A total of 86 fluvial sediment samples and 46 water samples were taken in the Nalon Basin. Twenty-five of the 86 sediment samples were taken at the head of the basin, in areas not anthropically affected, in order to define background values. Regarding the Esva Basin, 23 fluvial sediment samples (nine of them used to define background levels) and 12 water samples were taken. The location of the sediment and water samples is shown in the following images.
Sediment and water sampling in both basins is complete. The chemical analyses of the samples have been undertaken, as well as their grain size study.
The results obtained so far seem interesting. As an example:
• Small gold particles (up to 30 microns) have been found in some sediment samples from the Esva Basin.
• The sediments downstream of the mercury mines in the Caudal river basin present abnormally high arsenic contents, which undoubtedly justifies the poor ecological status of some sections of this basin.
• There are notable differences between both basins, as corresponds to their different geological substrate and degree of anthropic affection.