Preparation of chlorophyll a, chlorophyll b and bacteriochlorophyll a by means of column chromatography with diethylaminoethylcellulose

Chlorophyll a, chlorophyll b and bacteriochlorophyll a were prepared by means of column chromatography with Sephadex LH-20 and diethylaminoethylcellulose. This method provides purified preparations of chlorophylls in about 3 h.To prepare chlorophyll a, blue-green or red algae were used as the starting material. Chlorophyll a was extracted with 90% aqueous acetone from cells of blue-green algae, Anabaena variabilis, Anacystis nidulans and Tolypothrix tenuis, and with 90% aqueous methanol from thalli of a red alga, Porphyra yezoensis. Chlorophyll a was collected as precipitates by adding dioxane and water to the extract according to the method of Iriyama et al. [6]. The crude chlorophyll a preparation was applied to a Sephadex LH-20 column with chloroform as the eluent and then to a DEAE-cellulose column with a chloroform/methanol mixture (49 : 1, v/v) as the eluent. Analysis with thin layer chromatography revealed that the chlorophyll a preparation contained no detectable contaminants.Bacteriochlorophyll a was prepared in a similar manner from purple photosynthetic bacteria, Rhodopseudomonas spheroides and Chromatium vinosum.In order to prepare chlorophyll b, chloroplasts of spinach leaves were used as the starting material. A mixture of chlorophylls a and b was obtained in the same way as described for the preparation of chlorophyll a from the blue-green algae. To separate chlorophyll b from chlorophyll a, the mixture was applied to a diethylaminoethylcellulose column which was developed with a hexane/2-propanol mixture (5 : 2, v/v).     

Chloroplast biogenesis. XXIX. The occurrence of several novel chlorophyll a and b chromophores in higher plants

With the use of low temperature spectrofluorometry and matrix calculations it was demonstrated that the chlorophyll a pool of higher plants is made up of four different chlorophyll a chromophores. The latter were segregated by high pressure liquid chromatography on a silica column. They were designated Chl a (E432 F664), Chl a (E436 F670), Chl a (E443 F672) and Chl a (E446 F674), where E refers to the Soret excitation maximum and F to the fluorescence emission maximum at 77 K in ether. Likewise the Chl b pool was shown to consist of at least four different Chl b chromophores which were designated: Chl b (E465), Chl b (E470), Chl b (E475) and Chl b (E485). It was proposed that the various chlorophyll chromophores differed by the degree of oxidation of their side chains at the 2 and 4 positions of the macrocycle. It was also suggested that the chemical modifications at the 2 and 4 positions of the macrocycle may play an important role in positioning the different chlorophyll chromophores in the thylakoid membranes.     

Phytoplankton community composition and photosynthetic physiology in the Australian sector of the Southern Ocean during the austral summer of 2010/2011

Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. However, the relationship between phytoplankton community composition and primary productivity remains elusive in this region. We investigated the community composition and photosynthetic physiology of surface phytoplankton assemblages in the Australian sector of the Southern Ocean from December 2010 to January 2011. There were significant latitudinal variations in hydrographic and biological parameters along 110°E and 140°E. Surface (5 m) chlorophyll a (chl a) concentrations measured with high-performance liquid chromatography varied between 0.18 and 0.99 mg m^?3. The diatom contribution to the surface chl a biomass increased in the south, as estimated with algal chemotaxonomic pigment markers, while the contributions of haptophytes and chlorophytes decreased. In our photosynthesis–irradiance (P–E) curve experiment, the maximum photosynthetic rate normalized to chl a ( \(P_{ \hbox{max} }^{*}\) ), initial slope (α ^*), the maximum quantum yield of carbon fixation (Φ _{c max}), and the photoinhibition index (β ^*) were higher in the region where diatoms contributed >50 % to the chl a biomass. In addition, there were statistically significant correlations between the diatom contribution to the chl a biomass and the P–E parameters. These results suggested that the changes in the phytoplankton community composition, primarily in diatoms, could strongly affect photosynthetic physiology in the Australian sector of the Southern Ocean.     

High-light induced singlet oxygen formation in cytochrome b6f complex from Bryopsis corticulans as detected by EPR spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy was used to detect the light-induced formation of singlet oxygen (¹O₂*) in the intact and the Rieske-depleted cytochrome b₆f complexes (Cyt b₆f) from Bryopsis corticulans, as well as in the isolated Rieske Fe–S protein. It is shown that, under white-light illumination and aerobic conditions, chlorophyll a (Chl a) bound in the intact Cyt b₆f can be bleached by light-induced ¹O₂*, and that the ¹O₂* production can be promoted by D₂O or scavenged by extraneous antioxidants such as l-histidine, ascorbate, β-carotene and glutathione. Under similar experimental conditions, ¹O₂* was also detected in the Rieske-depleted Cyt b₆f complex, but not in the isolated Rieske Fe–S protein. The results prove that Chl a cofactor, rather than Rieske Fe–S protein, is the specific site of ¹O₂* formation, a conclusion which draws further support from the generation of ¹O₂* with selective excitation of Chl a using monocolor red light.     

Kinetics and efficiency of excitation energy transfer from chlorophylls,their heavy metal-substituted derivatives,and pheophytins to singlet oxygen

Time-resolved measurements of the singlet oxygen infrared (1269 nm) luminescence were used to follow the kinetics and efficiency of excitation energy transfer (EET) between chlorophyll (Chl) derivatives and oxygen in acetone. The studied pigments were Mg-Chl a and b and their heavy metal (Cu²⁺ and Zn²⁺)-substituted analogues, as well as pheophytin (Pheo) a and b. The efficiency of EET from chlorophyll to oxygen was highly dependent on the central ion in the pigment. Cu-Chl a and Cu-Chl b had the lowest efficiencies of singlet oxygen production, while Pheo a had a higher one, and Zn-Chl a had a similar one compared to Mg-Chl a. Also the side chain (position C-7, i.e. Chl a vs. Chl b) influenced the efficiency of singlet oxygen formation. In the case of square-planar complexes like Cu-Chl and Pheo, EET was more efficient in the Chl a derivatives than in those of Chl b; the opposite effect was observed in the case of the five- or six-coordinated Mg-Chl and Zn-Chl. As for the lifetime of the Chl triplet state, the most striking difference to Mg-Chl again was found in the case of Cu-Chls, which had much shorter lifetimes. Furthermore, the central ion in Chl affected the physical quenching of singlet oxygen: its efficiency was decreasing from Mg-Chl through Zn-Chl over Cu-Chl to Pheo. The results are discussed in the context of the oxidative stress accompanying heavy metal-induced stress in plants.     

Chlorophyllide b

Chlorophylls a,b and chlorophyllides a,b were isolated from pea chloroplasts as pheophorbides a,b following the administration of $\text{[}{}^{14}\text{C]δ-aminolevulinic}$ acid. Relative pool sizes suggest that chlorophyllide b precedes chlorophyll b and does not arise from the latter by the action of chlorophyllase.     

Spectral and photochemical properties of borohydride-treated D1-D2-cytochrome b-559 complex of photosystem II

The D1-D2-cytochrome b-559 reaction center complex of photosystem II with an altered pigment composition was prepared from the original complex by treatment with sodium borohydride (BH⁻₄). The absorption spectra of the modified and original complexes were compared to each other and to the spectra of purified chlorophyll a and pheophytin a (Pheo a) treated with BH⁻₄ in methanolic solution. The results of these comparisons are consistent with the presence in the modified complex of an irreversibly reduced Pheo a molecule, most likely 13¹-deoxo-13¹-hydroxy-Pheo a, replacing one of the two native Pheo a molecules present in the original complex. Similar to the original preparation, the modified complex was capable of a steady-state photoaccumulation of Pheo⁻ and P680⁺. It is concluded that the pheophytin a molecule which undergoes borohydride reduction is not involved in the primary charge separation and seems to represent a previously postulated photochemically inactive Pheo a molecule. The Q_y and Q_x transitions of this molecule were determined to be located at 5°C at 679.5–680 nm and 542 nm, respectively.     

Sedimentation of chlorophylls in an Arctic fjord under freshwater discharge

Sedimentation of chlorophylls was studied during summer 1997 in Adventfjorden (Spitsbergen, Arctic). During the period of study, the water column was found to be well stratified by a freshened surface layer (salinity <31 PSS). A high load of suspended particulate matter from riverine discharge reduced the euphotic zone to an interval of 0.4–1.1m. Total particulate matter sedimentation rates were about twice as high in June as in July. The following chlorophylls were distinguished in the sedimented particles: chl a and its degradation products (allomer chl a, phaeophytin a, phaeophorbide a, chlorophyllide a), chl b and chl c ₁+c ₂. The quantitatively most important derivative of chl a was phaeophorbide a (31--41% of porphyrin a). Generally, the sedimentation rate of chlorophylls increased with depth. Linear relationships between concentrations of chl a and phaeophorbide a (r ²=0.92), as well as between concentrations of chl a and phaeophytin a (r ²=0.90) indicated a strong connection between phytoplankton abundance and zooplankton grazing. The significant correlation between chl a and chlorophyllide a concentrations (r ²=0.82) showed that most of the sinking chl a belonged primarily to diatoms, and low chlorophyllide a:chl a ratio (0.03) indicated that cellular senescence was not an important reason for the sinking of chl a. Moreover, very low chl b:chl a ratios (about 0.05 calculated for samples where chl b was detectable) suggest that contributions of green algae and/or higher plant detritus were negligible in sinking particles. The ratio of chl c ₁+c ₂:chl a was 0.85 indicating that chl c-containing algae were dominating.     

Polymorphism and weak antiferromagnetic interactions in dibromo[(−)-sparteine-N,N]copper(II)

Two polymorphic crystal structures of the title compound, dibromo[(−)-sparteine-N,N^′]copper(II), 1, were determined. The structures of two isomorphs of 1, 1a [orthorhombic, P2₁2₁2₁, a=11.0463(9) Å, b=11.9839(15) Å and c=12.7835(19) Å] and 1b [orthorhombic, P2₁2₁2₁, a=7.6779(9) Å, b=12.0927(14) Å and c=18.090(2) Å], are composed of the same basic structural unit, Cu(C₁₅H₂₆N₂)Br₂. The bond distances in the molecular structures of 1a and 1b are identical to each other within the esds. However, there are slight differences in the bond angles around the Cu(II) center and considerable differences in their packing structure. Crystal 1a exhibits weak anti-ferromagnetism (J=−1.89 cm⁻¹) as opposed to the magnetically isolated paramagnetism observed for the analogous dichloro[(−)-sparteine]copper(II), 2. The results of a magneto-structural investigation of 1a and 2, and other supporting evidence, suggest that the pathway for the weak antiferromagnetic super-exchange in 1a might be through a Cu-Br ? Br-Cu contact.     

Both chlorophylls a and d are essential for the photochemistry in photosystem II of the cyanobacteria, Acaryochloris marina

We have measured the flash-induced absorbance difference spectrum attributed to the formation of the secondary radical pair, P⁺Q⁻, between 270 nm and 1000 nm at 77 K in photosystem II of the chlorophyll d containing cyanobacterium, Acaryochloris marina. Despite the high level of chlorophyll d present, the flash-induced absorption difference spectrum of an approximately 2 ms decay component shows a number of features which are typical of the difference spectrum seen in oxygenic photosynthetic organisms containing no chlorophyll d. The spectral shape in the near-UV indicates that a plastoquinone is the secondary acceptor molecule (Q_A). The strong C-550 change at 543 nm confirms previous reports that pheophytin a is the primary electron acceptor. The bleach at 435 nm and increase in absorption at 820 nm indicates that the positive charge is stabilized on a chlorophyll a molecule. In addition a strong electrochromic band shift, centred at 723 nm, has been observed. It is assigned to a shift of the Qy band of the neighbouring accessory chlorophyll d, Chl_D1. It seems highly likely that it accepts excitation energy from the chlorophyll d containing antenna. We therefore propose that primary charge separation is initiated from this chlorophyll d molecule and functions as the primary electron donor. Despite its lower excited state energy (0.1 V less), as compared to chlorophyll a, this chlorophyll d molecule is capable of driving the plastoquinone oxidoreductase activity of photosystem II. However, chlorophyll a is used to stabilize the positive charge and ultimately to drive water oxidation.     

Ring V reactions of chlorophylls and pheophytins with amines

A study of the kinetics of the reaction of chlorophyll a with propylamine and isobutylamine indicates a low activation energy (～5 kcal) and high negative entropy (～60 eu). Propylamine and isobutylamine react with Ring V cleavage more readily with chlorophyll b and pheophytin b compounds than with the a compounds, and more readily with the pheophytins than with chlorophylls.     

An improved method for determining phytoplankton chlorophyll a concentration without filtration

The common and routine procedure for the quantification of chlorophyll a (chl a) in aquatic studies has a series of steps. Here, we sought to find optimal conditions for phytoplankton cell harvesting, chl a extraction, and chl a measurement and calculation, to find an effective, cost-saving, safe, and environment-friendly procedure for determining phytoplankton chl a concentration. We replaced the traditional GF/C filters with inorganic polymer flocculants (IPFs) and clay for phytoplankton harvesting, and then various solvents (acetone, ethanol, DMF, and DMSO), IPFs (PAC, PFS, and PAFS) and clay were tested for their suitability for chl a extraction, with or without homogenization at different temperatures for different extraction durations. About 0.3–1.0 g l^?1 of PAC or PFSA combined with 1.0–2.5 g l^?1 clay were found to provide optimal conditions in terms of yield and cost for phytoplankton cell harvesting from water samples. Based on our results, we recommend flocculation and centrifugation instead of glass-fiber membrane filtration for harvesting phytoplankton cells from environmental water samples, 95% ethanol for chl a extraction without homogenization and heating, and spectrophotometry to determine chl a concentration.     

Studies on the phytoplankton ecology of the trondheemsfjord. II. Chloroplast pigments in relation to abundance and physiological state of the phytoplankton

The quantitative composition of the chloroplast pigments of phytoplankton sampled weekly at one station in the Trondheimsfjord was studied by circular paper chromatography throughout 18 months. The concentrations of total chlorophyll a (T-chl a obtained by the trichromatic method) as well as of chromatographically purified chlorophyll a (chl a) followed the variations in phytoplankton concentration. Two spring blooms and a weak autumn flowering of phytoplankton were clearly reflected in the pigment contents found, namely 14–16 mg T-chl a/m³ for the spring maxima, corresponding to nearly 300 mg T-chl a/m² for the euphotic zone; and 3–4 mg/m³ or 32 mg/m² for the autumn peak. The concentrations between blooms amounted to ≈ 1 mg T-chl a/m³, while concentrations down to 0.03 mg/m³ were found for winter samples.The content of T-chl a was high in diatom cells prior to a bloom (20–40 × 10^?9 mg/cell). During rapid growth (a more or less exponential phase) the cell content of chloroplast pigments decreased (to 5–10 × 10^?9 mg). No degradation product of chlorophylls could be detected during this phase and the percentage of chl a (of T-chl a) was high (70–80 %). At the peak of the bloom, and especially when the nitrate content in the surrounding water had been exhausted, low values for T-chl a were found ($\text{0.3–0.5 × 10}{}^{\mathrm{<mtext>9</mtext><mtext>?</mtext>}}\text{mg/cell}$). As soon as the cell counts started to fall, or even before the decline could be clearly detected, the percentage of chl a dropped (to 40-20 %) and derived chlorophylls (not phaeophytin a) were present in the samples. Model studies with cultured algae showed a similar behaviour.It is concluded that the proportion of chl a to T-chl a and the occurrence of chlorophyll derivatives in phytoplankton samples can give valuable information on the stage of development of the algal populations involved.     

Single-step immunoaffinity purification and characterization of dodecylmaltoside-solubilized human neutrophil flavocytochrome b

Flavocytochrome b (Cyt b) is a heterodimeric, integral membrane protein that serves as the central component of an electron transferase system employed by phagocytes for elimination of bacterial and fungal pathogens. This report describes a rapid and efficient single-step purification of Cyt b from human neutrophil plasma membranes by solubilization in the nonionic detergent dodecylmaltoside (DDM) and immunoaffinity chromatography. A similar procedure for isolation of Cyt b directly from intact neutrophils by a combination of heparin and immunoaffinity chromatography is also presented. The stability of Cyt b was enhanced in DDM relative to previously employed solubilizing agents as determined by both monitoring the heme spectrum in crude membrane extracts and assaying resistance to proteolytic degradation following purification. Gel filtration chromatography and dynamic light scattering indicated that DDM maintains a predominantly monodisperse population of Cyt b following immunoaffinity purification. The high degree of purity obtained with this isolation procedure allowed for direct determination of a 2:1 heme to protein stoichiometry, confirming previous structural models. Analysis of the isolated heterodimer by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry allowed for accurate mass determination of p22^phox as indicated by the gene sequence. Affinity-purified Cyt b was functionally reconstituted into artificial bilayers and demonstrated that catalytic activity of the protein was efficiently retained throughout the purification procedure.     

Purification and Properties of Chlorophyllase from Ailanthus altissima (Tree-of-Heaven)

Chlorophyllase from Ailanthus altissima leaves has been purified 63-fold by a combination of heat treatment, ultracentrifugation, gel filtration, and chromatography on diethylaminoethyl cellulose. While the enzyme is inhibited to some degree by Triton X-100, a modification of the assay procedure of Klein and Vishniac has been shown to be far superior to the use of aqueous acetone systems. The enzyme was found to have a pH optimum on pheophytin a of 4.5. Chlorophylls a and b, pheophytins a and b, and pyropheophytin a were hydrolyzed by the enzyme while protochlorophyll a and 4-vinyl protochlorophyll a were not hydrolyzed but were competitive inhibitors. p-Nitrophenyl acetate was not hydrolyzed. The enzyme does not appear to contain an essential sulfhydryl group since sodium tetrathionate and p-chloromercuribenzoate did not affect its activity.     

Purification and characterization of a stable oxygen-evolving Photosystem II complex from a marine centric diatom, Chaetoceros gracilis

Oxygen-evolving Photosystem II particles (crude PSII) retaining a high oxygen-evolving activity have been prepared from a marine centric diatom, Chaetoceros gracilis (Nagao et al., 2007). The crude PSII, however, contained a large amount of fucoxanthin chlorophyll a/c-binding proteins (FCP). In this study, a purified PSII complex which was deprived of major components of FCP was isolated by one step of anion exchange chromatography from the crude PSII treated with Triton X-100. The purified PSII was still associated with the five extrinsic proteins of PsbO, PsbQ', PsbV, Psb31 and PsbU, and showed a high oxygen-evolving activity of 2135 μmol O₂ (mg Chl a)^− 1 h^− 1 in the presence of phenyl-p-benzoquinone which was virtually independent of the addition of CaCl₂. This activity is more than 2.5-fold higher than the activity of the crude PSII. The activity was completely inhibited by 3-(3,4)-dichlorophenyl-(1,1)-dimethylurea (DCMU). The purified PSII contained 42 molecules of Chl a, 2 molecules of diadinoxanthin and 2 molecules of Chl c on the basis of two molecules of pheophytin a, and showed typical absorption and fluorescence spectra similar to those of purified PSIIs from the other organisms. In this study, we also found that the crude PSII was significantly labile, as a significant inactivation of oxygen evolution, chlorophyll bleaching and degradation of PSII subunits were observed during incubation at 25 °C in the dark. In contrast, these inactivation, bleaching and degradation were scarcely detected in the purified PSII. Thus, we succeeded for the first time in preparation of a stable PSII from diatom cells.     

Synthesis, in vitro and in vivo biological evaluation,COX-1/2 inhibition and molecular docking study of indole-N-acylhydrazone derivatives

The objective of this work was to obtain and evaluate anti-inflammatory in vitro, in vivo and in silico potential of novel indole-N-acylhydrazone derivatives. In total, 10 new compounds (3a–j) were synthesized in satisfactory yields, through a condensation reaction in a single synthesis step. In the lymphoproliferation assay, using mice splenocytes, 3a and 3b showed inhibition of lymphocyte proliferation of 62.7% (±3.5) and 50.7% (±2), respectively, while dexamethasone presented an inhibition of 74.6% (±2.4). Moreover, compound 3b induced higher Th2 cytokines production in mice splenocytes cultures. The results for COX inhibition assays showed that compound 3b is a selective COX-2 inhibitor, but with less potency when compared to celecoxib, and compound 3a not presented selectivity towards COX-2. The molecular docking results suggest compounds 3a and 3b interact with the active site of COX-2 in similar conformations, but not with the active site of COX-1, and this may be the main reason to the COX-2 selectivity of compound 3b. In vivo carrageenan-induced paw edema assays were adopted for the confirmation of the anti-inflammatory activity. Compound 3b showed better results in suppressing edema at all tested concentrations and was able to induce an edema inhibition of 100% after 5?h of carrageenan injection at the 30?mg?kg^?1 dosage, corroborating with the COX inhibition and lymphoproliferation results. I addition to our experimental results, in silico analysis suggest that compounds 3a and 3b present a well-balanced profile between pharmacodynamics and pharmacokinetics. Thus, our preliminary results revealed the potentiality of a new COX-2 selective derivative in the modulation of the inflammatory process.     

Chlorophyll-protein complexes of a Codium species,including a light-harvesting siphonaxanthin-Chlorophylla ab-protein complex,an evolutionary relic of some Chlorophyta

Eight chlorophyll-protein complexes were isolated from thylakoid membranes of a Codium species, a marine green alga, by mild SDS-polyacrylamide gel electrophoresis. CP 1a¹, CP 1a², CP 1a³ and CP 1a⁴ were partially dissociated Photosystem (PS) I complexes, which in addition to the core reaction centre complex, CP 1, possessed PS I light-harvesting complexes containing chlorophyll (Chl) a, Chl b and siphonaxanthin. LHCP¹ and LHCP³ are orange-brown green chlorophyll $\text{a}\text{b-}\text{proteins}$ ($\text{Chl}\text{a}\text{Chl}\text{b}$ ratios of 0.66) that contain siphonaxanthin and its esterified form, siphonein. CP a and CP 1, the core reaction centre complexes of PS II and PS I, respectively, had similar spectral properties to those isolated from other algae or higher plants. These P-680- or P-700-Chl a-proteins are universally distributed among algae and terrestrial plants; they appear to be highly conserved and have undergone little evolutionary adaptation. Siphonaxanthin and siphonein which are present in the Codium light-harvesting complexes of PS II and PS I are responsible for enhanced absorption in the green region (518 and 538 nm). Efficient energy transfer from both xanthophylls and Chl b to only Chl a in Codium light-harvesting complexes, which have identical fluorescence emission spectra at 77 K to those of the lutein-Chl $\text{a}\text{b-}\text{proteins}$ ($\text{Chl}\text{a}\text{Chl}\text{b}$ ratios of 1.2) of most green algae and all higher plants, proved that the molecular arrangement of these light-harvesting pigments was maintained in the isolated Codium complexes. The siphonaxanthin-Chl $\text{a}\text{b-}\text{proteins}$ allow enhanced absorption of blue-green and green light, the predominant light available in deep ocean waters or shaded subtidal marine habitats. Since there is a variable distribution of lutein, siphonaxanthin and siphonein in marine green algae and siphonaxanthin is found in very ancient algae, these novel siphonein-siphonaxanthin-Chl $\text{a}\text{b-}\text{proteins}$ may be ancient light-harvesting complexes which were evolved in deep water algae.     

Environmental and behavioural factors affecting activity in the intertidal gastropod Hydrobia ulvae

Laboratory microcosms were used to investigate the mud snail Hydrobia ulvae (Pennant) bioturbation activities and behavioural changes in response to snail density, algal food, sediment moisture content, light regime and water cover conditions. Density-dependent kinetics of bioturbated muddy areas were described by von Bertalanffy equations, which provided reliable estimates of mud surface covering rates by snail tracks (m² h⁻¹ snail⁻¹). Snails need a wet habitat to be active either covered by seawater or by moving in fluid layers for low-tide conditions. Light and microphytobenthic biomass, which are less potent to affect snail activity, are positively interrelated to increase covering rates in the tested chl a concentrations within the range of 1-15 μg g⁻¹. Experimental results suggested us the relevance of microphytobenthos migration processes in affecting crawling activities of H. ulvae that appeared to adjust their foraging efforts in response to benthic algal biomass. Behavioural processes of H. ulvae, in terms of floating, crawling, burrowing and inactive snails, were described using a Markov model. Finally, an empirical model based on von Bertalanffy equations was proposed to describe kinetics of sediment covering by snail tracks under the influences of snail density, sediment moisture content, chl a concentrations and the four combinations of presence/absence of light and seawater. This model should provide a base for further development of a hydrosedimentary model to simulate the effects of H. ulvae bioturbation activities on the resuspension of the intertidal cohesive sediment-water interface for various in situ conditions.