为评估四湖流域生态修复后水质的时空变化特征及污染源,基于2022—2023年水环境调查数据,结合水质环境质量指数(WQI)、相关性分析及主成分分析,对丰水期、平水期及枯水期水质指标进行了监测和分析。结果表明: ①四湖流域水质表现出明显的时空变化规律,丰水期水温(WT)、氨氮( {\mathrm{NH}}_4^{+}-N)浓度、总磷(TP)浓度及高锰酸盐指数(COD_Mn)较平、枯水期明显升高,而溶解氧(DO)及总氮(TN)浓度的变化趋势则相反;平水期浊度(TUR)大于其他时期,化学需氧量(COD)和生化需氧量(BOD₅)的变化差异不显著。空间分布上,下游水体的TUR、COD_Mn、COD和BOD₅浓度明显高于中上游,中游水体的 {\mathrm{NH}}_4^{+}-N浓度高于上、下游,上游水体的TP和TN浓度较低,且干流水质普遍较支流差。②WQI范围为15.61~32.88,整体水质为“差”“非常差”水平,且WQI呈现平水期 > 枯水期 > 丰水期的趋势,空间上为上游 > 中游 > 下游、支流 > 干流的变化特征。③主成分分析表明,污染源主要来自生活污水、工业废水、养殖及农业灌溉排水等外源污染,以及水体沉积物和动植物残体腐烂等内源污染。综上所述,尽管四湖流域已实施生态修复工程,但水质改善仍面临挑战,研究结果为区域污染防治与生态环境保护提供了科学依据。

[Objective] The Four Lakes (Changhu Lake, Sanhu Lake, Bailu Lake, and Honghu Lake) Basin, located in the hinterland of the Jianghan Plain in the middle reaches of the Yangtze River, is an essential agricultural production area and an ecologically sensitive wetland area in Hubei Province. To reveal the spatiotemporal distribution characteristics of nutrients and their pollution sources in the water bodies of the Four Lakes Basin after ecological restoration, this study systematically analyzes the variation patterns of water quality and the main driving factors based on measured monitoring data, aiming to provide a scientific basis for watershed water environment management and ecological restoration effectiveness assessment. [Methods] Based on field survey data from wet, normal, and dry seasons during 2022-2023, a total of 12 sampling sites were set up in the Four Lakes Basin, covering the upstream, midstream, and downstream areas, as well as mainstream and tributaries. Nine water quality indicators were measured, including water temperature (WT), dissolved oxygen (DO), turbidity (TUR), permanganate index (COD_Mn), chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD₅), ammonium nitrogen ( {\mathrm{NH}}_4^{+}-N), total phosphorus (TP), and total nitrogen (TN). The water quality was comprehensively evaluated using the water quality index (WQI) method. Correlation analysis and principal component analysis (PCA) were combined to identify the main pollution factors and sources. The characteristics of water quality evolution were systematically revealed from temporal, spatial, and pollution source aspects through data statistics, significance tests, and graphical visualization performed using software such as Excel, SPSS, and CANOCO. [Results] Water quality indicators in the Four Lakes Basin exhibited significant differences both temporally and spatially. Temporally, WT, {\mathrm{NH}}_4^{+}-N, TP, and COD_Mn were the highest during the flood season, while DO and TN showed opposite trends. TUR peaked during the normal season. Spatially, the concentrations of TUR, COD_Mn, COD, and BOD₅ in the downstream water bodies were significantly higher than those in the midstream and upstream. The {\mathrm{NH}}_4^{+}-N concentration was the highest in the midstream, while the TP and TN concentrations were the lowest in the upstream. Overall, the concentrations of various nutrient indicators demonstrated a pattern of “mainstream > tributaries”. The WQI values ranged from 15.61 to 32.88, indicating that the overall water quality in the Four Lakes Basin was at a “poor” to “very poor” level. Its temporal variation followed the order: normal season > dry season > wet season, and its spatial variation was characterized by upstream > midstream > downstream, and tributaries > mainstream. Correlation analysis showed that WT, DO, COD, {\mathrm{NH}}_4^{+}-N, TP, and TN were the main factors affecting WQI, among which N H_4^{+}-N, TP, and TN were significantly negatively correlated with WQI (P<0.05). PCA results indicated that pollutants during wet season were dominated by nutrients, primarily originating from external inputs such as agricultural fertilization, livestock and poultry farming, and domestic sewage. Pollution during normal season was mainly organic matter, largely from domestic sewage and industrial wastewater discharge. Pollution during dry season was influenced by both external input and internal release, with sediment resuspension and decomposition of plant and animal residues being important internal pollution sources. Overall, although the water quality in the Four Lakes Basin improved slightly after the implementation of ecological restoration, significant seasonal and regional pollution characteristics remained. [Conclusion] In summary, the water quality in the Four Lakes Basin exhibits significant temporal differences across the flood, normal, and dry seasons, while spatially, the upstream areas are superior to the midstream and downstream areas, and the tributaries are superior to the mainstream.. Although ecological restoration projects have been effective, the overall water quality of the basin remains at a moderate to severe pollution level. Agricultural fertilization, livestock and poultry breeding wastewater, domestic sewage, and industrial discharge are the main exogenous pollution sources, while the release of water body sediments and the decomposition of organic residues are the main endogenous pollution pathways. The innovation of this study lies in systematically revealing the spatiotemporal distribution pattern and pollution causes of nutrients in the Four Lakes Basin under the background of ecological restoration for the first time. This study also constructs a multi-level analytical framework of “WQI comprehensive evaluation-correlation analysis-PCA”, which can effectively identify key pollution factors and dominant sources, thereby providing scientific support for assessing the performance of watershed ecological restoration and implementing targeted management in the basin. The findings indicate that agricultural non-point source pollution control and sediment remediation should be further strengthened, and an integrated management system combining exogenous reduction and endogenous treatment should be established to promote the sustained improvement of the water environment and long-term restoration of ecological functions in the Four Lakes Basin.