Tidal flushing of ammonium from intertidal sediments of Ria Formosa,Portugal |
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Authors: | Manuela Falcão Carlos Vale |
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Affiliation: | (1) Present address: Institute Português de Investigação Marítima/CIMSul, Av. 5 de Outubro, 8700 Olhão, Portugal;(2) Present address: Instituto Português de Investigação Marítima, Av. Brasilia, 1400 Lisboa, Portugal |
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Abstract: | Ammonium concentrations were determined in near-bottom water and intertidal surface sediments collected in February and July 1993 at five stations of Ria Formosa, a shallow meso-tidal coastal lagoon in southern Portugal. At each station, samples were taken a few minutes before tidal inundation, and subsequently 2, 10, 15 and 20 minutes thereafter. Ammonium concentration in near-bottom waters increased dramatically in the first 2 minutes followed by a decrease during the 18 minutes of flooding (maximum range 10.3-2.2 M). The highest levels in the flooding water were concomitant with a decrease of extractable ammonium recorded in the upper sediment layer (2 cm). Laboratory experiments indicated that ammonium is easily extracted from the sediment solids by physical perturbation, as one would expect when tidal water flushes over the intertidal area. This perturbation results in the export of ammonium from the sediment, by pulse mechanisms of short time intervals. On a daily scale this amount is two orders of magnitude higher than transport resulting from molecular diffusion. |
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Keywords: | Ammonium sediment-water interface tidal flushing Ria Formosa |
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