Recent aquatic ecosystem to environmental events revealed from 210-Pb sediments profiles

MULSOW, S.; PIOVANO, E.; CÓRDOBA, F.

MARINE POLLUTION BULLETIN

Año: 2009 p. 175 - 181

0025-326X

The 210Pb dating method was first introduced by Goldberg (1963), and since then has been applied in studies of lakes, estuaries and coastal marine sediments for the estimation of sedimentation rates. Hundreds of studies around the world have used 210Pb as a  geochronological tool. However few attention has been paid to the potential of this naturally occurring isotope as an environmental tracer in sediments. Here we report three instances in which 210Pb profiles measured on undisturbed sediment cores from lakes, rivers and fjords show us the potential  of 210Pb as a tracer of natural and anthropogenic processes. The methodology used is a suite of techniques combining biogeochemistry (micro-electrodes), paleomagnetism (susceptibility), sediment characteristics (LOI) and visualization (SPI and x-ray) applied to the interpretation of 210Pb profiles. We measured 210Pb profiles on sediments from the Cruces River (Chile) that recorded a clear shift in the water chemistry caused by a pulp mill effluent to the river. Here metal mobilization and remobilization of the tracer may be the cause of the observed profile. We also measured 210Pb profiles in sediment from two fjords of Southern Chile (Pillan and Reñihue), the sudden deposition change of fresh 210Pb with depth observed could very well be the result of bioturbation but it occurred in a seafloor area deprived of bioturbators. In this latter case, 210Pb recorded the onset of aquaculture activities (fish farming) that took place two decades ago. Finally, 210Pb profiles measured in two lakes in Argentina: Epecuen and Venado showed a particular shape with depth. These profiles apparently registered sudden depositional event with recent 210Pb material probably related to strong shifts in precipitation and drought cycles in that part of the world. These three examples show that 210Pb profiles provide valuable information not only on geochronology, but also about natural and anthropogenic short term processes, but these are not always reported and well understood.