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Research Project
Dynamics of cyanobacteria and cyanotoxins in the Guadiana estuary (DYNCYANO)
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Bottom-up regulation of phytoplankton in the Guadiana estuary
Publication . Domingues, Rita B.; Galvão, Helena M.; Barbosa, Ana B.; Sommer, Ulrich
Phytoplankton are key players in the aquatic environment and they can be effectively
used to understand and predict the functioning and production of aquatic
ecosystems. Given that phytoplankton is affected by natural and human-induced
perturbations, such as eutrophication and global climate change, it is pressing to
understand which factors regulate phytoplankton communities. The main goal of
this work was, therefore, to understand how phytoplankton growth and production
in the turbid Guadiana estuary, particularly in the freshwater tidal zone, is regulated
by bottom-up factors, namely nutrients and light.
Enrichment bioassays were carried out to evaluate nutrient and light limitation of
phytoplankton growth. Nutrient limitation, specifically by nitrogen, was observed
during the productive period. Nitrogen, as nitrate, became limiting to phytoplankton
growth at concentrations lower than 20 WM. Although nitrate was the main nitrogen
source in the Guadiana estuary, an overall preference for ammonium was observed,
mainly by cyanobacteria and green algae. Diatoms were the most nutrient-limited
group, and they clearly preferred nitrate as their N-source. Regarding light
availability, phytoplankton was not acclimated to the low light conditions that
prevail in the Guadiana estuary and light limitation occurred throughout the year.
Diatoms were the most light-limited group, whilst cyanobacteria seemed to be more
acclimated to low light. Primary production was higher in the more turbid regions,
where light availability was the lowest, but nutrient concentrations, although
occasionally limiting, were the highest. Therefore, phytoplankton in such turbid
regions were the most efficient in using limiting resources. River flow was a major
regulator of nutrient and suspended matter inputs to the estuarine zone. Tidallyinduced
variability of phytoplankton and environmental drivers in the freshwater
tidal estuarine zone was low and resulted from seasonal and fortnightly variability in
river flow and tidal currents.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
3599-PPCDT
Funding Award Number
PTDC/AMB/64747/2006