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  • Springer  (1)
  • Wiley  (1)
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  • 1
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    Ammonium, nitrate and phytoplankton interactions in a freshwater tidal estuarine zone: potential effects of cultural eutrophication (2011)
    Springer
    In:  Aquatic Sciences, 73 (3). pp. 331-343.
    Details
    Publication Date: 2019-09-23
    Description: Nitrate and ammonium are the most important nitrogen sources for phytoplankton growth. Differential utilization of inorganic nitrogenous compounds by phytoplankton has been observed and may have significant impacts on primary productivity at local scales. We used enrichment experiments with natural phytoplankton populations from the freshwater tidal zone of the Guadiana estuary, a coastal ecosystem increasingly subjected to anthropogenic influences, to study the effects of nitrate and ammonium on N-consumption and phytoplankton growth. In addition, we used combined additions of nitrate and ammonium to understand the inhibitory effect of ammonium over nitrate uptake. Ammonium concentrations in the freshwater tidal reaches of the Guadiana estuary throughout the sampling period were too low to exert an inhibitory effect on nitrate uptake or a toxic effect on phytoplankton growth. Nitrate was clearly the main nitrogen source for phytoplankton at the study site. Overall, nitrate seemed to become limiting at concentrations lower than 20 mu M and N-limitation was particularly significant during summer. A trend of decreasing nitrate uptake with increasing ammonium concentrations and uptake suggested an overall preference for ammonium. However, preference for ammonium was group-specific, and it was observed mainly in green algae and cyanobacteria. In fact, cyanobacteria relied only on ammonium as their N-source. On the contrary, diatoms preferred nitrate, and did not respond to ammonium additions. The increasing eutrophication in the Guadiana estuary and particularly increased inputs of nitrogen as ammonium due to urban waste effluents may result in a shift in phytoplankton community composition, towards a dominance of cyanobacteria and green algae.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00027-011-0180-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Tidal Variability of Phytoplankton and Environmental Drivers in the Freshwater Reaches of the Guadiana Estuary (SW Iberia) (2010)
    Wiley
    In:  International Review of Hydrobiology, 95 (4-5). pp. 352-369.
    Details
    Publication Date: 2017-05-31
    Description: The effects of different phases of semidiurnal and spring-neap tidal cycles on phytoplankton and environmental drivers were evaluated in a tidal, freshwater location of a mesotidal estuary (Guadiana estuary, SW Iberia). An Eulerian approach was used and sampling covered different seasons during 2008. Samples were collected during spring and neap tides, at high tide, mid-ebb, low tide and mid-flood. Several physical-chemical variables were measured, as well as phytoplankton abundance and biomass. Salinity was higher at high-tide and suspended particulate matter was higher during spring tides and flood, due to higher vertical mixing and resuspension of bottom sediments. Chlorophyll a concentration during winter and summer neap tides was higher than during spring tides, whilst the abundance of pennate diatoms was higher during winter and Spring spring tides than during neap tides, probably reflecting differences in river discharge. Overall, tidally-induced differences detected in the freshwater tidal reaches of the Guadiana estuary were not as considerable as those observed in the lower estuary. However, the occurrence of tidally-induced variability in some seasons reflects that thorough sampling programs to study estuarine tidal dynamics should be conducted throughout the year. Occasional sampling will not reflect the typical variability of these highly dynamic systems. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/iroh.201011230
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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