Search

The conversion processes of macroalgae for biofuels can be divided into thermochemical (dry) and microbiological (wet) processes. The chemical composition of macroalgae together with the pre-treatment method, conversion conditions, and the characteristics of the microbes involved (wet processes) determine the yield and the properties of the biofuel produced. Macroalgae are often rich in carbohydrates, and therefore well suited for biogas, biobutanol and bioethanol productions. The content of triacylglycerols (TAGs) is the best indicator for the suitability of the alga for biodiesel production. TAGs have a high conversion rate to biodiesel, high percentage of fatty acids, and they lack phosphorus, sulfur and nitrogen. Macroalgae can have high metal concentrations, which can have an impact on conversion processes: metals may inhibit or catalyse the processes. High sulfur (especially in green algae) and nitrogen contents are also characteristic to macroalgae, and may be problematic in the production of biogas (NH3-toxicity) and the use of the oil and biodiesel (high concentrations of H2S and NOx-compounds). Macroalgae have proven to be suitable material for conversion processes, but further optimization of the processes is needed. At present, macroalgae are not economically, or in many cases not even environmentally, sustainable material when the whole production chain is considered. In this review we summarize information on the chemical composition of macroalgae in a prospect of biofuel production, and the current situation in the field of macroalgal-based biofuel production. more...

Steep redoxclines form between oxic surface water and the stagnant, sulfidic hypolimnion in the eutrophied, brackish water Baltic Sea. Nitrification, denitrification, and anammox were measured at and below the redoxcline to quantify the role of water-column nitrogen processes in the overall magnitude of nitrogen removal in the Baltic Sea. Rates of nitrification were very high (up to 85 nmol N L21 d21) at the oxic–anoxic interface, but, surprisingly, nitrification was separated from the processes reducing nitrate to N2 (up to 810 nmol N L21 d21 )b y tens of meters in depth. N2 production was dominated by chemolithotrophic denitrification, with anammox playing only a negligible role, and limited to the water layers in which nitrite or nitrate coexisted with sulfide. The alternating oxygen concentrations in the basin induce irregular bursts of nitrogen removal. Nitrification takes place after mixing of ammonium-rich deep water with oxic water, and denitrification uses the formed nitrite and nitrate once anoxic conditions re-establish. Although removal rates can be high, conditions allowing such rates are likely short-lived. While the sedimentary denitrification rates at the shallower, oxic areas are lower, they are more constant in time, highlighting the need to avoid hypoxia, which would prevent sedimentary denitrification. The Baltic Sea is a large and shallow brackish inland sea in northern Europe (415,266 km 2 , average depth 52 m) that suffers from heavy anthropogenic nutrient loading, and large cyanobacterial blooms are a regular phenomenon. It has been suggested that internal feedbacks sustain the eutrophication (Vahtera et al. 2007). One of the key factors in this feedback mechanism is the effect that increased hypoxia has on the biogeochemical cycles of nutrients. The mechanisms that lead to phosphorus release from the sediments during anoxia are well known, but the effects of hypoxia on nitrogen cycling are still uncertain (Conley et al. 2009), despite the critical role nitrogen has as one of the main nutrients regulating not only the extent but also the species composition of phytoplankton blooms (Smith 1983). Two naturally occurring microbial processes, denitrification and anammox, have the potential to remove nitrogen from the water via the production of N2 gas (Codispoti et al. 2001; Kuypers et al. 2005). These anaerobic processes reduce oxidized substrates (nitrate and nitrite), originating from an aerobic nitrification process, to harmless dinitrogen gas. Therefore, nitrification and the processes that mediate the production of N2 are more...

Seasonal Baltic Sea ice is structurally similar to polar sea ice and provides habitats for diverse ice organism assemblages that are integral to the biogeochemistry and ecology of the sea during winter. Temperature and inorganic nitrogen sources have been suggested to control bacterial growth, with increasing dependence on ammonium at low temperatures. To study the bacterial growth and preference for the nitrogen source, we conducted experiments at 0 and 4°C, using ammonium and nitrate as nitrogen sources at two coastal fast-ice stations in the Gulf of Finland and in the Gulf of Bothnia during three successive winters. The two study sites differ markedly in relation to the allochthonous dissolved organic matter supply from the catchment area. High levels of bacterial growth were recorded at both study sites, with community generation times of 15–37 h. The measured bacterial growth efficiencies of 20–58% suggest that the Baltic sea ice brines provide a rich medium for bacterial growth and efficient functioning of bacteria-based food webs. Our experiments with sea ice samples showed a preference for ammonium at both temperatures and high potential growth in both types of nitrogen supplies. No major differences in phosphorus depletion rates were found at the two temperatures, but rates were always highest when ammonium was added to the experiments. These experiments point out that ice maturity, presumably through changes in bacterial community structure, impacts nitrogen processes and that these processes are pronounced prior to melting of the ice. more...

We studied the microbial food web in the upper 100 m of the water column in iron-limited sub-Antarctic HNLC waters south-east of New Zealand in the SAGE experiment in 2004, with focus on bacterioplankton. Samples were collected daily from inside and outside the iron enriched patch. Short term enrichment experiments were conducted on board in 4 L polycarbonate bottles with water outside the iron enriched patch to study single and combined effects of micronutrient additions on microbial food web. Low bacterial growth was recorded in the study area with community turnover times of 50 h or more during the study period. Measurements of bacterial standing stocks and production rates in the study show minor responses to the large scale iron enrichment, with increase in rates and stocks after the first enrichment and at the end of the study period after the third iron enrichment when solar radiation increased and wind mixing decreased. The average daily bacterial production rates were 31.5 and 33.7 mgCm −2 d −1 for the OUT and IN stations, respectively; thus overall there was not a significant difference between the control and the iron-enriched patch. In the bottle experiments bacterial thymidine incorporation showed responses to single iron and silicic acid enrichments and a major growth response to the combined iron and sucrose enrichments. Phytoplankton chlorophyll- a showed clear stimulation by single additions of iron and silicic acid and silicic acid enhanced the iron impact. Cobalt additions had no effect on bacteria growth and a negative effect on phytoplankton growth. Low bacterial in situ growth rates and the enrichment experiments suggest that bacteria are co-limited by iron and carbon, and that bacterial iron uptake is dependent on carbon supply by the food web. With the high iron quota (μmol Fe mol C −1 ) bacteria may scavenge considerable amounts of the excess iron, and thus influence the relative importance of the microbial food web as a carbon sink. more...

The S OLAS A ir–Sea G as E xchange (SAGE) experiment was conducted in Sub-Antarctic waters off the east coast of the South Island of New Zealand in the late summer of 2004. This mesoscale iron enrichment experiment was unique in that chlorophyll a (chl a ) and primary productivity were only 2× OUT stations values toward the end of the experiment and this enhancement was due to increased activity of non-diatomaceous species. In addition, this enhancement in activity appeared to occur without a significant build up of particulate organic carbon. Picoeukaryotes ( a , only accumulated when phytoplankton growth exceeded grazing and when net algal growth exceeded dilution rate. The SAGE results highlight the function of the smallest phytoplankton size fraction described by the ecumenical Iron Hypothesis. Thus, adding iron to HNLC-low silicic acid regions during certain times of the year may simply transfer more carbon through the microbial food web. A primary implication of this study is that any iron-mediated gain in fixed carbon with this set of environmental conditions has a high probability of being recycled in surface waters. more...

The SOLAS air–sea gas exchange experiment (SAGE) was a multiple-objective study investigating gas-transfer processes and the influence of iron fertilisation on biologically driven gas exchange in high-nitrate low-silicic acid low-chlorophyll (HNLSiLC) Sub-Antarctic waters characteristic of the expansive subpolar zone of the southern oceans. This paper provides a general introduction and summary of the main experimental findings. The release site was selected from a pre-voyage desktop study of environmental parameters to be in the south-west Bounty Trough (46.5°S 172.5°E) to the south-east of New Zealand and the experiment was conducted between mid-March and mid-April 2004. In common with other mesoscale iron addition experiments (FeAX’s), SAGE was designed as a Lagrangian study, quantifying key biological and physical drivers influencing the air–sea gas exchange processes of CO2, DMS and other biogenic gases associated with an iron-induced phytoplankton bloom. A dual tracer SF6/3He release enabled quantification of both the lateral evolution of a labelled volume (patch) of ocean and the air–sea tracer exchange at tenths of kilometer scale, in conjunction with the iron fertilisation. Estimates from the dual-tracer experiment found a quadratic dependency of the gas exchange coefficient on windspeed that is widely applicable and describe air–sea gas exchange in strong wind regimes. Within the patch, local and micrometeorological gas exchange process studies (100 m scale) and physical variables such as near-surface turbulence, temperature microstructure at the interface, wave properties and windspeed were quantified to further assist the development of gas exchange models for high-wind environments. There was a significant increase in the photosynthetic competence (Fv/Fm) of resident phytoplankton within the first day following iron addition, but in contrast to other FeAX’s, rates of net primary production and column-integrated chlorophyll a concentrations had only doubled relative to the unfertilised surrounding waters by the end of the experiment. After 15 days and four iron additions totalling 1.1 ton Fe2+, this was a very modest response compared to other mesoscale iron enrichment experiments. An investigation of the factors limiting bloom development considered co-limitation by light and other nutrients, the phytoplankton seed-stock and grazing regulation. Whilst incident light levels and the initial Si:N ratio were the lowest recorded in all FeAXs to date, there was only a small seed-stock of diatoms (less than 1% of biomass) and the main response to iron addition was by the picophytoplankton. A high rate of dilution of the fertilised patch relative to phytoplankton growth rate, the greater than expected depth of the surface mixed layer and microzooplankton grazing were all considered as factors that prevented significant biomass accumulation. In line with the limited response, the enhanced biological draw-down of pCO2 was small and masked by a general increase in pCO2 due to mixing with higher pCO2 waters. The DMS precursor DMSP was kept in check through grazing activity and in contrast to most FeAX’s dissolved dimethylsulfide (DMS) concentration declined through the experiment. SAGE is an important low-end member in the range of responses to iron addition in FeAX’s. In the context of iron fertilisation as a geoengineering tool for atmospheric CO2 removal, SAGE has clearly demonstrated that a significant proportion of the low iron ocean may not produce a phytoplankton bloom in response to iron addition. more...

Over the past 30 yr, microbial ecology has taken major leaps in bringing microscopic organisms into the context of aquatic ecosystems and shown that they regulate carbon and nutrient processes on a global scale. More recently, molecular biology has enabled prokaryotic organisms to be identified at the species level and contributed information on functional groups of specific significance to the ecosystem. Although microbial ecology has covered all common aquatic systems it has spatially been focused on a narrow range of habitats, leaving, for example, polar ice with modest activity and the deep, dark oceans practically untouched. In addition, temporal scales have been skewed towards daylight studies and only recent studies have focused on day/night process controls, recognizing that the diel rhythm is connected to fast-growing prokaryotic organisms. The key to going forward with predictions on the fate of microbial food webs in the ecosystem is to recognize physical structures and their persistence in the water body and identify the biological hotspots in terms of spatial and temporal significance. The present ecological models do not handle short-term, spatially restricted hotspot events adequately. Evidently, we need to combine our research efforts into targeted approaches, coupling modeling activity with physical and chemical oceanography as well as fisheries biology and 'sell our goods', even though our primary interest is microbial processes. Understanding the micro-environment of a single cell and its interaction with the environment should, by extrapolation, enable us to predict global processes. In the nitrogen cycle, this understanding has evolved rapidly, but in the carbon cycle, the role of microbes is still far from fully understood, especially in terms of loss processes. This should rapidly be addressed, instead of undertaking further major questionable experiments such as fertilizing the seas at very large scales. more...

Coastal fast ice and underlying water of the northern Baltic Sea were sampled throughout the entire ice winter from January to late March in 2002 to study the succession of bacterial biomass, secondary production and community structure. Temperature gradient gel electrophoresis (TGGE) and sequencing of TGGE fragments were applied in the community structure analysis. Chlorophyll-a and composition of autotrophic and heterotrophic assemblages were also examined. Overall succession of ice organism assemblages consisted of a low-productive stage, the main algal bloom, and a heterotrophic post-bloom situation, as typical for the study area. The most important groups of organisms in ice in terms of biomass were dinoflagellates, plasticidic flagellates, rotifers and ciliates. Ice bacteria showed a specific succession not directly dependent on the overall succession events of ice organisms. Sequenced 16S rDNA fragments were mainly affiliated to α-, β-, and γ-proteobacterial phyla and Cytophaga–Flavobacterium–Bacteroides-group, and related to sequences from cold environments, also from the Baltic Sea. Temporal clustering of the TGGE fingerprints was stronger than spatial, although lower ice and underlying water communities always clustered together, pointing to the importance of ice maturity and ice–water interactions in shaping the bacterial communities. more...

Benthic processes were measured at a coastal deposition area in the northern Baltic Sea, covering all seasons. The N-2 production rates, 90-400 mu mol N m(-2) d(-1), were highest in autumn-early winter and lowest in spring. Heterotrophic bacterial production peaked unexpectedly late in the year, indicating that in addition to the temperature, the availability of carbon compounds suitable for the heterotrophic bacteria also plays a major role in regulating the denitrification rate. Anaerobic ammonium oxidation (anammox) was measured in spring and autumn and contributed 10% and 15%, respectively, to the total N-2 production. The low percentage did, however, result in a significant error in the total N-2 production rate estimate, calculated using the isotope pairing technique. Anammox must be taken into account in the Gulf of Finland in future sediment nitrogen cycling research. Benthic processes were measured at a coastal deposition area in the northern Baltic Sea, covering all seasons. The N-2 production rates, 90-400 mu mol N m(-2) d(-1), were highest in autumn-early winter and lowest in spring. Heterotrophic bacterial production peaked unexpectedly late in the year, indicating that in addition to the temperature, the availability of carbon compounds suitable for the heterotrophic bacteria also plays a major role in regulating the denitrification rate. Anaerobic ammonium oxidation (anammox) was measured in spring and autumn and contributed 10% and 15%, respectively, to the total N-2 production. The low percentage did, however, result in a significant error in the total N-2 production rate estimate, calculated using the isotope pairing technique. Anammox must be taken into account in the Gulf of Finland in future sediment nitrogen cycling research. Benthic processes were measured at a coastal deposition area in the northern Baltic Sea, covering all seasons. The N-2 production rates, 90-400 mu mol N m(-2) d(-1), were highest in autumn-early winter and lowest in spring. Heterotrophic bacterial production peaked unexpectedly late in the year, indicating that in addition to the temperature, the availability of carbon compounds suitable for the heterotrophic bacteria also plays a major role in regulating the denitrification rate. Anaerobic ammonium oxidation (anammox) was measured in spring and autumn and contributed 10% and 15%, respectively, to the total N-2 production. The low percentage did, however, result in a significant error in the total N-2 production rate estimate, calculated using the isotope pairing technique. Anammox must be taken into account in the Gulf of Finland in future sediment nitrogen cycling research. more...

Baltic Sea phytoplankton responses during N 2 -fixing cyanobacterial blooms, dominated by Nodularia spp., Aphanizomenon sp., and Anabaena spp., were studied using nutrient enrichment experiments. Nitrogen fixation, phytoplankton growth, primary productivity, and phytoplankton species' responses were investigated in areas representing open Baltic Sea water and Gulf of Finland water. Responses to additions of N, P, Fe, and the organic chelator EDTA were studied. Phytoplankton biomass and primary productivity were N, P, or N+P-limited. Phosphorus limitation was more prominent at the Gulf of Finland sites, where the dissolved inorganic-nitrogen to phosphorus (DIN:DIP) ratio was >16:1 during the study period. At the open sea sites, with DIN:DIP ratio more...

The coastal sea ice in the vicinity of Dumont d'Urville station, Antarctica (66° 40' S, 140° 01' E) supports a diverse microbial community. To investigate seasonal changes in bacterial, microalgal and protozoan biomass during the ice-coverage period, a survey was conducted on fast ice in the continental shelf of Terre Adelie. A reference station was sampled twice a month from April to December 1997. In April and May, during sea ice formation, the autotrophic biomass reached rela- tively high levels ranging from 400 to 800 mgC m -3 in the subsurface ice. A second increase reach- ing 1500 mgC m -3 in mid-December occurred in early summer in the bottom ice layer. Bacterial bio- mass ranged from 200 mgC m -3 in May. Maximal levels of bacterial biomass were detected during ice formation and just before the summer thaw. Total pro- tozoan biomass increased from May to July. Maximum protozoan biomass (31.8 mgC m -3 ) occurred in the surface ice layer in July. Except for during a short period (late May to early June), ciliates were dominant, accounting for 50 to 77% of the total protozoan biomass. During the ice-covered period, phototrophic biomass was always dominant. Microalgal biomass contributed on average 80.6% of total biomass whereas bacterial and protozoan biomass accounted for only 16.4 and 3%, respectively. Despite their low biomass, protozoa seem to play a major role in bacterial regulation. more...

Six strains of Nodularia spp., both toxic and non-toxic, were tested for their ability to incorporate leucine and thymidine. All axenic cyanobacterial strains studied showed high leucine incorporation (1.4 to 12 pmol μg chl a -1 h -1 at a concentration of 212 nM leucine), whereas thymidine was either taken up at a very low rate or not at all (0 to 0.2 pmol μg chl a -1 h -1 at a concentration of 121 nM thymidine). We therefore recommend using the thymidine incorporation method instead of that of leucine for measuring heterotrophic bacterial production during cyanobacterial blooms. more...

During 2–12 August 1999, the development of a surface bloom dominated by the cyanobacterium Nodularia spumigena was followed in the western Gulf of Finland, Baltic Sea. Intense surface scums of aggregated N. spumigena existed on calm days. The low-nutrient N. spumigena-dominated water mass was separated by a front from a nutrient-rich water mass dominated by Aphanizomenon cf. flos-aquae (Nostocales, Cyanobacteria). Owing to inadequate mixing of the two water masses, it is likely that N. spumigena growth was based mainly on the use of internal phosphorus stores. Signs of cell decay were observed on 5 August, and the proportion of empty filaments in the community increased towards the end of the survey period. A high number of Nitzschia spp. (Bacillariophyceae) was recorded within the N. spumigena aggregates on 8 August, suggesting nutrient leakage from the N. spumigena filaments. Senescence of N. spumigena and a decrease in the proportion of intact N. spumigena cells in dry material resulted in de... more...

The effects of addition of algae (340 mg C m−2) and of the amphipod Monoporeia affinis (1500 ind m−2) on denitrification; porewater nutrient profiles; nutrient fluxes between sediment and water; and bacterial production were studied. A laboratory experiment was conducted using cores filled with sediment from the Gulf of Finland (Baltic Sea). Denitrification (isotope pairing method) was dramatically reduced in the cores enriched with algae (from 200–300 to 10–20 μmol N m−2 day−1). However, the addition of M. affinis together with algae negated this effect. Monoporeia affinis alone increased the coupled nitrification-denitrification as compared to the control cores. Bioturbation by the amphipods oxidised the sediment surface layers and consequently, PO43−concentration in the porewater decreased. In the cores enriched with algae, the loss of N from the sediment porewater was dominated by the efflux of NH4+which formed 90% of the loss. In the M. affinis enriched cores, the share of the NH4+efflux was 60% of which the excretion by M. affinis was 5–10%. The effects of M. affinis were found to be caused mainly by the improved O2conditions in the sediment. more...

Benthic bacterial production was measured with a modified ['4C]leucine incorporation method in the northern Baltic Sea in 1996 and 1997. Samples were incubated and TCA extractions were done in microcentrifuge tubes. Unincorporated label was removed by repeated centrifugation. Pellets were suspended in scintillation cocktail and counted as a gel using internal standardisation, a method that gave highly comparable counts with combustion of the sample. Bacterial production varied between 0.15 and 0.8 mg C 1-' h-' (90 to 350 mg C m-2 d-'). The highest production was found at Stn GF2 in the Gulf of Finland and the lowest in the northern Baltic Proper Bacterial growth rates were 0.07 to 0.84 d-'. Comparison of these results with published data from sedimentation trap measurements suggests that only a part of the benthic bacterial C demand can be explained by sedimentation. more...

Denitrification in the sediments of the open northern Baltic Sea was measured using the isotope pairing method. The highest denitrification activity was found in the central Gulf of Finland, where denitrification varied between 150 and 650 μmol N m-2 d-1. The bulk of the denitrification was coupled to the NO3- production by nitrification. The mass of benthic fauna was found to be the most significant factor affecting the rate of denitrification. Denitrification rate was highest in late summer and early autumn. Calculated as an average for the Gulf of Finland, the denitrification rate obtained in the present study is 45 kt N yr-1. This gives a release of ca 30% of the external N input by denitrification. more...

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca, four times, lower in the north (Bothnian Bay) than ... more...

A 2-week multidisciplinary study of the physical, chemical, and biological mechanisms controlling the initiation of the late summer blooms of the diazotrophic cyanobacteria, Aphanizomenon jlos-aqua2 Ralfs and Nodularia spumigena Mertens, in the Baltic Sea was carried out in a frontal region at the entrance to the Gulf of Finland in July 1993. The front is formed by inflowing sa‘itier waters of the northern Baltic proper and outflowing fresher waters from the gulf, and its position and shape are largely controlled by wind conditions. In general, the waters of the northern Baltic proper are less stratified than the outflowing lesssaline waters. At the time of the study, the two major water masses differed in terms of phytoplankton community structure, both at species level and at the level of functional groups. Wind-induced vertical mixing was instrumental in bringing nutrient pulses to the upper mixed layer in the less-stratified, high-saline water mass. Nutrient pulses were followed by enhancement of primary productivity and assimilation number (primary productivity/Chl a) in cyanobacterial (> 20 pm) and flagellate (< 20 vrn) size fractions. It is proposed that mesoscale blooms of A. flos-aquae benefit from the nutrient-pulsing events. Calm weather and solar heating, as reflected by rising temperatures in the upper mixed layer and overriding of water masses in the frontal region, resulted in substantial shallowing of the upper mixed layer, which initiated the bloom of N. spumifena. more...

The main compartments of the nucrobial food web were studied in a hydrodynamically complicated area to determine the response of bacterioplankton to spatio-temporal discontinuities in the water column structure. The samples were divided according to water masses into those repre- senting frontal areas and those representing low-saline areas. In the upper mixed water layer (UML) bacterial production was higher in the frontal water (average 4.5 mg C m3 dl) than in the low-saline water (3.7 mg C irr3 d-I). However, the proportion of bacterial production of the primary production was about the same in the frontal water (15 5%) and in the low-saline (16 %) water. The data implied that the recorded frontal upwelling event did not drastically change the mode of production from regenerated to new production. Furthermore, the data indicated that heterotrophic flagellates did not respond to increased bacterial abundance during the intervals between hydrodynamic events. Below the thermochne, the turnover time of bacterial numbers was less than in the UML, as was thymidine incorporation (TdR) per cell, but leucine incorporation (Leu) per cell was highest in the UML. The average molar ratio of Leu to TdR was 7.7 in the UML and 3 below the thermocline. The molar ratio showed an increase in the growth rate during a storm event. Leu and TdR methods did not give equivalent rates of bacterial production over the daily timescale, although they gave quite similar estimates when averaged over the whole study penod (11 d). Our data indicated that one should be very cautious in using conversion factors, which are derived from surface water, to calculate bactenal production throughout the water column, and that sometimes even higher conversion factors should be used below the thermocline than in the UML. more...

Increasing biomasses of gelatinous zooplankton presumably have major implications for the structure and function of marine food webs at large; however, current data on lower trophic levels are scarce, as most studies have focused on the immediate effects on zooplankton and fish larvae only. We examined the short-term impact of larvae and adults of the invasive ctenophore Mnemiopsis leidyi on a summer planktonic food web in the estuarine southern Baltic Sea, with special emphasis on the microbial loop. Grazing by M. leidyi reduced the mesozooplankton biomass, followed by increased dinoflagellate biomass in treatments with M. leidyi. While chlorophyll a increased most in the treatments with M. leidyi, small phytoplankton and ciliates decreased in all treatments. M. leidyi had a slight effect on bacterial abundance, but not on bacterial production, ectoenzymatic activities, or community composition. Undetectable levels of phosphate and a gradual accumulation of dissolved organic carbon during the experiment suggested a malfunctioning microbial loop scenario. The experiment shows that direct and indirect short-term effects of M. leidyi on the estuarine food web are limited to higher trophic levels and indicates that top-down and bottom-up consequences of M. leidyi expansions on the microbial loop will likely depend on local nutrient conditions. 2017-07-24 more...

Experimental enclosures were used to follow responses of the plankton~c microbial food web to varying short-tern~ (5 d) perturbations induced by adding inorganic nutrients (N and P) and a top predator (fish) during a 21 d period in late summer, on the coastal area of the Baltic Sea. Biomass, production, growth and grazing of picoand nanoplankton assemblages were estimated, and a carbon budget for the microbial loop during the experiment was constructed. The microbial food web was a highly dynamic system. Varying perturbations due to nutrient loading and the top predator provoked eutrophication in the enclosures, but they affected the microbial loop only slightly. The amplitudes of oscillation in abundance of coupled communities were amplified, but the frequencies of oscillations in the microbial loop were not affected by the perturbations. Changes in the route of carbon flow through the microbial food web occurred In relatively short time scales. These changes seemed to be dependent on the phasing of the coupled oscillations between the communities, and the structure within the different communities. Ciliates were only loosely connected to the microbial loop: although ciliates and heterotrophic nanoflagellates (HNF) showed predator-prey-like coupled oscillations, the ciliates gained most of their carbon from other sources, and most of the HNF carbon loss was due to factors other than ciliates. HNF were the most important consumers of picoplankton during the HNF maximum, but they were also dependent on other sources of nutrition. more...

Nutrient limitation and grazing control of the planktonic community were studied in the northern Baltic Sea off the SW coast of Finland during the phytoplankton growth season of 1985. In situ experiments based on a 23 factorial design were performed in mesocosm enclosures on 10 occasions. The manipulations used included phosphorus (PO,? ) and nitrogen (NH,+ ) additions and the removal of metazooplankton by 1 OO+m prefiltration. In each experiment, the responses of phytoplankton, bacterioplankton, heterotrophic nanoflagellates, and protozooplankton were followed for 2 d. Orthogonal multiple regression analysis was used to reveal which manipulations had statistically significant effects. Nitrogen was found to be the basic limiting nutrient for phytoplankton throughout the productive season. During early summer, only the combined addition of P and N evoked a clear increase in the growth of phytoplankton. In general, bacterial productivity was not highly affected by the manipulations. In summer the removal of metazooplankton caused a rapid increase in the amount of protozooplankton in the units with loo-pm prefiltration or prefiltration combined with N addition. In the absence of metazooplankton, the nutrient-induced increase in primary productivity was channeled to protozooplankton, whose growth in the units where metazooplankton was present was severely limited by food competition or by direct metazooplankton grazing. more...

A cyanobacterial bloom in the Gulf of Finland, Baltic Sea, was sampled throughout the development and senescence of aggregates in August 1999. While conditions inside the aggregates were favourable for denitrification (rich in nitrogen and carbon, with anoxic microzones), essentially none was detected by a sensitive isotope pairing method. Polymerase chain reaction-based methods, targeting functional genes encoding the key enzymes of denitrification and nitrification processes (nirS, nirK, amoA), revealed that the non-aggregated filaments harboured amoA gene fragments with high similarity to Nitrosospira amoA sequences, as well as both types of nitrite reductase genes, nirS and nirK. Only the nirS-type nitrite reductase gene and no amoA was detected in aggregated filaments. Thus, despite optimal environmental conditions and genetic potential for denitrification, the blooms of filamentous nitrogen-fixing cyanobacteria must be seen solely as a source, and not as a sink of nitrogen in the Baltic Sea. more...

Variations in the thymidine incorporation rate, bacterial abundance, and mean cell volumes in the surface water (0.5 m) of the Baltic Sea in spring and summer were compared in studies with different spatial scales (570 nautical miles [nmi] [ca. 1056 km], 220 nmi [ca. 407 km], 24 nmi [ca. 44 km], 12 nmi [ca. 22 km], and 200 m). The objective of the comparison was to investigate whether a single sample taken at one sampling point is representative enough for researchers to make generalizations about a larger water area. Bacterioplankton variation was connected more to seasonal characteristics than to the spatial scale of sampling. Variation was greater and more random in spring than in summer. The state variables (bacterial abundance and mean cell volume) varied less than the rate variable (thymidine incorporation). The results suggest that the sampling design for bacterioplankton studies in northern temperate seas should be planned primarily according to the season and that more stress should be put on rate variable measurements than on those of state variables. more...

Growth and herbivory of heterotrophic dinoflagellates (Gymnodinium sp.) from the Weddell Sea and the Weddell/Scotia Confluence were studied in 1988 in 100-liter microcosms. The microcosms were screened through 200-µm or 20-µm mesh nets and incubated for 12 d at 1 °C under artificial light. Mean cell volume of dinoflagellates was 1 000 to 1 500µm3, and that of their phytoplankton prey 360 to 430µm3. Dinoflagellate growth rate followed a Holling type II functional response, with a maximum growth rate of 0.3 d−1 and half-saturation food concentrations of 1.0µg chlorophylla l−1, 50µg C l−1, or 1 500 cells ml−1. Carbon budgets based on14CO2 assimilation and biomasses of phytoplankton and heterotrophic dinoflagellates suggested a balance between phytoplankton grazing loss and dinoflagellate consumption, assuming a dinoflagellate carbon conversion efficiency of 40%. Applying this to the functional response yielded estimates of maximum ingestion rate (0.8µg Cµg−1 C d−1, or 6 pg C dinoflagellate−1 h−1) and maximum clearance (0.8 to 1.2 × 105 body volumes h−1, or 80 to 120 nl ind.−1 h−1). The microcosm experiments suggested that heterotrophic dinoflagellates may contribute significantly to maintenance of low phytoplankton biomass in the Southern Ocean. more...

Several conversion factors are r e q w e d for the eshmation of bacterial biomass, net production and carbon demand from epifluorescence microscopy and measurements of [3 H]-thymidlne and [3 H]-leucine incorporation rates. These conversion factors were evaluated simultaneously in mixed cultures of bacterial assemblages from the Weddell/Scoha Confluence of the Southern Ocean. The cultures were grown in the dark at + l 'C. Conversion factors were calculated for each culture by regression analyses of cumulative parameters. Average conversion factors were: 1.1 X 1018 cells per m01 thymidme incorporated into cold TCA precipitate, 7.5 X 1015 pm3 of biovolume per m01 leucine incorporated into cold TCA precipitate, 0 4 pgC biomass per wm3 of biovolume, and 40% carbon growth yield. more...

Estuaries have been suggested to have an important role in reducing the nitrogen load transported to the sea. We measured denitrification rates in six estuaries of the northern Baltic Sea. Four of them were river mouths in the Bothnian Bay (northern Gulf of Bothnia), and two were estuary bays, one in the Archipelago Sea (southern Gulf of Bothnia) and the other in the Gulf of Finland. Denitrification rates in the four river mouths varied between 330 and 905 mu mol N m(-2) d(-1). The estuary bays at the Archipelago Sea and the Gulf of Bothnia had denitrification rates from 90 mu mol N m(-2) d(-1) to 910 mu mol N m(-2) d(-1) and from 230 mu mol N m(-2) d(-1) to 320 mu mol N m(-2) d(-1), respectively. Denitrification removed 3.6-9.0% of the total nitrogen loading in the river mouths and in the estuary bay in the Gulf of Finland, where the residence times were short. In the estuary bay with a long residence time, in the Archipelago Sea, up to 4.5% of nitrate loading and 19% of nitrogen loading were removed before entering the sea. According to our results, the sediments of the fast-flowing rivers and them estuary areas with short residence times have a limited capacity to reduce the nitrogen load to the Baltic Sea. Estuaries have been suggested to have an important role in reducing the nitrogen load transported to the sea. We measured denitrification rates in six estuaries of the northern Baltic Sea. Four of them were river mouths in the Bothnian Bay (northern Gulf of Bothnia), and two were estuary bays, one in the Archipelago Sea (southern Gulf of Bothnia) and the other in the Gulf of Finland. Denitrification rates in the four river mouths varied between 330 and 905 mu mol N m(-2) d(-1). The estuary bays at the Archipelago Sea and the Gulf of Bothnia had denitrification rates from 90 mu mol N m(-2) d(-1) to 910 mu mol N m(-2) d(-1) and from 230 mu mol N m(-2) d(-1) to 320 mu mol N m(-2) d(-1), respectively. Denitrification removed 3.6-9.0% of the total nitrogen loading in the river mouths and in the estuary bay in the Gulf of Finland, where the residence times were short. In the estuary bay with a long residence time, in the Archipelago Sea, up to 4.5% of nitrate loading and 19% of nitrogen loading were removed before entering the sea. According to our results, the sediments of the fast-flowing rivers and them estuary areas with short residence times have a limited capacity to reduce the nitrogen load to the Baltic Sea. Estuaries have been suggested to have an important role in reducing the nitrogen load transported to the sea. We measured denitrification rates in six estuaries of the northern Baltic Sea. Four of them were river mouths in the Bothnian Bay (northern Gulf of Bothnia), and two were estuary bays, one in the Archipelago Sea (southern Gulf of Bothnia) and the other in the Gulf of Finland. Denitrification rates in the four river mouths varied between 330 and 905 mu mol N m(-2) d(-1). The estuary bays at the Archipelago Sea and the Gulf of Bothnia had denitrification rates from 90 mu mol N m(-2) d(-1) to 910 mu mol N m(-2) d(-1) and from 230 mu mol N m(-2) d(-1) to 320 mu mol N m(-2) d(-1), respectively. Denitrification removed 3.6-9.0% of the total nitrogen loading in the river mouths and in the estuary bay in the Gulf of Finland, where the residence times were short. In the estuary bay with a long residence time, in the Archipelago Sea, up to 4.5% of nitrate loading and 19% of nitrogen loading were removed before entering the sea. According to our results, the sediments of the fast-flowing rivers and them estuary areas with short residence times have a limited capacity to reduce the nitrogen load to the Baltic Sea. more...

The community structure of the bacteria associated with Nodularia spumigena (Mertens) cyanobacterial aggregates in the Baltic Sea was studied with temperature gradient gel electrophoresis (TGGE), using a 16S rRNA gene fragment as a target. Various developmental stages of the aggregates and free-floating cyanobacterial filaments were sampled to reveal possible changes in associated microbial community structure during development and senescence of the aggregates. The microbial community structures of all samples differed, and the communities of young and decaying aggregates were separated by cluster analysis of the TGGE fingerprint data. Sequencing of the TGGE fragments indicated the presence of bacteria from the alpha-, beta-, and gamma-proteobacterial groups, as well as members of Cytophaga-Flexibacter-Bacteroides lineages and gram-positive Actinobacteria spp. The majority of the Nodularia-associated sequences were not closely related to previously reported 16S rDNA sequences from the Baltic Sea or any other environment. The structure of the bacterial assemblage reflects the environmental changes associated with the succession and decay of the cyanobacterial aggregates. In addition, the sequence data suggest that the N. spumigena (Mertens) blooms in the Baltic Sea may host thus far uncharacterized bacterial species. more...

Suspended and Solid Surfaces as Microenvironments Formation of Aggregates and Consortia Ecological and Biogeochemical Roles of Aggregates and Consortia Cyanobacterial Aggregates in Lakes, Oceans, and in the Brackish Baltic Sea Nitrogen-Fixing Cyanobacterial (Trichodesmium spp.) Aggregates in the Subtropical and Tropical Ocean Cyanobacterial Mats in a Temperate Marine Ecosystem: Bird Shoal, North Carolina Stromatolitic Mats of Highborne Cay, Exuma Sound, Bahamas Microbial Mats in Hypersaline Lakes: Consortia “At the Edge of Life” Aggregates and Mats in the Permanent Ice Cover of Lake Bonney, Mcmurdo Dry Valleys, Antarctica Characterizing Aggregate and Mat Consortial Structure and Function Keywords: aggregates, microbial; consortia, microbial; mats, microbial; stromatolites more...

Fluid motion within and around sinking aggregates is an important factor in particle scavenging and solute exchange between sinking aggregates and the surrounding water and, hence, vertical fluxes and remineralization processes in the ocean. In the present study, we analyzed O-2 uptake rates in >2-mm porous diatom aggregates and in model aggregates impermeable to flow by measuring, on the same aggregates, the interface diffusive uptake rates with microsensors and the total (diffusive + advective) O-2 uptake rate by the Winkler method. The uptake rates were measured in a flow field similar to that experienced by sinking aggregates. The ratio of total O-2 uptake rate to diffusive uptake rate was 0.97 +/- 0.10 (n = 14) in model aggregates impermeable to flow. In contrast, total O-2 uptake was similar to or higher than diffusive uptake rate calculated from the O-2 gradients at the aggregate-water interface in 85% of all field-sampled and roller tank diatom aggregates examined. The highest ratio of total O-2 uptake rate relative to diffusive uptake rate measured in more...

Denitrification in sediments is of major importance to the Baltic Sea nitrogen (N) budget. However, little is known about denitrification in the water column in the Baltic. We tested whether denitrification could be active in pelagic cyanobacterial aggregates, commonly found in the Baltic Sea during warm summer months. In these aggregates, anoxic microniches may form. Such micro-zones suggest a possibility for anaerobic processes, such as denitrification by the heterotrophic bacteria associated with the cyanobacteria. Denitrification and nitrogen (N 2 ) fixation in a cyanobacterial bloom were measured on a 3 wk cruise in the Baltic Sea in order to determine whether the Baltic Sea cyanobacterial blooms act as sources or sinks of N. Experimental conditions analogous to formation of anoxic microniches within cyanobacterial aggregates did not activate the denitrification process, even when anoxic conditions prevailed for several hours. Only in 3 cases was denitrification, measured using the 15 N-isotope pairing method, detectable, giving rates of 0.8 to 1.8 nmol N 2 l -1 h -1 . Nitrogen fixation, determined using the acetylene reduction assay, varied from 0.03 to 1.85 μmol N 2 l -1 h -1 . According to this study, the blooms of N 2 -fixing cyanobacteria in the Baltic Sea must be seen solely as sources, not sinks for N in the marine pelagic environment. more...

The Baltic Sea is a large transition area between fresh and marine conditions with a drainage area that includes vast forested lands as well as some of the most densely populated regions in Europe. Substantial quantities of allochthonous material enter the Baltic via rivers and streams and the net outflow of water through the Danish straits is very large, being comparable to the Mississippi River (Bergstrom and Carlsson 1994). In view of such large terrestrial influences extensive monitoring programs exist whose goal is to gain predictive knowledge of ecosystem behavior and ecosystem response to perturbation. more...

Publisher Summary This chapter deals with the autotrophic and heterotrophic picoplankton in the Baltic Sea. The introduction of the concept of a size-structured plankton food web greatly stimulated studies of aquatic microbial ecology in earlier times. The Baltic Sea is a large brackish water basin with limited connection to the North Sea from the southwestern end. The bottom waters of the Baltic Sea are renewed only after exceptionally strong inflows of North Sea water from the Kattegat. In most parts of the Baltic Sea, a thermocline develops at depths between 15 and 20m in summer. Another key factor influencing the Baltic Sea picoplankton is the fact that the Baltic is a northern sea, with Arctic characteristics, especially in its northern parts. The winter conditions emphasize differences between the subareas and their biology. more...

We applied two methods to measure bacterioplankton production, the [3H]-thymidine (TTI) and the [3]-leucine (LEU) incorporation into cold trichloroacetic acid precipitate. Both methods gave similar results of the distribution of production in time and space (r 2 = 0.82, n = 66). Using empirically determined conversion factors the TTI gave production values from 21 to 125 mg Cm−2 day−1, which are within the range reported earlier from the Southern Ocean. Highest production rates were associated with the open water in the Confluence area (59°S –60°S) and with the Scotia Sea front. Low production rates were recorded from the ice covered areas in the Weddell Sea and in the open Scotia Sea waters. Good correlation on an areal basis was found between bacterioplankton production and other measures of heterotrophy, including ETS (r2 = 0.93, n = 9) and NH4(r2 = 0.50, n = 21). Good correlation was also found between bacterioplankton and phytoplankton production (r2 = 0.63, n=19). Bacterioplankton production seems to be driven by products from photosynthesis and heterotrophic processes, most likely grazing, which are tightly coupled to autotrophy. Quantitatively, bacterioplankton production was on an average 11% of net primary production, which is clearly a lower value than the 30% based on a review from temperate freshwater and marine ecosystems, but is comparable with values reported from the spring period in subarctic ecosystems. In comparison with the measurements of ETS, bacterioplankton contribution to community respiration was also lower than predicted from results from temperate ecosystems. We concluded from these results and the results obtained from microcosm experiments (Bjornsen and Kuparinen 1991b) that the flux of organic matter to eucaryote heterotrophs via bacterioplankton during spring and early summer periods in the Southern Ocean is of considerable, but not of equivalent importance as in temperate waters. more...

We have studied bottom-up and top-down control of the Southern Ocean microbial food web by microcosm experiments. Water from the Weddell Sea and Weddell Scotia Confluence were used for the experiments. Microcosms were manipulated by nutrients and light, and by size-selective screening. Incubation at the higher light level doubled phytoplankton growth rates from 0.12 to 0.24 day-1 in the Weddell experiment and from 0.15 to 0.30 day-1 in the Confluence experiment. Nutrient enrichment had no significant effect on growth rates in either of the experiments, indicating that phytoplankton growth was not nutrient-limited. In the microcosms where dinoflagellate growth rate was different, high dinoflagellate numbers were reflected as depressed nanoflagellate growth as well as depressed growth of phytoplankton, suggesting that dinoflagellates controlled both heterotrophic nanoflagellates and autotrophic nanoplankton. Only during short periods, when dinoflagellate numbers were low, could exponential growth of nanoflagellates be demonstrated. Bacterioplankton growth rates were, on average, 0.26 day-1 in the Weddell experiment and 0.22 day-1 in the Confluence experiment. Bacteria were controlled by heterotrophic nanoflagellates. Potential growth rates up to 0.75 day-1 were measured from batch cultures without predators. With the microcosm experiments, we could demonstrate a strong top-down control by dinoflagellates on phytoplankton and on heterotrophic nanoflagellates, and a control by heterotrophic nanoflagellates on bacteria. We could also demonstrate weak nutrient limitation on autotrophs and substrate limitation on heterotrophic bacteria. In the two study areas, biomass production and carbon flow were mediated mainly by organisms that passed through a 20 μm net and had growth rates in the order of 0.20 to 0.30 day-1. more...

Four commonly used techniques for preparation of 14C-labeled algal samples on membranes for liquid scintillation counting were compared and a simple technique for apparent net assimilation measurement from aqueous samples was introduced. All four techniques yielded similar radioactivities from the test cultures and are thus suitable for measurements of 14C algal samples. The possibly carcinogenic solvent dioxane was not necessary with PCS scintillation cocktail for dissolving radioactivity from algae on filters. more...

A simplified technique to trap respired carbon dioxide in a closed bottle system was developed from the technique introduced by Hobbie & Crawford in 1969. In this technique carbon dioxide was trapped in ethanolamine in a glass cup without the use of chromatographic paper. The results show that there is no need to enlarge the absorption surface with filter paper as practically complete recovery was achieved with ethanolamine alone in the cup. more...

The spring development of both phytoplankton and bacterioplankton was investigated between 18 April and 7 May 1983 in mesotrophic Lake Erken, Sweden. By using the lake as a batch culture, our aim was to estimate, via different methods, the production of phytoplankton and bacterioplankton in the lake and to compare these production estimates with the actual increase in phytoplankton and bacterioplankton biomass. The average water temperature was 3.5�C. Of the phytoplankton biomass, >90% was the diatom Stephanodiscus hantzchii var. pusillus , by the peak of the bloom. The 14 C and O 2 methods of estimating primary production gave equivalent results ( r = 0.999) with a photosynthetic quotient of 1.63. The theoretical photosynthetic quotient predicted from the C/NO 3 N assimilation ratio was 1.57. The total integrated incorporation of [ 14 C]bicarbonate into particulate material (>1 μm) was similar to the increase in phytoplankton carbon determined from cell counts. Bacterioplankton increased from 0.5 � 10 9 to 1.52 � 10 9 cells liter −1 (∼0.5 μg of C liter −1 day −1 ). Estimates of bacterioplankton production from rates of [ 3 H]thymidine incorporation were ca. 1.2 to 1.7 μg of C liter −1 day −1 . Bacterial respiration, measured by a high-precision Winkler technique, was estimated as 4.8 μg of C liter −1 day −1 , indicating a bacterial growth yield of 25%. The bulk of the bacterioplankton production was accounted for by algal extracellular products. Gross bacterioplankton production (production plus respiration) was 20% of gross primary production, per square meter of surface area. We found no indication that bacterioplankton production was underestimated by the [ 3 H]thymidine incorporation method. more...

The respiration percentage of 3 H-labeled glucose by heterotrophic microorganisms in water samples was determined by a method based on equimolar addition of [ 3 H]- and [ 14 C]glucose to samples. The respiration percentage of [ 3 H]glucose exceeded that of [ 14 C]glucose by 10% over the assayed range of respiration rates. Respiration percentages diminished with decreasing temperature, the relation between respiration of [ 3 H]- and [ 14 C]glucose remaining the same. The significance of tritiated water respiration with regard to experimental design is emphasized. more...

The influence of sulphite mill effluents on the heterotrophic activity of natural populations in the recipient water was studied during the summer of 1979. A single concentration method (3-H-glucose, 0.05 μg 1−1) was used to measure the heterotrophic activity. The influence of the effluent was studied by adding it in concentrations varying from 0.001 to 10% to water samples derived from different sections of the watercourse. Adaptation to rather high concentrations of the effluent was observed near to the point of discharge. Low concentrations of the effluent had a stimulatory effect on heterotrophic activity. Short turnover times (5–20 h) of glucose and inhibition of primary productivity demonstrated the influence of effluents on planktonic populations. more...

This paper compiles biological and chemical sea-ice data from three areas of the Baltic Sea: the Bothnian Bay (Hailuoto, Finland), the Bothnian Sea (Norrby, Sweden), and the Gulf of Finland (Tvärminne, Finland). The data consist mainly of field measurements and experiments conducted during the BIREME project from 2003 to 2006, supplemented with relevant published data. Our main focus was to analyze whether the biological activity in Baltic Sea sea-ice shows clear regional variability. Sea-ice in the Bothnian Bay has low chlorophyll a concentrations, and the bacterial turnover rates are low. However, we have sampled mainly land-fast level first-year sea-ice and apparently missed the most active biological system, which may reside in deformed ice (such as ice ridges). Our limited data set shows high concentrations of algae in keel blocks and keel block interstitial water under the consolidated layer of the pressure ridges in the northernmost part of the Baltic Sea. In land-fast level sea-ice in the Bothnian Sea and the Gulf of Finland, the lowermost layer appears to be the center of biological activity, though elevated biomasses can also be found occasionally in the top and interior parts of the ice. Ice algae are light limited during periods of snow cover, and phosphate is generally the limiting nutrient for ice bottom algae. Bacterial growth is evidently controlled by the production of labile dissolved organic matter by algae because low growth rates were recorded in the Bothnian Bay with high concentrations of allochthonous dissolved organic matter. Bacterial communities in the Bothnian Sea and the Gulf of Finland show high turnover rates, and activities comparable with those of open water communities during plankton blooms, which implies that sea-ice bacterial communities have high capacity to process matter during the winter period. more...