Contrasting Water Quality Responses During Drought Development Versus Recovery in Poyang Lake

Drought leads to declining water levels and reduced water volume in lakes, significantly altering their water quality. Current research has primarily examined water quality during drought episodes or compared conditions before and after such events. However, the variations in water quality indicators and their relationships with hydrological factors across different drought stages, particularly during development and recovery periods, remain poorly understood. To address this gap, we investigated the stage-specific impacts of hydrological drought on lake water quality. Hydrological drought events were identified and segmented into development and recovery stages using the Standardized Water Level Index. Eight water quality indicators, including total nitrogen (TN) and total phosphorus (TP), were analyzed together with hydrological variables using Grey Relational Analysis (GRA). Poyang Lake, the largest freshwater lake in China, served as the case study. The results revealed significant spatio-temporal heterogeneity in both drought characteristics and water quality responses. Development periods were generally longer than recovery periods. Dissolved oxygen (DO) was consistently lower during drought development, whereas TP increased during recovery. GRA indicated that the main drivers of TN and TP shifted across drought stages. During the development period, TN and TP were more closely coupled, and permanganate index and turbidity exerted strong influences. In contrast, during the recovery period, TN was primarily associated with conductivity, while TP became mainly dominated by turbidity. This paper not only supplements the theoretical understanding of the interaction between hydrological drought and water quality, but also provides scientific support for water quality early warning, and the water resource management of large freshwater lakes under drought scenarios.