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1.
The molecular size distribution of humic substances has been investigated in two recent sediment samples of different ages taken from a single core sample collected off Walvis Bay, south-west Africa. Extractable humic acids were found to be by far the major form of organic carbon in both sediments, the near-surface younger sample containing predominantly high molecular weight (>100 000 molecular weight) humic acids and little fulvic acids whilst the deeper, older sample contained relatively less humic acid and relatively more fulvic acid of a range of molecular weights. A significant age difference was found between the >300 000 molecular weight and the <30 000 molecular weight fractions of the near-surface sample, the lower molecular weight fraction being older than the higher molecular weight fraction.The data suggest that in this rapidly accumulating, organic-rich sediment the first step en route from the planktonic matter to the humic complexes is direct and rapid incorporation of the biogenic material into high molecular weight humic acids.  相似文献   

2.
This work has investigated the possible formation of humic and fulvic acids, particularly high molecular weight moieties, in degrading diatom debris. The diatom debris was collected, freshly sedimented, from a well characterized natural field diatom population and allowed to degrade under conditions similar to those found at the sediment-water interface of many marine, organic-rich sediments.Samples of the detritus and overlying water were taken regularly over a period of 4 months and analysed for the presence of humic compounds. In the case of the detrital material, a sequential series of extractions were used. Molecular weight fractionation of the extracted humic material was carried out using Diaflow Ultrafiltration Membranes and two different fractionation methods have been compared. It appears that the choice of method may have an important effect on the determined distribution of the humic material, particularly when humic acid concentrations are low.High molecular weight (> 300 000- > 100 000) humic and fulvic acids were found in all the detrital samples, the content increasing with the period of decomposition. No evidence of any humic material was found in extracts of the living diatoms, the conclusion being that this material had been formed in situ during the degradation of the diatom debris. Most (65–90%) of the humic material was extracted from the detritus using a mild 0·05 m NaOH extraction at room temperature. Fulvic acids comprised approximately 90% of the total 0·05 m NaOH extraction, being composed mainly of either low molecular weight compounds (40–50% < 10000) or high molecular weight compounds (38–48% > 100000). Levels of humic acids were much lower and included a wide range of molecular weight fractions.The relevance of these findings to the possible origin of humic material in certain marine sediments is discussed.  相似文献   

3.
The chloroform-extractable ‘lipid’ fraction of dissolved organic matter in seawater was analyzed by gravimetry, liquid chromatography, gas chromatography (GC), and gas chromatography—mass spectrometry (GC—MS). Gravimetric concentrations of dissolved lipids in the Gulf of Mexico were in the range of 60–160 μg 1?1 in near-surface waters and 61–116 μg 1?1 in near bottom waters and accounted for ～4% of the dissolved organic carbon. Over a 12-h sampling period and a 5-d sampling period extensive variability in dissolved lipid quantity and quality were observed. The major percentage of extractable weight was collected in the polar liquid chromatographic fraction (55–95%). Gas chromatographic concentrations of the aliphatic fractions were in the range of 0.014-0.187 μg 1?1. Concentrations derived from gas chromatography were consistently lower than gravimetrically-derived concentrations. A number of compounds were tentatively identified by a combination of GC, GC—MS, and authentic standards. The major components of the analyzable dissolved lipids were n-alkanes (C16C32), pristane, phytane, methyl, ethyl and propyl esters of fatty acids. Minor components included olefins and cycloalkanes, aromatics, short-chained acids, and possibly a lactone and an alcohol. All concentrations and compounds were indicative of a fairly pristine environment. The n-alkane distribution appears to be the result of marine and terrestrial inputs superimposed on a chronic low-level background of oil pollution. It is suggested that the fatty acid esters and other fragment molecules are the résult of the degradation of humic substances. A number of potential indicators of source were isolated.  相似文献   

4.
While concern over anthropogenic marine litter around coastlines is increasing worldwide, information on this litter in trenches on the seafloor is very sparse. We investigated the amount of marine litter on the deep-sea bottom around the Ryukyu Islands in the Northwest Pacific, based on trawl samples. The density of litter observed in the axis of the Ryukyu Trench (7100 m) and in the basin of the Okinawa Trough ranged from 1.2 × 103 to 7.1 × 103 items km?2, or 7.5–121.4 kg km?2, which was significantly higher than that observed on the adjacent shallower continental slopes or abyssal plain (0.1 × 103 to 0.6 × 103 items km?2; 0.03–9.2 kg km?2). This suggests that trenches and troughs function as “depocenters” for anthropogenic litter because of their deeper and enclosed topographies.  相似文献   

5.
Vertical distributions of carbohydrates in humic and fulvic acids isolated from coastal sediments in Suo sound were investigated by gas chromatography and Sephadex gel chromatography. Humate carbohydrates were composed of fulvic acid carbohydrates (70 to 95%). Apparent molecular weight distribution of fulvic acid carbohydrates in vertical direction of sediments was 3·5 to 7·4% below molecular weight (M.W.) 1000, 32 to 42% for M.W. 1000 to 5000, 7·4 to 24% for M.W. 5000 to 10 000, 11·5 to 15·5% for M.W. 10 000 to 25 000, and 28 to 34% for M.W. over 25 000, respectively. Humic acid carbohydrates are present in high molecular weight over 25 000. Fulvic acid carbohydrates decreased with increasing depth. A decrease of humate carbohydrates occurred between the surface layers to 20 cm depth, below 20 cm vertical change of carbohydrates was not observed.  相似文献   

6.
The dynamics of methane (CH4) flux in relation to populations of methanogenic and methanotrophic bacteria was studied under the different biophysical conditions of the Indian Sundarban mangrove ecosystem. Soil depth profile analysis (up to 60 cm) in the lower littoral zone (LLZ) revealed that a methanogenic population of 6.45 ± 0.19 × 104 cells/g dry weight (dry wt) of soil accounted for a CH4 production rate of 6.23 ± 3.53 × 103 µmol m?2 day?1, whereas in the surface soil, a methanogenic population of 3.34 ± 0.37 × 104 cells/g dry wt of soil accounted for a CH4 production rate of 31.6 ± 0.57 µmol m?2 day?1. The CH4 oxidation rate at 60 cm depth in the LLZ was 24.42 ± 1.28 µmol m?2 day?1, with an average methanotrophic population of 1.33 ± 0.43 × 104 cells/g dry wt of soil, whereas in the surface soil, the oxidation rate and average population were 3.38 ± 1.43 × 103 µmol m?2 day?1 and 12.80 ± 2.54 × 104 cells/g dry wt of soil, respectively. A similar soil profile in terms of CH4 dynamics and the populations of methanogenic and methanotrophic bacteria was found in the mid‐littoral and upper littoral zones of the studied area. The results demonstrate that most of the produced CH4 (approximately 60%) was oxidized by methanotrophic bacteria present in the soil, thus revealing their principal role in regulating the CH4 flux from this unique ecosystem.  相似文献   

7.
A sediment budget for the Choptank River, one of the three largest estuaries on the eastern shore of Chesapeake Bay, was developed from measurements of sediment carried in upland runoff, shore erosion, sedimentation, and levels of suspended sediments in estuarine waters. Shore erosion was the major source of sediment (340 × 106 kg y?1), contributing seven times more sediment than upland runoff. Low relief, the rural character of the Coastal Plain drainage basin, and the susceptibility of poorly consolidated shoreline materials to erosion contributed to the dominance of shore erosion over runoff as a sediment source. Box modelling indicated a net annual flux (14–44 × 106 kg y?1) of sediment from the Choptank River to Chesapeake Bay. A mass balance estimate of sedimentation, calculated as the difference between total inputs and loss at the mouth of the estuary, (350 × 106 kg y?1) agreed well with an estimate based on 210Pb profiles (340 × 106 kg y?1) measured along the longitudinal axis of the estuary. Lead-210 sedimentation rates correspond to accumulation rates of 1·5–7·9 mm y?1.  相似文献   

8.
Charcoal column chromatography and a dialysis system using a Visking tube were used for the concentration and separation of dissolved carbohydrates in seawater. Recoveries of mono-, oligo-, and polysaccharides were 46–74, 61–89 and 70%, respectively, relative to the total amount of sugars initially submitted to analysis. The combined charcoal column chromatography and dialysis system was used to separate dissolved carbohydrates in seawater samples from Mikawa Bay into mono-, oligo- and polysaccharide fractions. The polysaccharides are separated into two fractions with molecular weights of <4,000 and >4,000 using Sephadex G-25 column chromatography. Monosaccharides, oligosaccharides, polysaccharides with M.W.<4,000 and polysaccharides with M.W. >4,000 accounted for 7–9, 15–26, 7–13 and 20–33% of total dissolved carbohydrates, respectively. However, 32–38% of dissolved carbohydrates were lost during the analytical procedures. Glucose, galactose, mannose, xylose, arabinose, ribose, fucose, and rhamnose were found upon acid hydrolysis of the oligo- and polysaccharide fractions, while fucose and rhamnose were not present in the monosaccharide fraction. Possible sources of the carbohydrates in these fractions are discussed with reference to the monosaccharide composition of cellular carbohydrate in marine algae.  相似文献   

9.
The concentrations of the trace metals Cd, Cu, Fe, Ni, Pb and Zn in the Göta River estuary have been investigated. The following metal fractions have been determined: acid-leachable, dissolved, labile and particulate.The estuary represents a salt wedge type estuary and is situated in a densely populated region of Sweden. The metal concentrations found for the dissolved fraction is in the range of what can be considered as background levels for freshwater. It is difficult to evaluate any estuarine processes other than conservative mixing for Cd, Cu, Ni and Zn. The dissolved levels in the freshwater end member are Cd, 9–25 ngl?1; Cu, 1·1–1·4 μgl?1; Fe, 20–75 μg l?1: Ni, 0·7–0·9 μg l?1: Pb 0·09–0·2 μg l?1; and Zn, 6–7 μg l?1:The results from the acid-leachable fraction show that at high suspended load the particles sediment in the river mouth. The trace metal levels in this fraction are subject to large variations.  相似文献   

10.
The interactions in seawater of cadmium, copper, and zinc with natural levels of marine humus (fulvic and humic acids) were studied using differential pulse anodic stripping voltammetry (DPASV). Interactions with Cu were also examined by ultraviolet spectrophotometry. The degree of interaction relates to the structure of the particular fulvic or humic acid tested. Marine fulvic and humic acids with different equivalent weights and varying degrees of aromaticity and heteroatom substitution were tested to assess the relative importance of these fundamental structural features in determining the degree of interaction. An index of heteroatom substitution, derived from proton magnetic resonance spectra of these materials, when combined with equivalent weights correlated with the nature and degree of metal interaction. Both marine fulvic and humic acids appreciably interacted with Zn. In contrast, the extent of interaction of fulvic acids with Cu appears to be related to their structure while humic acids appear to interact with Cu regardless of structure. Cadmium interacts only with mature, highly crosslinked humic acids.  相似文献   

11.
Stoichiometry among bioactive trace metals in the Chukchi and Beaufort Seas   总被引：1，自引：1，他引：0  
The distribution of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in seawater was investigated in the Chukchi and Beaufort Seas of the western Arctic Ocean in September 2000. The unfiltered and filtered seawater samples were used for determination of total dissolvable metal (TDM) and dissolved metal (DM), respectively. The concentration of labile particulate metal (LPM) was estimated with the difference between that of TDM and DM. The concentrations of TDAl, TDMn, TDFe, TDCo and TDPb varied substantially in the study area. The high concentrations occurred at stations near the Bering Strait, in the Mackenzie delta, and above reductive sediments on the shelf and slope. These elements were mostly dominated by labile particulate species, such as Fe?CMn oxides and species adsorbed on terrestrial clay. DCo was correlated with DMn over the study area (r?=?0.78, n?=?135), and the slope of the regression line was 27 times higher at a pelagic station than at a shelf station. TDNi, TDCu, TDZn and TDCd showed relatively small variations and were generally dominated by dissolved species. There was a moderate correlation between DCd and phosphate for all samples (r?=?0.79), whereas there were no significant correlation between the other DMs and nutrients. TDNi and TDCu showed a remarkable linearity for most stations except those near the Bering Strait (R 2?=?0.95, n?=?126). These results suggest that biogeochemical cycling including uptake by phytoplankton and remineralization from settling particles has only minor control over the distribution of trace metals in this area. Using the present data, the annual input of bioactive trace metals form the Bering Strait and the Mackenzie River was estimated. Also, the trace metal compositions of major water masses were evaluated. The dissolved elemental ratio was P:Al:Mn:Fe:Co:Ni:Cu:Zn:Cd?=?1:1.2?×?10?2:4.4?×?10?4:1.4?×?10?3:3.7?×?10?5:3.7?×?10?3:1.4?×?10?3:4.5?×?10?3:2.2?×?10?4 for Canada Basin deep water (CBDW). This ratio was significantly different from that for Pacific deep water and Bering Sea water, suggesting substantial modification of the trace metal compositions of seawater in the study area.  相似文献   

12.
The KwaZulu-Natal Bight is a shallow indentation of the eastern seaboard of South Africa, characterised by a narrow (45 km wide) extension of the continental shelf, with a shelf break at about 100 m. It has a complex hydrography: the waters of the bight are derived from the fast-flowing, southward-trending Agulhas Current, which is fed mostly by the tropical and subtropical surface waters of the South-West Indian Ocean subgyre, which are generally oligotrophic in nature, notably depleted in reduced nitrogen and phosphate except at river mouths and during periodic upwelling of deeper nutrient-rich water. Despite this, the bight is believed to be relatively productive, and it is suggested that efficient nutrient recycling by prokaryotes may sustain primary productivity efficiently, even in the absence of new nutrient inputs. Here we have measured bacterial numbers, biomass and heterotrophic productivity during summer and winter in conjunction with phytoplankton standing stock and factors that influence it. Bacterial distribution closely matched phytoplankton distribution in surface waters, and was highest close to the coast. Bacterial standing stocks were similar to those of oligotrophic systems elsewhere (0.5–5.0 × 105 cells ml–1; 1 × 10–8 to 1.25 × 10–7 g C ml–1) and increased in association with the development of phytoplankton blooms offshore and with inputs of allochthonous material by rivers at the coast. Heterotrophic productivity in summer was lowest in the far south and north of the bight (0.5 × 10–10 g C ml–1 h–1) but higher close to the shore, over shallow banks, and in association with increased phytoplankton abundance over the midshelf (1.0–3.5 × 10–9 g C ml–1 h–1). There were marked seasonal differences with lower bacterial standing stocks (5 × 104 to 2 × 105 cells ml–1; 4–5 × 10–9 to 1–2 × 10–8 g C ml–1) and very low bacterial productivity (4 × 10–11 to 1 × 10–10 g C ml–1 h–1) in winter, probably resulting from lowered rates of primary productivity and dissolved organic matter release as well as reduced riverine allochthonous inputs during the winter drought.  相似文献   

13.
Oxy-anionic species of V, As, Se, Mo, Sb, Te and W were measured in solution and suspension in samples obtained during several cruises in the Dutch Wadden Sea, the offshore region of the Southern Bight (North Sea) and in the estuaries of the Rhine and Scheldt. Dissolved concentrations at salinities above 34·5 × 10?3 ( = 34·5%. S) agreed generally well with published open ocean values. It is suggested that Se speciation differs from the open ocean.In the Wadden Sea, concentrations of V, Se, Mo and Sb were linearly related to salinity (10–35 × 10?3). The good agreement between measured and extrapolated values at a salinity of 0·5 × 10?3 suggests conservative behaviour in the Rhine estuary (with residence time of freshwater in the order of a few days).Dissolved concentration vs. salinity plots in the Scheldt estuary (residence time 2–3 months) showed pronounced minima and maxima. These occurred in the low or medium salinity range for V, As and Sb. Linear behaviour was observed for Se and Mo (in some cases, relatively large differences between cruises were detected). Deviations from linearity in the plots are interpreted in terms of thermodynamic equilibrium conditions involving species with different solubilities (V), local input from land (As, Se, Sb, Te) and removal from solution (As), probably through coprecipitation with Fe(OH)3.In the offshore samples, the contributions of particulate forms to the total element concentrations were small (<15%). At higher SPM concentrations (about 30 mg dm?3), this percentage remained small for Se, Mo and Sb (<15%); it was substantial for V and As (25–50%).  相似文献   

14.
对海带综合利用生产中剩下的浓缩浸泡液所含腐植质进行了分离,并对分离出的腐植酸、富里酸和乙醇可溶物三级分做了化学表征和性质研究,包括三级分的得率、紫外和红外光谱分析,元素、官能团、氨基酸和总糖含量分析,分子量分布,以及它们对鱼卵生长和褐藻酸钠粘度的影响。  相似文献   

15.
The partitioning of annual organic carbon fluxes from five stations located in the vicinity of the Pacific-Antarctic Ridge and the Peru continental margin suggests that 35–85% of the total near-bottom organic carbon flux is utilized at or near the sediment-water interface. These estimates have large uncertainties, but illustrate that assessments of organic carbon utilization can be made by several stepwise approaches which are generally applicable to a wide spectrum of marine environments.In one approach, the mineralization of organic carbon from the sediments was predicted from both sedimentary organic carbon and pore water nutrient profiles with comparable results. Neglecting sediment mixing, the rate constants of the anoxic sediments off Peru range from 0.1 × 10?3 to 4 × 10?3 y?1, and rate constants derived for oxic SW Pacific sediments range from 3 × 10?4 to 7 × 10?4 y?1. As with other values reported for sulfate reducing sediments by Toth and Lerman (1977) and for oxic central Pacific sediments by Müller and Mangini (1980), log-log plots of rate constants vs. sedimentation rate define two parallel linear relationships for oxic and anoxic sediments, respectively. The apparently enhanced rates for oxic environments may result from large benthic organisms which redistribute a portion of the available detritus and in doing so convert it into more easily accessible and metabolizable organic matter. In low-oxygen environments, bottom feeders and infauna are less abundant and more likely to irrigate rapidly accumulating sediments.  相似文献   

16.
In the framework of the German contribution to the Joint Global Ocean Flux Study (JGOFS), deep-water fluxes of particle-associated trace elements were measured in the northeast Atlantic Ocean. The sinking particles were collected almost continuously from 1992 to 1996 at three time-series stations, L1 (33°N/22°W), L2 (47°N/20°W), and L3 (54°N/21°W), using sediment traps. The focus of the present study is the temporal variability of the particle-associated elemental fluxes of Al, Ca, Cd, Co, Cu, Fe, Mn, Ni, P, Pb, Ti, V, and Zn at a depth of 2000 m.A clear seasonality of the fluxes that persisted for several years was documented for the southernmost station (L1) at stable oligotrophic conditions in the area of the North Atlantic Subtropical Gyre East (NASTE). At L2 and L3, an episodic nature of the elemental fluxes was determined. Mesoscale eddies are known to frequently cause temporal and spatial variability in the flux of biogenic components in that area. These events modified the simple seasonal pattern controlled by the annual cycle at L2, in the North Atlantic Drift Region (NADR), and at L3, which was influenced by the Atlantic Arctic province (ARCT). All stations were characterized by an additional episodic lithogenic atmospheric supply reaching the deep sea.The integrated annual fluxes during the multi-year study revealed similar flux magnitudes for lithogenic elements (Al, Co, Fe, Ti, and V) at L2 and L3 and roughly twofold fluxes at L1. Biogenic elements (Cd, P, and Zn) showed the opposite trend, i.e., two to fourfold higher values at L2 and L3 than at L1. For Mn, Ni, and Cu, the spatial differences were smaller, perhaps because of the intermediate behavior, between lithogenic and biogenic, of these elements. Similarly, among the three study sites, there were no noticeable differences in the total annual flux of Pb.The respective lithogenic fractions of the deep-sea fluxes of Cd, Co, Cu, Mn, Ni, V, and Zn were subtracted based on the amount of Al, with the average composition of the continental crust as reference. This procedure allowed estimation of the labile trace element fraction (TEexc) of the particles, i.e., TE taken up or scavenged during particle production and sedimentation. The ratios of TEexc/P clearly demonstrated an enrichment of TE over labile P from biogenic surface material to the deep sea for Zn (factor 4–6), Mn (12–27), Ni (3–5), and Cu (9–25); an intermediate status for Co (0.5–2.2); and depletion for Cd vs. P (0.2–0.4). Surprisingly, the recycling behavior of excess Co was found to be similar to that of P. Hence, Coexc behaved like a biogenic element; this is in contrast to total Co, which is dominated by the refractory lithogenic fraction.Moreover, it is argued that these excess elemental fluxes caused a loss of the dissolved elements in upper waters, since their transport reaches the deep-sea waters at 2000 m, a depth far below of deep-winter mixing and upwelling. The annual amount of excess TE exported from surface waters was estimated to be 1.3×109 mol Zn y?1, 4.4×109 mol Mn y?1, 4.9×108 mol Ni y?1, 2.2×107 mol Cd y?1, 7.4×108 mol Cu y?1, and 2.7×107 mol Co y?1 for the whole North Atlantic Ocean. Important primary sources that could replenish these losses are the aeolian and fluvial supply processes.  相似文献   

17.
We have investigated the chemical forms, reactivities and transformation kinetics of Fe(III) species present in coastal water with ion exchange and filtration methods. To simulate coastal water system, a mixture of ferric iron and fulvic acid was added to filtered seawater and incubated for a minute to a week. At each incubation time, the seawater sample was acidified with hydrochloric acid and then applied to anion exchange resin (AER) to separate negatively charged species (such as fulvic acid, its complexes with iron and iron oxyhydroxide coated with fulvic acid) from positively charged inorganic ferric iron (Fe(III)′). By monitoring the acid-induced Fe(III)′ over an hour, it was found that iron complexed by fulvic acid dissociated rapidly to a large extent (86–92% at pH 2), whereas amorphous ferric oxyhydroxide particles associated with fulvic acid (AFO-L) dissociated very slowly with the first-order dissociation rate constants ranging from 6.1 × 10− 5 for pH 3 to 2.7 × 10− 4 s− 1 for pH 2. Therefore, a brief acidification followed by the AER treatment (acidification/AER method) was likely to be able to determine fulvic acid complexes and thus differentiate the complexes from the AFO-L particles (the dissolution of AFO-L was insignificant during the brief acidification). The acidification/AER method coupled with a simple filtration technique suggested that the iron–fulvic acid complexes exist in both the < 0.02 μm and 0.02–0.45 μm size fractions in our coastal water system. The truly dissolved iron (< 0.02 μm) was relatively long-lived with a life-time of 14 days, probably due to the complexation by strong ligands. Such an acid-labile iron may be an important source of bioavailable iron in coastal environments, as a significant relationship between the chemical lability and bioavailability of iron has been well recognised.  相似文献   

18.
Measurements of the specific absorption coefficients of phytoplankton (a*ph) are currently required to estimate primary productivity at regional to global scales using satellite imagery. The variability in a*ph and phytoplankton size fraction was determined during January 2002 in the southern region of the California Current. Median values of a*ph at 440 nm and 674 nm were 0.061 and 0.028 m2 (mg Chl-a)?1 and significant variability was found between inshore and offshore stations. A decrease of a*ph is associated with increased phytoplankton abundance and larger species. The a*ph tends to be high when the photoprotector zeaxanthin is present in elevated concentrations and phytoplankton abundance lower. The nano-microphytoplankton (>5 µm) community consisted of 28 diatom and 15 dinoflagellate genera with mean abundance values of 2.8 and 1.6 × 103 cells l?1, respectively. The picophytoplankton (<5 µm) community consisted of Prochlorococcus sp. (mean 8.2 × 106 cells l?1) and Synechococcus sp. (mean 19.5 × 106 cells l?1), as well as a mixture of picoeukaryotes (mean 8.6 × 106 cells l?1). The contributions of nano-microphytoplankton and picophytoplankton to the total biomass (µg C l?1) were 46% and 54%, respectively. This study showed that picophytoplankton cells increased 2.5 times up during January 2002 compared with the previous year. It was concluded that the waning of La Niña conditions had a clear effect on the pelagic ecosystem in January 2002 and that the higher microphytoplankton abundance in the California Current was dominated by local and regional seasonal processes.  相似文献   

19.
《Oceanologica Acta》1998,21(3):485-494
Release of amino acids was examined in the laboratory in the form of dissolved primary amine (DPA) by two marine planktonic protozoa (the oligotrichous ciliate, Strombidium sulcatum and the aplastidic flagellate Pseudobodo sp.) grazing on bacteria. DPA release rates were high (19–25 × 10−6 and 1.8–2.3 × 10−6 μmol DPA cell−1 h−1 for flagellates and ciliates, respectively) during the exponential phase, when the ingestion rates were maximum. Release rates were lower during the other growth phases. The release of DPA accounted for 10 % (flagellates) and 16 % (ciliates) of the total nitrogen ingested. Our data suggest that the release of DPA by protozoa could play an important role in supporting bacterial and consequently autotrophic pico- and nanoplankton growth, especially in oligotrophic waters, where the release of phytoplanktonic dissolved organic matter is low.  相似文献   

20.
In order to improve the understanding of structural and reactive features of sediment organic matter from mangrove swamp as well as evaluate the relationship between such features and the impact from different sources (marine and terrestrial), humic and fulvic acids were isolated from two mangrove swamp sediments located in the Qinglan harbors on Hainan Island, China. One is a forest surface sediment site (WWM2), and the other is an estuary subaqueous sediment site (BMW). The humic and fulvic acids were characterized and compared using chemical and spectroscopic methods, including elemental analysis, thermogravimetric analysis (TGA), Fourier Transformed Infrared Spectroscopy (FTIR), 13C nuclear magnetic resonance (13C NMR) and potentiometric titrations. The results indicated that there were less aliphatic compounds but more aromatic compounds and oxygen-containing functional groups in fulvic acids. Humic acids contained more long-chain hydrocarbons and nitrogen compounds. Comparison of the C/N ratios and δ13C values for the humic substances at both sites indicated a larger marine and/or microbial contribution to the BMW site. Humic substances at the WWM2 site have more acidic functional groups than those of the BMW site. Compared to the literature, more phenolic groups existed in the samples of both sites, which may be due to the autochthonous contribution of mangrove plants.  相似文献   

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