HEAVY-METAL CONSERVATION IN LAKE-CADAGNO SEDIMENTS - HISTORICAL RECORDS OF ANTHROPOGENIC EMISSIONS IN A MEROMICTIC ALPINE LAKE

Currently, pollution by heavy metals is one of our most serious enviro nmental problems. Metals such as lead and cadmium enter the biosphere through biogenic and anthropogenic emissions and have been steadily ac cumulating in soils and sediments. We report on a remote mountain lake in the Swiss Alps where the unusual conditions present have led to th e accumulation of several heavy metals in the sediments. The sulfide r ich environment contains precipitates of cadmium, lead and zinc. The a noxic conditions and prevalence of sulfate reducing bacteria in the wa ter column have prevented the remobilisation of the metals leaving the m trapped in the sediments. This has resulted in the formation of surp risingly ''stable'' metal profiles which have been correlated to level s of human and industrial activity and provide the means of reconstruc ting a record of human impact and pollution over the past 50 to 100 ye ars. We suggest that such metals in sediment profiles can also be used as chronological markers in cases where cost or sampling difficulties Preclude the use of radiological Cs-137 and Pb-210 dating. Stable met al profiles are valuable sources of environmental data, they reveal pe rtinent information on the atmospheric transport of contaminants and a re relatively simple to analyse.