Trophic evolution of Laguna Grande de San Pedro (VIII Region, Chile) during the last century, by means of the analysis of sedimentary records

This research reconstructs the trophic evolution of Laguna Grande de San Pe dro (VIII Region, Chile) during the last century, through both the stratigr aphic analyses of diatom remains and geochemical parameters preserved in a sediment core obtained in this lake, The results obtained show that the com munity of diatoms has changed its composition throughout time, showing four different periods, representing each one a distinctive trophic condition. On the other hand, the geochemical records increase their accumulation rate s to the profile surface layers, making evident an increase of the producti vity to the present time. In this context, it is possible to conclude that the productivity at Laguna Grande has experienced significant changes, evol ving from an oligo-mesotrophic system (earlier period) to an eutrophic one (recent period). The most drastic changes would have happened during the la st decades, as response to both the intense development of urbanization and forest activities in the basin of this lake.