As critical biological components of freshwater ecosystems, aquatic insects are highly sensitive to cumulative anthropogenic disturbances and can effectively reflect long-term variations in river ecological quality, serving as ideal bioindicators for aquatic ecological monitoring and assessment. However, most existing benthic biotic integrity indices integrate diverse macroinvertebrate groups, which dilute the unique indicative value of aquatic insect communities, and few targeted evaluation systems have been independently developed for highly disturbed plain river basins in northern China. In this study, a field investigation of aquatic insect communities was conducted across 32 sampling sites in the Haihe River Basin from April to September 2023, aiming to construct a novel Aquatic Insect-based Index of Biotic Integrity (Ai-IBI) and systematically evaluate the basin’s river ecosystem health status. A total of 10,267 aquatic insect individuals belonging to eight orders and 43 families were identified, with Chironomidae dominating the community and predominantly distributing in midstream and downstream reaches. Based on ecological principles, discriminant ability analysis, and redundancy analysis, four core metrics were ultimately screened out to establish the Ai-IBI system, including total taxa richness, percentage of the top three dominant taxa, density of tolerant groups, and percentage of predators. Considering the widespread background ecological degradation of the Haihe River Basin, a localized reference-site selection framework integrating water quality standards, physical habitat assessment, and field ecological surveys was adopted to determine eight minimally disturbed reference sites, which effectively improved the regional applicability of the evaluation model. The health assessment results indicated that only a small proportion of river reaches maintained a healthy state, while most sites were classified as sub-healthy or fair, presenting a distinct spatial differentiation pattern wherein upstream mountainous reaches exhibited superior ecological integrity compared with downstream plain reaches. The constructed Ai-IBI showed high consistency with conventional physicochemical indicators and habitat evaluation results, verifying its excellent reliability and robustness. Different from traditional empirical IBI models suitable for near-natural watersheds, the Ai-IBI fully adapts to the unique ecological background of long-term water resource overexploitation, urbanization-induced habitat fragmentation, and nutrient enrichment in the Haihe River Basin. The Ai-IBI developed in this study provides a refined biological evaluation tool for quantitative diagnosis of river ecological degradation, offers empirical support for differentiated ecological protection and precise restoration strategies in the Haihe River Basin, and serves as a feasible methodological reference for ecological health assessment in other human-dominated plain river basins globally.

Phytoplankton are the primary producers in freshwater lake ecosystems and play a fundamental role in maintaining the structure and function of lacustrine food webs. Baiyangdian Lake, located at the core of Xiong’an New Area, is vital for regional aquatic ecological security. However, systematic data on phytoplankton community dynamics throughout the phytoplankton critical growing season are scarce. In this study, we conducted a monthly investigation of phytoplankton communities in Baiyangdian Lake from April to October 2025, analyzing community composition, abundance, and diversity patterns. A total of 152 phytoplankton taxa across 8 major algal groups were identified, with Chlorophyta, Bacillariophyta, and Cyanobacteria being the dominant groups. Phytoplankton abundance exhibited distinct seasonal variation, peaking in August and reaching its lowest in October. The Shannon–Wiener diversity index (H′) and Pielou evenness index (J′) were generally at favorable levels, indicating a relatively stable community structure. The mean phytoplankton density across all sampling sites during the growing season was 8.70 × 10⁶ cells/L, categorizing the lake as having “no obvious bloom” according to standard bloom severity classifications. The overall trophic state of Baiyangdian Lake during the study period was mesotrophic. These findings provide fundamental baseline data and scientific support for the management of algal bloom risks and the long-term conservation of the lake’s aquatic ecosystem.