Coastal Surface Seawater Research Articles

Proteolytic enzymes in coastal surface seawater: Significant activity of endopeptidases and exopeptidases

We assayed proteolytic enzymes in coastal surface seawater using 16 types of fluorogenic substrates, including those for aminopeptidase, trypsin, elastase, and chymotrypsin. Hydrolysis rates were similar or higher for substrates of trypsin and chymotrypsin than for those of aminopeptidase. Substrates for elastase were hardly hydrolyzed. The results strongly suggest trypsin-type and chymotrypsin-type endopeptidases and aminopeptidases were present in the seawater. In most previous studies of proteolytic enzymes in aquatic environments, leucine-aminopeptidase activity measured using a fluorogenic substrate has been used as a model of proteolytic activity. From the results of this study using various peptide analog fluorogenic substrates, the significance of endopeptidases, which could play a key role in downsizing of dissolved proteins and polypeptides to oligopeptides prior to microbial respiration, was confirmed

Scavenging of 234Th and 210Po in surface water of Jinhae Bay, Korea during a red tide

This observation was carried out on the surface seawater of Jinhae Bay, southeastern Korea during a red tide in July, 1991 in order to understand the removal processes of reactive trace elements using natural radionuclides of 234Th and 210Po as co-tracers. Comparing the results of 234Th and 210Po activities against chlorophyll a and TSM (total suspended matter), the two nuclides have different scavenging process in the surface coastal seawater during algal blooming. Particulate and dissolved 234Th and particulate 210Po are subject to dilution by chlorophyll a and TSM, showing the negative correlation with 234Th and particulate 210Po, while they are positively correlated with dissolved 210Po. This suggests that scavenged 210Po may be preferentially re-dissolved at the bottom waters and/or surface sediments and reappear at the surface by tidal current. The calculated distribution coefficients (Kd) of 210Po to particle (TSM) relative to that of 234Th was relatively large, demonstrating that the affinity of 210Po to TSM is greater than that of 234Th during algal blooming. These results suggest that particulate matter, especially biogenic matter, plays a significant role in controlling the scavenging of reactive trace metals in coastal seawater.

Saturation levels of methyl bromide in the coastal waters off Tasmania

Methyl bromide (CH3Br) was highly supersaturated for over 2 years in the surface coastal seawater off Tasmania. Persistent supersaturations were observed near to shore throughout the year with no evidence of a seasonal cycle. At the same time, a site farther offshore (still under coastal influence) was also predominantly supersaturated but to a lesser extent. Notably, the annual pattern varied over the consecutive years covered in this systematic study. The observed supersaturations are in broad agreement with that which would be predicted by the relationships with the sea surface temperature (SST) derived by Groszko and Moore [1998] and King et al. [2000] for SSTs in the range of 12° to 20°C, although not the seasonal variation predicted by King et al. [2002]. There is much variability, as expected, which is not explained by the SST relationships. The presence of the prymnesiophyte Phaeocystis is found to be related to the seawater concentrations of CH3Br in this work. Our results tentatively indicate that the release of CH3Br into the seawater may be a response to nitrate limiting conditions.

Temporal variations of 90Sr and 137Cs concentrations in Japanese coastal surface seawater and sediments from 1974 to 1998

Abstract 90 Sr and 137 Cs concentrations were determined in surface water and bottom sediments collected at 11 sites offshore from Japan during the period 1974–1998, to investigate their temporal variations and behaviour in the coastal marine environment. The concentrations of 90 Sr and 137 Cs in surface water have decreased with time since 1974. After the period of atmospheric nuclear weapons tests, the mean residence times of 90 Sr and 137 Cs were about 41 and 51 years, respectively. The 137 Cs/ 90 Sr activity ratios in coastal seawater during the atmospheric nuclear weapons tests (up until 1980) were lower than those after the tests due to the inflow of 90 Sr in river water. A sharp increase in 137 Cs levels was observed in airborne dust, in precipitation on the Japanese islands, and in coastal surface seawater in 1986 following the Chernobyl accident. However, the 137 Cs levels in surface water returned to pre-1986 levels quickly, indicating rapid removal of Cs from the surface to deeper water. Concentrations of 90 Sr in sediments were generally much lower than those for 137 Cs, reflecting the more effective scavenging of Cs from the water column. In Ca-rich sediments, consisting of corals and shells, higher 90 Sr levels and 90 Sr/ 137 Cs activity ratios were found, reflecting higher accumulation of Sr than Cs in marine organisms. Higher accumulation of 90 Sr than 137 Cs was also found in seaweed (gulfweed and wakame).

Effects of virus infection on respiration rates of marine phytoplankton and microplankton communities

The possible influence of viral infection on respiration rates in marine microbial pelagic communities was assessed by means of 3 experiments on respiration rate with viral concentrate addi- tion on single-species cultures of Mantoniella sp. and Micromonas pusilla and another 3 on natural microplankton communities (organisms <200 µm) from the Kattegat Sea (Astol) and the Baltic Sea. Coastal surface seawater samples were taken during cruises of the RVs 'Ancylus' and 'Argos' during winter and spring 2000. Approximately 50 to 70 l of seawater were concentrated by ultrafiltration. The experiments were started by adding a viral particle concentrate to a container with algae or a natural microplankton community; a control container was kept free of the viral concentrate addition. Oxygen concentration determinations were carried out on each treatment and control to measure respiration rates throughout the incubation period. The in vivo chlorophyll a fluorescence was also monitored as an indication of algal infection. The rates of respiration indicated that the addition of the viral particle concentrate affected the respective metabolisms of the Mantoniella sp. and Micromonas pusilla cultures as well as natural microplankton communities. Viral infection decreased the Man- toniella sp. respiration rate (by 96%) and increased the Micromonas pusilla respiration rate (by 235%). Hence, if our results can be extrapolated to nature, then, at least in a bloom situation, the fate of primary production and carbon fluxes could be strongly modulated by viral infection. The addition of a viral particle concentrate to the microplankton community generated complex responses in terms of respiration rates, which increased (by 84%) or remained similar to the controls. Our results suggest that viral infection of microplanktonic organisms could be one of the factors significantly modifying pelagic carbon fluxes.

Novel biogenic iodine‐containing trihalomethanes and other short‐lived halocarbons in the coastal east Atlantic

Reactive halogen photochemistry and its impact on tropospheric oxidant levels have recently attracted intense research interest following the observation of the iodine oxide radical at midlatitudes. During September 1998, short‐lived organoiodines including CH3I, C2H5I, CH2ICl, CH2IBr, CH2I2, and the hitherto undetected CHIBr2, as well as the organobromines CHBr3, CH2Br2, CHBr2Cl, CH3Br, and C2H5Br, were measured in air and seawater at and around Mace Head, on the west coast of Ireland. The release rates of organic bromines and iodines from seaweeds were determined from incubations of 10 species of brown, red, and green macroalgae collected in the intertidal or subtidal zones of the rocky shore. For all the brown algae studied, iodine was released mainly as CH2I2. However, for several seaweeds, the novel iodine‐containing trihalomethanes CHIBr2 and CHI2Cl represented a significant fraction of the released organic iodine. The macroalgae incubation experiments as well as monitoring of the in situ concentrations in a rock pool indicated that natural halocarbon production by seaweeds was stimulated by incident light. The halocarbon fluxes derived from the seaweed incubations, coupled with published detailed biomass surveys, enabled coastal organohalogen seawater concentrations to be estimated. The CHBr3, CH2Br2, and CHBr2Cl concentrations calculated by this method compared well with coastal surface seawater measurements, implying that macroalgae were the major sources of the polybromomethanes. Measured CH3Br, CH3I, and CH2ICl levels were higher than calculated, which may be due to the existence of additional sources. CH3Br production by macroalgae accounted for less than 10% of measured levels in coastal waters. Short‐lived iodocarbons such as CH2I2 and CHIBr2 were depleted in surface seawater compared to calculated levels, implying their photolytic loss within the upper water column.

Determination of arsenic species in seawater by flow injection hydride generation in situ collection followed by graphite furnace atomic absorption spectrometry: Stability of As(III)

Dissolved arsenic is present in seawater at the 1 μg l −1 level in various chemical forms: mainly, As(III) and As(V) inorganic arsenic, MMA, DMA, and eventually, unknown organic compounds. The concentrations of the minor arsenic species are well below the detection limit of graphite furnace atomic absorption spectrometry (GFAAS). Therefore, a preconcentration/separation step is generally required before their determination. In this study, arsenic species were determined in seawater by flow injection hydride generation (FI-HG), collection within the graphite furnace, followed by atomic absorption spectrometry. This protocol permitted a preconcentration factor of about 1000 lowering the detection limit of arsenic in seawater to about 1.5 ng l −1 for a 10 ml sample volume under optimized experimental conditions. Based on the different responses of arsenic species towards hydride generation, an experimental protocol for arsenic speciation was proposed. Total arsenic could be determined after a thermal or a UV irradiation treatment in an alkaline persulfate medium after the conversion of all arsenic species to inorganic As(V). Total hydride-reactive species (As(III), As(V), monomethylarsenic (MMA) and dimethylarsenic (DMA)) could be determined for high NaBH 4 and HCl concentrations because a similar analytical response was obtained for these individual species. As(III) could be determined alone by performing hydride generation in seawater at a pH of about 7–8. Non-hydride-reactive arsenic species were determined by the difference between total arsenic and hydride-reactive species. According to this analytical protocol, arsenic species were determined in reference estuarine and coastal seawaters. Hydride-reactive arsenic species were the major compounds, probably mainly As(V); this study tended also to confirm the presence of non-hydride-reactive organic species in seawater (15%). We also showed that As(III) was not stable in acidified seawater and was also slowly converted to As(V) in a coastal surface seawater at its natural pH. These results indicated that time and preservation conditions could severely modify the speciation of arsenic in seawater, particularly for the preservation of As(III).

Dissolved free amino acids in coastal seawater using a modified fluorometric method

The method of Parsonset al. (1984) for measuring dissolved free amino acids (DFAA) in coastal seawater was modified. We found considerable interference in DFAA determination from ammonia dissolved in coastal seawater, although the interference of urea could be ignored. For DFAA analysis for coastal seawater samples, ammonia determinations for the same sample are needed to correct DFAA values. For coastal surface seawater samples from all over the Seto Inland Sea, Japan, values of DFAA ranged from undetectable to 1.87 μg-at N/l when corrected for ammonia, while uncorrected values ranged from undetectable to 2.61 μg-at N/l. DFAA, urea, nitrate+nitrite, ammonia and DON concentrations in surface seawater collected in the Seto Inland Sea were analyzed simultaneously. DFAA at four seasons constituted from 1.4 to 10.1% of DON, with a mean value of 6.5%. The concentration of urea was similar to that of DFAA and often higher than that of ammonium, although generally lower than that of nitrate.

Determination of selenium species in seawater by flow injection hydride generation in situ trapping followed by electrothermal atomic absorption spectrometry†

In this study, SeIV was determined in seawater by flow injection hydride generation, trapping within the graphite furnace, followed by electrothermal atomic absorption spectrometry. The optimized protocol permitted a preconcentration factor of 1000 lowering the detection limit of SeIV in seawater to about 1.5 ng l–1 for a 25 ml sample volume. Because this technique is specific to SeIV, various physico-chemical treatments leading to the conversion of other chemical forms into SeIV were investigated. Thermal and UV irradiation treatments of seawater samples in acidic or basic medium permitted the conversion of Se–II-selenomethionine and SeVI to SeIV. Based on the different responses of selenium species towards the photochemical treatments, an operational speciation model of selenium species in seawater is proposed. According to our analytical protocol, 21 ng l–1 SeVI, 10 ng l–1 SeIV and 13 ng l–1 organic Se–II species were determined in a coastal surface seawater collected near Brest.

Distribution ratio of dissolved and particulate REE in surface coastal seawater.

Dissolved and particulate forms of rare earth elements (REE) in the surface seawater of coastal area were separately determined with Inductively Coupled Plasma ion source Mass Spectrometry (ICP-MS) in order to discuss the REE partitioning between them. Two different samples were prepared on the occasion of each sampling: one sample was acidified before it was filtrated (AF) and another sample was acidified after filtrated (FA). On the two samples (AF and FA) we measured the REE abundances of the filtrate and the collected matter on the filter separately. In either sample, the filtrate showed a “W type tetrad effect”-like variation in the chondrite normalized REE pattern. The partitioning pattern of sample FA shows a clearer “W type tetrad effect”-like variation than that of sample AF, indicating that “labile” showed a “M type tetrad effect”-like variation. Besides Ce anomaly, anomalous behavior of Tb has been observed in the filtrate of the sample FA. Th in the collected shows rather capricious behavior.

Iron(II) in rainwater, snow, and surface seawater from a coastal environment

Abstract Using a newly developed HPLC method for the determination of Fe(II) concentration in a variety of aqueous environmental samples we found that Fe(II) accounts for 50–74% of the total filterable Fe in coastal surface seawater, 25–53% in rain samples, and 25–74% in snow collected from the vicinity of Massachusetts Bay, and Boston Harbor. We also found the residence time of Fe(II) in natural seawater to follow pseudo-first-order kinetics with an apparent half-life on the order of 30–70 min, much longer than previously thought. The observation of high Fe(II) concentrations and long apparent half-life reflect the product of as yet undefined chemical processes occurring in either atmosphere and/or seawater environments. These significant concentrations of Fe(II) may represent an important source of Fe influencing phytoplankton growth in coastal seawater.

Bacterial viruses in coastal seawater: lytic rather than lysogenic production

It has recently been suggested that the majority of virus production in seawater is through lysogen induction. Here, we examine the mechanism of virus production in coastal surface seawater. Bacteria and viruses were removed from seawater by ultrafiltration (0.2 or 0.02 pm) and introduced back to the water in 0.6 pm filtered inocula. Viral and bacterial abundance was followed during sample incubations using transmission electron microscopy and acridine orange direct counts. Bacteria increased in abundance in aU cases. When initial abundances were less than 1.3 X 106 viruses rnl-', (with extremely low initial bacterial densities), viruses disappeared at a rate of 20 to 50% d-l for the first 2 d and did not increase in abundance over the 7 d incubation period. Continuous sunlight exposure or a pulse of sunlight did not lead to detectable virus production, indicating that natural UV light did not induce lysogens. In samples with initial abundances above 1.3 X 106 viruses ml-l, significant increases as well as fluctuations in virus numbers were observed after the second day. This suggests that lytic infection, rather than the induction of lysogenic bacteria, is responsible for the majority of bacteriophage production in these experiments. Since lytic infection is dependent on encounter frequency, which is controlled by densities of both viruses and bactena, the product of these 2 concentrations determines if infection may take place. We observed lytic infection only when the product of virus and bacteria numbers equalled 10'' or more. Reported abundances of viruses and bacteria in natural seawater san~ples frequently fall above this level in surface waters and below it in mid and deep waters, suggesting that lytic infection may occur in all but deeper waters. However, due to the specificity of hosthirus interactions, infection is also dependent on the quantitative bacterial species composition and diversity, which are presently unknown.

High abundance of sulfur containing amino acids in low molecular weight proteinaceous fraction isolated from coastal surface seawater.

Dissolved proteinaceous materials in surface seawater in Funka Bay, Hokkaido, Japan were fractionated according to their molecular weight and analyzed for their amino acid composition by HPLC. Ultrafiltration membranes with different nominal cut-off sizes were used to fractionate the proteinaceous materials into molecular weight classes of approximately 500, 10, 000, and 100, 000 daltons. Amino acid content in the low molecular weight fraction (500 to 10, 000 daltons) accounted for 57 and 80% of the total amino acid contents in proteinaceous materials. The amino acid composition of this fraction was characterized by a relatively high abundance of cystine (10 to 15% of total amino acid content) during a spring bloom of phytoplankton. It was suggested that the high abundance of cystine in the fraction was caused by the spring bloom of diatom.

The behaviour of a Cu(II) ion selective electrode in seawater; copper consumption capacity and copper determinations

Determinations of copper consumption capacity (CuCs.C) and labile copper concentrations in surface coastal seawater, using a copper ion selective electrode (Cu-ISE) potentiometric method under predominantly diffusive conditions, are reported. For evaluation of the copper concentrations, the points of the endpoint contiguity zone of the CuCs.C titration curve were treated by an ISE multiple standard addition technique. The results were compared with those obtained by means of a Chelex-100 (calcic form) ‘batch’ procedure-potentiometric stripping analysis. The labile copper of the sample was determined at concentrations down to 10.70 nM with an average RSD of 12%, independent of the Cu-ISE employed. For adjacent subsamples, the mean CuCs.C values obtained for El Way seawater were equivalent to 81.05 and 48.00 nM copper, with an RSD of 4 and 7%, and for Isla Santa Maria seawater the value was equivalent to 70.27 nM copper, with an RSD of 7%. The theoretical approach of the electrode diffusive mechanism proposed, which would depend, fundamentally, on the adsorptive, complexing and reducing properties of the dissolved organic matter in the seawater sample, allows simultaneous analytical determination of CuCs.C and labile copper concentration in seawater.

Seasonal variation of atmospheric dimethylsulfide at Amsterdam Island in the southern Indian Ocean

Daily measurements of atmospheric concentrations of dimethylsulfide (DMS) were carried out for two years in a marine site at remote area: the Amsterdam Island (37°50′S–77°31′E) located in the southern Indian Ocean. DMS concentrations were also measured in seawater. A seasonal variation is observed for both DMS in the atmosphere and in the sea-surface. The monthly averages of DMS concentrations in the surface coastal seawater and in the atmosphere ranged, respectively, from 0.3 to 2.0 nmol l-1 and from 1.4 to 11.3 nmol m-3 (34 to 274 pptv), with the highest values in summer. The monthly variation of sea-to-air flux of DMS from the southern Indian Ocean ranges from 0.7 to 4.4 μmol m-2 d-1. A factor of 2.3 is observed between summer and winter with mean DMS fluxes of 3.0 and 1.3 μmol m-2 d-1, respectively.

Analysis of lead in polluted coastal seawater

The concentrations of total lead were determined in both ordinary coastal seawater and in coastal waters highly polluted with sewage. The average concentration of total lead ranged from about 25 ng/kg in surface samples of the former type to an average of 150 ng/kg in the latter type. 0.4 − μm filtrate lead was found to be equivalent to lead extracted from untreated seawater by dithizone in chloroform. In highly polluted waters, particle lead ranged from 56 to 39% of the total lead, with the proportion increasing as the amount of sewage in the seawater increased. Virtually all of the lead in sewage is contained in the particle phase before it enters the ocean but about 11% is made freely available by cation exchange when the sewage is mixed with seawater. In ordinary coastal waters that are not highly polluted with sewage lead, particle lead ranged from 90 to > 20%, and most of this lead was associated with plankton. About one-third of total lead, or one-half of particle lead, in untreated seawater adheres to the walls of the water container within the first day. Upon prolonged standing (> 3 months) most of the remaining particle lead can be collected on the surface of algal colonies growing on the walls of the water container. The concentrations of freely available lead in seawater do not seem to be significantly affected by wall adsorption. The 206 Pb/ 207 Pb ratio of total lead in coastal surface seawater collected near Los Angeles was 1.194, and a day earlier was 1.188 near La Jolla. It is believed that this shows lack of mixing of contributions from two different sources of lead pollution: a pulse of rain-storm runoff of gasoline lead( 206 Pb/ 207 Pb ∼ 1.197) from paved surfaces added to Los Angeles waters; and sewage lead ( 206 Pb/ 207 Pb ∼ 1.188) from San Diego added to La Jolla waters.

PHYTOPLANKTON GROWTH AND COMPOSITION IN SHIPBOARD CULTURES SUPPLIED WITH NITRATE, AMMONIUM, OR UREA AS THE NITROGEN SOURCE1

Coastal surface seawater off southern California was enriched with phosphate, silicate, vitamins B12, B1, and biotin, a chelated trace metal mixture, and with nitrogen as nitrate, ammonium, or urea, and the cultures were incubated on deck in daylight. Natural phytoplankton present in the seawater served as inoculum. Samples were taken every 6 hr, once the cultures were established. Diel periodicity was noted in diatom cell division, in nitrate and ammonium assimilation rate, in phosphate assimilation rate, and in photosynthetic rate measured at intervals under constant, artificial irradiance, but not in the rate of chlorophyll a synthesis. The chemical composition of the crops was influenced by the nitrogen source used for growth and by diel periodicity in assimilation rates. Most of the vitamin Bi content of the crop was synthesized by the organisms, only a small proportion being supplied initially from the medium. Some species known to require vitamins continued to grow after vitamin depletion from the medium, their requirements apparently satisfied by vitamins released by other species.