ABSTRACT Discovered in 1980 and unleashed an utter gold rush of the modern era, Serra Pelada was the largest open-air mine in Brazil. About 80,000 gold prospectors worked there until 1984, when the gold pits were flooded. The environmental impact caused by mining inflicted irreversible damage to the ecosystem, with the formation of a large lake and piles of waste rock and sterile overburden, still evident 28 years after the mine was closed. This study aimed to evaluate the available and pseudo total contents of potentially toxic elements (PTEs), the contamination and pollution levels, and to understand how the biological soil factors are related to the chemical properties of the soil and the available PTE contents in the Serra Pelada - Amazônia, Brazil. Soil was collected from seven areas around the lake: Area 1 - margin of the mine without waste and/or sterile deposits; Area 2 - margin with waste and/or sterile deposits; Area 3 - area with sterile deposit; Area 4 - mine tailings, denominated curimã by the prospectors, from which gold had been extracted; Area 5 - sediment dredged from the lake in the mine pit; Area 6 - area with agroforestry system; Area 7 - riparian forest, unaffected by the artisanal gold extraction process (control treatment). Apart from selenium (Se), all evaluated elements, in at least one of the studied areas, exceeded the contents of the investigation values (defined as the content of a given substance in soil or groundwater above which the human health is under potential direct or indirect risks, considering a standardized exposure scenario) in agricultural areas in Brazil, as determined by the National Council of the Environment. Soil enrichment and contamination with Co, Ba, Mn, and Hg were investigated. Principal component analysis showed that the available levels of PTEs influenced the soil biological properties, in particular basal respiration, indicating that important ecosystem processes are being affected by PTE contamination.

Estudos que visem à seleção de espécies, ou de grupos de espécies de plantas de cobertura do solo adaptadas as condições edafoclimáticas amazônicas parece ser uma estratégia viável para a melhoria da qualidade ambiental por propiciar o estabelecimento do SPD atenuando problemas relacionados ao monocultivo. O objetivo foi avaliar o comportamento de plantas de cobertura, no Nordeste paraense, quanto a persistência, tempo de meia vida, teor e acúmulo de macronutrientes e relação C/N na palhada, em Argissolo Vermelho Amarelo. O delineamento experimental foi em blocos ao acaso, com cinco tratamentos e cinco repetições. As plantas foram cultivadas a partir do mês de julho e cortadas aos 105 dias de cultivo e então foi feita a avaliação da produção. Ao final dos 84 dias a percentagem de cobertura do solo correspondeu a 97, 85, 52, 50 e 15%, para a braquiária (Brachiaria brizantha) (syn. Urochloa), capim colônia (Panicum purpurascens), feijão de porco (Canavalia ensiformes), milheto (Pennisetum americanum) e crotalária (Crotalaria juncea,), respectivamente. A braquiária apresentou maior produção de matéria seca (9.696 kg ha-1), elevada relação C/N (38,4), alto tempo de meia vida (86,5 dias) e grande persistência no campo. O feijão de porco apresentou alta produção de matéria seca (8.950 kg ha-1), porém menor relação C/N (17,4) e tempo de meia vida (39 dias), quando comparada as gramíneas. Por estas características, a braquiária e o feijão de porco são espécies com potencial utilização como plantas de cobertura no SPD no estado do Pará.

Studies to select one or more species of coverage plants adapted to Amazonian soil and climate conditions of the Amazon are a promising strategy for the improvement of environmental quality, establishing no-till agricultural systems, and thereby reducing the impacts of monoculture farming. The aim of this study was to assess the persistence time, half-life time, macronutrient content and accumulation, and C:N ratio of straw coverage in a Ultisol in northeastern Pará. Experimental design was randomized blocks with five treatments and five replicates. Plants were harvested after 105 days, growth and biomass production was quantified. After 84 days, soil coverage was 97, 85, 52, 50, and 15% for signalgrass (Brachiaria brizantha) (syn. Urochloa), dense crowngrass (Panicum purpurascens), jack bean (Canavalia ensiformes), pearl millet (Pennisetum americanum) and sunn hemp (Crotalaria juncea,), respectively. Signalgrass yielded the greatest dry matter production (9,696 kg ha-1). It also had high C:N ratio (38.4), long half-life (86.5 days) and a high persistence in the field. Jack bean also showed high dry matter production (8,950 kg ha-1), but it had low C:N ratio (17.4) and lower half-life time (39 days) than the grasses. These attributes indicate that signalgrass and jack bean have a high potential for use as cover plants in no-till agricultural systems in the State of Pará.