Measurement of trace nitrate concentrations in seawater by ion chromatography with valve switching

An ion chromatographic method with a valve switching facility was developed to determine trace nitrate concentrations in seawater using two pumps, two different suppressors, and two columns. A carbohydrate membrane desalter was used to reduce the high concentrations of sodium salts in samples. In this method, trace nitrate was eluted from the concentrator column to the analytical columns, while the matrix flowed to waste. Neither chemical pre-treatment nor sample dilution was required. In the optimized separation conditions, the method showed good linearity （R〉0,99） in the 0.05 and 50 mg/L concentration range, and satisfactory repeatability （RSD〈5%, n=6）. The limit of detection for nitrate was 0.02 mg/L. Results showed that the valve switching system was suitable and practical for the determination of trace nitrate in seawater.     

Photochemical degradation of crude oil in seawater

1 INTRODUCTION Marine photochemistry is a newly developed subject in marine sciences. Photochemical degrada- tion is important in decomposing and removing various organic contaminants in oceans (Ali et al., 1995a, b; Yang, 2000; Yang and Qi, 2002; 2003). …     

Photodegradation of methylene blue in natural seawater

This paper reports the photochemical degradation of Methylene Blue(MB)in natural seawater(NSW).The photodegradation reaction conformed to the first-order reaction kinetics with the rate constant 0.0158 min-1.MB was photochemically degradated faster under high-pressure mercury lamp(HPML)than under sunlight.When MB was in lower concentrations,salinity could inhibit the photoreaction whereas MB in higher concentration,salinity could accelerate the photoreaction.Humid acid could also inhibit the photoreactions.Toxicity tests with marine phytoplankton Skeletonema costatum(Sk)and Heterosigma akashiwo Hada (Ha)showed decreased acute toxicity after photodegradation.     

Photochemical degradation of triadimefon in seawater

The photochemical degradation of triadimefon in seawater was investigated under different reaction conditions in this study. The results showed that triadimefon could be effectively degraded by the irradiation of a high-pressure mercury lamp and the photodegradation rotes were influenced by aquatic media, heavy metal ions and photosensitizers. The photochemical degradation of triadimefon followed the first-order reaction kinetic behavior, with the rate constants ranging from 0.0027 to 0.0128 min-1 under the studied conditions. The photolysis of triadimefon was slower in natural seawater than in distilled water or synthetic seawater. All the heavy metal ions studied in this paper had inhibition effects on the photolysis of triadimefon. Acetone, as a common photosensitizer, could accelerate the photolysis of triadimefon. Three photoproducts were identified by GC-MS analysis. Our study confirmed that photochemical degradation is an effective pathway to remove triadimefon in seawater.     

Photochemical oxidation of benzothiophene in seawater

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Preliminary study on limiting nutrients in seawater ponds

INrnODUCTIONTheaqUacultareindustryofChinaedsfirstintheworld-Fertilizationinfreshwatershasalonghistory,andiseffectivelyaPpliedforfishcultUre.Scholarsfromvchouscotm-trieshaveheenstudytngfertiliZationtheory,tecboqUeandaqUactiltUreecologyinfertilizedPOnds-SPecialattentionisgiventothetwncyandaPPlicationlevelwhenmantireisused,andtothekindandN:PraioOfchethecalfertilizersused(Boyd,l99o;li,I993;MoriartyandPullin,l987).Thedrpthecchacteristicsofphosphorus,andtheroleofureaappliedintoPOndswere…     

STRESS CORROSION CRACKING OF AISI 321 STAINLESS STEEL IN ACIDIC SEAWATER

ImooUonONSCCisoneofthemosttwortantcausoffailureofstaiuleSsstalequipmentandfacilitieS.Studiesonunh0refacilitiesshowedthatanaddicchloridesolutionfilmcouldbefo~onthescheeofstalandthatstaiuleSSstalisinaCtivedissolutionstateinaedicchloridesolutionopinetal.,l99O;Gnanamoorthyetal.,l99O).ltisgenerallythoughtxthatSCCcannotoimrwhenthematerialisinaCtiveanodicdissolutionstate,soitsomcewithresultingcasualties(0ldfieldetal.,l99O)arousedattentiont0it.SomeSCCmeCanisrnsproposedpeuang,l988,Newmanctal.,…     

Electrochemical corrosion behavior of hot dip coating in artificial seawater

INTR0DUCnONAlloycoatingscandetivelyproteCtsteelagainstcormsioninseri0uscormsionenvir-orunent,suchasthedrinesplashandtidalzones-TwoInainhodiptincaldrinumalloycOaingswidelyusedcommroiallyareGalfancoaing(contalningZn-5wt%kl-us)devel-oPedbytheIntemaionaltalZincReenhheZaionandhocoating(c0n-talningZn-55Wt%Al-1.6Wt%Si)develoPedbytheBethlehemSteelCorpOration-Anewrinc-basedalloycOaingdevel0PedbyNortheaStemUniversityisdiscussedinthesPaperbyelecthehendcalmethod.FromSun(l996),welmOWthecorms…     

STUDY ON DETERMINATION OF DIC IN SEAWATER BY COULOMETRIC METHOD

lareODUcrIONThetotalcarbondi0xideisandriportantparametrforestirnatingthespatiotem0ralinorganiccarbontransport,andanthropogeniccarb0ndi0xideincreasesintheoonn.Ap~coulomericednique(MethodG0fASTMD5l3-82)formeasuringDICinanwaterdevelopedbyJohnsonetal.(l985)istheshipkoardmehodchosenfortheglobeocanicinofganiccarb0nsurveyt0bemadeinconjunCtionwiththeW0riddrinCirmlationExperirnentWorklHydrographicProgram(WOCEWHP)andtheJointGobal~nFluxStudy(JGOFS)program(Catherine,G.etal.,l993).Thecruxof…     

Precipitation of calcium carbonate from seawater

Slight perturbations of the oceanic DOC by addition of oxalic acid, tryptophan, and sodium humate did not affect the magnesium content of spontaneously precipitated Mg-calcites. However, the copresence of spontaneously precipitated aragonite and of Mg-calcite as a function of the initial degree of supersaturation was changed by the dissolved organic matter. Times of nucleation for carbonates was affected by organic matter at low organic concentrations because of coating and at high concentrations due to complexation.     

A new spectrophotometric method for measuring COD of seawater

This research studied a new spectrophotometric method for measuring the chemical oxygen demand （COD） of seawater. In this method, the COD was measured using a spectrophotometer instead of titrating with sodium thiosuiphate. The measuring wavelength was selected to be 470 nm, and the COD of three standard glucose solutions （COD = 0.5, 1.5 and 2.5 mgL^-1, respectively） and two seawater samples （from the South Yellow Sea and Jiaozhou Bay） were measured using the spectrophotometric method and titrimetric method respectively. The results showed that the spectrophotometric method was somewhat better than the titrimetric method. The relative standard deviation （RSD） of the spectrophotometric method was less than 2.7%, and the recovery of seawater samples ranged from 96.3% to 103.8%. In addition, the spectrophotometric method has other advantages such as expeditiousness, operation simplicity, analysis automatization, etc. Therefore the spectrophotometric method can be used to measure the COD of seawater with satisfactory results.     

Influence of Seawater Temperature on Phytoplankton Growth in Jiaozhou Bay, China

The phytoplankton reproduction capacity (PRC), as a new concept regarding chlorophyll-a and primary production (PP) is described. PRC is different from PP, carbon assimilation number (CAN) or photosynthetic rate ( P^B ) . PRC quantifies phytoplankton growth with a special consideration of the effect of seawater temperature. Observation data in Jiaozhou Bay, Qingdao, China, collected from May 1991 to February 1994 were used to analyze the horizontal distribution and seasonal variation of the PRC in Jiaozhou Bay in order to determine the characteristics, dynamic cycles and trends of phytoplankton growth in Jiaozhou Bay; and to develop a corresponding dynamic model of seawater temperature vs. PRC. Simulation curves showed that seawater temperature has a dual function of limiting and enhancing PRC. PRC‘s periodicity and fluctuation are similar to those of the seawater temperature. Nutrient silicon in Jiaozhou Bay satisfies phytoplankton growth from June 7 to November 3. When nutrients N, P and Si satisfy the phytoplankton growth and solar irradiation is sufficient, the PRC would reflect the influence of seawater temperature on phytoplankton growth. Moreover, the result quantitatively explains the scenario of one-peak or two-peak phytoplankton reproduction in Jiaozhou Bay, and also quantitatively elucidates the internal mechanism of the one- or two-peak phytoplankton reproduction in the global marine areas.     

DISTRIBUTION OF DISSOLVED AND PARTICULATE TRACE METALS IN ANOXIC SEAWATER, SAANICH INLET, B . C. CANADA

This paper discusses the spatial and seasonal distribution character of dissolved and paniculate trace metals in the anoxic seawater of Saanich Inlet, B.C., Canada. The study showed that concentration of dissolved and paniculate trace metals in anoxic seawater is closely related to (1) the concentration of H2S and the depth of the O2-H2S interface, (2) the exchange of seawater in Saanich Inlet with outside seawater, (3) biotic action, and (4) the flushing event. The study was based in part on the ratio between trace metals and nutrients. There was a steep change in the concentration of dissolved trace metals at the O2-H2S interface. The concentration of dissolved trace metals in the H2S-controlled zone was dependent on the H2S there. The suspended matter in Saanich Inlet comes from the Hero Strait seawater, phytoplankton production and resuspension of flushed-up sediments. The concentration of particulate trace metals was rather low in Saanich Inlet and tended to increase with depth. The total concentra     

Numerical simulation of seawater intrusion from estuary into river using a coupled modeling system

One of the most important causes of the freshwater shortage in estuarine area is the increasing seawater intrusion into the river. To simulate seawater intrusion properly, two important factors should be considered. One is the bidirectional and time-dependent coupling effects between river discharges and tidal forces. The other is the three-dimensional and stratified structure of dynamic processes involved. However, these two factors have rarely been investigated simultaneously, or they were often simplified in previous researches, especially for the estuary connected with an upstream river network through multiple outlets such as the Pearl River Estuary (PRE). In order to consider these two factors, a numerical modeling system, which couples a one-dimensional river network model with a three-dimensional unstructured-grid Finite-Volume Coastal Ocean Model (FVCOM), has been developed and successfully applied to the simulation of seawater intrusion into rivers emptying into the PRE. By treating the river network with a one-dimensional model, computational efficiency has been improved. With coupling 1D and 3D models, the specification of up-stream boundary conditions becomes more convenient. Simulated results are compared with field measured data. Good agreement indicates that the modeling system may correctly capture the physical processes of seawater intrusion into rivers.     

Evaluation and classification of seawater corrosiveness by environmental factors

According to the data of main environmental factors and the depth of localized corrosion of carbon steel and low alloy steels in China seas, combined with the result of grey interrelation analysis, double-factor method was proposed to evaluate and classify seawater corrosiveness. According to the temperature of seawater and the biologically adhesive area on steels, the corrosiveness of seawater from low to high level is classified into five levels （C l-C5）, which was identified by the data of corrosion depth of carbon steel immersed in water for one year.     

Investigations of natural and artificial radioactive isotopes in seawater and sediments in the Yellow Sea and adjacent southeast area

Investigations of natural and artificial radioisotopes including 90Sr,137Cs, gross B and U carried out in the Yellow Sea and adjacent southeast area in 1963. 1964, 1975 and 1978 showed that radioactive pollution by 90Sr and 137Cs from atmospheric fallout had gradually decreased with time due to the cessation of atmospheric nuclear weapons tests in the 70s. The distributions of natural and artificial radioactive isotopes (U, Ra, Th. 40K and 137Cs) in sediments southwest of Jizhou Island were uniform. The more uniform may be related to the soluble species of U[Uo2(CO3)4] in the seawater.The high value of Th at stations 3 and 6 was related to the sandy clay sediment; the low value at station 8 was related to sandy sediment. The content of 137Cs in the eddy area being less than about half of that in the China inshore area showed that the source of Cs may be insufficient orthat the conditions for enriching " Cs in the circulation eddy area were not favorable.     

Chemical oxygen demand of seawater determined with a microwave heating method

This paper investigates a microwave heating method for the determination of chemical oxygen demand (COD) in seawater. The influences of microwave-power, heating time and standard substances on the results are studied. Using the proposed method, we analyzed the glucose standard solution, the coefficient of variation being less than 2%. Compared with the traditional electric stove heating method, the results of F-test and T-test showed that there was no significant difference between the two methods, but the microwave method had slightly higher precision and reproducibility than the electric stove method. With the microwave heating method, several seawater samples from Jiaozhou Bay and the South Yellow Sea were also analyzed. The recovery was between 97.5% and 104.3%. This new method has the advantages of shortening the heating time, improving the working efficiency and having simple operation and therefore can be used to analyze the COD in seawater.     

Assessing seawater quality with a variable fuzzy recognition model

With the rapid development of the marine economy industry, human exploitation of marine resources is increasing, which is contributing to the growing trend of eutrophication and frequent occurrence of red tide. Accordingly, investigations of seawater quality have attracted a great deal of attention. This study was conducted to construct a seawater environmental quality assessment model based on the variable fuzzy recognition model. The uncertainty and ambiguity of the seawater quality assessment were then considered, combining the monitoring values of evaluation indicators with the standard values of seawater quality. Laizhou Bay was subsequently selected for a case study. In this study, the correct variable model for different parameters was obtained according to the linear and nonlinear features of evaluation objects. Application of the variable fuzzy recognition model for Laizhou Bay, water quality evaluation and comparison with performance obtained using other approaches revealed that the generated model is more reliable than traditional methods, can more reasonably determine the water quality of various samples, and is more suitable for evaluation of a multi-index, multi-level, nonlinear marine environment system; accordingly, the generated model will be an effective tool for seawater quality evaluation.     

Hydrochemical indexes of seawater intrusion and comprehensive judgement on intrusive degree

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Use of microelectrodes for electrochemical measurement of nitric oxide in natural seawater

In this paper, the application of a homemade Nation and Co(Salen) modified platinum microelectrode and an ISO-NOPMC microsensor (World Precision Instruments, USA ) to measure nitric oxide in natural seawater is reported. These two microelectrodes are suitable for the measurement. In natural seawater, the sensitivity and stability of the ISO-NOPMC microsensor are higher than that of the homemade Nation and Co(Salen) modified platinum microelectrode.