Invertebrate drift densities in the Njoro and Kamweti Rivers in the Kenyan highlands that differ in the level of anthropogenic disturbances

Invertebrate drift is one of several fundamental ecological processes in streams. However, little is known about the dynamics of invertebrate drift in Kenyan streams. In this study, we assessed invertebrate drift in two rivers, i.e. Njoro and Kamweti, that differ in the level of anthropogenic disturbances, between February and March, 2016. The aim was to evaluate the effect of river sampling duration (5, 10, 15, 20 and 25 min) and sampling period (day or night) on invertebrate drift densities. The 5-minute sampling period resulted in significantly higher mean drift densities than the other time intervals in both rivers. The highest mean drift density (2.0 ± 0.9 individuals m−3) was recorded at the Njoro River during the day, whereas the lowest drift density (0.3 ± 0.2 individuals m−3) was recorded at the Kamweti River during the day. A strong nocturnal drift pattern was noted at the less disturbed river (Kamweti). The present results suggest that anthropogenic perturbations influence invertebrate drift densities, and sampling duration and sampling period are important factors to consider when sampling invertebrate drift.

无脊椎动物漂流（invertebrate drift）是溪流中若干核心生态过程之一。然而，目前学界对肯尼亚溪流中无脊椎动物漂流的动态变化规律尚缺乏充分认知。本研究于2016年2月至3月期间，选取人为干扰程度存在显著差异的两条河流——恩乔罗河（Njoro）与卡姆韦蒂河（Kamweti），对其无脊椎动物漂流情况开展调查。本研究旨在评估采样时长（5、10、15、20及25分钟）与采样时段（日间或夜间）对无脊椎动物漂流密度的影响。研究结果显示，两条河流中，5分钟采样时长下测得的平均漂流密度均显著高于其余采样时长。其中，日间在恩乔罗河测得的平均漂流密度最高，为2.0±0.9 个·m⁻³；而日间在卡姆韦蒂河测得的漂流密度最低，仅为0.3±0.2 个·m⁻³。在受干扰程度更低的卡姆韦蒂河，观测到显著的夜间漂流模式。本研究结果表明，人为扰动会对无脊椎动物漂流密度产生影响，且采样时长与采样时段均为开展无脊椎动物漂流采样时需重点考量的关键因素。