Influence des facteurs écologiques et de l'utilisation des terres sur les niveaux de mercure des poissons amazoniens

[Departement_IRSTEA]RE [TR1_IRSTEA]GES / USAGESInternational audienceThe objective of this study was to identify the characteristics of aquatic environments that are associated to high ichthyofauna Hg levels. Our research aimed at determining the influence of variables related to fish ecology, types of aquatic environment, fishing activities realized by local riparian populations and watershed use on the ichthyofauna contamination levels. Six sites were sampled during two distinct periods of the hydrological cycle, that is, at the beginning of descending waters and at low waters. We focused on ten dominant fish species representing four trophic levels and that are frequently consumed by local populations. The studied sites, which included lotic and lentic habitats, are under exploitation year-round by local riparian communities. Independently of studied sites and phase of the hydrologic cycle, fish Hg contamination follows this trend: piscivores > omnivores > herbivores > detritivores. In all studied aquatic sites, Hg levels in predatory species were often higher than the 500 ng/g fresh weight threshold. Mean Hg levels in key species were significantly higher during descending waters and in lotic environments in comparison to low waters and lentic environments. Data arising from this study demonstrated that simple models based on watershed use and on easily obtained variables such as suspended particulate matter (SPM) load and SPM Hg, number of inhabitants, habitat types and hydrological cycle allow a very good prediction of fish Hg levels. Our cartographical data clearly showed that the site that was characterized by the most important aquatic vegetation cover (6% of the watershed) and by the lowest forest cover (62 % of the watershed) corresponded to the highest Hg concentrations in fish. On the contrary, the site which has a 94 % forest-covered and 1 % aquatic vegetation-covered watershed was associated to the lowest fish Hg contamination. These results suggest that land uses characterizing watersheds play a key role in the Hg contamination level of local ichthyofauna