Roulet M, Lucotte M, Guimarães J R, Rheault I
Chaire de Recherche en Environnement H-Q/CRSNG/UQAM, Univ. du Québec à Montreal, Canada.
Sci Total Environ. 2000 Oct 16;261(1-3):43-59. doi: 10.1016/s0048-9697(00)00594-5.
Levels and accumulation of MeHg were characterized in filtered water, suspended organo-mineral matter, phytoplankton, zooplankton and epiphyton during the dry season and the wet season. In open water of the lentic and lotic ecosystems, the MeHg in filtered water (< 0.2 microm) was near or below the detection limit (< 0.02-0.03 ng/l). These concentrations represent < 5% of the Hgtot. content in filtered water. Inundated forests (Igapó) and macrophyte floating mats were the only sites where MeHg was significantly detected (0.07-0.24 ng/l), representing 3-22% of the Hgtot. in filtered water. MeHg concentrations in organo-mineral suspended matter (2-26 ng/g dry wt. representing 0.6-7.3% of Hgtot.) were correlated with the N content but not with the C content. Data suggest that MeHg enrichment of suspended matter is strongly influenced by the presence of degraded planktonic remains relatively rich in N and MeHg. In zooplankton, MeHg concentrations (20-140 ng/g dry wt.) increased from the dry season to the end of the wet season. This increase was followed by higher proportions of MeHg during the wet season in comparison to the dry season (15-40 to 50-70% of the Hgtot.). The epiphytic material collected from the roots of macrophyte floating mats contained 2-8.5 ng/g dry wt. of MeHg. The proportion of MeHg to Hgtot. in epiphyton (1.5-8.3%) correlated with its C and N contents. The data suggest a greater bioavailability of MeHg in the Tapaj6s River ecosystems due to the seasonal increase in water level and the consequent inundation of the floodplain. Inundation favours the development of large macrophyte floating mats which increases the bioavailability of epiphyton to herbivorous/detritivorous fish. The root zone of floating macrophytes and the flooded organic horizon of the Igapó forest are the only sites along the Tapajós River where significant MeHg can be detected in the water column and sediment. This new study supports the hypothesis that MeHg production and transfer to the first link of the food chain in Amazonian river systems is closely related to organic matter biogeochemistry in the floodplain environment.
在旱季和雨季对过滤水、悬浮有机矿物质、浮游植物、浮游动物和附生植物中的甲基汞水平及积累情况进行了表征。在静水和流水生态系统的开阔水域中，过滤水（<0.2微米）中的甲基汞接近或低于检测限（<0.02 - 0.03纳克/升）。这些浓度占过滤水中总汞含量的<5%。被淹没的森林（伊加波）和大型植物漂浮垫是仅有的能显著检测到甲基汞的地点（0.07 - 0.24纳克/升），占过滤水中总汞的3 - 22%。有机矿物质悬浮物中的甲基汞浓度（2 - 26纳克/克干重，占总汞的0.6 - 7.3%）与氮含量相关，但与碳含量无关。数据表明，悬浮物中甲基汞的富集受到相对富含氮和甲基汞的降解浮游残骸的强烈影响。在浮游动物中，甲基汞浓度（20 - 140纳克/克干重）从旱季到雨季结束有所增加。与旱季相比，雨季甲基汞的比例更高（占总汞的15 - 40%至50 - 70%）。从大型植物漂浮垫根部收集的附生物质含有2 - 8.5纳克/克干重的甲基汞。附生植物中甲基汞与总汞的比例（1.5 - 8.3%）与其碳和氮含量相关。数据表明，由于水位季节性上升以及随之而来的泛滥平原淹没，塔帕若斯河生态系统中甲基汞的生物有效性更高。淹没有利于大型植物漂浮垫的生长，这增加了附生植物对草食性/碎屑食性鱼类的生物有效性。大型漂浮植物的根区和伊加波森林被淹没的有机层是塔帕若斯河沿岸仅有的能在水柱和沉积物中检测到大量甲基汞的地点。这项新研究支持这样一种假设，即亚马逊河系统中甲基汞的产生以及向食物链第一环节的转移与泛滥平原环境中的有机物质生物地球化学密切相关。
