Effect of land use on mayfly assemblages structure in Neotropical headwater streams

The aim of this study was to test the effect of agricultural and forestry land use on the structure of mayfly assemblages in low-order streams. Twenty-nine headwater streams were investigated in the state of São Paulo. We analyzed 15 streams in pristine areas (mixed tropical rainforest, semideciduous forest and dense tropical rainforest), and 14 streams covered with sugarcane, eucalyptus and pasture. Mayfly richness obtained by rarefaction curves was higher in pristine areas (21 genera), especially in mixed and semideciduous forest when compared to land use (9 genera), where values were particularly low in sugarcane plantation (3 genera). The non-metric multidimensional scaling (NMDS) ordination showed clear difference in mayfly assemblages between land uses and pristine areas, supported by analysis of similarity (R=0.67, p=0.001). In partial redundancy analysis (pRDA), the environmental descriptors that best explained differences in assemblage structure were Riparian, Channel and Environmental Inventory (RCE) index score, percentage of fine sediment stream substrate, water pH and land elevation. Our results show that agricultural and forestry land use has a strong negative effect on the structure of mayfly assemblages. These results also support the use of mayflies as environmental indicators, as some genera were sensitive to changes in land use, while others responded to naturally occurring changes in the study area.

本研究旨在探究农林土地利用对低等级溪流（low-order streams）中蜉蝣群落（mayfly assemblages）结构的影响。研究于圣保罗州选取29条源头溪流（headwater streams）开展调查：其中15条溪流位于原生区域（涵盖混合热带雨林、半落叶林与茂密热带雨林），剩余14条溪流的土地利用类型为甘蔗种植园、桉树林与牧场。通过稀疏曲线（rarefaction curves）计算得到的蜉蝣类群丰富度在原生区域更高，共计21个属，其中混合林与半落叶林的丰富度尤为突出；相较而言，农林土地利用区域的蜉蝣丰富度仅为9个属，其中甘蔗种植园的丰富度最低，仅为3个属。非度量多维尺度排序（non-metric multidimensional scaling, NMDS）结果显示，不同土地利用类型区域与原生区域的蜉蝣群落结构存在显著差异，相似性分析（analysis of similarity）进一步验证了这一结论（R=0.67, p=0.001）。在偏冗余分析（partial redundancy analysis, pRDA）中，对群落结构差异解释度最高的环境因子包括河岸-河道-环境调查指数（Riparian, Channel and Environmental Inventory, RCE）得分、溪流基质细泥沙占比、水体pH值以及地面海拔。本研究结果表明，农林土地利用对蜉蝣群落结构具有显著的负向影响。同时，研究结果也证实了蜉蝣可作为环境指示生物：部分蜉蝣属对土地利用变化敏感，而另一些属则对研究区域内的自然环境变化产生响应。