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1.
Cross-flow ultrafiltration (CFF) is often used to obtain separation and concentration of colloids from bulk natural water samples. Application of the ultrafiltration permeation model allows the quantitative determination of the low molecular weight material (LMW, < 1 kDa) and colloids in bulk dissolved organic matter (DOM) from measurements of time series permeate samples obtained from CFF. Detailed analysis of a Yukon River water sample shows that DOM absorption coefficient and fluorescence follow the permeation model and that the complex spectral optical properties of LMW DOM can be reconstructed from CFF data. A combination of measured and modeled data indicates that the LMW contribution to bulk DOM optical properties obtained from CFF can be grossly underestimated by the use of a low concentration factor (CF, the ratio of initial sample volume to retentate volume). Even at a relatively high CF of 19, optical properties of LMW DOM calculated from measurements of the retentate or integrated permeate would underestimate true values by 5–36%. In the Yukon River sample, LMW dissolved organic carbon represented 26% of the bulk concentration, but only 3–14% of the colored DOM was in the LMW fraction while 31–33% of bulk DOM florescence was due to LMW DOM. The contrasting optical properties of LMW and colloidal DOM support the concept that analysis of bulk DOM absorption and fluorescence properties reveals information about DOM molecular weight.  相似文献   

2.
The distribution of molecular masses of organic ligands for copper(II) in oceanic water was investigated. The bulk dissolved organic matter (DOM) was fractionated by ultrafiltration and organic ligands were extracted from the resultant fractions by using immobilized metal ion affinity chromatography (IMAC). Contributions of total organic ligands were 2.0–4.4% of the bulk DOM in surface waters, as determined by the UV absorbance. In the distribution of molecular masses of organic ligands, relative contribution of the fraction with low molecular masses (<1000 Da) was dominant (49–62%), while 26–33% of the total organic ligands was in the 1000–10,000 Da fraction, leaving 10–19% in the >10,000 Da fraction. The distribution of molecular masses of organic ligands shifted to higher molecular masses, as compared with that of the bulk DOM. The fluorescence intensities of organic ligands were shown to be associated with carboxyl contents, based on peak excitation/emission wavelengths and the pH-dependence of fluorescence. Two ligand classes with different conditional stability constants (log KCuL′≈7 and 9) were determined from fluorescence quenching of ligand fractions during copper(II) titration. Organic ligands in low molecular mass fractions were relatively weak and strong ligands occurred in higher molecular mass fractions. It is suggested that the weaker ligand sites would consist of two or more carboxyl groups (log KHL′=4), whereas carboxyl groups (log =2), which are protonated at lower pH, and primary amine may additionally contribute to the formation of more stable copper(II) complexes of the stronger ligand.  相似文献   

3.
Peculiarities of the spatial distribution of intermediate Mediterranean waters (MW), which are the main source to maintain the heat and salt budgets at depths of 600–1500 m in the Atlantic Ocean, have been studied using the ARGO floats measurements database. About 75000 temperature and salinity profiles recorded by 900 ARGO floats in 2005–2014 in the Atlantic Ocean for latitudes from 20° to 50° N were used. To process these data, we used the ARGO-Based Model for Investigation of the Global Ocean (AMIGO). This technique allowed us for the first time to obtain a complete set of oceanographic characteristics up to a depth of 2000 m for different time averaging intervals (month, season, years). Joint analysis of the temperature, salinity, and velocity distributions at 700–1000 m depths made it possible to revise the distribution of MW and their penetration into the western part of the ocean across the Mid-Atlantic Ridge (MAR). It is shown that at depths of 700 and 1000 m, the Mid-Atlantic Ridge is a barrier to advective propagation of salty waters (>35.5 PSU) to the west and is transparent to fragments of destroyed intrathermocline lenses (ITL) with lower salinity (<35.4 PSU). In the Atlantic region, from 20° to 35° N and from 30° to 70° W, individual lens profiles with an anomalous salinity distribution were sought using ARGO measurements to detect ITL and its separate fragments. About 24 000 measurements from 370 ARGO floats were analyzed, and only about 3% of them showed weak salinity anomalies at 800–1200 m depths. No ITL were found from these observations. Analysis of long-term drifting of individual floats recording temperature and salinity profiles with anomalous layers made it possible to study the nature of MW transport through the MAR.  相似文献   

4.
Dissolved organic matter (DOM) is comprised of a myriad of macromolecules with specific physical and chemical properties that may influence the bioavailability of hydrophobic pesticides to animals. This study was conducted to assess the role of various forms of DOM on the uptake and bioconcentration of the organophosphate insecticide chlorpyrifos (CHPY) to the bivalve Mercenaria mercenaria. Bivalves were exposed to DOM-free seawater (30 per thousand) or to seawater containing a single form of DOM. DOM forms included two filtrate fractions of natural salt-marsh sediment DOM (DOM-(<0.45 mum) and DOM-(<3 kDa)); natural purified humic (HA) and fulvic (FA) acids; and water soluble cyclic oligosaccharides alpha and beta cyclodextrins (CD-alpha and CD-beta). In (14)C-CHPY uptake and elimination experiments, juvenile bivalves were exposed to uniformly-labeled (14)C-CHPY and collected at time intervals during 48 h. The remaining bivalves were transferred to (14)C-CHPY-free elimination chambers with bivalve collection at time intervals over 144 h. Total uptake of (14)C-CHPY by bivalves in DOM-free seawater was >40% greater than in bivalves exposed to (14)C-CHPY in the presence of most DOM forms. These results are consistent with much faster (14)C-CHPY uptake rates estimated using a simple two parameter model. After the elimination period, bivalves exposed to DOM-free seawater had (14)C-CHPY body residue concentrations between 25% and 86% greater than bivalves in the presence of DOM forms. Experiments with larger bivalves showed that pulse-chase exposures with a 1.5 h exposure period to (14)C-CHPY was not long enough to detect differences in (14)C-CHPY tissue accumulation efficiencies across treatments. Our findings suggest that natural forms of DOM, at environmentally realistic organic carbon concentrations, reduced pesticide uptake and bioconcentration, consistent with much lower uptake rates relative to bivalves exposed to (14)C-CHPY in the absence of DOM. Interestingly, at the tested organic carbon concentrations CD-alpha and CD-beta did not reduce (14)C-CHPY bioconcentration in M. mercenaria.  相似文献   

5.
Reversed-phase liquid chromatography/mass spectrometry (LC/MS) is introduced as a new molecular fingerprinting technique for tracing terrigenous dissolved organic matter (DOM) and its photochemical decay in the ocean. DOM along a transect from the mangrove-fringed coast in Northern Brazil to the shelf edge was compared with mangrove-derived porewater DOM exposed to natural sunlight for 2–10 days in a photodegradation experiment. DOM was isolated from all samples via solid-phase extraction (C18) for LC/MS analysis. DOM in the estuary and ocean showed a bimodal mass distribution with two distinct maxima in the lower m/z range from 400 to 1000 Da (intensity-weighted average of 895 Da). Terrigenous porewater DOM from the mangroves was characterized by a broad molecular mass distribution over the detected range from 150 to 2000 Da (intensity-weighted average of 1130 Da). Polar compounds, i.e., those that eluted early in the reversed-phase chromatography, absorbed more UV light and had on average smaller molecular masses than the more apolar compounds.  相似文献   

6.
In this study, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) is utilized to molecularly characterize DOM as it is transported along a river to estuary to ocean transect of the lower Chesapeake Bay system. The ultrahigh resolving power (greater than 500,000) and mass accuracy of FTICR-MS allow for the resolution of the thousands of components in a single DOM sample, and can therefore elucidate the molecular-level changes that occur during DOM transformation from a terrestrial location to the marine environment. An important feature of FTICR-MS is that its sensitivity allows for direct analysis of low salinity samples without employing the traditional concentration approaches involving C18 extraction or ultrafiltration. To evaluate the advantages of using direct analysis, a C18 extract of riverine water is compared to its whole, unfractionated water, and it was determined that the C18 extraction is selective in that it eliminates two major series of compounds. One group is aliphatic amines/amides that are not adsorbed to the C18 disk because they exist as positive ions prior to extraction. The second group is tannin-like compounds with higher oxygen contents and a more polar quality that also allow them not to be adsorbed to the C18 disk. This direct approach could not be used for brackish/saline waters, so the C18 method is resorted to for those samples. Along the subject transect, a significant difference is observed in the molecular composition of DOM, as determined from assigned molecular formulas. The DOM tends to become more aliphatic and contain lower abundances of oxygen-rich molecules as one progresses from inshore to the offshore. A considerable amount of molecular formula overlap does exist between samples from sites along the transect. This can be explained as either the presence of refractory material that persists throughout the transect, due to its resistance to degradation, or that the assigned molecular formulas are the same but the chemical structures are different. ESI-FTICR-MS is a powerful technique for the investigation of DOM and has the ability to detect compositional variations along the river to ocean transect. Visualization tools such as two dimensional and three dimensional van Krevelen diagrams greatly assist in highlighting the shift from the more aromatic, terrestrial DOM to the more aliphatic, marine DOM.  相似文献   

7.
Here we present results of an initial assessment of the impacts of a water diversion event on the concentrations and chemical composition of dissolved organic matter (DOM) and bacterioplankton community composition in Barataria Bay, Louisiana U.S.A, an important estuary within the Mississippi River Delta complex. Concentrations and spectral properties of DOM, as reflected by UV/visible absorbance and fluorescence, were strikingly similar at 26 sites sampled along transects near two western and two eastern areas of Barataria Bay in July and September 2010. In September 2010, dissolved organic carbon (DOC) was significantly higher (568.1-1043 μM C, x=755.6+/-117.7 μM C, n=14) than in July 2010 (249.1-577.1 μM C, x=383.7+/-98.31 μM C, n=14); conversely, Abs254 was consistently higher at every site in July (0.105-0.314) than in September (0.080-0.221), averaging 0.24±0.06 in July and 0.15±0.04 in September. Fluorescence data via the fluorescence index (FI450/500) revealed that only 30% (8 of 26) of the July samples had an FI450/500 above 1.36, compared to 96% (25 of 26) for the September samples. This indicates a more terrestrial origin for the July DOM. Bacterioplankton from eastern sites differed in composition from bacterioplankon in western sites in July. These differences appeared to result from reduced salinities caused by the freshwater diversion. Bacterioplankton communities in September differed from those in July, but no spatial structure was observed. Thus, the trends in bacterioplankton and DOM were likely due to changes in water masses (e.g., input of Mississippi River water in July and a return to estuarine waters in September). Discharge of water from the Davis Pond Freshwater Diversion (DPFD) through Barataria Bay may have partially mitigated some adverse effects of the oil spill, inasmuch as DOM is concerned.  相似文献   

8.
Dissolved organic matter(DOM) from freshwater, mid-salinity, and seawater endmember samples in the Jiulong River Estuary, China were fractionated using cross-flow ultrafiltration with a 10-kDa membrane. The colloidal organic matter(COM; 10 kDa–0.22 μm) retentate, low molecular weight(LMW) DOM(10 kDa) permeate, and bulk samples were analyzed using absorption spectroscopy and three-dimensional fluorescence excitation-emission-matrix spectroscopy. The UV-visible spectra of COM were very similar to those obtained for permeate and bulk samples, decreasing monotonically with increasing wavelength. Most of the chromophoric DOM(CDOM, expressed as the absorption coefficient a355) occurred in the LMW fraction, while the percentage of CDOM in the colloidal fraction was substantially higher in the freshwater endmember(13.4% of the total) than in the seawater endmember(6.8%). The bulk CDOM showed a conservative mixing behavior in the estuary, while there was removal of the COM fraction and a concurrent addition of the permeate fraction in the mid-salinity sample, implying that part of the colloidal CDOM was transformed into LMW CDOM. Two humic-like components(C1: 250, 325/402 nm; and C2: 265, 360/458 nm) and one protein-like component(C3: 275/334 nm) were identified using parallel factor analysis. The contributions of the C1, C2, and C3 components of the COM fraction to the bulk sample were 2.5%–8.7%, 4.8%–12.6%, and 7.4%–14.7%, respectively, revealing that fluorescent DOM occurred mainly in the LMW fraction in the Jiulong River Estuary. The C1 and C2 components in the retentate and permeate samples showed conservative mixing behavior, but the intensity ratio of C2/C1 was higher in the retentate than in the permeate fractions for all salinity samples, showing that the humic component was more enriched in the COM than the fulvic component. The intensity ratio of C3/(C1+C2) was much higher in the retentate than in the permeate fraction for mid-salinity and seawater samples, revealing that the protein-like component was relatively more enriched in COM than the humic-like component. The contribution of the protein-like component(C3) to the total fluorescence in the retentate increased from 14% in the freshwater endmember to 72% for the seawater endmember samples, clearly indicating the variation of dominance by the humic-like component compared to the protein-like component during the estuarine mixing process of COM.  相似文献   

9.
利用微滤和超滤技术研究了九龙江河口区表层水中铀及其同位素组成的粒级分布和地球化学行为.结果表明,溶解态(<0.4μm)中低分子量组分(<10 000 u)占主要份额,胶体态(10 000 u~0.4μm)238U所占比例不足1%,且随盐度的增加其所占份额逐渐降低.溶解态、低分子量组分和胶体态238U的比活度与盐度之间存在良好的线性正相关关系,证实它们在九龙江河口区呈现保守行为.在颗粒态(>0.4μm)中,各粒级组分238U所占份额主要受控于相应颗粒物的浓度,在盐度小于20的区域,各粒级颗粒组分238U占颗粒态的份额有如下变化次序:10~53μm>2~10μm>0.4~2μm>大于53μm,而在盐度大于30的近外海站位,该次序发生一些变化:0.4~2μm>10~53μm>2~10μm>大于53μm,最小粒级颗粒组分238U的贡献有所增加,反映了自生铀贡献的加强.九龙江河口区表层水中溶解态(包括低分子量组分和胶体态)的234U/238U)A.R.均大于1,显示出234U过剩的特征,而各粒级颗粒组分中的234U/238U)A.R.则接近于平衡值(1.0).这一现象与陆地岩石风化过程中水体对铀的淋滤释出量及234U的优先浸出有关.对232Th/238U质量比的研究显示,溶解态及其所包括的低分子量组分和胶体态的232Th/238U质量比均小于1,而颗粒态及其所包括的4个粒级组分中的232Th/238U质量比均大于1,反映了向外海输送过程中铀、钍地球化学行为的差异.  相似文献   

10.
The Climatic variability of the seasonal water exchange in the Strait of Gibraltar and the spatial structure of the tongue of the Mediterranean Waters (MW) in the Atlantic Ocean are studied. The analysis is based on the results of a numerical experiment using a 3D ocean circulation model developed at the Institute of Computational Mathematics (ICM RAS) with a resolution of the dataset over the latitude and longitude equal to 0.25 degree. The seasonal evolution of the salinity and density fields is calculated in the North Atlantic (from 20 °S, including the Mediterranean Sea) and in the Arctic Ocean (including the Bering Sea). The comparison of the model estimates with the results of field observations demonstrated good agreement. The transport of the MW into the Atlantic is close to the observed data (during the year, it varies from 1.8 Sv in the winter to 0.9 Sv in the summer). The complex pattern of the currents in the region of the MW spreading is confirmed. The alternating character of the saline MW tongue at the 1000-m level is shown for the first time. It is found that the zones of maximum salinities in the open part of the ocean coincide with the main trajectories of migration of MW lenses and the regions of their decomposition.  相似文献   

11.
海洋模式中Boussinesq近似误差讨论   总被引：4，自引：0，他引：4  
根据全球增暖的特点,设计了一个理想的数值试验方案,用Boussinesq POP海洋模式和改进的非Boussinesq POP海洋模式定量讨论了Bousiinesq近似在海洋模式计算中的误差。结果发现,在只有热力驱动的热力环流背景下,由热膨胀引起的海平面上升在水平方向上是基本均匀的,在所给的初始边界条件下,这种由Boussinesq近似引起的最大海平面误差可以达到59％,在Boussinesq POP模式中,热源中心处的海面高度要远小于由非Boussinesq模式计算的海面高度,而其周围有虚假的海面高度下降;在只有加热引起的热盐环流过程中,当模式作了Boussinesq假设以后,计算的经向和纬向垂直环流都会产生虚假的加强,虽然这种误差只是在1％左右;在Bousiinesq近似假定下,热量经向通量在赤道上垂直剖面的积分误差比质量经向通量在赤道上垂直剖面的积分误差大一个量级;非Boussinesq模式计算的气压梯度所做功的垂向分布在3000m以下是有波动的,而Boussinesq模式计算的气压梯度所做功的垂向分布在3000m以下基本上是均匀的,它的误差在10％以上。  相似文献   

12.
Rock crabs, Cancer irroratus, were examined grossly and microscopically to estimate the influence of molting activity, geographical source and seabottom sediments on gill color, carapace color and tissue pathology. Collections were made from deepwater stations (20–55 m) in the Hudson Shelf Valley near dredge- and sewage-sludge disposal sites in the New York Bight apex, and from nearshore waters near Boothbay Harbor, Maine. Extensive gill blackening was noted in up to 30 % of the crabs from the New York stations when all specimens were in the intermolt condition. Blackening was not noted in intermolt crabs collected in Maine. Carapace blackening was present in up to 79 % of the New York crabs but absent in those from Maine. Severe blackening was attributed to direct contact of Cancer irroratus with blackened, highly organic sediments in the Hudson Shelf Valley. Fouling microorganisms on gill epicuticle included bacteria, diatoms, stalked ciliates, amoebae, flagellates and copepods. Bacteria, diatoms, amoebae and flagellates were common on crab gills from both locations. Ciliates and copepods counted in histological sections were considerably fewer in crabs from the New York stations than in those from Maine. Melanized nodules (hemocyte clumps) were present in gill tissue in up to 58 % of the New York crabs and in up to 68 % of Maine crabs. Unidentified microsporidans were found in up to 55 % of the New York specimens and in less than 2 % of those from Maine. Histological data accumulated since 1975 are summarized to provide a list of endoparasites, polychaete worms and barnacles observed in Cancer irroratus from the northeastern United States. Gill blackening, but not parasitism or microbial fouling, proved to be the best indicator or monitoring the effects of ocean dumping on the health of a benthic crustacean species.  相似文献   

13.
This study addresses sources and diagenetic state of early-season dissolved organic matter (DOM) in the Northeast Water Polynya (NEWP) area northeast of Greenland from distributions of humic substance fluorescence (HSfl), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) in the water column inside and outside the NEWP area. The water masses of the polynya area had acquired their spring/summer temperature–salinity characteristics at the time of sampling, and also had individual, different DOM signatures. DOC concentrations were variable within and among water masses in the polynya area, indicating patchy local sources and sinks of DOC. PySW and polynya intermediate water (PyIW) had higher average DON concentrations and average lower C:N ratios than polynya bottom water (PyBW), indicating a larger fraction of fresh DOM in PySW and PyIW than in PyBW. Ice-covered, polynya area surface waters (PySW) had higher DOC concentrations (113±14 μM, n=68) than surface water (SW) outside the polynya area (96±18 μM, n=6). The DOM C:N ratios in a low-salinity, ice-melt subgroup of PySW samples indicate labile material, and these low-salinity surface waters appeared to have a local DOC and DON source. In contrast, HSfl was significantly lower inside than outside the NEWP area. Despite the lower HSfl values within the NEWP area, the PySW values were high when compared to open-ocean water. There were no local terrestrial sources for HSfl to the NEWP area and the East Greenland Current is therefore proposed as a likely source of allochtonous HSfl. When HSfl was used as a conservative tracer, up to 70% of the water in PySW and PyIW was found to be derived from SW, which contains a high fraction of water from the East Greenland Current. Similarly, a mixing model based on HSfl indicated that 80% of early-season DOC and 90–100% of early-season DON in PySW and PyIW were derived from SW, indicating a potentially high fraction of terrestrially-derived, relatively refractory DOM in the early-season NEWP area.  相似文献   

14.
The objectives of this study were to investigate the seasonality, abundance, sources and bioreactivity of organic matter in the water column of the western Arctic Ocean. The concentrations of particulate and dissolved amino acids and amino sugars, as well as bulk properties of particulate and dissolved organic matter (DOM), were measured in shelf, slope and basin waters collected during the spring and summer of 2002. Particulate organic matter concentrations in shelf waters increased by a factor of 10 between spring and summer. Dissolved organic carbon (DOC) and nitrogen (DON) concentrations exhibited only minor seasonal variations, whereas dissolved amino acid concentrations doubled between spring and summer, and dissolved amino sugars increased by 31% in shelf waters of the Chukchi and Beaufort Seas. Concentrations of DOC did not exhibit a significant seasonal change in surface waters of the Canada Basin, but dissolved amino acid concentrations increased by 45% between spring and summer. No significant seasonal differences were detected in the concentration or composition of DOM in waters below 100 m in depth. Concentrations of particulate and dissolved amino acids and amino sugars were strongly correlated with chlorophyll-a, indicating a plankton source of freshly produced organic matter. The amino acid and amino sugar compositions of freshly produced DOM indicated that a large portion of this material is bioavailable. While freshly produced DOM was found to be relatively bioreactive, preformed DOM in the Arctic appears to be less bioreactive but similar in degradation state to average DOM in the Atlantic and Pacific. These data demonstrate substantial summer production of POM and DOM on the Chukchi and Beaufort shelves that is available for utilization in shelf waters and export to the Canada Basin.  相似文献   

15.
Dissolved organic matter (DOM) and dissolved copper-organic complexes were isolated from the estuarine waters of Narragansett Bay, RI, using reverse-phase liquid chromatography employing C18 Sep-Pak cartridges (Waters Associates). The cartridges were found to have a constant retention efficiency for processing ? 1-l volumes of seawater. Fractionation of the isolated material, by sequential elution of the Sep-Pak with water: methanol mixtures of increasing organic solvent concentration, yielded a fraction of the organic matter with a specific copper activity six times greater than the overall activity for the isolated DOM. Analysis of this fraction by high performance liquid chromatography suggested that the organic components are of intermediate polarity and have appreciable aromatic character.An investigation of the protonation characteristics of the isolated complexes indicated that most of the copper is associated with a broad range of acidic sites on the DOM. Analysis by electron paramagnetic resonance spectroscopy confirmed the organic association of the isolated copper and also suggested the presence of several types of binding sites which probably involve oxygen donor ligands.Studies of the exchange of 64Cu with these binding sites on the isolated DOM indicated that 70% of the sites undergo rapid exchange with copper in seawater while 20% of these sites did not exchange in a 24-h time period.  相似文献   

16.
In a previous study we monitored fluctuations in the concentration of lysozyme in the hemolymph of copper stressed bay mussels, Mytilus edulis, concurrently by measuring enzymatic activity and by an enzyme-linked immunosorbent assay (ELISA).1 In a number of instances the data collected by the two techniques from copper stressed mussels yielded contradictory results. In these instances the quantity of lysozyme, determined enzymatically, was significantly greater than the quantities determined by ELISA. These results prompted subsequent investigation into the cause of the discrepancies. In the course of the study a high molecular weight protein fraction (35 000 MW) from mussel hemocytes was isolated. Decreasing the ionic strength and concentration of the fraction caused dissociation into a 14 600 MW fraction characteristically identical to lysozyme.2 Association to the 35 000 MW form is reversible upon an increase in ionic strength and concentration, and is presumed to be a dimer of lysozyme.3,4 The ionic strength and pH optima for hydrolysis of suspensions of Micrococcus luteus were determined for the dimer. Polyclonal anti-lysozyme gammaglobulin preparations1 were used in determinations of the relative immunological reactivity of various lysozyme preparations by immunodiffusion.5 The monomer form was more favorably precipitated or detectable than the lysozyme in hemocytes. disturbed hemocytes indicate an apparent increase in the extracellular concentration of the dimer as a result of cell damage. The observed low immunological reactivity would allow for the lack of detection by ELISA, and may have interfered with antibody-monomer interactions.  相似文献   

17.
Photochemical production rates and steady-state concentrations of the highly reactive OH radical were determined in Antarctic seawater in the Weddell-Scotia Confluence during the austral spring of 1993 and along the Antarctic Peninsula during the austral summer of 1994. OH radical photoproduction rates were 30±2 nM/day and 46±2 nM/day in surface open oceanic and coastal waters, respectively. Corresponding steady-state concentrations were 2.6×10−19 and 4.3×10−19 M which are similar to those found in tropical latitudes. In-situ irradiation experiments (drifter deployments) at different depths in the upper water column indicated that multiple sources for the OH radical existed at three Antarctic stations. Ultrafiltration studies and model calculations based on wavelength-dependent OH radical quantum yields indicated that the main sources were photochemical reactions of low molecular weight dissolved organic matter (DOM), nitrate, and nitrite. Production of the OH radical from nitrate photolysis was almost exclusively UV-B dependent, while OH radical production from nitrite photolysis was mainly UV-A dependent. OH production from DOM photolysis was both UV-A and UV-B dependent. In the upper few meters at open oceanic sites, nitrate and DOM were the dominant OH radical sources, while deeper in the water column DOM and nitrite were important because of the greater importance of UV-A with depth. During non-ozone hole conditions, nitrate contributed about 33%, while DOM plus nitrite contributed about 67% of the predicted OH radical production in open oceanic surface waters. During an ozone hole (151 Dobson units), the corresponding percentages changed to about 40 and 60% for nitrate and DOM due to the higher UV-B irradiance. Model calculations predict that during an ozone hole (151 Dobson units), OH radical production in surface waters will be enhanced by at least 20%, mostly from nitrate photolysis and to a lesser extent from DOM photochemical reactions. This study indicates that ozone hole events significantly increase OH radical production, as well as the photolysis of DOM, in Antarctic waters, and that rates can be as high or higher than those at lower latitudes, especially if differences in temperature and solar irradiance are taken into account.  相似文献   

18.
由于海水盐度大、有机质含量低,从海水中提取和纯化克级溶解性有机质(dissolved organic matter,DOM)一直十分困难。基于Bond Elut PPL固相萃取小柱法进行海水DOM固体样品提取的放大试验,建立DOM自动化调酸、PPL树脂吸附技术,最后形成提纯、冷冻干燥PPL-DOM(通过PPL树脂提取的DOM)完整工艺。采用元素分析、三维荧光光谱、红外光谱和固态13C核磁共振(NMR)波谱法进行样品表征。结果表明:(1)该方法对近海表层海水DOM回收率稳定在50%以上,搭建的提取装置DOM日吸附量可达230mg;(2)鳌山湾四个季节批次PPL-DOM整体分析结果表明,样品的元素组成和光谱特征相似,表明方法适用性和稳定性较好;(3)三种水生态环境的PPL-DOM13C NMR谱图显示样品的基本特征相似,以烷基碳、碳水化合物碳、芳香碳和羧基碳/酰胺碳为主,其中偶极去相(dipolar dephasing)谱显示了DOM前体化合物来源的差异。多种结果表明放大后的PPL固相萃取法可稳定提取克级DOM样品。  相似文献   

19.
Production of dissolved organic matter (DOM) by heterotrophic microbial communities isolated from Loch Creran (Scotland) was studied in time course incubations in which cells were re-suspended in artificial seawater amended with variable proportions of glucose, ammonium and phosphate. The incubation experiments demonstrated that microheterotrophs released part of the substrate as new DOM, with a production efficiency of 11 ± 1% for DOC, 18 ± 2% for DON and 17 ± 2% for DOP. Estimating the impact of this production in Loch Creran, showed that from 3 ± 1% (DOC) to 72 ± 16% (DOP) of DOM could originate from the heterotrophic microbial community. The produced DOM (PDOM) was both bioavailable (BDOM) and refractory (RDOM). Bioavailability as assessed by the difference between the maximum and the end DOM concentration, was generally higher than found in natural systems, with DOP (73 ± 15%, average ± SD) more bioavailable than DON (70 ± 15%), and DON than DOC (34 ± 13%).The stoichiometry of PDOM was linked to both nutrient uptake and BDOM ratios. Absorption and fluorescence of DOM increased significantly during the incubation time, indicating that microheterotrophs were also a source of coloured DOM (CDOM) and that they produce both bioavailable protein-like and refractory humic-like fluorophores.  相似文献   

20.
Water vapor is one of the basic climate gases playing a key role in various processes at different altitudes of the Earth’s atmosphere. An intercomparison and validation of different total precipitable water (TPW) measurement methods are important for determining the true accuracy of these methods, the shared use of data from multiple sources, the creation of data archives of different measurements, etc. In this paper, the TPW values obtained from measurements of solar IR spectral radiation (~8–9 μm absorption band) and thermal MW radiation of the atmosphere (1.35 cm absorption line) for 138 days of observation are compared. Measurements have been carried out from March 2013 to June 2014 at Peterhof station of the St. Petersburg State University in (59.88° N, 29.82° E). It is shown that MW measurements usually give higher TPW values than IR measurements. The bias between the two methods varies from 1 to 8% for small and large TPW values, respectively. With increasing TPW values, the bias reduces and for TPW > 1 cm it is ~1%. Standard deviation (SD) between the two methods reaches 7% for TPW < 0.4 cm and 3–5% for TPW > 1 cm. These data show the high quality of both remote sensing methods. Moreover, the IR measurements have a higher accuracy than MW measurements for small TPW values.  相似文献   

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