Large reservoirs are an increasingly common feature across tropical landscapes because of their importance for water supply, flood control and hydropower, but their ecological conditions are infrequently evaluated. Our objective was to assess the range of disturbances for two large tropical reservoirs and their influences on benthic macroinvertebrates. We tested three hypotheses: i) a wide variation in the level of environmental disturbance can be observed among sites in the reservoirs; ii) the two reservoirs would exhibit a different degree of disturbance level; and iii) the magnitude of disturbance would influence the structure and composition of benthic assemblages. For each reservoir, we assessed land use (macroscale), physical habitat structure (mesoscale), and water quality (microscale). We sampled 40 sites in the littoral zones of both Três Marias and São Simão Reservoirs (Minas Gerais, Brazil). At the macroscale, we measured cover percentages of land use categories in buffer areas at each site, where each buffer was a circular arc of 250 m. At the mesoscale, we assessed the presence of human disturbances in the riparian and drawdown zones at the local (site) scale. At the microscale, we assessed water quality at each macroinvertebrate sampling station using the Micro Disturbance Index (MDI). To evaluate anthropogenic disturbance of each site, we calculated an integrated disturbance index (IDI) from a buffer disturbance index (BDI) and a local disturbance index (LDI). For each site, we calculated richness and abundance of benthic macroinvertebrates, Chironomidae genera richness, abundance and percent Chironomidae individuals, abundance and percent EPT individuals, richness and percent EPT taxa, abundance and percent resistant individuals, and abundance and percent non-native individuals. We also evaluated the influence of disturbance on benthic macroinvertebrate assemblages at the entire-reservoir scale. The BDI, LDI and IDI had significantly greater average scores at São Simão than at Três Marias Reservoir. The significantly greater differences in IDI scores for São Simão Reservoir were reflected in 10 of the 13 Ekman-Birge dredge biotic metrics and in 5 of 13 of the kick-net biotic metrics. We also observed clear ranges of disturbances within both reservoirs at macro (BDI) and mesoscales (LDI) and in water quality, but an insignificant range in MDI results. However, we found no significant relationship between the benthic macroinvertebrate metrics and the BDI, LDI, and IDI among sites within a single reservoir. Hence, we believe that benthic macroinvertebrate distributions in those reservoirs were influenced by other factors or that reservoir macroinvertebrates (dominated by chironomids) were poor indicators of disturbance at the site scale.

中文翻译：

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两个大型热带水库三个空间尺度的扰动评估

由于大型水库对供水、防洪和水电的重要性，大型水库在热带景观中越来越常见，但很少对其生态条件进行评估。我们的目标是评估两个大型热带水库的干扰范围及其对底栖大型无脊椎动物的影响。我们检验了三个假设：i) 可以观察到水库中不同地点的环境干扰水平存在很大差异；ii) 两个水库将表现出不同程度的扰动水平；iii) 扰动的大小会影响底栖组合的结构和组成。对于每个水库，我们评估了土地利用（宏观尺度）、自然栖息地结构（中尺度）和水质（微观尺度）。我们在 Três Marias 和 São Simão 水库（巴西米纳斯吉拉斯州）的沿岸地区对 40 个地点进行了采样。在宏观尺度上，我们测量了每个站点缓冲区中土地利用类别的覆盖百分比，其中每个缓冲区是一个 250 m 的圆弧。在中尺度上，我们评估了当地（场地）尺度的河岸和水位下降区中人为干扰的存在。在微观尺度上，我们使用微扰指数 (MDI) 评估了每个大型无脊椎动物采样站的水质。为了评估每个站点的人为干扰，我们从缓冲干扰指数 (BDI) 和局部干扰指数 (LDI) 计算了综合干扰指数 (IDI)。对于每个地点，我们计算了底栖大型无脊椎动物的丰富度和丰度、摇蚊科属的丰富度、丰度和摇蚊科个体的百分比，EPT 个体的丰度和百分比，EPT 分类群的丰度和百分比，抗性个体的丰度和百分比，以及非本地个体的丰度和百分比。我们还评估了干扰对整个水库规模的底栖大型无脊椎动物组合的影响。São Simão 的 BDI、LDI 和 IDI 平均得分明显高于 Três Marias Reservoir。圣西芒水库 IDI 得分的显着差异反映在 13 项 Ekman-Birge 疏浚生物指标中的 10 项和 13 项踢网生物指标中的 5 项中。我们还在宏观 (BDI) 和中尺度 (LDI) 以及水质方面观察到两个水库中明显的扰动范围，但 MDI 结果的范围不显着。然而，我们发现底栖大型无脊椎动物指标与 BDI、LDI、和单个水库内站点之间的 IDI。因此，我们认为这些水库中的底栖大型无脊椎动物分布受到其他因素的影响，或者水库大型无脊椎动物（以摇蚊类为主）在现场尺度上是较差的干扰指标。