Development of the diatom-Phaeocystis spring bloom in the Dutch coastal zone of the North Sea:the silicon depletion versus the daily irradiance threshold hypothesis

The Dutch coastal zone of the North Sea is characterized by high nutrient inputs and low water column irradiance due to high concentrations of suspended matter. The vernal phytoplankton blooms are dominated by diatoms and the flagellate Phaeocystis (Haptophyta). Two hypotheses that predict the timing of the Phaeocystis bloom were tested with field data collected in 1992. The first one, stating that the Phaeocystis bloom starts when silicon has been depleted by a preceding diatom bloom, could not be bracketed with observations. The second hypothesis, predicting that Phaeocystis blooms under nitrogen-and phosphorus-replete conditions after a daily irradiance threshold has been passed could be supported by field observations. Furthermore, it is shown that the Dutch coastal zone is not continuously homogeneously mixed. It is argued that this is an important factor in the life cycle of Phaeocystis and in foam formation on nearby shores. Grazing by the ciliate Strombidium sulcatum and heterotrophic gymnodinoid flagellates accounted for 92% of Phaeocystis cell loss after the bloom

Observations of flagellates in colonies of Phaeocystis globosa (Prymnesiophyceae); a hypothesis for their position in the life cycle

Flagellates of Phaeocystis globosa were observed inside colonies in North Sea samples in 1992. Field data suggest that low phosphate concentrations (less than or equal to0.5 muM) and, as a consequence of sedimentation, a 20- to &gt;100-fold reduction of daily irradiance (to m), (ii) the haploid mesoflagellate (4.2 +/- 0.1 mum), (iii) the diploid macroflagellate (6-7 mum) which is Kornmann's (Kornmann, 1955) 'Makrozoospore', and (iv) the diploid non-flagellate colonial cell (6.1 +/- 0.2 mum). A life cycle for Phaeocystis is presented, and the life-cycle transitions still to be tested are identified.</p

Observations of flagellates in colonies of Phaeocystis globosa (Prymnesiophyceae); a hypothesis for their position in the life cycle

Flagellates of Phaeocystis globosa were observed inside colonies in North Sea samples in 1992. Field data suggest that low phosphate concentrations (less than or equal to0.5 muM) and, as a consequence of sedimentation, a 20- to >100-fold reduction of daily irradiance (to m), (ii) the haploid mesoflagellate (4.2 +/- 0.1 mum), (iii) the diploid macroflagellate (6-7 mum) which is Kornmann's (Kornmann, 1955) 'Makrozoospore', and (iv) the diploid non-flagellate colonial cell (6.1 +/- 0.2 mum). A life cycle for Phaeocystis is presented, and the life-cycle transitions still to be tested are identified

[Eutrophication and its policy, which way to go?]

Abstract niet beschikbaarIn the report papers and discussions are presented of a workshop on eutrophication and future policy (North Sea, lakes and small waterbodies). New target values for total-phosphorus in lakes were proposed 50 mug 1-1 total-P at 40 mug 1-1 chlorophyll. A project to control regional measures was also proposed. Concerning the North Sea the workshop did not agree to a common point of view. Setting target values for small waterbodies (ditches, brooks etc.) was found to be the responsibility of regional authorities, since the variety of regional waterbodies is larger. Some advices for future research are given by the workshop.RWS DGM/DW

Lipidomic profiling identifies signatures of metabolic risk

BACKGROUND:Metabolic syndrome (MetS), the clustering of metabolic risk factors, is associated with cardiovascular disease risk. We sought to determine if dysregulation of the lipidome may contribute to metabolic risk factors. METHODS:We measured 154 circulating lipid species in 658 participants from the Framingham Heart Study (FHS) using liquid chromatography-tandem mass spectrometry and tested for associations with obesity, dysglycemia, and dyslipidemia. Independent external validation was sought in three independent cohorts. Follow-up data from the FHS were used to test for lipid metabolites associated with longitudinal changes in metabolic risk factors. RESULTS:Thirty-nine lipids were associated with obesity and eight with dysglycemia in the FHS. Of 32 lipids that were available for replication for obesity and six for dyslipidemia, 28 (88%) replicated for obesity and five (83%) for dysglycemia. Four lipids were associated with longitudinal changes in body mass index and four were associated with changes in fasting blood glucose in the FHS. CONCLUSIONS:We identified and replicated several novel lipid biomarkers of key metabolic traits. The lipid moieties identified in this study are involved in biological pathways of metabolic risk and can be explored for prognostic and therapeutic utility

Nutrient Limitation on Phytoplankton Growth in the Upper Barataria Basin, Louisiana: Microcosm Bioassays

The Davis Pond Diversion (DPD) was constructed to divert Mississippi River (MR) water into the Barataria Basin to reduce the salinity in support of wetland restoration on the Louisiana coast. To assess the phytoplankton nutrient limitation in adjacent water systems and potential impacts of DPD, 12 seasonal nutrient-phytoplankton bioassay experiments were conducted from October 2003 to July 2004 using the natural phytoplankton assemblages from freshwater and brackish-water lakes, Cataouatche and Salvador, LA (USA), which receive Mississippi River water from the DPD, and from a nearby freshwater lake, Lac des Allemands, that does not. Dissolved inorganic nitrogen (N), phosphorus (P), and silicate (Si) were added with different combinations at Redfield ratios in 10-l microcosms. Nitrogen was found to be the sole or primary limiting nutrient in all 12 experiments. N and P colimitations were found in seven of 12 experiments, but N was always the stronger limiting factor. P limitation was never observed to be the sole limiting nutrient. The results showed that a low concentration of P and a relatively high concentration of N do not necessarily indicate only P limitation in these lakes. Lake Cataouatche and Lake Salvador were dominated by centric diatoms, and Anabaena spp. were detected at high levels, particularly in summer. Lac des Allemands was generally dominated by N-fixing Anabaena spp. and other cyanobacteria, and their biomass responded significantly to N addition but not to P addition, indicating that nitrogen fixation in Lac des Allemands may be inhibited by other factors such as iron. Our bioassay results demonstrate that whether a water body is N- or P-limited is the consequence of the nutrient status and not the salinity regime. The results suggest that the addition of nutrient-rich waters via diversions of Mississippi River water into these lakes might increase the frequency of algal blooms, including noxious and toxic freshwater cyanobacteria