Inorganic Nutrient Concentrations Research Articles

Impact of environmental factors on couplings between bacterial community composition and ectoenzymatic activities in a lacustrine ecosystem

This study examined the effects of temporal changes in bacterial community composition (BCC) and environmental factors on potential ectoenzymatic activities (alpha-glucosidase, beta-glucosidase, alkaline phosphatase and leucine aminopeptidase) in a lacustrine ecosystem (Sep reservoir, France). BCC was assessed by terminal restriction fragment length polymorphism. Physical parameters, and inorganic and organic nutrient concentrations (dissolved carbohydrates and proteins) were measured in lakes and tributaries. According to the multivariate statistics (redundancy analysis), physical and chemical factors explained the largest part of leucine aminopeptidase activity, whereas the temporal changes of other ectoenzymatic activities were partly dependent on the variations in the BCC. In particular, the occurrence of occasional bacterial populations seemed to explain a lot of the variation in rates and patterns of polymer hydrolysis. The relation observed in this study between the bacterial structure and activity is discussed within the framework of biodiversity-ecosystem functioning.

Organic matter characterisation and turnover in the sediment and seawater of a tourist harbour

A survey of a Ligurian tourist harbour was carried out during winter 2006 and summer 2007 in order to study the organic matter (OM) turnover through extracellular enzymatic activity. Seawater and sediments were sampled at six stations, three inside the port boundaries, one outside the port and two in an area influenced by the outflow of a minor river (Boate). The seawater showed OM turnover times similar to other oligo-mesotrophic coastal areas, and low concentrations of chlorophyll-a and inorganic nutrients. The sediments, instead, revealed high OM loads and a predominance of proteolysis. A significant reduction of the OM loads was observed in the outside station, indicating that the OM accumulation was due to the structures and activities of the harbour and to the Boate influence. The OM biotic recycling via enzymatic activity was enhanced especially during summer. Although the carbohydrates were probably highly refractory, their turnover was notably faster, due to glycolytic enzymatic activity that was enhanced more than the proteolytic in both the sediment and in the seawater. This suggested that the removal and recycling of OM were potentially efficient, and prevented the shift to eutrophication of the Rapallo harbour area.

Coral sand O2 uptake and pelagic–benthic coupling in a subtropical fringing reef, Aqaba, Red Sea

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 6:133-142 (2009) - DOI: https://doi.org/10.3354/ab00181 Coral sand O2 uptake and pelagic–benthic coupling in a subtropical fringing reef, Aqaba, Red Sea Christian Wild1,*, Malik S. Naumann1, Andreas Haas1, Ulrich Struck2, Florian W. Mayer1, Mohammed Y. Rasheed3, Markus Huettel4 1Coral Reef Ecology Group (CORE), GeoBio-Center & Department of Earth and Environmental Science, Ludwig-Maximilians University, Richard Wagner Str. 10, 80333 Munich, Germany 2Museum für Naturkunde, Humboldt-Universität zu Berlin, Invalidenstrasse 43, 10115 Berlin, Germany 3Marine Science Station, University of Jordan and Yarmouk University, PO 195, Aqaba, Jordan 4Department of Oceanography, Florida State University, Tallahassee, Florida 32306-4320, USA *Email: c.wild@lrz.uni-muenchen.de ABSTRACT: Calcareous sands are major sites for recycling of organic matter in coral reef ecosystems. O2 uptake and pelagic–benthic coupling were studied in coral sands using benthic chambers and sediment traps during several seasonal expeditions between May 2004 and May 2008 along a fringing reef on the Jordanian Red Sea coast. A total of 12 independent dark chamber experiments were conducted at 2.5 to 16.5 m water depth on the highly permeable calcareous reef sands covering the seafloor at the reef and back-reef lagoon. Sedimentary O2 uptake ranged from 20 to 39 mmol m–2 d–1 and was positively correlated with water depth in the lagoon, but not in the reef, where O2 uptake was significantly lower. Comparison of sedimentary O2 uptake rates recorded at the same locations revealed little temporal and seasonal variation, and no significant responses to changes in environmental factors in the water column, such as temperature and concentrations of organic or inorganic nutrients. These results suggest that efficient recycling in the pelagic food web of the nutrient-deprived coral reef limits the supply of degradable organic matter to the reef sediments. Increase of sedimentary O2 uptake with water depth in the lagoon sands may therefore be a function of lateral transport of labile organic particles produced by reef organisms (e.g. benthic algae and corals) rather than sedimentation of water column production. KEY WORDS: Coral reefs · Calcareous sands · O2 flux · Spatial and temporal changes · Seasonality · Pelagic–benthic coupling · Red Sea · Advection chambers Full text in pdf format PreviousNextCite this article as: Wild C, Naumann MS, Haas A, Struck U, Mayer FW, Rasheed MY, Huettel M (2009) Coral sand O2 uptake and pelagic–benthic coupling in a subtropical fringing reef, Aqaba, Red Sea. Aquat Biol 6:133-142. https://doi.org/10.3354/ab00181 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 6. Online publication date: August 04, 2009 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2009 Inter-Research.

Effects of green macroalgal blooms on intertidal sediments: net metabolism and carbon and nitrogen contents

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 380:81-93 (2009) - DOI: https://doi.org/10.3354/meps07923 Effects of green macroalgal blooms on intertidal sediments: net metabolism and carbon and nitrogen contents A. Corzo*, S. A. van Bergeijk, E. García-Robledo Department of Biology, Faculty of Marine and Environmental Science, University of Cádiz, 11510 Puerto Real, Spain *Email: alfonso.corzo@uca.es ABSTRACT: Eutrophication in coastal areas promotes blooms of green macroalgae that accumulate on the sediment, affecting the exchange of mass and energy at the sediment–water interface. The effects of macroalgal blooms on the microbenthic net metabolism and on the carbon and nitrogen contents of the sediment were studied during an in situ experiment. Two sediment enclosures (with and without macroalgae) of 1.5 × 1.5 m2 were installed and maintained 2 to 3 wk during every season on an intertidal sediment flat in the Sancti Petri Channel (Bay of Cádiz, Spain) from summer 2002 to spring 2003. Biomass of the macroalgae changed seasonally, with a minimum in winter and a maximum in summer (annual mean: 188.3 ± 97.3 g dry wt m–2). This relatively low macroalgal biomass always suppressed the photosynthetic activity of microphytobenthos, decreased the oxygen availability for the sediment and reduced the oxygen penetration depth in the light and in the dark. The microbenthic community metabolism clearly shifted to heterotrophic, while the photoautotrophic activity was located in the macroalgal canopy. This macroalgal mat was net autotrophic, and more productive than the microphytobenthic community inhabiting the bare sediment. Part of the macroalgal production was buried in the sediment, increasing its carbon and nitrogen contents with respect to bare sediment during all seasons except spring. Concentrations of inorganic nutrients in the sediment were always higher below the macroalgal mat than in bare sediment, likely due to a direct input of inorganic nitrogen and phosphate associated with macroalgal debris. KEY WORDS: Macroalgal bloom · Microbenthos · Microphytobenthos · Sediment net metabolism · Microelectrodes · Intertidal sediments · Bay of Cadiz Full text in pdf format PreviousNextCite this article as: Corzo A, van Bergeijk SA, García-Robledo E (2009) Effects of green macroalgal blooms on intertidal sediments: net metabolism and carbon and nitrogen contents. Mar Ecol Prog Ser 380:81-93. https://doi.org/10.3354/meps07923 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 380. Online publication date: April 07, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Inorganic nutrients and contaminants in subsistence species of Alaska: linking wildlife and human health

Objectives. To determine inorganic nutrient and contaminant concentrations in subsistence foods consumed by Alaska Natives, concentration changes related to common preparation methods and provide a basic risk-benefit analysis for these foods.Study design. Eleven essential and six non-essential elements were measured in foods derived from spotted seals and sheefish.Methods. Essential nutrients in foodstuffs were compared to Daily Recommended Intake (DRI) criteria. Non-essential elements were compared to Tolerable Daily Intake Limits (TDIL). These comparisons serve as a risk-benefit analysis, not as consumption advice.Results. Cooking altered nutrient and contaminant concentrations. Spotted seal muscle and kidney are rich in Fe and Se; liver in Cu, Fe, Mo and Se; and sheefish muscle in Se. TDIL was exceeded in a 100 g serving of seal for THg in raw and fried liver and boiled kidney; MeHg in dried muscle and raw and fried liver; Cd in raw and boiled kidney; and As in raw and rendered blubber. Arsenic exceeded TDIL in sheefish muscle. However, toxicity potential is likely reduced by the element form (i.e., organic As, inorganic Hg) and the presence of protective nutrients such as Se.Conclusions. Preparation methods alter wildlife tissues from their raw state, significantly affecting element concentrations. Direct evaluation of actual food items is warranted to determine risk-benefit ratios of traditional diets. Traditional foods provide many essential nutrients with a very limited risk from contaminants. We encourage continued consumption of traditional foods, and urge public health agencies to develop applicable models for providing consumption advice, incorporating food processing considerations.

The Effects of Tidal Export from Salt Marsh Ditches on Estuarine Water Quality and Plankton Communities

Salt marshes are an important transition zone between terrestrial and marine ecosystems, and in their natural state, they often function to cycle or trap terrestrially derived nutrients and organic matter. Many US salt marshes were ditched during the twentieth century, potentially altering their functionality. The goal of this 4-year study was to assess the impact of water from ditches within seven salt marshes on estuarine water quality and plankton communities within four estuaries on Long Island, NY, USA. We found that concentrations of inorganic nutrients (ammonium, phosphate), dissolved and particulate organic nitrogen and carbon (POC, PON, DOC, DON), and total coliform bacteria were significantly enriched in salt marsh ditches compared to the estuaries they discharged into. In addition, concentrations of ammonium and DON became more enriched in ditches as tidal levels decreased, suggesting these constituents were generated in situ. Quantification of nitrogen sources in Flanders Bay, NY, suggested salt marsh ditches could represent a substantial source of N to this estuary during summer months. Experimental incubations demonstrated that water from salt marsh ditches was capable of significantly enhancing the growth of multiple classes of phytoplankton, with large diatoms and dinoflagellates displaying the most dramatic increases in growth. Experiments further demonstrated that salt marsh ditchwater was capable of significantly enhancing pelagic respiration rates, suggesting discharge from ditches could influence estuarine oxygen consumption. In summary, this study demonstrates that tidal draining of salt marsh ditches is capable of degrading multiple aspects of estuarine water quality.

Assessment of the Water Purification Ability of Mangrove (Sonneratia caseolaris) in Mesocosm Tanks

Model experiments using mangrove mesocosm tanks were performed two times at the campus of Kasetsart University, Thailand. Replicates of 13 mangrove (Sonneratia caseolaris) saplings were planted in 7 mesocosm tanks and water and soil samples were collected during the 2 experimental periods. The nitrogen removal rate showed 57 and 73 mgN/m 2 /day in the tanks where wastewater from shrimp aquaculture ponds was supplied and exchanged, and 164-425 mgN/m 2 /day in the tanks where the additional nutrients were provided. The phosphorus removal rate was 5.7 and 17 mgP/m 2 /day in tanks supplied and exchanged with wastewater, and 48 and 97 mgP/m 2 /day in the tanks provided with additional nutrients. Both nitrogen and phosphorus showed high removal rates in the mangrove mesocosm tanks. However, there was no marked increase in the bacterial community either in the water or surface soil, despite the organic matter-rich wastewater from shrimp aquaculture ponds or high concentrations of inorganic nutrients that were supplied.

Marine ecosystem community carbon and nutrient uptake stoichiometry under varying ocean acidification during the PeECE III experiment

Abstract. Changes to seawater inorganic carbon and nutrient concentrations in response to the deliberate CO2 perturbation of natural plankton assemblages were studied during the 2005 Pelagic Ecosystem CO2 Enrichment (PeECE III) experiment. Inverse analysis of the temporal inorganic carbon dioxide system and nutrient variations was used to determine the net community stoichiometric uptake characteristics of a natural pelagic ecosystem perturbed over a range of pCO2 scenarios (350, 700 and 1050 μatm). Nutrient uptake showed no sensitivity to CO2 treatment. There was enhanced carbon production relative to nutrient consumption in the higher CO2 treatments which was positively correlated with the initial CO2 concentration. There was no significant calcification response to changing CO2 in Emiliania huxleyi by the peak of the bloom and all treatments exhibited low particulate inorganic carbon production (~15 μmol kg−1). With insignificant air-sea CO2 exchange across the treatments, the enhanced carbon uptake was due to increase organic carbon production. The inferred cumulative C:N:P stoichiometry of organic production increased with CO2 treatment from 1:6.3:121 to 1:7.1:144 to 1:8.25:168 at the height of the bloom. This study discusses how ocean acidification may incur modification to the stoichiometry of pelagic production and have consequences for ocean biogeochemical cycling.

Net Sediment N2 Fluxes in a Coastal Marine System—Experimental Manipulations and a Conceptual Model

Environmental factors, including the supply of organic matter and inorganic nutrient concentrations, are thought to influence rates of two opposing processes in the nitrogen (N) cycle, denitrification and N fixation. Using sediment cores from a temperate estuary we examined the effects of nitrate, phosphate, and ammonium enrichment of the overlying water on the net N2 flux across the sediment–water interface. In addition, we used sediment cores and large marine mesocosms to determine the effect of organic matter amendment. The addition of nitrate (50 μM), ammonium (50 μM), and phosphate (10 μM) to the overlying water had no effect on the net N2 flux. However, high ammonium fluxes (145 μmol m−2 h−1) were observed in the nitrate-amended cores, which is suggestive of dissimilatory nitrate reduction to ammonium. Organic matter enrichment first increased rates of N fixation, but ultimately switched the sediments from being a net source (N fixation dominated) to a net sink (denitrification dominated) of N. We observed a threshold where N fixation took place when organic matter deposition fell below about 0.3 g C m−2 day−1. On the basis of these results and the findings of others, we developed a conceptual model that links net sediment N2 flux with the organic matter production of a system.

Is inorganic nutrient enrichment a driving force for the formation of red tides?: A case study of the dinoflagellate Scrippsiella trochoidea in an embayment

Red tides (high biomass phytoplankton blooms) have frequently occurred in Hong Kong waters, but most red tides occurred in waters which are not very eutrophic. For example, Port Shelter, a semi-enclosed bay in the northeast of Hong Kong, is one of hot spots for red tides. Concentrations of ambient inorganic nutrients (e.g. N, P), are not high enough to form the high biomass of chlorophyll a (chl a) in a red tide when chl a is converted to its particulate organic nutrient (N) (which should equal the inorganic nutrient, N). When a red tide of the dinoflagellate Scrippsiella trochoidea occurred in the bay, we found that the red tide patch along the shore had a high cell density of 15,000 cells ml −1, and high chl a (56 μg l −1), and pH reached 8.6 at the surface (8.2 at the bottom), indicating active photosynthesis in situ. Ambient inorganic nutrients (NO 3, PO 4, SiO 4, and NH 4) were all low in the waters and deep waters surrounding the red tide patch, suggesting that the nutrients were not high enough to support the high chl a >50 μg l −1 in the red tide. Nutrient addition experiments showed that the addition of all of the inorganic nutrients to a non-red-tide water sample containing low concentrations of Scrippsiella trochoidea did not produce cell density of Scrippsiella trochoidea as high as in the red tide patch, suggesting that nutrients were not an initializing factor for this red tide. During the incubation of the red tide water sample without any nutrient addition, the phytoplankton biomass decreased gradually over 9 days. However, with a N addition, the phytoplankton biomass increased steadily until day 7, which suggested that nitrogen addition was able to sustain the high biomass of the red tide for a week with and without nutrients. In contrast, the red tide in the bay disappeared on the sampling day when the wind direction changed. These results indicated that initiation, maintenance and disappearance of the dinoflagellate Scrippsiella trochoidea red tide in the bay were not directly driven by changes in nutrients. Therefore, how nutrients are linked to the formation of red tides in coastal waters need to be further examined, particularly in relation to dissolved organic nutrients.

Virioplankton and microbial communities in two Czech rivers (Svratka and Morava River)

Viruses are identified as the most abundant and dynamic component of aquatic communities in marine and freshwater environments. However, there is still limited information about viral abundance and ecology in the rivers. We studied virioplankton abundance in relation to bacterial abundance, chlorophyll a (Chl a; expressed as total Chl a, Chl a in green algae, and in cyanobacteria), and environmental parameters (inorganic nutrient concentration, temperature) in two Czech rivers throughout a 6-month period. Viral abundances reached similar values in both rivers and ranged from 1.85 to 58.1 x 106 viruses/ mL and from 1.68 to 47.4 x 106 viruses/mL in the Svratka and the Morava River, respectively. The temporal variations in viral and bacterial abundances were large in both rivers, as they varied by more than one order of magnitude during the study. We did not observe a spatial variability in viruses or other biotic parameters in spite of differences in some environmental parameters within each river and also between the two rivers. Significant cross-correlations among viruses, bacteria, Chl a, and orthophosphate concentration were found, suggesting that these parameters may influence viral abundance and dynamics in the rivers.

Variable importance of viral‐induced bacterial mortality along gradients of trophic status and humic content in lakes

Summary1. The goals of this study were to assess which environmental gradients can be important in predicting viral abundance (VA), the frequency of virus‐infected cells (FVIC) and burst size (BS), and to assess which lake characters favour viral‐induced bacterial mortality (VBM) as opposed to potential grazer‐induced bacterial mortality (PGBM).2. The epilimnion and hypolimnion of 21 lakes differing in trophic status and humic content were investigated. Samples were obtained for viral and bacterial abundance, the FVIC and burst size, flagellate and ciliate abundances and water chemistry. The potential importance of VBM in relation to PGBM was calculated based on data on FVIC and flagellate and ciliate abundance.3. Partial least squares regression (PLS) analysis showed that VA as well as the ratio between viral and bacterial abundance were positively related to inorganic nutrient concentrations, dissolved organic carbon concentration, chlorophyll‐a concentration and bacterial production.4. The PLS model also revealed that FVIC decreased with increasing trophic status whereas BS increased. Furthermore, potential grazing was positively related to increasing trophic status and decreasing humic content. PGBM appeared to be dominating over VBM in the majority of lakes sampled, especially in the epilimnion.5. Thus, the relative importance of viruses for bacterial mortality was potentially highest in humic lakes of medium trophic status and it was also greater in the hypolimnion than in the epilimnion.

High Diversity of Fungi may Mitigate the Impact of Pollution on Plant Litter Decomposition in Streams

We investigated how a community of microbial decomposers adapted to a reference site responds to a sudden decrease in the water quality. For that, we assessed the activity and diversity of fungi and bacteria on decomposing leaves that were transplanted from a reference (E1) to a polluted site (E2), and results were compared to those from decomposing leaves either at E1 or E2. The two sites had contrasting concentrations of organic and inorganic nutrients and heavy metals in the stream water. At E2, leaf decomposition rates, fungal biomass, and sporulation were reduced, while bacterial biomass was stimulated. Fungal diversity was four times lower at the polluted site. The structure of fungal community on leaves decomposing at E2 significantly differed from that decomposing at E1, as indicated by the principal response curves analysis. Articulospora tetracladia, Anguillospora filiformis, and Lunulospora curvula were dominant species on leaves decomposing at E1 and were the most negatively affected by the transfer to the polluted site. The transfer of leaves colonized at the reference site to the polluted site reduced fungal diversity and sporulation but not fungal biomass and leaf decomposition. Overall, results suggest that the high diversity on leaves from the upstream site might have mitigated the impact of anthropogenic stress on microbial decomposition of leaves transplanted to the polluted site.

Temporal variability and characterization of physicochemical properties in the neritic area of Sagami Bay, Japan

Seasonal and interannual variations in physicochemical properties were investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from December 2000 to December 2005. Physicochemical properties (i.e. temperature, salinity, density, dissolved oxygen and dissolved inorganic nutrient concentration) revealed clear seasonal variations, which were similar to each other during all 5 years. Temperature, salinity and dissolved inorganic nutrients showed rapid, drastic variations within a few days and/or weeks. These variations are related to sea levels, principally due to the shifting effects of the Kuroshio Current axis: they were strongly affected by the Kuroshio Water and other waters, when sea level difference was greater than ca. 35 cm and lower than ca. 15 cm, respectively. Temperature difference (DFT) increased with sea level difference, and the difference of salinity and dissolved inorganic nutrients (NH4+-N, NO3−+NO2−-N, NH4++NO3−+NO2−-N, PO43−-P and SiO2-Si) increased and decreased with DFT, respectively. All these correlations are significant. Total dissolved inorganic nitrogen (N), phosphate (P) and silicate (Si) revealed seasonal variations in the ranges of 0.57–16.08, 0.0070–0.91 and 0.22–46.38 µM, respectively. From the regression equations between these elements allowed the following relation to be obtained; Si:N:P = 14.8:13.4:1. Dissolved inorganic nutrients were characterized by Si and/or P deficiency, especially in the upper layer (0–20 m depth) during summer. Single and/or combined elements are discussed on the basis of potential and stoichiometric nutrient limitations, which could restrict phytoplankton (diatom) growth as a limiting factor.

Biological, physical and chemical properties at the Subtropical Shelf Front Zone in the SW Atlantic Continental Shelf

The physical aspects of the Subtropical Shelf Front (STSF) for the Southwest Atlantic Continental Shelf were previously described. However, only scarce data on the biology of the front is available in the literature. The main goal of this paper is to describe the physical, chemical and biological properties of the STSF found in winter 2003 and summer 2004. A cross-section was established at the historically determined location of the STSF. Nine stations were sampled in winter and seven in summer. Each section included a series of conductivity-temperature-depth (CTD) stations where water samples from selected depths were filtered for nutrient determination. Surface samples were taken for chlorophyll a (Chl- a) determination and plankton net tows carried out above and below the pycnocline. Results revealed that winter was marked by an inner-shelf salinity front and that the STSF was located on the mid-shelf. The low salinity waters in the inner-shelf indicated a strong influence of freshwater, with high silicate (72 μM), suspended matter (45 mg l −1), phosphate (2.70 μM) and low nitrate (1.0 μM) levels. Total dissolved nitrogen was relatively high (22.98 μM), probably due to the elevated levels of organic compound contribution close to the continental margin. Surface Chl -a concentration decreased from coastal well-mixed waters, where values up to 8.0 mg m −3 were registered, to offshore waters. Towards the open ocean, high subsurface nutrients values were observed, probably associated to South Atlantic Central Waters (SACW). Zooplankton and ichthyoplankton abundance followed the same trend; three different groups associated to the inner-, mid- and outer-shelf region were identified. During summer, diluted waters extended over the shelf to join the STSF in the upper layer; the concentration of inorganic nutrients decreased in shallow waters; however, high values were observed between 40 and 60 m and in deep offshore waters. Surface Chl -a ranged 0.07–1.5 mg m −3; winter levels were higher. Three groups of zoo and ichthyoplankton, separated by the STSF, were also identified. Results of the study performed suggest that the influence of freshwater was stronger during winter and that abundance distribution of Chl -a, copepods and ichthyoplankton was related to the Plata Plume Waters (PPW), rather than to the presence of the STSF. During summer, when the presence of freshwater decreases, plankton interactions seem to take place in the STSF.

Submersible‐operated porewater sampler for permeable sediments

A sampler was developed to collect porewater from permeable (sandy) sediments during manned‐submersible operations. The sampler uses vacuum (or atmospheric‐pressure) reservoirs to draw porewater into a sediment probe and then into inline sample loops. The sampler is relatively inexpensive, easy to construct, and self‐contained, operating without an external power supply. The sample‐loop/reservoir system (without the probe) can also be used to sample wells or other apparatus installed in or on the seafloor, and would be comparatively easy to automate. In addition, the sampler should be adaptable to SCUBA diving operations (including rebreather or mixed‐gas diving). The sampler was used with Pisces submersibles to determine dissolved chemical profiles in sandy sediments inside and outside the extensive deepwater meadows of macroalgae offshore of the main Hawaiian Islands. The sampler collected porewater (to 25 cm sediment depth) from sites at 40‐200 m water depth. Porewater inorganic nutrient concentrations were comparable with those in nearshore permeable sediments, but showed distinct differences between a vegetated and an unvegetated site.

Influence of salinity, temperature, dissolved inorganic carbon and nutrient concentration on the photosynthesis and growth of Fucus vesiculosus from the Baltic and Irish Seas

Fucus vesiculosus from the northern Baltic Sea (5 psu) and from the Irish Sea (35 psu) were cultivated at different temperatures, salinities and dissolved inorganic carbon (DIC) concentrations with the addition of different nutrient concentrations. The influence of these abiotic factors was assessed by measuring photosynthesis as electron transport rate (ETR) and growth as relative growth rate (RGR). The maximal ETR and the RGR of the Irish Sea plants in their natural seawater (50.8 µmol electrons m−2 s−1; 0.024 g g−1 day−1) were significantly higher than those of the Baltic plants in their natural seawater (21.9 µmol electrons m−2 s−1; 0.007 g g−1 day−1). When Baltic F. vesiculosus was cultivated at a DIC concentration similar to that of the Irish Sea, the ETR as well as RGR increased, but never equalled the rates of the marine F. vesiculosus from the Irish Sea. Cultivation at different salinities showed that F. vesiculosus from the Baltic has a higher ETRmax and RGR at low salinities (5–10 psu) than F. vesiculosus from the Irish Sea, whose ETR and RGR decreased sharply in salinities below 20 psu. Plants from both sites grown at high nutrient concentrations, however, performed better at low salinities than those grown under low nutrient conditions. Salinity had the greatest impact on differences in ETR and RGR between the two populations, followed by differences in DIC and nutrient concentrations. There was a highly significant correlation between ETRmax and RGR in plants from both sites and across the full range of culture conditions, indicating that the same amount of energy from photosynthesis is used for growth in both varieties of the species at different salinities. The photosynthesis of F. vesiculosus in the northern Baltic is close to the minimum demand for growth, which may account for their small size. The temperature optimum for F. vesiculosus from the Baltic was 4–10°C, while that for F. vesiculosus from the Irish Sea was 15–20°C. The photosynthesis of Irish Sea plants was less strongly affected by exposure to high irradiances than that of plants from the Baltic.

First approach to understanding riparian wetlands in the Middle Ebro River floodplain (NE, Spain): Structural characteristics and functional dynamics

First approach to understanding riparian wetlands in the Middle Ebro River floodplain (NE, Spain): structural characteristics and functional dynamics In Spring of 2005, the relationships between the physical and chemical characteristics of the aquatic and benthic environments and macroinvertebrate assemblages in seven wetlands representative of the floodplain of the Middle Ebro River (NE Spain), were analyzed. The selected wetlands differed in their hydrological connectivity, local environmental conditions and anthropic influence. Through multivariate analyses, two environmental gradients and three main wetland groups were detected. The hydrological connectivity differences generate a heterogenous landscape of structurally and functionally different wetlands in the Ebro Middle floodplain. Confined wetlands, such as older ox bow lakes, showed higher salt and organic matter contents and lower macroinvertebrates' density and biodiversity than did the other wetlands. This suggests that confinement and lack of disturbance events have led to water salinization and eutrophication, habitat homogenization and natural succession of the communities towards more adapted structures with lower biodiversity. Wetlands that still maintain some functional relationship with the river, such as newer ox bow lakes, constructed wetlands, and backwaters, show a higher inorganic nutrient concentration and suspended solids. They also show higher taxa richness and evenness, which suggests that higher disturbance frequencies enhance habitat's heterogeneity and resource availability, and therefore primary and secondary production that allow adapted and opportunistic species to coexist. The progressive flow regulation tends to homogenise this complex system, endangering its conservation. Therefore, the key processes identified here should be taken under consideration for the planning and execution of ecological monitoring, management and restoration.

Time-series observation of dissolved inorganic carbon and nutrients in the northwestern North Pacific

Time-series measurements of dissolved inorganic carbon (DIC) and nutrient concentrations were conducted in the northwestern North Pacific from October 2002 to August 2004. Assuming that data obtained in different years represented time-series seasonal data for a single year, vertical distributions of DIC and nutrients showed large seasonal variabilities in the surface layer (∼100 m). Seasonal variabilities in normalized DIC (nDIC) and nitrate concentrations at the sea surface were estimated to be 81–113 µmol kg−1 and 12.7–15.7 µmol kg−1, respectively, in the Western Subarctic Gyre. The variability in nutrients between May and July was generally at least double that in other seasons. In the Western Subarctic Gyre, estimations based on statistical analyses revealed that seasonal new production was 39–61 gC m−2 and tended to be higher in the southwestern regions or coastal regions. The seasonal new productions in the northwestern North Pacific were two or more times higher than in the North Pacific subtropical gyre and the northeastern North Pacific. It is likely that this difference is due to spatial variations in the concentrations of trace metals and the species of phytoplankton present. In addition, from estimations of surface pCO2 it was verified that the Western Subarctic Gyre is a source of atmospheric CO2 between February and May and a sink for CO2 between July and October.

Spatial and temporal dynamics of stream water particulate and dissolved N, P and C forms along a catchment transect, NE Scotland

The dynamics of dissolved and particulate N, P and organic C were examined for field drains, through a headwater (4 km2), into a mesoscale stream (51 km2) and river (1844 km2) catchment. Distributions of N and P forms were similar in the agricultural headwater and field drains; annual P fluxes of particulate and dissolved forms were of equal magnitude, whilst N was dominated by NO3–N. Across all scales organic P was an important, often dominant, component of the dissolved P. Temporal variation in nutrient concentrations and proportions was greatest in the headwater, where storms resulted in the generation of large concentrations of suspended particulate matter, particulate and dissolved P, particularly following dry periods. The data suggest that groundwater and minor point source inputs to the mesoscale catchment buffered the temporal variability in hydrochemistry relative to the headwater. Summer low flows were associated with large PO4–P concentrations in the mesoscale catchment at a critical time of biological sensitivity. At the largest river catchment scale, organic forms of C, N and P dominated. Inorganic nutrient concentrations were kept small through dilution by runoff from upland areas and biological processes converted dissolved N and P to particulate forms. The different processes operating between the drain/headwater to the large river scale have implications for river basin management. Given the prevalence of organic and particulate P forms in our catchment transect, the bioavailability of these fractions needs to be better understood.