Spatiotemporal monitoring of small and Micro wetlands for urban ecological security assessment: A case study of Linyi City, China

Small and micro wetlands (SMWs) have critical ecological value. However, they are frequently neglected in urban ecological security assessments due to the challenges in large-scale mapping, leading to a potential overestimation of security levels. Utilizing long-term Landsat imagery (2001−2020), this study developed a robust method to extract SMWs in Linyi City, which is a typical semi-humid region in China. The minimum mapping unit was 0.09 ha. Our findings revealed that SMWs total area decreased by 36.58 ha (−0.80%) from 2001 to 2020, while patch number increased by 279 (+5.07%). Over the study period, SMWs area experienced an initial sharp decline from 2001 to 2006 (decreasing by 33.9%), followed by a gradual recovery and eventual stabilization after 2010. And the SMWs centroid migrated 13.25 km from urban centers to peripheral mountainous areas, reflecting intense urbanization pressure. The Geodetector model identified GDP (q = 0.118) and precipitation (q = 0.115) as the dominant drivers of SMWs changes. Crucially, by incorporating the landscape metrics of SMWs into the Pressure-State-Response assessment frame-work, we demonstrated that SMWs act as sensitive ecological indicators. In years with abundant precipitation (e.g. 2020), the inclusion of SMWs reduced Comprehensive Ecological Security Index by 12.1% (from 0.672 to 0.591), changing the city's status from “Relatively Safe” to “Warning”. The risk signal was obscured when only large and medium-sized wetlands were considered. This study reveals the mechanism of SMWs as sensitive ecological indicators, emphasizes the necessity of integrating SMWs data for accurate evaluation of urban ecological security, and provides a scientific basis for precise protection of SMWs and sustainable urban management.