Trophic transfer of methylmercury and trace elements by tropical estuarine seston and plankton

Methylmercury (MeHg) and trace elements (TE), mercury, selenium, cadmium, lead and copper, were determined in a microbial loop composed by three size classes of autotrophic and heterotrophic microorganism samples, 1.2–70 μm (seston, SPM), 70–290 μm (microplankton) and ≥290 μm (mesoplankton) from five sampling stations within a polluted eutrophic estuary in the Brazilian Southeast coast and one external point under the influence of the bay. TE concentrations were within the range reported for marine microorganisms from uncontaminated locations. Microplankton was primarily composed of proto-zooplankton and diatoms (>90%) while approximately 50% of mesoplankton was composed mainly of copepods. MeHg and TE in samples did not differ among the five sampling stations within the bay. Cd, Pb and Cu in seston were higher in the stations sampled inside Guanabara Bay (0.67 μg Cd g⁻¹, 9.26 μg Pb g⁻¹, 8.03 μg Cu g⁻¹) than in the external one (0.17 μg Cd g⁻¹, 3.98 μg Pb g⁻¹ and 2.09 μg Cu g⁻¹). Hg, MeHg and Se did not differ among the five points within the more eutrophic waters of the estuary and the external sampling station. The trophic transfer of MeHg and Se was observed between trophic levels from prey (seston and microplankton) to predator (mesoplankton). The successive amplification of the ratios of MeHg to Hg with increasing trophic levels from seston (43%), to microplankton (59%) and mesoplankton (77%) indicate that biomagnification may be occurring along the microbial food web. Selenium, that is efficiently accumulated by organisms through trophic transference, was biomagnified along the microbial food web, while Hg, Cd, Pb, Cu did not present the same behavior. Concentrations differed between the three size classes, indicating that MeHg and TE accumulation were size-dependent. MeHg and TE concentrations were not related to the taxonomic groups' composition of the planktonic microorganisms. Results suggest the importance of the role of the trophic level and microorganism size in regulating element transfers. Eutrophication dilution may provide a process-oriented explanation for lower MeHg and TE accumulation by the three size classes of microorganisms collected at the five sampling stations within the bay.     

Particulate suspended matter concentrations in the Bahía Blanca Estuary,Argentina: Implication for the development of phytoplankton blooms

The inner zone of the Bahía Blanca Estuary is shallow, nutrient-rich and turbid. Tidal energy and water turbulence strongly affect the water column resulting in a well-mixed structure and high concentrations of suspended sediment. The phytoplankton community is mostly dominated by diatoms and the annual pattern has been characterized by a recurrent winter-early spring bloom. Here, we investigated to what extent the temporal variations of suspended particulate matter (SPM) regulate the phytoplankton blooms in the head of the estuary by light-limitation. Sampling was done on a fortnightly basis (weekly during the blooming season) at a fixed station in the inner zone of the estuary from January 2007 to February 2008. SPM concentrations and light extinction coefficients (k) in the water column were significantly correlated and showed relatively lower values during the phytoplankton maximal biomass levels. During winter, SPM and k reached values of 23.6 mg l⁻¹ and 0.17 m⁻¹ which were significantly lower than the annual means of 77.6 mg l⁻¹ and 2.94 m⁻¹, respectively. The particulate organic matter (POM) concentration was significantly correlated with the calculated phytoplankton biomass although the contribution of the latter to the total POM was rather low. Both, POM and biomass, had maximal values during winter (21.8 mg l⁻¹ and 393.5 μg C l⁻¹) and mid summer (24.3 mg l⁻¹ and 407.0 μg C l⁻¹), with cell densities up to 8 × 10⁶ cells l⁻¹ and chlorophyll a up to 24.6 μg l⁻¹. Our results suggest that the decrease of SPM concentrations in the water column with a concomitant increase in the penetration of solar radiation seems to be one of the main causes for the development of the phytoplankton winter bloom in the Bahía Blanca Estuary.     

Mass balance of lead through a small macrotidal estuary: The Morlaix River estuary (Brittany,France)

Dissolved and particulate lead were measured over an annual cycle (12 surveys between February 1998 and January 1999) in the Morlaix River estuary (Brittany, France). The concentrations were investigated in both the water column and the sediment of the river bottom in relation to hydrological conditions. In the water column, dissolved and particulate lead concentrations ranged from 0.1 to 4.4 nM and from 0.04 to 1.9 μmol g^− 1, respectively. Lead concentrations in surface sediment varied from 0.04 to 0.19 μmol g^− 1 and concentrations in the sediment pore water of the estuary were below the detection limit. Compared with the ranges known for pristine estuaries, concentrations of Pb in the water column of the Morlaix River estuary were found to be much higher. Concentrations of Pb also exceeded the lower range of those known for industrialized estuaries. Extensive agricultural activities in the drainage basin may be responsible for Pb levels above pristine conditions. Furthermore, the sediment appeared not to be contaminated. A mass balance was constructed quantifying all known sources and sinks for the Pb in the estuary. Riverine input accounts for most of the total annual metal flux. Burial in sediments was the major sink within the estuary, which acts as a trap especially for the particulate lead. The mass balance shows that the metal accumulation ranged between 414.6 and 446.0 kg year^− 1.     

Behaviors of dissolved and particulate Co,Ni, Cu,Zn, Cd and Pb during a mesoscale Fe-enrichment experiment (SEEDS II) in the western North Pacific

During mesoscale Fe enrichment (SEEDS II) in the western North Pacific ocean, we investigated dissolved and particulate Co, Ni, Cu, Zn, Cd and Pb in seawater from both field observation and shipboard bottle incubation of a natural phytoplankton assemblage with Fe addition. Before the Fe enrichment, strong correlations between dissolved trace metals (Ni, Zn and Cd) and PO₄³⁻, and between particulate trace metals (Ni, Zn and Cd) and chlorophyll-a were obtained, suggesting that biogeochemical cycles mainly control the distributions of Ni, Zn and Cd in the study area. Average concentrations of dissolved Co, Ni, Cu, Zn, Cd and Pb in the surface mixed layer (0–20 m) were 70 pM, 4.9, 2.1, 1.6, 0.48 nM and 52 pM, respectively, and those for the particulate species were 1.7 pM, 0.052, 0.094, 0.46, 0.037 nM and 5.2 pM, respectively. After Fe enrichment, chlorophyll-a increased 3 fold (up to 3 μg L⁻¹) during developing phases of the bloom (<12 days). Mesozooplankton biomass also increased. Particulate Co, Ni, Cu and Cd inside the patch hinted at an increase in the concentrations, but there were no analytically significant differences between concentrations inside and outside the patch. The bottle incubation with Fe addition (1 nM) showed an increase in chlorophyll-a (8.9 μg L⁻¹) and raised the particulate fraction up to 3–45% for all the metals, accompanying changes in Si/P, Zn/P and Cd/P. These results suggest that Fe addition lead to changes in biogeochemical cycling of trace metals. The comparison between the mesoscale Fe enrichment and the bottle incubation experiment suggests that although Fe was a limiting factor for the growth of phytoplankton, the enhanced biomass of mesozooplankton also limited the growth of phytoplankton and the transformation of trace metal speciation during the mesoscale Fe enrichment. Sediment trap data and the elemental ratios taken up by phytoplankton suggest that export loss was another reason that no detectable change in the concentrations of particulate trace metals was observed during the mesoscale Fe enrichment.     

Summer mesozooplankton structure in the Pechora Sea (south-eastern Barents Sea)

Mesozooplankton composition and distribution were investigated by Juday net hauls in the Pechora Sea (south-eastern Barents Sea) in July 2001. A total of 66 taxa were identified. The total mesozooplankton abundance varied between 2416 ind m⁻² in the northern part and 1458?935 ind m⁻² in the south. The biomass ranged between 81 and 19?078 mg DW m⁻². Three groups differed greatly in composition, abundance and biomass as delineated by cluster analysis. Copepod species Calanus finmarchicus, Pseudocalanus species and Limnocalanus macrurus dominated in terms of the total biomass within each single cluster. There were significant Spearman rank correlations between mesozooplankton abundance and oceanographic variables, and phytoplankton concentration. Salinity was the main factor affecting the mesozooplankton distribution in the coastal waters, while temperature had greater influence on the abundance and biomass in the central and northern parts. The mean mesozooplankton biomass in the region was higher in comparison with some previous investigations probably due to higher water temperature in summer 2001.     

Effects of upwelling,tides and biological processes on the inorganic carbon system of a coastal lagoon in Baja California

The role of coastal lagoons and estuaries as sources or sinks of inorganic carbon in upwelling areas has not been fully understood. During the months of May–July, 2005, we studied the dissolved inorganic carbon system in a coastal lagoon of northwestern Mexico during the strongest period of upwelling events. Along the bay, different scenarios were observed for the distributions of pH, dissolved inorganic carbon (DIC) and apparent oxygen utilization (AOU) as a result of different combinations of upwelling intensity and tidal amplitude. DIC concentrations in the outer part of the bay were controlled by mixing processes. At the inner part of the bay DIC was as low as 1800 μmol kg⁻¹, most likely due to high water residence times and seagrass CO₂ uptake. It is estimated that 85% of San Quintín Bay, at the oceanic end, acted as a source of CO₂ to the atmosphere due to the inflow of CO₂-rich upwelled waters from the neighboring ocean with high positive fluxes higher than 30 mmol C m⁻² d⁻¹. In contrast, there was a net uptake of CO₂ and HCO₃⁻ by the seagrass bed Zostera marina in the inner part of the bay, so the pCO₂ in this zone was below the equilibrium value and slightly negative CO₂ fluxes of −6 mmol C m⁻² d⁻¹. Our positive NEP and ΔDIC values indicate that Bahía San Quintín was a net autotrophic system during the upwelling season during 2005.     

Bioaccessibility and mobilisation of copper and zinc in estuarine sediment contaminated by antifouling paint particles

Clean estuarine sediment amended with antifouling paint particles has been digested in biologically relevant reagents in order to evaluate the bioaccessibilities of Cu and Zn to deposit feeders in coastal environments where boat maintenance is important. Concentrations of Cu and Zn in the estuarine sediment of about 20 and 70 μg g⁻¹, respectively, increased to about 930 and 330 μg g⁻¹, respectively, on addition of 1.3% of a composite of fractionated paint particles collected from a boat repair facility. Seawater containing the vertebrate bile salt, sodium taurocholate, representative of surfactants in the digestive environment of deposit feeders, mobilised significantly greater quantities of metal (up to about 2 μg g⁻¹ of both Cu and Zn) than seawater alone, presumably through complexation and exchange reactions. Seawater solutions of the protein, bovine serum albumin (BSA), a surrogate for proteinaceous material and amino acids encountered in the digestive tract, mobilised even greater quantities of metal (up to about 80 and 40 μg g⁻¹ of Cu and Zn, respectively) via strong complexation, although addition of taurocholate reduced this capacity through interactions between the two reagents. Overall, and through feeding, burrowing and bioirrigation, infaunal invertebrates are predicted to greatly accelerate the rate of mobilisation and local dispersal of metals in sediment contaminated by antifouling paint particles.     

The fate of production in the central Arctic Ocean - top-down regulation by zooplankton expatriates?

We estimated primary and bacterial production, mineral nutrients, suspended chlorophyll a (Chl), particulate organic carbon (POC) and nitrogen (PON), abundance of planktonic organisms, mesozooplankton fecal pellet production, and the vertical flux of organic particles of the central Arctic Ocean (Amundsen basin, 89-88° N) during a 3 week quasi-Lagrangian ice drift experiment at the peak of the productive season (August 2001). A visual estimate of ≈15% ice-free surface, plus numerous melt ponds on ice sheets, supported a planktonic particulate primary production of 50-150 mg C m⁻² d⁻¹ (mean 93 mg C m⁻² d⁻¹, n = 7), mostly confined to the upper 10 m of the nutrient replete water column. The surface mixed layer was separated from the rest of the water column by a strong halocline at 20 m depth. Phototrophic biomass was low, generally 0.03-0.3 mg Chl m⁻³ in the upper 20 m and <0.02 mg Chl m⁻³ below, dominated by various flagellates, dinoflagellates and diatoms. Bacterial abundance (typically 3.7-5.3 × 10⁵, mean 4.1 × 10⁵ cells ml⁻¹ in the upper 20 m and 1.3-3.7 × 10⁵, mean 1.9 × 10⁵ cells ml⁻¹ below) and Chl concentrations were closely correlated (r = 0.75). Mineral nutrients (3 μmol NO₃ l⁻¹, 0.45 μmol PO₄ l⁻¹, 4-5 μmol SiO₄ l⁻¹) were probably not limiting the primary production in the upper layer. Suspended POC concentration was ∼30-105 (mean 53) mg C m⁻³ and PON ∼5.4-14.9 (mean 8.2) mg N m⁻³ with no clear vertical trend. The vertical flux of POC in the upper 30-100 m water column was ∼37-92 (mean 55) mg C m⁻² d⁻¹ without clear decrease with depth, and was quite similar at the six investigated stations. The mesozooplankton biomass (≈2 g DW m⁻², mostly in the upper 50 m water column) was dominated by adult females of the large calanoid copepods Calanus hyperboreus and Calanus glacialis (≈1.6 g DW m⁻²). The grazing of these copepods (estimated via fecal pellet production rates) was ≈15 mg C m⁻² d⁻¹, being on the order of 3% and 20% of the expected food-saturated ingestion rates of C. hyperboreus and C. glacialis, respectively. The stage structure of these copepods, dominated by adult females, and their unsatisfied grazing capacity during peak productive period suggest allochthonous origin of these species from productive shelf areas, supported by their long life span and the prevailing surface currents in the Arctic Ocean. We propose that the grazing capacity of the expatriated mesozooplankton population would match the potential seasonal increase of primary production in the future decreased ice perspective, diminishing the likelihood of algal blooms.     

Trace metals in the Göta river estuary

The concentrations of the trace metals Cd, Cu, Fe, Ni, Pb and Zn in the Göta River estuary have been investigated. The following metal fractions have been determined: acid-leachable, dissolved, labile and particulate.The estuary represents a salt wedge type estuary and is situated in a densely populated region of Sweden. The metal concentrations found for the dissolved fraction is in the range of what can be considered as background levels for freshwater. It is difficult to evaluate any estuarine processes other than conservative mixing for Cd, Cu, Ni and Zn. The dissolved levels in the freshwater end member are Cd, 9–25 ngl^?1; Cu, 1·1–1·4 μgl^?1; Fe, 20–75 μg l^?1: Ni, 0·7–0·9 μg l^?1: Pb 0·09–0·2 μg l^?1; and Zn, 6–7 μg l^?1:The results from the acid-leachable fraction show that at high suspended load the particles sediment in the river mouth. The trace metal levels in this fraction are subject to large variations.     

Salt marsh plants (Juncus maritimus and Scirpus maritimus) as sources of strong complexing ligands

This work aimed to evaluate, in vitro, the capability of roots of salt marsh plants to release strong Cu-complexing ligands and to ascertain whether Cu contamination would stimulate ligands' exudation or not. The sea rush Juncus maritimus and the sea-club rush Scirpus maritimus, both from the lower Douro river estuary (NW Portugal), were used. Plants were collected seasonally, four times a year in 2004, during low tide. After sampling, plant roots were washed for removal of adherent particles and immersed for 2 h in a solution that matched salinity (3) and pH (7.5) of the pore water from the same location and spiked with Cu²⁺ in the range 0–1600 nM to obtain plant exudates. In the final solutions as well as in sediment pore water total dissolved Zn and Cu, Cu-complexing ligand concentrations and the respective conditional stability constants (K_CuL^′) values were determined by voltammetry. This study demonstrated that plants are able to release, in a short period of time, relatively high amounts of strong Cu-complexing ligands (56–265 nmol g_root⁻¹), which differed among plants and sampling site but were independent of the season. Cu contamination did not stimulate exudation of Cu-complexing ligands. On the other hand, in media contaminated with Cu both plants accumulated relatively high amounts (29–83%) of the initially dissolved Cu, indicating that they have alternative internal mechanisms for Cu detoxification. Cu exchange between roots and medium (either accumulation in contaminated medium or release in the absence of Cu) was more intense for S. maritimus than for J. maritimus. It was observed that exudate solutions obtained in the absence of added Cu and sediment pore water (the densities of roots observed inside the salt marsh where comparable to those used in the in vitro experiments), displayed similarities in terms of total dissolved metals, Cu-complexing ligands concentrations, values of K_CuL^′ (12 < log K_CuL^′ < 14), as well as patterns of variation among seasons (only observed for Zn). These results are novel and point out that salt marsh plants may be the source at least partially of the strong organic ligands found in the sediment pore water in shallow marginal areas. The capability of salt marsh plants to release strong organic ligands into the environment, conjugated with their known capacity to oxidize anaerobic sediment around roots, indicate that these plants can play a role in controlling metal speciation in the water/sediment interface.     

Nereis diversicolor and copper contamination effect on the erosion of cohesive sediments: A flume experiment

The effect of bioturbation on the erodability of natural and manipulated copper spiked sediments (3 μmol Cu g⁻¹ dw) was investigated using sediments collected in the Tagus estuary and Nereis diversicolor (900 ind m⁻²). The input of particulate matter and Cu into the water column as a result of erosion was quantified in an annular flume at 7 shear velocities (1–13 cm s⁻¹). The biogeochemical characteristics of the sediment were analysed in depth down to 8 cm. Cu contamination elicited lower levels of eroded matter and lower shear strength profiles. Eroded matter and sediment shear strength values were higher (up to 1.7 kg m⁻²) in the presence of N. diversicolor, whose effect was less pronounced under contamination. Sediment erodability was not only related to hydrodynamics but was highly affected by the biogeochemical characteristics and contamination of the sediments.     

In vitro simulation of oxic/suboxic diagenesis in an estuarine fluid mud subjected to redox oscillations

Estuarine turbidity maxima (ETMs) are sites of intense mineralisation of land-derived particulate organic matter (OM), which occurs under oxic/suboxic oscillating conditions owing to repetitive sedimentation and resuspension cycles at tidal and neap-spring time scales. To investigate the biogeochemical processes involved in OM mineralisation in ETMs, an experimental set up was developed to simulate in vitro oxic/anoxic oscillations in turbid waters and to follow the short timescale changes in oxygen, carbon, nitrogen, and manganese concentration and speciation. We present here the results of a 27-day experiment (three oxic periods and two anoxic periods) with an estuarine fluid mud from the Gironde estuary. Time courses of chemical species throughout the experiment evidenced the occurrence of four distinct characteristic periods with very different properties. Steady oxic conditions were characterised by oxygen consumption rates between 10 and 40 μmol L⁻¹ h⁻¹, dissolved inorganic carbon (DIC) production of 9–12 μmol L⁻¹ h⁻¹, very low NH₄⁺ and Mn²⁺ concentrations, and constant NO₃⁻ production rates (0.4 - 0.7 μmol L⁻¹ h⁻¹) due to coupled ammonification and nitrification. The beginning of anoxic periods (24 h following oxic to anoxic switches) showed DIC production rates of 2.5–8.6 μmol L⁻¹ h⁻¹ and very fast NO₃⁻ consumption (5.6–6.3 μmol L⁻¹ h⁻¹) and NH₄⁺ production (1.4–1.5 μmol L⁻¹ h⁻¹). The latter rates were positively correlated to NO₃⁻ concentration and were apparently caused by the predominance of denitrification and dissimilatory nitrate reduction to ammonia. Steady anoxic periods were characterised by constant and low NO₃⁻ concentrations and DIC and NH₄⁺ productions of less than 1.3 and 0.1 μmol L⁻¹ h⁻¹, respectively. Mn²⁺ and CH₄ were produced at constant rates (respectively 0.3 and 0.015 μmol L⁻¹ h⁻¹) throughout the whole anoxic periods and in the presence of nitrate. Finally, reoxidation periods (24–36 h following anoxic to oxic switches) showed rapid NH₄⁺ and Mn²⁺ decreases to zero (1.6 and 0.8–2 μmol L⁻¹ h⁻¹, respectively) and very fast NO₃⁻ production (3 μmol L⁻¹ h⁻¹). This NO₃⁻ production, together with marked transient peaks of dissolved organic carbon a few hours after anoxic to oxic switches, suggested that particulate OM mineralisation was enhanced during these transient reoxidation periods. An analysis based on C and N mass balance suggested that redox oscillation on short time scales (day to week) enhanced OM mineralisation relative to both steady oxic and steady anoxic conditions, making ETMs efficient biogeochemical reactors for the mineralisation of refractory terrestrial OM at the land-sea interface.     

The influence of prolonged mouth closure on selected components of the hyperbenthos in the littoral zone of the temporarily open/closed Kasouga Estuary,South Africa

The influence of prolonged mouth closure on the population dynamics of the caridian shrimp, Palaemon peringueyi and the estuarine isopod, Exosphaeroma hylocoetes, in the littoral zone of temporarily open/closed Kasouga Estuary located on the south-eastern coastline of southern Africa was assessed monthly over the period October 2007 to September 2008. Prolonged mouth closure of the estuary contributed to hypersaline conditions (psu > 35) prevailing throughout the estuary for the last four months of the study. The high salinities coincided with a decrease in the areal extent (up to 80%) of the submerged macrophytes, mainly Ruppia maritima, within the littoral zone of the estuary. Total abundance and biomass values of the shrimp and isopod over the period of investigation ranged from 0 to 14.6 ind m⁻², from 0 to 13.3 mg dwt m⁻², from 12 to 1540 ind m⁻² and from 0.1 to 2.16 mg dwt m⁻², respectively. Maximum values of both the shrimp and isopod were recorded in the upper reaches of the estuary in close association with R. maritima. Over the course of the investigation, both the abundance and biomass values of the shrimp decreased significantly (P < 0.05 in both cases) which could be related to reduced habitat availability, R. maritima, that acts as a refuge against fish predation. Additionally, the decrease in abundance and biomass values could be attributed to reduced recruitment opportunities for the shrimp and the cessation of reproduction in the estuarine isopod. The establishment of a link to the marine environment following an overtopping event in September 2008 contributed to a decrease in salinity within the system although no recruitment of either the isopod or shrimp was recorded.     

Current status and ecological roles of Zostera marina after recovery from large-scale reclamation in the Nakdong River estuary,Korea

Large Zostera marina meadows (covering 13.6 km²) existed in the Nakdong River estuary on the south coast of Korea until the mid-1980s, but these Z. marina beds nearly disappeared due to reclamation of adjacent mud flats for the construction of a port and industrial complex during the late 1980s. Partial recovery of Z. marina meadows occurred recently, and Z. marina coverage of about 0.3 km² was observed in this estuary. In this study, shoot morphology, density, biomass, productivity, and tissue nutrient content were measured to evaluate the current status of the Z. marina meadows by comparing these data to those for persistent seagrass meadows in similar geographical areas. Additionally, we examined the ecological roles of Z. marina in this estuary after recovery from the large-scale disturbance. Shoot density (151 shoots m⁻²) and total biomass (141 g DW m⁻²) in the estuary were similar to those reported from other Z. marina meadows in Korea. Annual leaf production (1726 g DW m⁻² y⁻¹) was higher than generally observed for Z. marina in other geographical areas. These results imply that the existing Z. marina meadows in this estuary have adjusted to local environmental conditions that changed after large-scale reclamation. Estimated annual whole plant carbon (C) and nitrogen (N) incorporations based on shoot production and tissue C and N content were 810.0 g C m⁻² y⁻¹ and 59.7 g N m⁻² y⁻¹, respectively. These values were equivalent to 2.4 × 10⁵ kg C y⁻¹ and 1.8 × 10⁴ kg N y⁻¹ for all Z. marina beds in the Nakdong River estuary. This high C and N incorporation into Z. marina tissues suggests that existing Z. marina meadows play important roles in C and N cycles in this estuary. Although the currently existing Z. marina beds in this estuary are persisting and play an important ecological role, anthropogenic factors that cause seagrass declines still affect the estuary. Thus, effective management and monitoring of Z. marina beds and environmental factors are critical to protecting and conserving this invaluable component of the Nakdong River estuary.     

Potentially mobile pools of phosphorus and silicon in sediment from the Bay of Brest: Interactions and implications for phosphorus dynamics

Competitive interactions between silicate and phosphate at ligand exchange sites in the sediment surface layer may increase the release of phosphorus (P) from the sediment into the water column. In this study, the role of silicon (Si) in the release of P from the sediment surface layer was studied in a marine estuarine environment, the Bay of Brest, with the aid of a sequential sediment fractionation procedure developed for P, and the addition of inorganic or diatom-bound Si to surface sediment samples in vitro. The potentially mobile pools of P in the surface sediment (loosely bound P + Fe/Al-bound-P) amounted to 5.0 μmol g⁻¹ dry sed., 42% of the total extractable and 33% of the total amount of P in the sediment, while the similarly extracted pools of Si were bigger (ca. 20 μmol g⁻¹ dry sed., 50% of the total extractable Si). Additions of inorganic Si increased the concentration of dissolved P in the sediment interstitial water in a bottle experiment, and the addition of both inorganic Si and cultivated diatoms to intact sediment cores increased the outward flux of dissolved P. Model calculations based on the regression equation from the bottle experiment and Si and P water column data showed that the sedimentation of spring diatoms could cause Si pulses to the sediment which would produce a P flux to the water column of ca. 44 μmol m⁻² d⁻¹. Field data from the bay show that in spring, decreases in P and Si and an increase in chl a due to diatom production are often followed by a small separate P peak which may be caused by Si-induced P fluxes from the sediment surface.     

Role of mysid seasonal migrations in the organic matter transfer in the Curonian Lagoon,south-eastern Baltic Sea

We investigated population dynamics, growth and feeding of an omnivorous mysid, Paramysis lacustris, performing seasonal horizontal migrations in the Curonian Lagoon. In autumn, increased predation pressure and deteriorated feeding conditions, due to zooplankton and phytoplankton decline in the open water, forces mysids to migrate to the shoreline, where large amounts of decaying submersed vegetation occur at the end of plant growth season. Using stable isotope analysis and mixing models, we evaluated relative importance of decaying submersed macrophytes, lagoon phytoplankton and mesozooplankton in the diet of mysids during this period. In September–November, mysids actively grew and produced three cohorts. Specific growth rates of adults (10.9 ± 1.9 mm) and subadults (6 ± 0.5 mm) were 3 and 9% DW d⁻¹, respectively, resulting in population somatic production of 36 g DW m⁻². Both δ¹⁵N and δ¹³C of mysids varied in concert with those in suspended and bottom particulate organic matter (POM) and mesozooplankton. The mixing models estimated that 45% of mysid diets were composed of bottom POM originated from the decaying macrophyte Potamogeton perfoliatus, 45% by suspended POM largely consisting of phytoplankton, while mesozooplankton contributed less than 10% of the diet. This diet composition differs from that in summer, when mysids rely mostly on zooplankton and phytoplankton. Therefore, mysid horizontal migrations and their ability to efficiently utilize littoral detritus improve the efficiency of macrophyte detritus transfer up the food chain and inshore/offshore habitat coupling in the Curonian Lagoon.     

The distribution of Mn,Fe, Zn,Cd and Cu in Baltic seawater; a study on the basis of one anchor station

A total of 150 samples were collected at a 10-days' anchor station in the Bornholm basin (55° 31.1′N, 15° 32.1′E) and analyzed for dissolved (< 0.4 μm) and particulate trace metals. For dissolved Mn, large gradients have been found in the vertical distribution with minimum concentrations (< 0.2 μgl^?1) in the halocline zone and considerably higher values in the deep waters (up to 50 μgl^?1). Ultrafiltration studies indicate that dissolved Mn is probably present as Mn²⁺ in the oxygenated bottom layer. The primary production process was not evident in the particulate Mn profile; the suspended particulate material (SPM), however, shows a considerable enrichment with depth, apparently due to Mn-oxide precipitation.The distribution of dissolved Fe was rather homogeneous, with average concentrations throughout the water column between 0.86 and 1.1 μgl^?1, indicating that the oxidation of Fe²⁺ ions released from the sediments must already be complete in the very near oxidation boundary layer. Relatively high concentrations of particulate Fe were actually measured in the bottom layer, with the maximum mean of 11.2 μgl^?1 at 72 m. Similarly to Mn, the profile of particulate Fe does not reflect the SPM curve of the eutrophic layer. On average, about 70% of the total Fe in surface waters was found to be particulate.The average concentrations of dissolved Zn, Cd and Cu were found to be rather homogeneous in the water column but showed a relatively high variability with time. A simplified model on trace-metal uptake by phytoplankton indicates no significant change in dissolved metal concentrations during the period of investigation. On average, only 1.7% Zn, 3.3% Cd and 9.8% Cu of the total metal concentrations were found in particulate form. SPM analyses showed significant correlations of Zn, Cd and Cu with Fe, indicating that particulate iron is an important carrier for particulate trace metals in Baltic waters.     

Distribution and sources of organochlorine pesticides in water and sediments from Daliao River estuary of Liaodong Bay,Bohai Sea (China)

The levels of 19 kinds of organochlorine pesticides (OCPs) in the aqueous phase, suspended particulate matter (SPM), pore water and sediments from Daliao River estuary of Liaodong Bay (Bohai Sea) in northeast China were investigated to evaluate their potential pollution risks. The total OCPs concentrations in the aqueous phase, SPM, pore water and sediments were 3.7–30.1 ng l⁻¹, 4.6–52.6 ng l⁻¹, 157–830 ng l⁻¹ and 2.1–21.3 ng g⁻¹ dry weight, respectively. The concentrations of OCPs, in the Daliao River estuary, are in the mid-range, as compared to those reported in other estuaries worldwide. The distribution of HCHs and DDTs were different indicating different contamination sources. Lindane is the main type of HCH and continuing use in northeast China of ‘pure’ HCH (lindane) rather than technical HCH accounts for the source. The ratios of (DDE + DDD)/DDT in the samples indicate no recent inputs of these chemicals to the estuary.     

Influence of allochthonous organic matter on bacterioplankton biomass and activity in a eutrophic,sub-tropical estuary

Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates, and growth efficiencies were studied in the Northern region of the Cananéia–Iguape estuarine system, which has recently experienced an intense eutrophication due to anthropogenic causes. Two surveys were carried out during spring and neap tide periods of the dry season of 2005 and the rainy season of 2006. This region receives large freshwater inputs with organic seston and phosphate concentrations that reach as high as 1.0 mg l⁻¹ and 20.0 μM, respectively. Strong decreasing gradients of seston and dissolved inorganic nutrients were observed from the river/estuary boundary to the estuary/coastal interface. Gradients were also observed in phytoplankton and bacterial production rates. The production rates of phytoplankton were 5.6-fold higher (mean 8.5 μg C l⁻¹ h⁻¹) during the dry season. Primary production rates (PP) positively correlated with salinity and euphotic depth, indicating that phytoplankton productivity was light-limited. On the other hand, bacterial biomass (BB) and production rates (BP) were 1.9- and 3.7-fold higher, respectively, during the rainy season, with mean values of up to 40.4 μg C l⁻¹ and 7.9 μg C l⁻¹ h⁻¹, respectively. Despite such a high BP, bacterial abundance remained <2 × 10⁶ cells ml⁻¹, indicating that bacterial production and removal were coupled. Mean specific growth rates ranged between 0.9 and 5.5 d⁻¹. BP was inversely correlated with salinity and positively correlated with temperature, organic matter, exopolymer particles, and particulate-attached bacteria; this last accounted for as much as 89.6% of the total abundance. During the rainy season, BP was generally much higher than PP, and values of BP/PP > 20 were registered during high freshwater input, suggesting that under these conditions, bacterial activity was predominantly supported by allochthonous inputs of organic carbon. In addition, BB probably represented the main pathway for the synthesis of high-quality (low C:N) biomass that may have been available to the heterotrophic components of the plankton food web, particularly nanoheterotrophs.     

Tiller dynamic and production on a SW Atlantic Spartina alterniflora marsh

We used non-destructive methods to study the bi-monthly changes in standing stock, turnover, and net aerial primary productivity (NAPP) of Spartina alterniflora in the Bahía Blanca Estuary, Argentina, from 2005 to 2007. Tillers were tagged and counted bimonthly and a weight:height relationship developed for the live and dead stems in a regularly flooded zone (low marsh, LM) and an irregularly flooded one (high marsh, HM). The annual tiller natality in year one compared to year two decreased from 440 ± 68 to 220 ± 58 new individuals m^–2 yr^–1 in the HM and from 500 ± 103 to 280 ± 97 new individuals m⁻² yr⁻¹ in the LM (μ ± 1 SE). Tiller mortality averaged 670 ± 70 individuals m⁻² yr⁻¹.