Temporal and spatial variability in the sediments of a tidal flat, Queule River Estuary, south-central Chile

Abstract

Microtidal flood plain estuaries are well represented along the coast of south - central Chile (ca. 35 - 41°S). The Queule River estuary (39°23'S, 73°12'W) has a small tidal flat, which formed after the earthquake and tsunami of May 1960 and is made up of sandy and muddy areas. Previous studies carried out at the Queule estuary only represented the results of short term sampling, thus the objectives of this study are to assess the seasonal textural changes, in order to interpret possible simultaneous variations in both areas, and to relate the sedimentological variability to tide and river discharge variables. Both areas were sampled 27 times from November 1995 to December 1997. Standard laboratory procedures were applied to determine the texture of the samples. Metereological information was also obtained from a nearby station, as well as tide forecast from national tables. This information was used to examine the temporal variability of the sedimentological characteristics as well as their possible relationships to environmental variables, by means of one-way ANOVA, multiple regression and canonical analysis models. Two variables, mean sand size and the relative percentage of the organic fraction of the mud, showed no differences between the areas. Most of the sedimentological parameters, i.e., percentages of organic sand, organic and inorganic mud, and mean sand size, changed simultaneously in both areas, but the variation was greater on the muddy flat. There are significant relationships between the variability of some sedimentological parameters, rainfall and tide range, and the most obvious changes were related to the rainy season caused by the 1997 El Niño event.