INVESTIGADORES
ISLA Federico Ignacio
artículos
Título:
Modern diatom assemblages in surface sediments from estuarine systems in the southeastern Buenos Aires Provincia, Argentina
Autor/es:
HASSAN, G; ESPINOSA, M. A; FEDERICO IGNACIO ISLA
Revista:
Journal of Paleolimnology
Editorial:
Springer
Referencias:
Lugar: Rotterdam; Año: 2006 vol. 35 p. 39 - 53
ISSN:
0921-2728
Resumen:
Paleoecological reconstructions of Holocene sea-level changes in Argentinean coastal regions were based
mainly on ecological data gathered from other regions, as there was a lack of information on modern
estuarine diatom distributions. The aim of the present work was to assess the spatial variation of diatom
assemblages in two representative estuaries of Argentina in order to gather ecological information for
paleoecological reconstructions in the region. The two selected estuaries have different geomorphologic
features and salinity regimes: Mar Chiquita Lagoon is shallow, which prevents the development of a stable
salinity gradient as it occurs in the Queque´n Grande River. Surface sediment samples were taken from
selected stations representative of the environmental gradient from the inlet to the inner reaches of both
estuaries. Cluster analysis defined three diatom zones at Mar Chiquita: marine/brackish assemblages
dominate the inlet (zone I), where salinity, tidal range and current speed are higher. The brackish/fresh-
water tychoplankton Staurosira construens var. venter and Staurosirella pinnata dominate the inner lagoon
(zone II), where environmental conditions are very variable and concentrations of suspended sediments are
higher. Brackish/freshwater euryhaline diatoms dominate the headwaters (zone III). On the other hand, the
Queque´n Grande River was divided into three diatom zones: coastal taxa are distributed at the inlet
(zone I), while the middle estuary (zone II) is dominated by brackish/freshwater euryhaline taxa. At the
upper estuary region (zone III), freshwater diatoms dominate, and the halophobous Nitzschia denticula
increased in abundance values. Diatom distributions were most closely related to the salinity gradient at
Queque´n Grande River than at Mar Chiquita Lagoon. Fossil data of a sequence from Mar Chiquita Lagoon
(Las Gallinas Creek) were compared to the modern data set in order to search for analogies between fossil
and modern diatom assemblages. DCA results showed that fossil diatom assemblages have modern coun-
terparts. Most diatom assemblages of Las Gallinas Creek fall within Mar Chiquita zone III, representing a
shallow brackish/freshwater environment, with low salinity fluctuations ( 1?9&) and no tidal influence.
Therefore, our modern diatom data provide useful analogs to interpret paleoenvironments in the region.