J. Phys. IV France 107 (2003) 859
DOI: 10.1051/jp4:20030433

Total-Hg and ²¹⁰Pb measurements in canopy and lake sediments at the pic Matecho, a pristine site in the tropical rainforest of French Guiana (South America)

M.-A. Mélières¹, M. Pourchet¹, D. Cossa², P. Charles-Dominique³ and P. Gaucher<sup>4

1</sup>  Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS, Université J. Fourier, BP. 96, 38402 Saint-Martin-d'Hères, France
²  Département Polluants Chimiques, IFREMER, BP. 21105, 44311 Nantes cedex 3, France
³  Laboratoire d'Écologie Générale, MNHN, 4 rue du Petit Château, 91800 Brunoy, France
⁴  Mission pour la Création du Parc de la Guyane, BP. 275, 97326 Cayenne, France

Abstract
We present results obtained from a pristine site of French Guiana (South America), at the Pic Matecho, a region far from gold mining activity. This area contains a small permanent lake, a rare situation in French Guiana. Tree canopy, soils and Lake Matecho sediments were analysed in total Hg and ²¹⁰Pb. The annual deposit of litterfall is estimated at 40  g (Hg)/m ²/y. The top sediment content of 0.2  g (Hg)/g indicates a large contribution of the atmospheric deposit. In sediment, the decrease of total Hg with depth is neither due to local human influence, nor to increase of atmospheric background during this century. It is attributed to remineralization of organic matter in the upper part of the sediment: the majority of the total Hg deposited at the water/sediment interface is not permanently trapped in the sediment but remobilized in water. Interpretation of the historical sediment profile suggests a constant deposit rate over the last millennium.

© EDP Sciences 2003