An Integrated Framework Consisting of Spatiotemporal Evolution and Driving Force Analyses for Early Warning Management of Water Quality

Accurate water quality diagnosis is of great importance for lake ecosystem restoration and regional ecological security. Addressing the challenges of uncertainties in water quality evaluation results and their complex nonlinear responses to driving factors, an integrated framework consisting of spatiotemporal evolution and driving force analyses was developed for early warning management of water quality. It included: (1) a water quality diagnosis module that accurately clarified the evolution patterns of water quality by coupling fuzzy theory and the Canadian Council of Ministers of the Environment Water Quality Index; and (2) a driving force analysis module that revealed the driving mechanism and identified the key driving forces of water quality evolution through the generalized additive model. The integrated framework was applied to Baiyangdian Lake with the following results. (1) Spatially, the water quality in the eastern region was better than that in the western region. Temporally, water quality showed an initial downward trend followed by an upward trend with 2008 as the breakpoint, highlighting the lagged effect of ecological water replenishment policies on water quality improvement. (2) The impact of human activities (59.92%) on water quality was higher than that of climate change (40.08%), and water replenishment amount, evapotranspiration, wetland coverage pattern, water level, and hydrological connectivity were identified as the crucial driving forces. (3) Linear and nonlinear effects coexisted among different driving forces, and the thresholds were determined for wetland coverage pattern (69%), water level (7.0 -7.5 m) and hydrological connectivity (0.117). Considering the complexity of water environment system, the integrated framework can improve the early warning capacity of water quality to risks, and support targeted recommendation strategies for adaptive management of water quality.