Urbanization driven landscape fragmentation and ecosystem service loss in Chalalaka Lake, Ethiopia

Urban lake ecosystems are vital freshwater resources but are increasingly threatened by unregulated human activities, particularly rapid and poorly planned urban expansion. However, previous studies in Ethiopia's data-scarce Rift Valley focused only on area-based land use and land cover (LULC) changes, neglecting spatial configuration and links between fragmentation and ecosystem service degradation. This study provides a comprehensive assessment of the ecological transformation of Chalalaka Lake, an urban-fringe crater lake in Ethiopia's data-scarce Rift Valley, by analyzing four decades (1984–2023) of LULC change and its impacts on landscape structure and ecosystem services. Geospatial and statistical techniques were applied to quantify LULC transitions, landscape fragmentation using FRAGSTATS metrics, and associated ecosystem service values (ESVs). This multi-dimensional framework conceptually links spatial patterns of urban growth to functional and economic degradation in the study area. Results show substantial losses, including 49.2% of water bodies, 39.2% of wetlands, and 74.9% of forests, alongside urban expansion from 6.0% to 34.8%. The lake’s water body declined from 206.4 ha to 104.9 ha, while wetlands decreased from 110.1 ha to 66.9 ha. Landscape fragmentation increased, reflected in declining patch indices and rising edge density. These structural changes led to significant reductions in ecological functions and associated ecosystem services. Total ecosystem service value declined from USD 5.5 million in 1984 to USD 3.1 million in 2023 (over 43% loss), mainly driven by degradation of regulating services, particularly water regulation (− 45.9%). The study highlights the urgent need for integrated spatial planning, ecosystem restoration, and protection of green–blue infrastructure.