Determinantes da diversidade beta : a importância relativa de processos ambientais e espaciais na estrutura de comunidades fitoplanctônicas de uma planície de inundação amazônica

OBJETIVO: A diversidade beta é definida como as mudanças na composição de espécies ao longo de um gradiente ambiental, e atualmente, ecólogos têm investigado a influência de fatores locais (i.e. ambiente) e regionais (i.e. dispersão) na estrutura de comunidades. Os objetivos desse trabalho foram avaliar a diversidade beta da comunidade fitoplanctônica da planície de inundação do Curuaí e determinar a importância relativa dos processos ambientais e espaciais em sua estrutura; MÉTODO: A comunidade fitoplanctônica foi amostrada em 16 lagos da planície de inundação do Curuaí (Bacia Amazônica) durante o período de águas altas em 2002 e 2003. Usou-se a análise de redundância parcial (pRDA) para avaliar o efeito do ambiente (seis variáveis) e espacial (filtros espaciais) na variabilidade da composição da comunidade fitoplanctônica; RESULTADO: Foram registradas 156 espécies em dois anos de estudos, 122 espécies em 2002 e 66 espécies em 2003. A beta diversidade (índice βSIM) foi 0.889 em 2002 e 0.789 em 2003. A análise de partição da variância revelou que a maior parte da variação da comunidade fitoplanctônica não foi significativamente explicada pelos únicos efeitos ambientais e espaciais. No entanto, as variáveis ambientais no presente estudo apresentaram maior coeficiente de determinação do que as variáveis espaciais; CONCLUSÃO: Outros fatores afetaram a ausência de resultados significativos nos presentes dados, como variáveis locais não mensuradas (i.e. interações biológicas, hidrologia e outros) e eventos estocásticos. Dessa forma, sugerimos que variáveis como interações biológicas e outras variáveis locais sejam consideradas nesse tipo de análise para aumentar o poder de explicação e elucidar a variação da diversidade biológica.AIM: Beta diversity is defined as the change in species composition along environmental gradients, and in the present study, we investigated the influence of local (i.e., environmental) and regional (i.e., dispersal) factors in community structure. The aims of this study were to evaluate the beta diversity of phytoplankton communities in the Curuaí floodplain and to determine the relative importance of environmental and spatial processes in shaping phytoplankton community structure; METHOD: The phytoplankton communities were sampled in 16 lakes of the Curuaí floodplain (Amazon Basin) during high-water periods in 2002 and 2003. We used partial redundancy analysis (pRDA) to evaluate the pure effect of environmental (six variables) and spatial (spatial filter) variability on phytoplankton community composition; RESULTS: There were 156 taxa recorded in the two study years, including 122 algae species in 2002 and 66 algae species in 2003. The beta diversity that we measured (βSIM index) was 0.889 in 2002 and 0.789 in 2003. The partitioning variation demonstrated that the majority of variation in phytoplankton community structure was not significantly explained by pure environmental and pure spatial components. However, environmental variables presented a larger coefficient of determination than the spatial variable; CONCLUSION: Other factors than those we measured in this study, such as local variables (i.e., biotic interactions, hydrology, etc.) and stochastic events, affected the absence of significant results in our data. Therefore, we suggest that additional variables, such as biological interactions and other local factors, should be considered in this type of analysis to increase its explanatory power for understanding the variation of diversity in these communities

Annexe 3. Le mercure dans les eaux de surface du bassin amazonien

L’entrée du mercure (Hg) dans la biosphère se fait : par voie naturelle dans des zones de fragilité de la croûte terrestre (siège de tremblements de terre et d’activités volcaniques), sous forme de vapeurs de Hg émises à partir du manteau terrestre, ainsi que par la solubilisation de certaines roches comme les schistes carbonatés formés dans des environnements anoxiques et riches en sulfures ; par voie anthropique en des lieux plus ponctuels de rejets de mercure provenant d’activités industri..

Contaminacion ambiental por mercurio de los rios Chairo y Huarinilla en el parque nacional y area natural de manejo integrado Cotapata

This work studies mercury contamination to gold-mining activities in the "Parque Nacional y Area Natural de Manejo Integrado Cotapata". The mining area takes place on the head of a subandina river basin, the Chairo and Huarinilla rivers, affluents of the Coroico river. Both run through the protected area and pass through the Chairo Village. The mercury concentratons were determined in suspended solids and fishes that were collected in the area of Cotapata National Park. The water samples were collected in 5 points of the study area and were processed carefully - ultraclean protocols were used (Ahlers et al, 1990). The mercury analysis results obtained in suspended solids in 2 points of the Chairo River head 4 and 15 micrograms/g. The obtained values in bottom sedminents are 11,5 micrograms/g in the river basin and 0,41 micrograms/g in the Chairo and Huarinilla rivers ; in the fishes in the Huarinilla river the average concentration is 0,142 micrograms/g. So here is a beginning of a contamination risk by mercury in the Chairo and Huarinilla rivers. (Résumé d'auteur

Analisis del mercurio por fluorescencia atomica en los principales rios de la cuenca amazonica boliviana

Un important problème d'environnement particulièrement à l'ordre du jour au Brésil et en Bolivie concerne la contamination du milieu aquatique par le mercure, utilisé pour extraire l'or par amalgamation. Cette étude présente un transect longitudinal, réalisé en juin 1995 et mai 1996, des concentrations en mercure dans les eaux de surface du bassin amazonien bolivien depuis les sous-bassins andins jusqu'aux points les plus aval des rivières Beni et au Mamore. La combinaison de techniques 'ultra-propres' de prélèvement et de stockage des échantillons avec la spectrophotométrie de fluorescence atomique permet de présenter, pour la première fois en Bolivie, des résultats fiables dans les phases dissoute et particulaire des eaux de surface. Les concentrations en mercure total varient de 2 ng/1 dans les eaux du Zongo, au pied du glacier, c'est-à-dire au point le plus amont du bassin, à 9.35 ng/l dans les eaux du Coroico à Teoponte avec une moyenne dans le bassin du Béni de 2,5 ng/l en mai 96 et de 6,0 ng/l en juin 95. On peut observer que si la teneur moyenne en mercure particulaire des eaux des sous-bassins andins du Béni, exploités pour leur or alluvial, est de 0,12 microg/g, en revanche, cette teneur atteint 0,29 microg/g à l'exutoire de ces sous-bassins, à Rurrenabaque. Ainsi, il apparaît que le mercure rejeté dans l'environnement au cours des activités minières liées à l'exploitation de l'or ne contaminent pas directement les rivières sur lesquelles sont implantées les mines mais en revanche, se fait sentir plus en aval dans le Béni, à plus de 150 km en aval, à Rurrenabaque, point d'intégration des sous-bassins andins étudiés. (Résumé d'auteur

Mercury distribution in waters and fishes of the upper Madeira rivers and mercury exposure in riparian Amazonian populations

In this paper, the results of mercury concentrations in two abiotic compartments (river and suspended particles) and two biotic compartments (fish and human hair) from the upper Madeira rivers of the Bolivian Amazon basin are presented. Because of the local hydrological regimes and a high deposition rate in the plain, due to the presence of a subsidence zone at the bottom of the Andean piedmont, in the dry season, the highest mercury concentrations and fluxes were not found in rivers where mining activities took place (2.25-6.99 ng l-1; and 1.07-8.67 mg Hg d-1 km-2), but at the outlet of the Andean basins exploited for their alluvial gold (7.22-8.22 ng l-1; and 9.47-9.52 mg Hg d-1 km-2). The total mercury concentrations measured in surface waters of the upper Beni basin varied during the dry season, from 2.24 to 2.57 ng l-1 in the glacial waters of the Zongo river, to 7.00 ng l-1 in the Madeira River at Porto Velho and 9.49-10.86 ng l-1 at its confluence with the Amazon. The results obtained from fish indicate, on one hand, that 86% of the piscivorous fishes collected in the Beni river were contaminated, and, on the other hand, their high mercury concentrations could exceed by almos four times the WHO (1976) safety limit. (Résumé d'auteur

Manaus'99 : hydrological and geochemical processes in large scale river

Total mercury concentration range measured in surface waters of the Bolivian Amazon basin vary from 2.24-2.57 ng 1-1 in glacial waters to 7.228.22 ng 1-1, in the Beni River at the end of the Andean piedmont. The highest mercury concentration were not found in the rivers where the mining activities take place but at the outlet of the Andean sub-basins exploited for their alluvial gold. The quite low concentrations of Hg in the sediments indicate a low sedimentary contamination due to the high particulate transport in the Andena tributaries. In piscivorous fishes, the mercury concentrations found vary in the Beni and Mamore rivers from 0.8-2.3 ug Hg g-1 and 0.4-2-1 ug Hg g-1 respectively, to 0.3-5.2 ug Hg g-1 in the Madeira River at its formatin. We found that 70% of the piscivorous fishes collected was highty contaminated. The major health impact caused by mercury affects people who are not working directly in gold cooperatives but who have a regular fish diet. (Résumé d'auteur

Vivre avec le risque sanitaire environnemental et les activités pétrolières en Amazonie équatorienne : une culture d’urgence

International audienceEn Amazonie équatorienne « faire face au risque » est la condition tacite d’un mode de développement presqu’entièrement tourné vers les activités pétrolières. Nous montrons que l’enjeu concret du « vivre avec » les risques liés aux activités pétrolières est de diminuer la vulnérabilité sociale, en combinant stratégiquement les contreparties offertes par les activités pétrolières (emplois et compensations financières ou matérielles). Nous montrons alors que « Vivre avec les risques de contamination » est un processus de régulation en constante évolution, où l’enjeu environnemental et le risque sanitaire ont peu de poids par rapport à la priorité économique. Dans ce processus interagissent une organisation socio-spatiale qui répartit inégalement les risques, une régulation « par le haut » des impacts sociaux, économiques et environnementaux des activités à risque et une « culture d’urgence » permettant de répondre aux enjeux majeurs du quotidien