Changes in phytoplankton biomass in the western Scheldt estuary during the period 1978-2006
Kromkamp, J.C.; Van Engeland, T. (2009). Changes in phytoplankton biomass in the western Scheldt estuary during the period 1978-2006, in: ASLO Aquatic Sciences Meeting 2009: A Cruise Through Nice Waters, 25-30 January 2009, Nice, France. pp. 141
Changes in annual mean chla concentrations were studied the eutrophic and turbid macrotidal Western Scheldt estuary. Three stations were investigated: WS1 (30 PSU at the mouth of the estuary, station WS6 (17 PSU) and station WS11 (10 PSU). No significant long term changes in yearly averaged chlorophyll a (chla) concentrations were observed in WS1 and WS6, but in WS11 a large decrease. Spectral analyses revealed a possible periodicity of 7 years in mean chla which we could not relate to abiotic factors. Strong phenological responses in the timing of the spring/summer bloom were observed: the center of gravity or the day at which 50% of the cumulative chla was reached during the year advanced with 1-2 days per year. All stations showed an earlier initiation of the bloom, whereas the day at which the phytoplankton bloom terminated also moved forward in time, WS11 excepted. As a result the bloom length decreased in station WS1, remained the same in station WS6 and increased in WS11. This complicated pattern in bloom phenology demonstrates the complex nature of ecosystem functioning in estuaries.
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