Modern diatom assemblages in surface sediments from estuarine systems in the southeastern Buenos Aires province, Argentina.

HASSAN, G. S., ESPINOSA, M. A. AND ISLA, F. I.

JOURNAL OF PALEOLIMNOLOGY

SPRINGER

Lugar: Belgica; Año: 2006 vol. 35 p. 39 - 53

0921-2728

Since there is no information about diatom distribution in estuaries of Argentina, palaeoecological reconstructions of Holocene sea-level changes were based on foreign ecological data. The aim of the present work is to asses diatom distribution in a coastal lagoon (Mar Chiquita) and a partially-mixed estuary (Quequén Grande) in Argentina, in order to recover information applicable to future paleoecological reconstructions in the region. At Mar Chiquita coastal lagoon, the shallow depth and particular dynamics of the lagoon prevents the development of a stable salinity gradient as occurs in the Quequén Grande river. Surfarce sediment samples were taken from ten selected stations representatives of the gradient from the inlet to the inner reaches of both estuaries. A total of 164 taxa were observed in both estuaries. Cluster analysis defined three diatom zones at Mar Chiquita: marine/brackish assemblages dominates the inlet (zone I), where salinity, tidal range and current speed are higher; the brackish/freshwater tychoplanktonic Staurosira construens var. venter dominates the transitional zone between the tidal inlet and the inner lagoon (zone II) and brakish/freshwater euryhaline diatoms dominates the inner lagoon (zone III) where environmental conditions are very variable and concentration of suspended sediments nutrients are higher than outer lagoon. On the other hand, Quequén Grande river was divided into four diatom zones: coastal taxa are distribured at the inlet (zone I) while middle estuary (zone II) is dominated by brackish/freshwater euryhaline species. At upper estuary (zones III and IV) freshwater diatoms dominate, and the halophobous Nitzschia amphibia and N. denticula apeared. Diatom distributions seems to be related with tolerances of marine and freshwater taxa at Quequén Grande and with the ability of taxa to tolerate salinity changes at  Mar Chiquita. Human disturbance, such as nutrient discharges at Quequén and the building of a bridge in Mar Chiquita, may be influencing diatom distribution and abundances.