Progress on urban wetland carbon sink accounting and natural solutions for carbon sequestration and sink enhancement

Urban wetlands, as critical ecosystems with remarkable carbon sequestration potential, demonstrate dual strategic significance in global climate governance and the transition to a zero-carbon economy. They serve not only as ‘natural reservoirs’ for carbon sequestration and storage but also as crucial carriers for implementing nature-based solutions, integrating urban green and blue infrastructure, and advancing the low-carbon transformation of socioeconomic systems. This paper reviews carbon sink measurement methods for urban wetlands, encompassing approaches based on empirical statistics, biomass surveys, carbon flux measurements, and carbon cycle modeling. The empirical statistical method, employing the IPCC (Intergovernmental Panel on Climate Change) National Greenhouse Gas Inventory methodology, is widely applied but limited by its susceptibility to estimation errors. The biomass survey method, utilizing plot inventories and remote sensing techniques, enables accurate quantification of vegetation and soil carbon pools; however, its upscaling often encounters challenges posed by urban green space fragmentation. While remote sensing techniques offer the advantage of transcending temporal and spatial constraints, their accuracy is vulnerable to urban heterogeneity. Carbon flux measurement methods, including the micrometeorological and chamber techniques, may face limitations such as demanding underlying surface requirements and susceptibility to environmental factors. Carbon cycle modeling estimates carbon sinks using various models, yet the localization of parameters and data quality require further optimization. Nature-based solutions for enhancing carbon sequestration and sink capacity in urban wetlands have evolved into a multi-dimensional technical framework, encompassing measures such as urban wetland conservation and restoration, optimizing the design of constructed wetlands to enhance their carbon sink capacity, and synergistic regulation of hydrology, vegetation, and substrate. Emphasizing carbon sink accounting methodologies and the corresponding NbS for urban wetlands can facilitate their transition from ‘ecological islands’ to ‘carbon neutrality hubs’.