Heavy metal transfer from Patagonia to the South atlantic Ocean

D. GAIERO; JEAN-LUC PROBST; PEDRO J. DEPETRIS; L. LELEYTER

Bahía Blanca

Workshop; South American Basin: LOICZ Global Change Assessment and Synthesis of River Catchment – Coastal Sea Interaction and Human Dimension; 1999

The occurrence and geochemical behaviour of Fe, Mn, Pb, Cu, Ni, Cr, Zn, and Co are studied in riverine detrital materials transported by Patagonian rivers. Their riverine inputs have been estimated and the nature of such inputs to the Atlantic Ocean is discussed in this contribution. Almost all of the studied metals are transported to the ocean via the suspended load. Gathered evidence indicates that Fe oxides and organic matter are important phases controlling their distribution in the detrital non-residual fraction. Most heavy metal concentrations found in bed sediments, in suspended matter, and in the dissolved load of Patagonian rivers were comparable to those reported for non-polluted rivers. There is indication, however, that human activity is altering metal riverine inputs to the ocean. In the northern basins - and indicating anthropogenic effects -, heavy metals distribution in the suspended load is very different to that found in bed sediments. The use of pesticides in the Negro River-valley seems to increase the riverine input of Cu, mostly bound to the suspended load. The Deseado and Chico rivers exhibit increased specific yield of metals as a consequence of extended erosion within their respective basins. The Santa Cruz is the least affected drainage basin by human activity and its metal exporting capacity should be taken as an example of a relatively unaffected large hydrological system. In opposition, coal mining modifies the transport pattern of heavy metals in the Gallegos River, inasmuch they are exported to the coastal zone mainly as dissolved load.