litre-1 in the 30-m wide track, 500m behind the barge. The relation between the waste concentration and seawater pH was studied. The white precipitate that forms immediately in the sea was identified as Mg6---Al2---CO3---(OH)16---4H20 (hydrotalcite-manasseite like). No trace of it was found in the local sediments.  相似文献   

19.
Relationships between light intensity and substrate concentration and rates of assimilation and oxidation of ammonium by microorganisms were investigated at four stations off the Washington coast and three stations in the Southern California Bight. Ammonium oxidation rates were negatively correlated with light in the photic zone at all stations; light inhibition of nitrifying bacteria forms an important control over the depth distribution of ammonium oxidation activity. Both assimilation and oxidation were positively correlated with ammonium concentration at the Washington coast stations, where ambient ammonium concentrations were high. Light and ammonium assimilation rate were positively correlated at the Southern California Bight stations (within the photic zone; i.e., excluding depths greater than 150m), but unrelated at the Washington coast stations. Assimilation and oxidation have nearly opposite distribution patterns with depth in the water column, but phytoplankton and nitrifying bacteria probably compete for ammonium at depths near the bottom of the photic zone.  相似文献   

20.
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   

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