Ecosystem services of lake-wetlands exhibit significant spatiotemporal heterogeneity and scale effects in a multi-lake megacity

Climate change and anthropogenic disturbances are altering global lake-wetlands (LWs) and their ecosystem services (ESs), posing a threat to sustainable development. Understanding the spatiotemporal heterogeneity and scale effects of LWESs has risen to be a critical concern in the sustainable management of wetlands. Although the LWESs of large lakes or at the macro-region are well documented, their complexity in urbanizing areas remains to be further addressed. Here we aim to reveal the spatiotemporal heterogeneity and scale effects of LWESs under the coinciding effects of wetland conservation and urbanization through a study in Wuhan, a multi-lake city of central China. The LWESs and their spatiotemporal variations from 1999 to 2019 were characterized by nine indicators based on time-series remote-sensing images and statistical data. A V-shaped trend was observed in the area of the LWs over time, which decreasing by 8.12% in 1999-2010 while recovering by 9.57% in 2010-2019. The LW loss in the main urban area (MA) was mainly encroached by construction lands, while the restoration of croplands to LWs in the rural area (RA) completely offsets the loss of LWs. We found that the change rates of most LWESs were more severely degraded along a rural-urban gradient, except for cultural services. Specifically, the water supply (-57.39%), flood regulation (-34.19%), climate regulation (-31.36%), and biodiversity conservation (-62.13%) services were the most severely damaged in LWs in the MA. However, the carbon sink services of LWs in the RA suffer the most severe degradation. Not only with spatiotemporal heterogeneity but LWESs also showed obvious scale effects. The larger the LWs, the higher the ES capacity tends to be. Smaller LWs were heavily encroached, with the worst ES capacities. These results highlight that LW conservation should no longer be homogeneous, but should combine indicators of scale effects and spatial heterogeneity. Due to land resource constraints, those close to urban center should improve regulating and supporting service capacities, while further away, improvements in area and LWESs can be pursued to balance the demand growth. Further, it is important to conserve existing and small LWs from over-encroachment.