Abstract: Ephemeral wetlands are a distinctive category of small and micro wetlands characterized by intermittent hydrological dynamics. They are irreplaceable in biodiversity conservation and hydrological regulation, yet are frequently overlooked due to their small size and short hydroperiods. Here, we define ephemeral wetlands as small and micro wetland ecosystems formed in isolated depressions, which are characterized by recurrent wet-dry alternation. We synthesized current understanding of the types, ecological characteristics, dynamic change, and maintenance mechanisms of ephemeral wetlands. Ephemeral wetlands are defined by recurrent wet-dry alternation and can be classified, according to hydroperiod, into temporary, intermittent, seasonal, and near-permanent types. They provide preferred habitats and breeding sites for many key species, and their biological communities exhibit pronounced adaptation strategies, including the formation of dormant propagules, rapid life histories, and high dispersal capacity. Community structure exhibits predictable dynamics along the hydrological cycle, while food-web assembly is regulated by priority effects and the balance between predation and competition. The ecological integrity of ephemeral wetlands is maintained through four-dimensional coupling of hydrology characteristics, topography, substrate, and nutrient dynamics, with the hydrological cycle as the primary driver. However, global climate change, agricultural intensification, and other anthropogenic disturbances are threatening the persistence of widely distributed ephemeral wetlands. Future research and management should strengthen baseline inventories, promote multiscale dynamic monitoring, deepen mechanistic understanding of biodiversity maintenance, and develop adaptive management strategies to support the scientific conservation and sustainable management of ephemeral wetlands.

Key words: ephemeral wetland, hydrological characteristics, dynamic change, biological adaptation, maintenance mechanism, small and micro wetland