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Title : Volume : Issue : Pagination : 6

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Title : Volume : Issue : Pagination : 29

Title : Volume : Issue : Pagination : 10

Title : Volume : Issue : Pagination : 41

Title : Volume : Issue : Pagination : 12

In deze studie werd de performantie van de huidige indexen voor macro-invertebraten (de Multimetrische Macro-Invertebraat Index Vlaanderen – MMIF) en fytobenthos (Procentuele Abundantie van Impact Sensitieve en Impact Geassiocieerde Diatomeeën – PISIAD) geëvalueerd voor het Vlaamse watertype polderwaterlopen (P) met opsplitsing in zoete (Pz) en brakke (Pb) polderwaterlopen. Eveneens werd de fysicochemie van zoete en brakke polderwaterlopen met elkaar vergeleken. Op basis van chlorideconcentraties werd vastgesteld dat enkele waterlichamen die aangeduid staan als type Pb zouden moeten behoren tot het type Pz. Hiervoor werd een voorstel tot wijziging geformuleerd. De PISIAD-index bleek onvoldoende te presteren voor beide types. Voor een zinnige verandering in klasseindeling (de renspercentages van IA en IS taxa) werd namelijk geen bewijs gevonden Het werd duidelijk dat de MMIF voor de zoete(re) punten een associatie heeft met de waterkwaliteit. Voor brakke lopen vertoonde de MMIF geen zinvolle correlatie met de fysisch-chemische karakteristieken, maar eveneens werden er geen goede vervangindexen gevonden Er werd aangeraden om meer onderzoek te doen naar soortgemeenschappe in plaats van familie- en genus-gemeenschappen in brakke polderlopen. Vooral het effect van zoutfluctuatie dient hierin te worden meegenomen.

Several recent studies have revealed the impacts of the climate variability in the dynamic of zooplankton in different estuarine ecosystems, imposing a need for more and continued global studies. Presently, there is a growing appreciation in international collaborations to compare and contrast estuarine ecosystem response to climate variability across geographical gradients, including long-term changes in zooplankton. We performed a meta-analysis comprising field data from 7 location (Mondego estuary-Portugal, Seine estuary- France, Sheldt estuary- Belgium, Kiel fjord - Germany, Gulf of Riga- Latvia, Gulf of Bothnia – Sweden and Finland Archipelagos). The use of climatic modes (e.g. NAO, ENSO) has proven useful in investigating links between climatic variations and ecological patterns. Therefore, the main focus will be to test the influence of the NAO on abundance of organisms, key species, local environment and whether these relationships are generally positive, whether they are sensitive to methodological differences among studies, between taxonomic group and key species. The knowledge gained will contribute to quantitatively evaluate the multi-scale structure of climate and marine environment and to identify a set of environmental indicators to assess the estuarine ecosystem state and risks for ecological shifts.

We report a 40 year record of eutrophication and hypoxia on an estuarine ecosystem and its recovery from hypereutrophication. After decades of high inorganic nutrient concentrations and recurring anoxia and hypoxia, we observe a paradoxical increase in chlorophyll-a concentrations with decreasing nutrient inputs. We hypothesise that algal growth was inhibited due to hypereutrophication, either by elevated ammonium concentrations, severe hypoxia or the production of harmful substances in such a reduced environment. We study the dynamics of a simple but realistic mathematical model, incorporating the assumption of algal growth inhibition. It shows a high algal biomass, net oxygen production equilibrium with low ammonia inputs, and a low algal biomass, net oxygen consumption equilibrium with high ammonia inputs. At intermediate ammonia inputs it displays two alternative stable states. Although not intentional, the numerical output of this model corresponds to observations, giving extra support for assumption of algal growth inhibition. Due to potential algal growth inhibition, the recovery of hypereutrophied systems towards a classical eutrophied state, will need reduction of waste loads below certain thresholds and will be accompanied by large fluctuations in oxygen concentrations. We conclude that also flow-through systems, heavily influenced by external forcings which partly mask internal system dynamics, can display multiple stable states.