North Creek of Jiulong River is characterized by large falls and a high degree of cascade-driven hydropower development. In this paper, ecological health assessments for North Creek of Jiulong River were carried out by a field survey of seasonal phytoplankton community structure dynamics and constructing an index system, the planktonic index of biotic integrity, P-IBI, to compare ecosystem health across different seasons. North Creek were relatively healthy in the summer and fall, but exhibited the worst conditions in the winter. With the exception of fall samples, the assessments for more than 50% of the sites in the dam reservoir area were lower than “moderate.” Further, the ecological health of the mainstream was lower than that of the tributaries. The P-IBI index across different seasons was correlated with some basic water physicochemical parameters (chlorophyll a, COD and DO concentrations). Importantly, these assessment results were consistent with actual water quality monitoring results, indicating that it is feasible to use P-IBI to evaluate river health status. The assessment of seasonal changes in algal community health is helpful for developing management strategies for rivers with multiple dams.

九龙河北溪的特点是瀑布大，梯级驱动水电开发程度高。本文通过对季节性浮游植物群落结构动态的实地调查，并建立了生物系统完整性的浮游指标，建立了九龙江北溪生态健康评价指标体系。P-IBI，比较不同季节的生态系统健康状况。北溪在夏季和秋季相对健康，但在冬季则表现最差。除秋季样本外，对大坝水库区域超过50％的站点的评估低于“中等”。此外，主流的生态健康程度低于支流。不同季节的P-IBI指数与一些基本的水理化参数（叶绿素a，COD和DO浓度）。重要的是，这些评估结果与实际水质监测结果一致，表明使用P-IBI评估河流健康状况是可行的。评估藻类社区健康的季节性变化有助于制定多水坝河流的管理策略。