Natural Coastal Seawater Research Articles

New insights into estimation of bioavailable inorganic phosphorus in natural coastal seawater

Considering the impact of the high salinity and high turbidity of coastal seawater on phosphorus forms, a new method was proposed to determine bioavailable inorganic phosphorus (BIP). The phosphorus most relevant to eutrophication is BIP, and traditional analysis methods may underestimate the degree of eutrophication. In this study, a microelectrode of multigold (AuμE) was fabricated for direct voltammetric determination of BIP without filtration, and BIP environmental characteristics including distribution and correlation relationships with environmental factors in typical coastal seawater of Northern China were analyzed. The proposed AuμE showed a low detection limit of 0.03 μM. The surface and bottom BIP concentrations ranged from 1.00 to 2.13 and from 0.88 to 2.05 μM, respectively. BIP dominated the total P (TP) accounting for 48.5–67.5 % in the surface layer samples, and 32.6–92.7 % in the bottom layer samples, respectively. The concentrations of BIP were obviously higher than those of DIP, indicating that DIP may underestimate the probability of eutrophication occurring. And BIP was positively correlated with dissolved oxygen (DO) (P < 0.05). BIP may be a promising indicator of eutrophication potential in coastal areas with high salinity and high turbidity. The proposed reliable voltammetry method provides a new indicator for environmental assessment and represents a significant step in the comprehensive analysis of P species.

Photochemical Generation of Methyl Chloride from Humic Aicd: Impacts of Precursor Concentration, Solution pH, Solution Salinity and Ferric Ion.

Methyl chloride (CH3Cl) is presently understood to arise from biotic and abiotic processes in marine systems. However, the production of CH3Cl via photochemical processes has not been well studied. Here, we reported the production of CH3Cl from humic acid (HA) in sunlit saline water and the effects of the concentration of HA, chloride ions, ferric ions and pH were investigated. HA in aqueous chloride solutions or natural seawater were irradiated under an artificial light, and the amounts of CH3Cl were determined using a purge-and-trap and gas chromatography-mass spectrometry. CH3Cl was generated upon irradiation and its amount increased with increasing irradiation time and the light intensity. The formation of CH3Cl increased with an increase of HA concentration ranging from 2 mg L−1 to 20 mg L−1 and chloride ion concentration ranging from 0.02 mol L−1 to 0.5 mol L−1. The photochemical production of CH3Cl was pH-dependent, with the highest amount of CH3Cl generating near neutral conditions. Additionally, the generation of CH3Cl was inhibited by ferric ions. Finally, natural coastal seawater was irradiated under artificial light and the concentration of CH3Cl rose significantly. Our results suggest that the photochemical process of HA may be a source of CH3Cl in the marine environment.

The role of microbially-mediated exopolymeric substances (EPS) in regulating Macondo oil transport in a mesocosm experiment

Large-scale exopolymeric substances (EPS) formation was observed in contaminated surface waters of the Gulf of Mexico, after the Deepwater Horizon oil spill. The conditions under which EPS are produced can cause variations in their physico-chemical properties, affecting the fate of the oil through either emulsification or coagulation with particles, followed by aggregation and marine oil snow (MOS) sedimentation. Here, we report results from a four-day mesocosm experiment that examined EPS production, the change in the bulk chemical composition (mainly polysaccharides and proteins), as well as the partitioning into different size fractions (suspended particulate matter (SPM), colloidal fraction, and sinking MOS). The treatments included 1) natural coastal seawater (Control), 2) a water accommodated fraction of oil (WAF), 3) a chemically-enhanced WAF with addition of oil dispersant Corexit (CEWAF), and 4) a diluted CEWAF (DCEWAF). Generally, the presence of WAF stimulated more extracellular polysaccharide production, whereas the addition of Corexit promoted more protein production. Moreover, marine aggregates changed from a terrestrial signature (higher aromaticity, lower EPS content and more uniform monosaccharide distribution) in the early stages of the experiment, to a fresher autochthonous signature (less aromatic, higher EPS content and glucose-dominated monosaccharide distribution) in the later stage of the mesocosm experiment. Corexit promoted the association between oil and proteins, assisting to emulsify the oil in colloids and SPM and delay the settling of EPS and oil (MOS) for the duration of the mesocosm. Furthermore, when oil, especially Corexit-dispersed oil, was present, extracellular polysaccharides were preferentially incorporated into sinking MOS relative to proteins, as evidenced from a lower protein-C/carbohydrate-C ratio of the sinking MOS than those of SPM and colloidal fraction in WAF, CEWAF and DCEWAF, respectively. This is in contrast to a higher protein-C/carbohydrate-C ratio in the sinking marine snow than those of SPM and colloidal fraction in the control. Likely, microbially-mediated extracellular polysaccharides are the key component that anchors the mineral ballast until the aggregates become dense enough and overcome the buoyancy added to the aggregates as a result of their association with oil/Corexit. We conclude that interactions between Corexit and EPS components regulate petroleum hydrocarbon distribution between the water column and sinking MOS.

The impact of silver nanoparticles on marine plankton dynamics: Dependence on coating, size and concentration

During this study, three microcosm experiments were carried out with natural coastal seawater, collected in the Eastern Mediterranean Sea, in order to assess the effect of silver nanoparticle (AgNP) exposure to natural plankton communities. The impact of coating (branched-polyethyleneimine: BPEI vs. poly-vinylpyrrolidone: PVP), size (40 vs. 60nm), concentration (200, 500, 2000, 5000 and 10,000ng Ag L−1) and silver form (dissolved Ag+ vs. AgNPs) were tested. The results of chlorophyll a concentration revealed that PVP AgNPs caused a higher toxicity than BPEI AgNPs, and this was possibly related to the measured higher dissolution rate. Additionally, toxicity of BPEI AgNPs was size-dependent, with 40 being more toxic than 60 nm AgNPs, which was nevertheless not seen clearly for PVP AgNPs. Interestingly, community composition altered in response to AgNP exposure: cyanobacterial abundance was negatively affected at concentrations ≥200ng Ag L−1, and dinoflagellate abundance and composition were altered at a 2000ng Ag L−1 concentration. Specifically, dinoflagellate (Gymnodinium, Prorocentrum and Gyrodinium) and diatom (Nitzschia, Navicula and Climacosphenia) genera either increased or decreased, highlighting taxa-specific effects, with some of them being able to tolerate, compensate or even benefit from AgNPs. Silver in either form (dissolved Ag+ or in NPs) caused almost identical results in the plankton community, further indicating that Ag+ release is the primary cause of AgNP toxicity. This study employed for the first time environmentally relevant AgNP concentrations (minimum 200ng Ag L−1) in natural seawater without pre-filtration steps and showed that community changes were driven by the exposure but were largely dependent on ambient physico-chemical characteristics and should be further investigated.

Macroalgal Morphogenesis Induced by Waterborne Compounds and Bacteria in Coastal Seawater.

Axenic gametes of the marine green macroalga Ulva mutabilis Føyn (Ria Formosa, locus typicus) exhibit abnormal development into slow-growing callus-like colonies with aberrant cell walls. Under laboratory conditions, it was previously demonstrated that all defects in growth and thallus development can be completely abolished when axenic gametes are inoculated with a combination of two specific bacterial strains originally identified as Roseobacter sp. strain MS2 and Cytophaga sp. strain MS6. These bacteria release diffusible morphogenetic compounds (= morphogens), which act similar to cytokinin and auxin. To investigate the ecological relevance of the waterborne bacterial morphogens, seawater samples were collected in the Ria Formosa lagoon (Algarve, Southern Portugal) at 20 sampling sites and tidal pools to assess their morphogenetic effects on the axenic gametes of U. mutabilis. Specifically the survey revealed that sterile-filtered seawater samples can completely recover growth and morphogenesis of U. mutabilis under axenic conditions. Morphogenetic activities of free-living and epiphytic bacteria isolated from the locally very abundant Ulva species (i.e., U. rigida) were screened using a multiwell-based testing system. The most represented genera isolated from U. rigida were Alteromonas, Pseudoalteromonas and Sulfitobacter followed by Psychrobacter and Polaribacter. Several naturally occurring bacterial species could emulate MS2 activity (= induction of cell divisions) regardless of taxonomic affiliation, whereas the MS6 activity (= induction of cell differentiation and cell wall formation) was species-specific and is probably a feature of difficult-to-culture bacteria. Interestingly, isolated bacteroidetes such as Algoriphagus sp. and Polaribacter sp. could individually trigger complete Ulva morphogenesis and thus provide a novel mode of action for bacterial-induced algal development. This study also highlights that the accumulation of algal growth factors in a shallow water body separated from the open ocean by barrier islands might have strong implications to, for example, the wide usage of natural coastal seawater in algal (land based) aquacultures of Ulva.

Long-Term Corrosion of Mild Steel in Natural and UV-Treated Coastal Seawater

Highly polished coupons (25 by 25 by 1.5 mm) sourced from the same steel sheet were continuously immersion-exposed either to natural coastal seawater or to seawater from the same source subjected to filtration and UV irradiation to eliminate microbiologically influenced corrosion as much as possible. This was continued for 943 days (2.6 years). Dissolved oxygen levels were very similar in both environments. On average the UV-treated seawater was 2°C warmer, but all coupons exposed to it showed less localized corrosion than those exposed to natural seawater. The typical topographical difference was about 60% as measured by surface roughness parameter Sa. Mass losses in UV-treated seawater were about 10% higher than in natural seawater, but after temperature correction were similar to natural seawater for the first year and tended to be lower subsequently. At all exposure periods the rusts in UV-treated seawater were less voluminous than the rusts in natural seawater. Eventually they also contained a higher...

Pseudoalteromonas spp. Serve as Initial Bacterial Attractants in Mesocosms of Coastal Waters but Have Subsequent Antifouling Capacity in Mesocosms and when Embedded in Paint

The purpose of the present study was to determine if the monoculture antifouling effect of several pigmented pseudoalteromonads was retained in in vitro mesocosm systems using natural coastal seawater and when the bacteria were embedded in paint used on surfaces submerged in coastal waters. Pseudoalteromonas piscicida survived on a steel surface and retained antifouling activity for at least 53 days in sterile seawater, whereas P. tunicata survived and had antifouling activity for only 1 week. However, during the first week, all Pseudoalteromonas strains facilitated rather than prevented bacterial attachment when used to coat stainless steel surfaces and submerged in mesocosms with natural seawater. The bacterial density on surfaces coated with sterile growth medium was 10(5) cells/cm(2) after 7 days, whereas counts on surfaces precoated with Pseudoalteromonas were significantly higher, at 10(6) to 10(8) cells/cm(2). However, after 53 days, seven of eight Pseudoalteromonas strains had reduced total bacterial adhesion compared to the control. P. piscicida, P. antarctica, and P. ulvae remained on the surface, at levels similar to those in the initial coating, whereas P. tunicata could not be detected. Larger fouling organisms were observed on all plates precoated with Pseudoalteromonas; however, plates coated only with sterile growth medium were dominated by a bacterial biofilm. Suspensions of a P. piscicida strain and a P. tunicata strain were incorporated into ship paints (Hempasil x3 87500 and Hempasil 77500) used on plates that were placed at the Hempel A/S test site in Jyllinge Harbor. For the first 4 months, no differences were observed between control plates and treated plates, but after 5 to 6 months, the control plates were more fouled than the plates with pseudoalteromonad-based paint. Our study demonstrates that no single laboratory assay can predict antifouling effects and that a combination of laboratory and real-life methods must be used to determine the potential antifouling capability of new agents or organisms.

Lack of response in a marine pelagic community to short-term oil and contaminant exposure

Oil and contaminant inputs are co-occurring features of most estuaries and harbours in industrialised countries. However, there is limited knowledge as to how these different pressures interact. Oil may modulate the accumulation and effects of contaminants, and community response to contaminant stress would be expected to be coupled to food web structure. We performed an outdoor land-based 100-L microcosm experiments using natural coastal sea water in order to address these questions.Either mineral oil, emamectin (EMA; a pharmaceutical used in aquaculture and agriculture), or a combination was dosed to three replicate tanks for each treatment. Samples were taken at the start and each day of a four-day exposure period. For each sample, algal production and nutrients were quantified. Bacterial abundance was assessed by flow cytometry and the fate of emamectin investigated by filtration followed by extraction and LC/MS/MS analysis. Mesozooplankton were counted in samples taken at the end of the experiment.There were clear changes in chlorophyll a and bacterial numbers over the time course of the experiment in all treatments, but addition of oil, EMA or their combination did not alter nutrient concentrations, ecosystem components or the community structure compared to the control. There was however an unexplained apparent positive effect of low concentrations of acetone (0.005%) used as solvent in the mesocosms. Emamectin was predominantly found in the water phase at the end of the experiment with higher concentrations in both fractions of EMA–oil treatments compared to treatments with EMA only. The study shows that even high concentrations of the environmental stressors oil and emamectin may not have dramatic effects in a dynamic pelagic system over a four-day period, presumably indicating that longer exposure will be required for any effects through top-down processes to become evident.

Influence of trace metal release from volcanic ash on growth of Thalassiosira pseudonana and Emiliania huxleyi

Recent studies demonstrate that volcanic ash has the potential to increase phytoplankton biomass in the open ocean. However, besides fertilizing trace metals such as Fe, volcanic ash contains a variety of potentially toxic metals such as Cd, Cu, Pb, and Zn. Especially in coastal regions closer to the volcanic eruption, where ash depositions can be very high, toxic effects are possible. Here we present the first results from laboratory experiments, showing that trace metal release from different volcanic ashes can have both fertilizing and toxic effects on marine phytoplankton in natural coastal seawater. The diatom Thalassiosira pseudonana generally showed higher growth rates in seawater that was in short contact with volcanic ash compared to the controls without ash addition. In contrast to that, the addition of volcanic ash had either no effect or significantly decreased the growth rate of the coccolithophoride Emiliania huxleyi. It was not possible to attribute the effects to single trace metals, however, our results suggest that Mn plays an important role in regulating the antagonistic and synergistic effects of the different trace metals. This study shows that volcanic ash can lead to changes in the phytoplankton species composition in the high fall-out area of the surface ocean.

Technical Note:Influence of Experimental Conditions on the Outcome of Laboratory Investigations Using Natural Coastal Seawaters

Abstract Methods for handling and storing natural coastal seawater, particularly methods for deaeration over time, influenced the chemistry and microflora. Bubbling nitrogen into natural seawater t...

A mechanistic study on the photodegradation of Irgarol-1051 in natural seawater

The kinetics of the photoinduced degradation and transformation of the antifouling booster biocide, Irgarol-1051, in natural coastal seawater was studied. The measured first-order rate constant for the degradation of Irgarol-1051 was 4.02 ± 0.1 × 10 −4 h −1, while the rate constant for the formation of 2-methylthio-4- tert-butylamino-6-amino- s-triazine (M1), the most dominant degradation product of Irgarol-1051, was 4.6 ± 0.1 × 10 −5 h −1. This considerably slower rate suggested that the transformation of Irgarol-1051 to M1 may not be the predominant pathway of the photodegradation process. During the photodegradation study, a new s-triazine species was observed in the degradation mixtures which, together with M1, appeared immediately upon photolysis and continued to accumulate in the degradation mixture throughout the entire study duration. This is in contrast to the behaviour of the recently identified degradation product of Irgarol-1051, 3-[4- tert-butylamino-6-methylthiol- s-triazin-2-ylamino]- propionaldehyde (M2), which was only detected in the degradation mixture after a long induction period. High-resolution tandem mass spectrometric analysis hinted that the new degradation product (M4) may possess a terminal alcohol and is likely to be an N-allylic alcohol derivative of M1. This suggests that M4 may, indeed, be a precursor of M2 via redox transformation at its N-allylic alcohol functionality.

Influence of Seawater Nutrient Content on the Early Immersion Corrosion of Mild Steel—Part 1: Empirical Observations

Abstract A previous study of the immersion corrosion of mild and low-alloy steels in natural coastal seawater found a high degree of consistency between the corrosion losses observed at different testing sites when allowance was made for average seawater temperature and sites with obvious pollution and velocity effects were excluded. However, some sites showed early corrosion rates considerably below the trend. Carefully conducted laboratory experiments using real seawater also show low trends. It is proposed that the more severe early corrosion of steels in natural coastal immersion conditions is caused by elevated nutrient levels in seawater. Not only does this increase the rate of growth of biofilms and of marine fouling as normally assumed but it also raises the rate of metabolism of bacteria. It is contended that the latter is the principal cause of increased early corrosion at higher nutrient levels. A detailed analysis of an extensive range of field data provides support for this contention. It was...

Effects of glutamate and glucose on N cycling and the marine plankton community

Phosphate-enriched natural coastal seawater was incubated with the addition of gluta- mate and glucose, and the effects on coastal bacteria were studied, as well as subsequent effects on phytoplankton and heterotrophic nanoflagellates (HNF). Based on the changes in bacterial and HNF density, chlorophyll a concentrations and 15 N dilution, the addition of glucose resulted in bacteria out-competing phytoplankton for available nitrogen. Glutamate addition resulted in the enhance- ment of both bacterial and phytoplankton populations. However, the increased bacterial population returned to background level rapidly; this may have been caused by tight coupling between bacter- ial production and grazing on bacteria. In spite of adding the same amount of organic carbon in both treatments (about 90 µmol l -1 ), enhancement of the net particulate organic carbon production by the entire planktonic community was considerably higher when glutamate was added. These results suggest that the biochemical basis of the bacterial substrate controls not only bacteria but also phyto- plankton and HNF, through trophic interactions such as competition for nitrogen and predator-prey relationships.

Adsorption and uptake of Cu by Emiliania huxleyi in natural seawater.

Short-term kinetic experiments, carried out in natural coastal seawater (with predetermined background levels of trace metals and organic ligands, L) enriched with nitrate and phosphate, demonstrated that Emiliania huxleyi was able to uptake Cu very quickly. After 10 min of exposure (background Cu level in the inoculated cells: [Cu]total cellular = 9.3 x 10(-17) mol cell-1, [Cu]intracellular = 8.4 x 10(-17) mol cell-1, and [Cu]extracellular = 1.0 x 10(-17) mol cell-1) to a natural seawater which contained 29 nM total initial dissolved Cu concentration ([Cu]d) (29 nM [CuL] and 3.2 x 10(-13) M free Cu concentration, [Cu2+]) the intracellular Cu was already 28 x 10(-17) mol cell-1. This value corresponded to 85% of the intracellular metal observed in pseudoequilibrium conditions (after 24 h of exposure) and to 88% of the total metal sorption (adsorption plus uptake) after 10 min. In contrast, the external adsorption after 10 min was only 3.0 x 10(-17) mol cell-1 which corresponded to 60% of the extracellular metal in pseudoequilibrium conditions. Simultaneously occurred a very fast release of organic ligands (L) by E. huxleyi, the majority being identified by cathodic stripping voltammetry as glutathione. The production of exudates increased with both Cu concentration and exposure time. After 10 min of exposure, the production of exudates in a medium with 129 nM [Cu]d (72 nM [CuL] and 7.9 x 10(-13) M [Cu2+]) was 51 nM, about 42% of that observed in pseudoequilibrium. As the Cu complexes with the organic ligands present in the medium were very stable (logarithm of the conditional stability constant: 12.18 +/- 0.06) and the ligand concentration in the medium was relatively high (e.g. 123 nM CL in the medium with 129 nM initial [Cu]d after 10 min of exposure) most of the metal was organically bound in the medium.

Effect of organic matter on bubble surface tension

Bubble surface tension (BST) is measured by spinning single bubbles in a rotating cell and relating the resulting bubble deformation to the Centrifugal number Ce. Using this method, bubbles in “clean” fresh water (distilled, deionized, passed through activated charcoal and filtered at 0.2 μm) are found to have a BST similar to that reported for the “clean” air‐water interface (72.4 mN/m), whereas adsorption of organic films are observed to decrease the BST, with the effect increasing as the bubbles are aged. In natural coastal sea water (North West Arm, Halifax Harbour (10 m)) the BST decreases to 70.5 mN/m, and in phytoplankton culture (Nitzschia pungens) decreases to 67 mN/m. Saturated stearic acid solution shows a BST of 57 mN/m. Coalescence of two bubbles with equilibrium surface film is accompanied by a rapid decrease in the surface tension, a decrease that we attribute to compression of the merging surface films at the newly created smaller interface. The decrease is most pronounced in water rich in organic surfactants.

Dissolution of manganese from marine atmospheric participates into seawater and rainwater

A significant fraction of the Mn in a marine aerosol of Saharan origin was found to come into solution on contact with an artificial rainwater and also a natural coastal seawater, on a time scale of a few minutes. The fraction of the non-lattice Mn released on contact with the rainwater increased with decreasing pH from 29% at pH 5.1 to 85% at pH 2 (equivalent to 20% to 59% of the total Mn), whilst in coastal seawater, 36% (25% of the total Mn) came into solution. This behaviour is consistent with the environmental and limited experimental data available. The release of dissolved labile forms of Mn, and probably other metals, through such dissoluton reactions is potentially an important step in the geochemical cycles of these elements. The carbonate content of the aerosol appears to provide a neutralizing effect which modifies the release of Mn when the aerosol was added to a mildly acidic rainwater.

Complexation of Cu, Zn and Cd by metabolites excreted from marine diatoms

The excretion of photosynthetically fixed carbon from cultured marine diatoms and its influence on Cu, Zn and Cd complexation in seawater was studied for three species. For each species, an isolate from oligotrophic waters was compared with an estuarine isolate. Complexation of metal was determined with the use of differential pulse anodic stripping voltammetry. Excreted material from cells in log-phase growth complexed Cu > Zn > Cd, while material derived from senescent cells complexed only Zn. The filtrates of all cultures complexed these metals comparably with natural coastal seawater. There were no appreciable differences in complexing ability within or among species, suggesting that no excretion-complexation ‘strategy’ peculiar to each ecosystem exists among these species.

Phytoplankton enrichment experiments and bioassays in natural coastal sea water and in sewage outfall receiving waters off Southern California

Nutrient enrichment experiments with near-shore Southern California surface water showed that nitrogen was the principal nutrient limiting phytoplankton growth. Bioassays of receiving waters taken above major sewage outfalls were carried out using representative Southern California phytoplankton cultures. The bioassays showed that the receiving waters were sometimes stimulatory, and at other times inhibitory, to algal growth. These studies were done using in vivo fluorescence to measure the growth of the algae. In cultures, cell division rates and increases in vivo fluorescence were comparable and this indicates that fluorescence is a reasonable way of following growth.