Modern pollen source and spatial distribution from surface lake sediments in the southwestern Pampa grasslands, Argentina: Implications to interpret Holocene pollen records

Abstract

In the Pampa grasslands of Argentina nothing is known about the transport, deposition and spatial distribution of pollen in lakes. To analyze and understand how well lake surface sediment pollen assemblages reflect the contemporary vegetation in relation to pollen source area, bathymetry and grain size sediments 36 surface sediment samples from Chasicó Lake and 5 from its only tributary were analyzed. Lake pollen assemblages showed two major patterns above and below the range between 4 and 6 m depth. Below this range the percentage and concentration of main pollen taxa are relatively homogeneous, without overrepresented taxa and with well-preserved pollen. They reflect the extra-local and regional source areas from Pampa grasslands and xerophylous forest and indicate that pollen from cores taken below this range will be suitable for paleocological studies. Isopoll of the main taxa and grain size distribution maps allowed understand how pollen and sediment was transported, deposited and distributed in the lake. The spatial distributions of main pollen taxa differ considerably among them, generating various pollen assemblages at different sampling points. There is no significant correlation between total pollen concentration and both depth and grain size, suggesting that there are not a totally pollen and sediment focusing in the lake. The pollen distribution indicates that wind and surface runoff are the primary transport vectors to the lake. However, tributary also contributes with the waterborne pollen, particularly around the river mouth. Implications of these processes will be of particular interest for reliable interpretation of fossil pollen records in similar environments.