Lagged and cumulative effects of long-term reclamation on multitaxon biodiversity in large river deltas

Large river deltas are biodiversity hotspots, yet their structure and functioning are increasingly reshaped by coastal reclamation, and the lagged, cumulative and threshold responses of multiple taxa to these pressures remain poorly quantified. In this study, we develop an integrated spatiotemporal framework to quantify the delayed, cumulative and threshold effects of reclamation on biodiversity in the Yellow River Delta. Land-use trajectories and a reclamation-intensity index were reconstructed for 1982–2022 and linked to biodiversity indices of vegetation, waterbirds and benthic invertebrates. Natural wetlands were progressively converted into farmland, aquaculture ponds, salt pans and built-up land, with reclamation intensity strongly and positively associated with landscape fragmentation (R² = 0.80). Over the same period, vegetation diversity declined steadily, waterbird communities showed an initial decline followed by partial recovery, and benthic communities exhibited a nonlinear increase–decline–recovery trajectory. Distributed lag nonlinear models combined with vector autoregressive analysis revealed pronounced multi-year lagged responses of vegetation. Maximum responses of Simpson and Pielou indices at lags of 7 and 3 years, respectively. Waterbird richness had a rapid but short-lived response, and the signal of benthos dependence on habitats was weak. The cumulative-effect analysis further showed strong heterogeneity among taxa and wetland types, with vegetation experiencing positive cumulative effects in freshwater marshes but strong negative effects in coastal waters. Reclamation-intensity thresholds, together with distance thresholds to reclamation-project boundaries, jointly delineated a safe operating space for reclamation intensity and distance in large river deltas. These results provide a quantitative basis for defining ecological red lines, designing ecological buffer zones and informing wetland conservation and restoration strategies.