Annual reconstruction of seasonal isolated lakes reveals historical contraction and restoration baselines in the Poyang Lake floodplain.

Seasonal isolated lakes (SILs) are shallow water bodies defined by their temporary hydrological disconnection from the main lake and river network, yet their long-term abundance, turnover, and spatial legacy remain poorly resolved. Using a fused daily 30 m Seamless Data Cube (2000-2022), we extracted surface water, identified isolated states, generated annual maximum extents, and tracked polygons as Global ID lineages in the Poyang Lake floodplain. Total SIL area ranged from 372.31 to 650.73 km2 and increased at 5.74 km2 yr-1, while SIL counts increased across minimum area thresholds of 0.5-2.0 km2. Count increases were concentrated in the smallest size classes, whereas lakes larger than 10 km2 were few but contributed disproportionately to total area. Tracking identified 807 Global IDs; 510 (63.20%) were detected in only one annual map, whereas 39 were detected in 16-23 of the 23 annual maps. Maximum annual area was positively correlated with interannual occurrence persistence (Spearman's ρ = 0.595, p < 0.001), and this relationship remained robust under alternative tracking rules and stricter minimum detection requirements within a year. Topology between adjacent years showed that the increase in the number of small objects reflected reappearance, split-derived transitions, and newly detected objects, rather than providing evidence for the formation of new depressions. In 2022, SILs covered 458.16 km2, representing 37.02% of the 1237.50 km2 unique historical spatial footprint and 62.98% spatial contraction. Long-lived lineages were used to identify priorities for field assessment and reference candidates. These results reconcile increasing annual SIL area with historical spatial contraction and provide an object-based framework for defining restoration baselines for floodplain conservation and adaptive management.