Factors controlling phytoplankton ice-edge blooms in the marginal ice-zone of the northwestern Weddell Sea during sea ice retreat 1988:field observations and mathematical modelling

The factors controlling phytoplankton bloom development in the marginal ice zone of the northwestern Weddell Sea were investigated during the EPOS (Leg 2) expedition (1988). Measurements were made of physical and chemical processes and biological activities associated with the process of ice-melting and their controlling variables particularly light limitation mediated by vertical stability and ice-cover, trace metal deficiency and grazing pressure. The combined observations and process studies show that the initiation of the phytoplankton bloom, dominated by nanoplanktonic species, was determined by the physical processes operating in the marginal ice zone at the time of ice melting. The additional effects of grazing pressure by protozoa and deep mixing appeared responsible for a rather moderate phytoplankton biomass (4 mg Chl a m−3) with a relatively narrow geographical extent (100–150 km). The rôle of trace constituents, in particular iron, was minor. The importance of each factor during the seasonal development of the ice-edge phytoplankton bloom was studied through modelling of reasonable scenarios of meteorological and biological forcing, making use of a one-dimensional coupled physical-biological model. The analysis of simulations clearly shows that wind mixing events – their duration, strength and frequency – determines both the distance from the ice-edge of the sea ice associated phytoplankton bloom and the occurrence in the ice-free area of secondary phytoplankton blooms during the summer period. The magnitude and extent of the ice-edge bloom is determined by the combined action of meteorological conditions and grazing pressure. In the absence of grazers, a maximum ice-edge bloom of 7.5 mg Chl a m−3 is predicted under averaged wind conditions of 8 m s−1. Extreme constant wind scenarios (4-14 m s−1) combined with realistic grazing pressure predict maximum ice-edge phytoplankton concentrations varying from 11.5 to 2 mg Chl a m−3. Persistent violent wind conditions (≥ 14 m s−1) are shown to prevent blooms from developing even during the brightest period of the year

Dimethylsulfoniopropionate (DMSP) cell quota of key Southern North Sea spring diatoms and Phaeocystis globosa

Dimethylsulfide (DMS) in the ocean results of complex transformations of dimethylsulfoniopropionate (DMSP) produced by phytoplankton under different controls, including microbial transformation pathways. The phytoplankton composition is an important factor of variability due to the species dependence of the DMSP production and conversion to DMS. To better appraise the link between phytoplankton diversity and the DMS(P) cycling in the Southern North Sea we present measurements of the DMSP cell quota of key spring phytoplankton species (Skeletonema costatum, Thalassiosira rotula, Rhizosolenia delicatula, Asterionella glacialis, Nitzschia closterium, Chaetoceros debilis, Chaetoceros socialis and Phaeocystis globosa) isolated from the North Sea and maintained in non-limiting and axenic laboratory culture conditions. Results are discussed with regards to literature data and hypothesis currently used in DMS(P) biogeochemical models

DMSP cell quota and the conversion into DMS by key Southern North Sea spring diatoms (Skeletonema costatum and Chaetoceros socialis) and Phaeocystis globosa

DMSP cell quota and the conversion into DMS by key Southern North Sea spring diatoms (Skeletonema costatum and Chaetoceros socialis) and Phaeocystis globos

Nitrogen flows from European watersheds to coastal marine waters

Nitrogen flows from European watersheds to coastal marine waters Executive summary Nature of the problem • Most regional watersheds in Europe constitute managed human territories importing large amounts of new reactive nitrogen. • As a consequence, groundwater, surface freshwater and coastal seawater are undergoing severe nitrogen contamination and/or eutrophication problems. Approaches • A comprehensive evaluation of net anthropogenic inputs of reactive nitrogen (NANI) through atmospheric deposition, crop N fixation,fertiliser use and import of food and feed has been carried out for all European watersheds. A database on N, P and Si fluxes delivered at the basin outlets has been assembled. • A number of modelling approaches based on either statistical regression analysis or mechanistic description of the processes involved in nitrogen transfer and transformations have been developed for relating N inputs to watersheds to outputs into coastal marine ecosystems. Key findings/state of knowledge • Throughout Europe, NANI represents 3700 kgN/km2/yr (range, 0–8400 depending on the watershed), i.e. five times the background rate of natural N2 fixation. • A mean of approximately 78% of NANI does not reach the basin outlet, but instead is stored (in soils, sediments or ground water) or eliminated to the atmosphere as reactive N forms or as N2. • N delivery to the European marine coastal zone totals 810 kgN/km2/yr (range, 200–4000 depending on the watershed), about four times the natural background. In areas of limited availability of silica, these inputs cause harmful algal blooms. Major uncertainties/challenges • The exact dimension of anthropogenic N inputs to watersheds is still imperfectly known and requires pursuing monitoring programmes and data integration at the international level. • The exact nature of ‘retention’ processes, which potentially represent a major management lever for reducing N contamination of water resources, is still poorly understood. • Coastal marine eutrophication depends to a large degree on local morphological and hydrographic conditions as well as on estuarine processes, which are also imperfectly known. Recommendations • Better control and management of the nitrogen cascade at the watershed scale is required to reduce N contamination of ground- and surface water, as well as coastal eutrophication. • In spite of the potential of these management measures, there is no choice at the European scale but to reduce the primary inputs of reactive nitrogen to watersheds, through changes in agriculture, human diet and other N flows related to human activity

Marine Strategy Framework Directive - Task Group 5 Report Eutrophication

The Marine Strategy Framework Directive (2008/56/EC) (MSFD) requires that the European Commis-sion (by 15 July 2010) should lay down criteria and methodological standards to allow consistency in approach in evaluating the extent to which Good Environmental Status (GES) is being achieved. ICES and JRC were contracted to provide scientific support for the Commission in meeting this obligation. A total of 10 reports have been prepared relating to the descriptors of GES listed in Annex I of the Directive. Eight reports have been prepared by groups of independent experts coordinated by JRC and ICES in response to this contract. In addition, reports for two descriptors (Contaminants in fish and other seafood and Marine Litter) were written by expert groups coordinated by DG SANCO and IFREMER respectively. A Task Group was established for each of the qualitative Descriptors. Each Task Group consisted of selected experts providing experience related to the four marine regions (the Baltic Sea, the North-east Atlantic, the Mediterranean Sea and the Black Sea) and an appropriate scope of relevant scien-tific expertise. Observers from the Regional Seas Conventions were also invited to each Task Group to help ensure the inclusion of relevant work by those Conventions. This is the report of Task Group 5 Eutrophication.JRC.DDG.H.5-Rural, water and ecosystem resource

Phaeocystis blooms in the continental coastal areas of the Channel and the North Sea

Phaeocystis bloom, following a first diatom bloom, is observed each year in April-May in the French, Dutch and German coastal zones of the North Sea. Evidences are presented that both the duration and the maximum biomass reached by this bloom is increasing since the last 20 years in response to increasing nutrient discharges into the sea. Observations carried out during the "red" 1988 spring in the scope of a joint EEC study are presented. A model is currently being established with the purpose of allowing optimization of preventive actions against coastal eutrophication. the structure of the model is described.info:eu-repo/semantics/publishe

Etude écophysiologique du phytoplancton de la zone côtière belge

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

A statistical method to estimate the biochemical composition of phytoplankton in the Southern Bight of the North Sea

The knowledge of changes in the biochemical composition of phytoplankton and its degraded products is regarded as important for the understanding of an eco-system because it influences the heterotrophic activities of the seawater column and/or sediments. The linear regressions method of some specific metabolite (protein, carbohydrate, lipid) on chlorophyll a is considered as the better method to estimate the biochemical composition of natural phytoplankton in the coastal area of the Southern Bight of the North Sea. The validity of this statistical method depends on a correct assemblage of the results in time and space, and requires a good knowledge of the growth conditions of the phytoplankton cells. This essential condition is however difficult to realize for post-bloom periods where the growth conditions are more heterogeneous. The linear regressions lead on the one hand to the quantification of two components of the total particulate organic matter (phytoplankton and bacteria/detritus) and on the other hand to their biochemical characterization. The comparison of the biochemical composition of the two components shows that bacteria/detritus component has an effective nutritive value when phytoplankton is less abundant. The study of the influence of changes in the environmental conditions (light intensity and nitrogen availability), on the biochemical composition of the phytoplankton shows a similar protein content of about 50% when nitrogen is not limiting. On the other hand, a change in the light intensity does not change the biochemical composition of natural phytoplankton but increases the cellular chlorophyll content when nitrogen is sufficient to ensure a good phytoplanktonic growth.info:eu-repo/semantics/publishe

Gross excretion rates of natural marine phytoplankton and heterotrophic uptake of excreted products in the Southern North Sea, as determined by short-term kinetics

Phytoplankton extracellular production has been determined kinetically during the spring phytoplankton bloom in three marine biotopes representative of the Southern North Sea (Scheldt estuary, Belgian coast and English Channel), differing greatly in their biological activities. Short-term kinetics of phytoplankton extracellular compounds produced during 14C incubations have been shown to increase our present capability for estimating gross phytoplankton extracellular production, if compared with a single measure after 4 h incubation. Underestimates of up to 60%; were found when a fixed incubation of 4 h was used. This underestimate can be attributed either to heterotrophic uptake of excreted products or to the presence of a lag¬phase in 14C extra cellular compounds production, related to physiological properties of phytoplankton. The data indicate that the phytoplankton extracellular release percentage, expressed with respect to the total photo-assimilated carbon, ranges from 0 to 62% with lower values in the estuarine area. Seasonal variations show, in Belgian waters and in the English Channel, an increase in phytoplankton excretion percentage during the bloom from about 20 to 60%. Heterotrophic uptake of phytoplankton extracellular products has been calculated from the evolution curve of 14C phytoplankton excretion products by me ans of a simple mathematical model. Results indicate that heterotrophs can occasionally remove up to 39% of the total amount of excreted matter per hour indicating that phytoplankton excretion can sometimes produce substances with high turnover.info:eu-repo/semantics/publishe