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1.
The use of dissolved organic matter fluorescence as a tracer of river-sea mixing was examined in two South Carolina estuaries. Fluorescence declined linearly with seawater dilution in laboratory mixing studies, and also behaved conservatively in an estuary where a single river emptied into a bay. Fluorescence-salinity relationships were also studied in another estuary where a piedmont river (high suspended sediment, low fluorescence) and a coastal plains river (low sediment, high fluorescence) mixed with ocean water. The factor of 2 or greater difference in fluorescence between the two rivers allowed their relative contribution to the estuarine water mass to be distinguished. Petroleum hydrocarbons, measured in estuarine water at 0·7-1·8 μg l−1 concentrations, contributed negligibly to water fluorescence.  相似文献   

2.
A simple method for the determination of dissolved humic acid based on carbon analysis is presented. This method was used to measure the distribution of dissolved humic acids in seven coastal plain estuaries located in the middle-Atlantic United States. Results indicate that 100% of the dissolved humic acid was removed during estuarine mixing, although concurrent measurements of dissolved organic carbon showed either production or conservative behavior in regions of the estuary where humic acid removal was observed. It is apparent from these observations that removal of dissolved humic acid is a minor part of the estuarine transport of dissolved organic carbon.Laboratory experiments carried out by mixing river water with sea water demonstrated that salt-induced removal of dissolved humic acid was insignificant in two of three estuaries studied. These results suggest in situ removal of dissolved humic acid may not be universally caused by increasing estuarine salinity.  相似文献   

3.
The optical characteristics of a black water river estuary from the north coast of Scotland were examined in the filtered (0.4 µm), ultrafiltered (5 kDa) and colloid-enriched fractions of estuarine samples. The samples were collected over the full salinity range during a period when the pH was relatively constant (8.2–8.5) throughout the estuary, allowing the influence of salinity on estuarine colloidal processes to be distinguished. The properties examined in the bulk, the low molecular weight (LMW) and the colloidal fraction (HMW) were UV–visible absorption, 3-D fluorescence excitation–emission matrix (EEM) spectrum, inorganic and organic carbon, mean size (by dynamic light scattering), and size distribution by flow field-flow fractionation analysis (FlFFF). The combined results of these analyses support the view that river-borne, humic-rich colloids underwent two types of transformation upon mixing with the seawater end member. The first one resulted in an apparent increase in the abundance of LMW constituents and may be explained by coiling of the individual humic macromolecules. The second one resulted in an increase in the mean size measured in both the lower and higher colloidal size ranges, and may be explained by aggregation of colloids to form entities that were still mostly colloidal i.e., smaller than 0.4 µm. The LMW contribution to the bulk optical properties increased with increasing salinity. Very similar findings were obtained from simulated mixing experiments using a Nordic Reference NOM extract as a source of freshwater colloids. This indicates that changes in the molecular architecture and molar mass of river-borne colloids—not changes in their chemical nature—were responsible for the observed variations in the spectral characteristics of CDOM in this estuary.  相似文献   

4.
2007年夏季在东海舟山海域河口锋区开展了陆源溶解有机质的调查研究。测定了有色溶解有机质(CDOM)在激发波长370 nm/发射波长460 nm处的荧光强度和在λ=355 nm处的吸收系数,用于代表陆源CDOM浓度,并测定了荧光指数以指示CDOM来源。结果表明,CDOM的荧光值和紫外吸收系数之间呈显著正相关性,陆源CDOM浓度大体有向海方向降低的趋势,但是纵向上存在一些"突跃"现象。在舟山海域东北角不时观测到表层水体含有高浓度的CDOM,但变异性很大,推测可能该海区受到长江口羽状流的影响。在连续观测站发现陆源CDOM浓度在低平潮时往往比高平潮时要高。河海水在混合过程中CDOM浓度与盐度呈显著的线性负相关关系。在低盐度的悬沙锋区(S<24)CDOM浓度明显低于理论稀释值,而在较高盐度的羽状锋区,CDOM浓度接近于理论稀释值。在盐度为24~31范围内,大部分水样的荧光指数在1.50上下波动,表明其中CDOM来源以陆地来源为主;在较低盐度(S<24)的水样中荧光指数在1.70至1.90以上,表明CDOM以海洋来源为主,这与其陆源组分在高浊度的低盐度区存在显著的去除过程有关。研究表明,舟山海域水质存在着显著的变异性,与近岸羽状流密切相关,陆源溶解有机质的分布特征对此有较好的响应。  相似文献   

5.
Estuaries act as filters for land derived material reducing the river input to the coastal zone. Silicon (Si) removal from freshwater which is tightly linked to the growth of diatoms was studied in the estuarine mixing zone where the mixing of freshwater and seawater results in a salinity gradient. Three planktonic diatom species with different origin and salinity tolerance were grown in an artificial salinity gradient. Salinity stress and nutrient depletion led to a specific succession of the three diatoms along the salinity gradient. When available light was increased, diatoms reached higher biomass and the Si removal from water column was more efficient along the mixing. From this experiment, a conceptual model of Si transformations and removal from freshwater was build and applied to an idealized stratified estuary. Sensitivity analysis with varying initial conditions and parameter values pointed transit time of freshwater in the estuary, freshwater and seawater mixing rate and river turbidity as important interactive factors influencing Si removal from freshwater. Other factors like the total amount and the salinity tolerance of diatoms in the upstream river were shown to significantly affect riverine Si removal from the surface layer of an estuary. Finally it appears that Si removal from freshwater in estuarine mixing zones proceeds in two ways: a first rapid death and sedimentation of planktonic stenohaline diatoms imported from the river and second, the growth and subsequent settling of planktonic euryhaline diatoms of either freshwater or marine origin.  相似文献   

6.
亚甲基蓝在水体系中的光化学降解研究   总被引：1，自引：0，他引：1  
研究水体系中亚甲基蓝的光化学降解.结果表明,在高压汞灯照射下,亚甲基蓝在人工海水中降解得最快,蒸馏水次之,而在天然海水中降解得最慢.通过对比研究发现.重金属离子(Cu2+,Zn2+,Cd2+,Hg2+)和腐殖酸能够在一定程度上抑制亚甲基蓝的光降解;而丙酮能促进亚甲基蓝的光降解.由此可见,重金属离子和腐殖酸可能是造成亚甲基蓝在天然海水中降解缓慢的主要因素之一.  相似文献   

7.
2004-2009年黄河口近岸海域低盐区面积的变化趋势研究   总被引：1，自引：0，他引：1  
近年来黄河人海淡水量显著降低,而且年内分布极其不均匀,河口区的盐度场发生了重大变化.准确了解河口近岸海域的低盐区面积及其变化趋势,对于河口生态系统的研究极为重要.本文通过对2004-2009年丰、枯水期黄河口近岸海域低盐区面积大小的分析,建立了低盐区面积与黄河径流量的关系.结果表明,2004-2009年丰、枯水期低盐区面积与月径流量均呈现较好的线性关系,增加单位平方千米盐度小于27的低盐区面积需要增加的月径流量约为0.046亿m3;若要维持紧邻河口的3号方区海域的平均盐度小于27,月径流量应保持在50亿m3以上.此外,年内黄河口近岸海域低盐区面积的较大值主要集中在6～11月份,均高于370km2,而4、5月份的低盐区面积却不足200 km2,春季生态补水刻不容缓.  相似文献   

8.
Dimethylsulfide(DMS) is generally thought to be lost from the surface oceans by evasion into the atmosphere as well as consumption by microbe.However,photochemical process might be important in the removal of DMS in the oceanic photic zone.A kinetic investigation into the photochemical oxidation of DMS in seawater was performed.The photo-oxidation rates of DMS were influenced by various factors including the medium,dissolved oxygen,photosensitizers,and heavy metal ions.The photo-oxidation rates of DMS were higher in seawater than in distilled water,presumably due to the effect of salinity existing in seawater.Three usual photosensitizers(humic acid,fulvic acid and anthroquinone),especially in the presence of oxygen,were able to enhance the photo-oxidation rate of DMS,with the fastest rate observed with anthroquinone.Photo-oxidation of DMS followed first order reaction kinetics with the rate constant ranging from 2.5×10-5 to 34.3×10-5 s-1.Quantitative analysis showed that approximately 32% of the photochemically removed DMS was converted to dimethylsulfoxide.One of the important findings was that the presence of Hg2 could markedly accelerate the photo-oxidation rate of DMS in seawater.The mechanism of mercuric catalysis for DMS photolysis was suggested according to the way of CTTM(charge transfer to metal) of DMS-Hg2 complex.  相似文献   

9.
为研究多环芳烃从河口到近海的环境归趋行为与生态风险,考察了沉积物质量浓度、溶解性有机质、温度、盐度4种典型环境因子对菲在黄河口沉积物上吸附的影响,比较了黄河口与近海两种沉积物对菲的吸附性能。研究结果表明,沉积物质量浓度越低,单位质量颗粒物的菲吸附量越高;共存的溶解性有机质对菲的吸附具有增促作用,且腐殖酸比黄腐酸的作用更显著;温度的升高不利于菲的吸附,而盐度的增加有利于菲的吸附。菲在沉积物上的吸附是分配作用与表面吸附两种行为的耦合,其中黄河口沉积物以表面吸附为主,而近海沉积物以分配作用为主。近海沉积物菲吸附量显著高于黄河口沉积物菲吸附量。基于此,菲从河口到近海的迁移过程中,更易于在沉积物表面发生吸附沉降,从而可能降低水相中的生态危害,但对近海底栖生物具有潜在的健康生态风险。  相似文献   

10.
Iron, Mn, Cu, Pb and Zn have been determined in suspended particulate matter (SPM) collected in the estuarine plume regions of the Humber (during winter, spring and summer) and Thames (winter only). Metal concentrations (w/w) were found to increase with SPM concentration and could be defined in terms of the mixing of an ambient, slow settling population, with variable proportions of a diluent population. The end-members of the particle mixing series are fine material derived from coastal erosion, which is modified seasonally by biological production, and contaminated estuarine material which is contained within the estuarine discharge or derived from local resuspension of reworked deposits by tidal currents and wave activity. Iron-normalized metal concentrations exhibited an inverse relationship with SPM concentration in the Humber region and regression analyses enabled seasonal changes in end-member compositions to be evaluated. Since the metal:Fe ratios of the ambient population did not accord with those of local cliff samples, additional sources of metal were proposed whose importance to particle composition increases with a reduction in SPM concentration. Qualitatively, the seasonal variation of end-member compositions was consistent with (i) the coupling between redox processes occurring in the bed sediment and adsorption of metals (Mn, Cu, Zn) released from the pore waters onto ambient and diluent suspended particles in the overlying water column, and (ii) adsorption of metal (Pb) by ambient suspended particles from an extraneous (atmospheric) source. In the Thames plume, an increase in Fe-normalized metal concentrations with increasing particle concentration resulted from the mixing of end-member particles and the effects of additional metal from an internal or extraneous source were less clear, possibly because of metal desorption from suspended particles traversing the salinity gradient in the outer estuary. The processes described in this study regulate the internal cycling of trace metals in estuarine plume regions and the export of metals to neighbouring shelf sea environments.  相似文献   

11.
为了研究不同盐度对小黄鱼生理的影响,以人工养殖的4月龄小黄鱼(体质量为(12.6 ±3.1)g)为实验对象,将在自然海水(对照组盐度为22.1)中养殖的小黄鱼转入到盐度为5(低盐组)和34.5(高盐组)的海水中进行急性盐度胁迫处理10 d,测定并分析肝脏中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、碱性磷酸酶(AKP)和酸性磷酸酶(ACP)活力以及鳃和肾脏中的Na+/K+-ATP酶活力的变化情况。结果显示,在急性盐度胁迫下,小黄鱼肝脏抗氧化酶(SOD和CAT)活力均上升,其中,低盐组的SOD和高盐组的CAT活力均显著高于对照组(p<0.05);在不同盐度条件下,AKP和ACP表现出相反的变化趋势,即AKP活力随着盐度上升不断增强,而ACP活力则逐渐降低;鳃中Na+/K+-ATP酶活力在低盐组最低,而肾脏中高盐组的活力显著高于对照组(p<0.05)。上述研究结果表明,小黄鱼幼鱼在盐度下降到5时仍可正常存活;不同盐度胁迫可导致小黄鱼肝脏中的非特异性免疫酶以及鳃和肾脏中的Na+/K+-ATP酶活性发生显著变化,表明小黄鱼在适应盐度变化过程中肝脏、鳃和肾脏均发挥着一定的调节作用。研究结果对小黄鱼在高盐或者咸淡水区域养殖提供了一定参考作用。  相似文献   

12.
The southern portion of the Brazilian coast is dominated by coastal lagoons formed by sandy barrier spits with small inlets. This coastal configuration is a barrier to the surface flow of freshwater to the sea; thus, we suspect that a significant amount of freshwater flows through the permeable sands, beneath the barrier spits, where it mixes with seawater. We excavated an 18-m-deep well into the barrier spit which separates the Patos Lagoon from the South Atlantic. Using this well, we were able to sample interstitial waters from discrete layers, at 1-m intervals, which were analyzed for salinity, temperature, pH, nutrients (ammonium, nitrate, phosphate, and silicate), uranium, molybdenum, and barium. Similar analyses were made on surface water samples from the Patos Lagoon estuarine mixing zone.Results of well samples show a continuous increase in salinity with depth reaching 18 at the bottom. Ammonium and silicate are high, generally around 100 and 100–150 μM, respectively, throughout the subterranean profile. Phosphate shows a distinct maximum at about 6 m (ca. 25 μM), and nitrate is generally low in all well samples. Uranium and molybdenum exhibit a minimum in the well profile at about the same location where barium exhibits a maximum (greater than 2 μM). When results are compared to the surface lagoon–seawater mixing data, ammonium, phosphate, silicate, and barium in well samples of similar salinity show considerable enrichment, while a comparison of uranium and molybdenum data indicates significant depletion of these metals in most well samples.Based on these and other data, we deduce that the following processes are active: products of remineralization of organic detritus accumulated in lagoon sediments are advected through permeable sediments to the oceans; dissolution of biogenic solids and/or solid silicates mobilizes silicate; phosphate, uranium, and molybdenum are mobilized from phosphate-rich sediment layers; sulfate reducers remove uranium and perhaps molybdenum from solution throughout most of the well profile; barium is desorbed from solids in the subterranean mixing zone. These results demonstrate that freshwater discharged to the ocean through permeable sediments may have a significantly different composition than that discharged at the surface.  相似文献   

13.
A sensitive and selective photometric method of estimation of molybdenum has been developed based on the formation of a mixed ligand complex with bromopyrogallol red (BPR) and tri-n-octyl phosphine oxide (TOPO) and its subsequent extraction into nitrobenzene. The method is made selective by effectively eliminating the interference of several metal ions that commonly associate with molybdenum through the addition of nitrilotriacetic acid (NTA) and fluoride as masking agents. The proposed method is simple, rapid, fairly reproducible and superior to the existing methods for the photometric estimation of molybdenum in seawater. The concentration of molybdenum in harbour, coastal and offshore waters, particulate matter and sediments of Visakhapatnam (Bay of Bengal) was determined using this method. The results showed little variation of molybdenum concentration with depth in coastal waters, whereas its distribution was dominantly controlled by the salinity variation due to fresh water mixing.  相似文献   

14.
The concentrations of rare earth elements in the dissolved, acid-soluble and residual phases in surface waters of the Changjiang Estuary were determined using ICP-MS. The main purposes of the study are to understand the estuarine geochemistry of rare earth elements and to explore water-particle interactions in the Changjiang estuarine mixing zone. The results show that there are two distinct processes operating on dissolved rare earth elements in the estuary: large scale removal at low salinities due to salt-induced coagulation and remarkable release at mid to high salinities. These processes result in modification of the effective river water flux and the systematical fractionation of the dissolved rare earth elements toward the East China Sea. The increase in concentration of dissolved rare earth elements in the mid to high salinity waters of the Changjiang Estuary suggests a sediment source in the mixing zone of the estuary, which is located over a shallow, broad shelf where there is extensive physical contact between bottom sediment and estuarine waters. Acid-soluble rare earth elements, the concentrations of which also dropped sharply in the low salinity region, appear to be controlled by salt-induced coagulation process and intense deposition of suspended particulate matter in the low salinity region. In the mid to high salinities, all acid-soluble rare earth element concentrations increase slightly with increasing salinity, suggesting that resuspension of sediments occurred. In contrast, the residual rare earth element concentrations are relatively constant with salinity variation in the Changjiang estuarine surface waters.  相似文献   

15.
Organic complexes of magnesium, iron, zinc and copper have been isolated from seawater by adsorption onto octadecylsilyl-modified silica (SEP-PAK cartridges). The compounds were fractionated by HPLC and metals were detected in the eluate by atomic fluorescence. The most polar fraction contained a significant proportion of the metal—organics but only a low percentage of the UV-absorbing (254 nm) material. Magnesium—organics of low polarity were found in deep (5000 m), water but the compounds do not seem to be derived from tetrapyrroles. There were large systematic variations in the chromatograms as the column aged and it is thought that free silanol groups were removing metals from the metal—organic complexes. The effect was most pronounced for magnesium. Inorganic metal ions can be adsorbed by columns containing capped or uncapped C18-bonded silica and the adsorption of metals is enhanced by treatment with methanol. The cation exchange capacities of chromatographic packings must be taken into account when metal—organic compounds are analysed by HPLC.  相似文献   

16.
Self-diffusion coefficients of five major ions have been determined by a radioactive tracer method (capillary tube method) in seawater of salinity 34.86 at 25°C. Data are presented for Na+, Ca2+, Cl−, SO42, and HCO3−, which constitute about 95% by weight of sea salt. The influence of temperature and salinity on these coefficients has been studied for Na+ and Cl− which are the major components of sea salt: self-diffusion coefficients of these two ions have been measured in seawater, at different temperatures for a salinity of 34.86 and at different salinities for a temperature of 25°C. Diffusion coefficients of the same ions have been determined at 25°C by using another radioactive tracer method (quasi-steady cell method). In this experiment, seawater ions were allowed to diffuse from natural seawater into dilute seawater. Data have been obtained at 25°C for Na+, Ca 2+, Cl−, SO42− and HCO3−, corresponding to different salinity gradients.  相似文献   

17.
The effect of salinity on the distribution of copepoda in the Jiulong Estuary is studied in the present paper. The analysis of the samples collected during February 1983-January 1984 shows that the salinity of the Jiulong Estuary varies from 0.04 at Station E (head of estuary) to 31.7 at Station C (mouth of estuary). The distribution of copepoda is obviously affected by salinity. The results of the investigation show that the number of species, Shannon-Weaver H' index of diversity, species richness d and species evenness J' of copepoda increase with increasing salinity. Especially between the Station D and the Station C, being dominated by three predominant species. But, on the other hand, the total number of individuals apears to decrease with increasing salinity. According to the relation of distribution of copepoda with salinity, the copepoda may be divided into five ecological groups, i.e. fresh-water, low-salinity estuarine, meso-salinity estuarine, neritic and oceanic groups. Their horizontal succ  相似文献   

18.
Mixing of freshwater and seawater creates the well-known salinity gradients along the estuaries. In order to investigate how phytoplankton respond to the acute salinity changes, we exposed natural phytoplankton assemblies from the Jiulong River Estuary to differential saline field water while continuously monitoring their photosynthetic performances under both indoor-and outdoor-growth conditions. When the natural cell assemblies from salinity 30 field water were exposed to series low saline field water(salinity 25, 17, 13 and 7.5), the effective Photosystem II quantum yield(ΔF/F_m′) decreased sharply, e.g., to one-fifth of its initials after 5 min exposure to salinity 7.5 field water, and then increased fast during the following 40 min and almost completely recovered after 320 min. During such an exposure process, non-photochemical quenching(NPQ) sharply increased from 0 to 0.85 within 5 min, and then decreased to nearly 0 within the following 70 min. When these cells re-acclimated to salinity 7.5 field water were exposed to series high saline field water(salinity 13, 17, 25 and 30), a similar response pattern was observed, with the decreased ΔF/F_m′ accompanied with increased NPQ, and followed by the recovery-induced increase in ΔF/F_m′ and decrease in NPQ. A similar response pattern as ΔF/F_m′to the acute osmotic stress was also observed in the photosynthetic carbon fixation capacity according to radiocarbon(~(14)C) incorporation. Our results indicate that estuarine phytoplankton assemblies could rapidly recover from the acute osmotic stress, implying a potential cause for their frequent blooms in coastal-estuarine waters where despite drastically varying salinity, available nutrients are abundant due to the land-derived runoffs or mixing-caused relaxations from sediments.  相似文献   

19.
It is generally assumed that estuarine mixing is continuous for metals from terrestrial sources, gradually decreasing towards the open ocean endmember. Here we show that, chemical reactivity, determined by ion exchange method, and molecular weight distributions, obtained using cross-flow ultrafiltration, of dissolved Cd, Cu, and Ni in the surface waters of the Gulf of Mexico varied systematically across the estuarine mixing zone of the Mississippi River. Most size or chemical affinity fractions of dissolved metals (<0.4 μm) were linearly related to salinity (10.8–36.6), suggesting that the distribution of these elements was mainly controlled by continuous mixing processes. Dissolved concentrations across the salinity gradient ranged for Cd: 87–187 pM; Cu: 1.4–18.3 nM; and Ni: 2.6–18.8 nM, with highest values near the Mississippi river mouth, and lowest concentrations in a warm core ring in the Gulf of Mexico. Dissolved Cd was mostly present as a truly dissolved (<10 kDa, 97 ± 1%) and cationic fraction (Chelex-100 extractable, 94 ± 4%). A novel observation across the estuarine mixing zone was that colloidal metal concentrations were identical to either inert (for Cu, Ni) or AMPG-labile anionic (Cu, Cd) fractions. The difference in behavior between Cu and the other two metals might indicate differences in the biopolymeric nature of the metal–organic chelates. In particular, the anionic-organic Cd fractions accounted for just 3 ± 1%, on average. However, for Cu, it was 24 ± 4%, and for Ni, it was 9 ± 6%. The fractions of the total dissolved metal fractions that were “inert” averaged 31 ± 10% for Cu and 29 ± 12% for Ni. Small but noticeable amounts (6 ± 3%) of dissolved inert Cd fractions were also present. Apparent non-local transport processes, likely associated with cross-shelf sediment resuspension processes, could have been responsible for the relatively high concentrations of ‘inert’ and ‘anionic’ metal fractions in high salinity coastal waters, and accounting for the persistence of metals bound to humic substances in the Gulf of Mexico.  相似文献   

20.
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   

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