Biological Productivity of Rio Doce Valley Lake System, Brazil

这项研究于1987年6月至7月进行，目的是阐明里约多切河谷湖泊在旱季的湖沼学特征。浮游植物氮源的大部分是氨。浮游植物优先利用氨和尿素。再生态氮营养盐对湖泊真光层浮游植物的氮源具有重要作用.从脂肪酸组成的角度研究了Dom Helvecio湖和Amarela湖沉积有机质的富集机理。在两个湖泊的表层沉积物中，陆源贡献约为90 mg C/g干沉积物，Dom Helvecio湖和Amarela湖的自生贡献分别约为50和110 mg C/g干沉积物。测定了半挺水植物蓝凤眼莲的生物量。出叶期平均为8.7 ~ 11.0天。叶片寿命的平均值估计为70 - 74天。蒸汽的寿命估计为2年零4个月。在Dom Helvecio湖对Chaoborids的昼夜出现模式进行了研究。其中一个Chaoborus显示出最高的捕获率，高达整体的96%，主要出现在新月之夜。物种的出现在日出前活跃。该树种在月周期下的生长同步性受到强烈的干扰.调查期间共获得鱼类11科16种260余尾。与1985年相比，除Amarela湖外，其他湖泊的鱼类物种多样性和相对丰度均有所下降。作者得出结论，Carioca湖鱼类群落的急剧变化是由1985年引进的Tucunare（Cichla ocellaris）的捕食效应造成的。

The study was carried out from June to July 1987 to clarify the limnological feature of the Rio Doce valley Lakes in dry season.1. The greater part of the nitrogen source for phytoplankton was ammonia. The phytoplankton preferentially utilized ammonia and urea. the regenerated forms of nitrogenous nutrients played significant role as nitrogen source for phytoplankton in the euphotic layer in lakes.2. The accumulation mechanism of large quantities of sedimentary organic matter in Lakes Dom Helvecio and Amarela were studied based on the fatty acids composition. In both the surface sediments, about 90 mg C/g dry sediment was derived from terrigenous sources, and the autochtonous contributions in Lakes Dom Helvecio and Amarela were about 50 and 110 mg C/g dry sediment respect-ively.3. The biomass production of a semi-emergent plant Eichhornia azurea Kunth was determined. The mean rate of leaf emergence was 8.7 to 11.0 days. The mean value of the life span of leaves was estimated as 70 to 74 days. The life span of the steam was estimated as 2 years and 4 months.4. Diurnal and diel emergence patterns of chaoborids were investigated in Lake Dom Helvecio. One of Chaoborus showed the highest catch up to 96 % of the overall, which emerged largely on the night of a new moon. Emergence of species occureed actively before sunrise. The synchronization of growth of this species under the luner cycle is stronglyh suggested.5. More than 260 fish belonging to 16 species (11 families) were obtained during the survey period. Comparing with results in 1985, both species diversity and relative abundance of fish were decreased in all the lakes except Lake Amarela. The authors concluded that the drastic change observed in the fish community of Lake Carioca was caused by the predation effect of the Tucunare (Cichla ocellaris) introduced in 1985.