## 5 Discussion  
### Lake Diffusion Effects of HF and EQ in China's Lake-Ring Urban Agglomerations  
As an essential component of regional ecosystems, lakes provide key ecological services and act as critical spatial supports for urban expansion. From 2000 to 2020, the overall HF in China's lake-ring urban agglomerations exhibited an evolution trend characterized by a significant increase and likeward diffusion. The mean HF value increased progressively from west to east, forming a distinct gradient structure among the urban agglomerations. Regarding spatial patterns, the HF distribution in each urban agglomeration consistently exhibited hydrophilic characteristics. DTU and PYU primarily showed point-like diffusion, with high HF values radiating outward from the lakeside urban core. CHU and HZU formed multi-level aggregation patterns. THU exhibited a ring-shaped high-value zone around the lake and continued to expand along transportation corridors and coastal directions, reflecting the strong dependence of urban construction intensity on lake spaces. This \"lake-centered\" urban expansion pattern not only enhanced land development efficiency but also intensified stress on lake ecosystems [41].  
Compared to the continuous increase of HF, EQ exhibited a more fluctuating spatiotemporal evolution pattern, reflecting the ecosystem's complex response to urban expansion disturbances. Overall, the mean EQ values showed a \"higher in the west, lower in the east\" pattern, with the change process exhibiting significant phase characteristics and regional differences. CHU and HZU displayed frequent EQ pattern changes. Urban expansion significantly compressed high-EQ areas, leading to a continuous outward spread of low-EQ zones along the waterfront. The most typical case is THU, where EQ exhibited low-value clustering characteristics. They are densely distributed around the lake areas of cities like Shanghai and Suzhou, rapidly expanding along transportation corridors. This indicates that high-intensity urbanization activities have posed systemic impacts on ecosystems.  
The spatiotemporal evolution patterns of HF and EQ reveal a typical \"lake diffusion effect,\" where urban expansion concentrates near lakes due to a strong dependence on lake ecological resources during urban development [42]. Without ecological red lines and land-use zoning constraints, this trend will significantly reduce the lake ecosystems' carrying capacity. This phenomenon has also been reflected in previous studies. For example, [PERSON] pointed out that urban growth tends to \"grow toward the lake [43].\". [PERSON] et al. also pointed out that the development of urban infrastructure has led to habitat degradation in the Dongting Lake region [44]. Without ecological red lines and land-use zoning constraints, this trend may reduce the lake ecosystems' carrying capacity. This study validated this trend on a scale of lake-ring urban agglomerations. Lake-ring urban agglomerations are both urban expansion frontiers and ecologically sensitive areas. The intersection of HF and EQ spatiotemporal patterns makes lake surroundings the most prominent zones of human-environment conflict [45]. As spatial carriers of human-environment system evolution, the lake-ring diffusion paths of HF and EQ profoundly affect the coordinated development level of urban agglomerations.