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

Abstracl. Wc prescnt results obtained l'rom a pristine sitc of Frcnch Guiana (South America), at the Pic Matecho, a region far l'rom goldmining activity. This arca contains a small permanent lake, a rare situation in French Guiana. Trec canopy, soils and Lake Matccho sediments were analyscd in total Hg and 2IC'Pb. Thc an nuaI dcposit of lillerfall is estimated at 40 ~lg (I-Ig)/m 2 /y. The top scdimcnt content of 0.2 ~lg (I-Ig)/g indicatcs a large contribution of the atrnospheric deposit. in sediment, the decrease of total Hg with depth is neither duc ta localllllman influence, nor to incrcase of atrnospheric background during this ccntury. Il is allributcd to remineralization of organic matter in the upper part of the sediment: the rnt\jority of the total Hg deposited at the water/sedirncnt intcrface is not permanently trappcd in thc scdiment but rcrnobilized in \Vater. Interpretation of the historical scdiment profile suggests a constant deposit rate over the lastrnillennium.