How Do the Yangtze Delta Intertidal Zones Respond to Sea-Level Rise?

A research team examined how the Yangtze River delta, one of the world’s largest estuaries, will change as sea level rises. They divided the intertidal area into three zones: a high flat (H), a low flat (L) and a mudflat. Using flood‑ratio data and tidal‑elevation models, they simulated the effect of a few millimetres of sea‑level rise each year. The results show that with more water covering the ground, above‑ground plant biomass drops, while plant diversity rises. At the same time, the soil loses carbon and nitrogen, and leaf area index (LAI) decreases. To track these shifts, scientists combined two satellite indices: the Enhanced Vegetation Index (EVI) and the Land Surface Water Index (LSWI). The ratio and difference between them (ELR and ELD) quickly highlighted where vegetation reacts to flooding. In practice, the higher zones display high ELR values, indicating strong tidal influence. These findings help predict how coastal habitats will move and support more effective conservation strategies in a rapidly changing climate.

The meta‑ecosystem concept describes the interaction between terrestrial and aquatic systems that share flows of energy, matter, and organisms. In the Yangtze delta, the tidal inundation gradient creates distinct micro‑habitats: the high flat (H) experiences fewer frequent floods, while the low flat (L) and mudflat are regularly submerged. The flood‑ratio model, based on tidal height data and digital elevation models, quantifies the percentage of time each point is underwater. This approach allows projection of sea‑level rise (SLR) scenarios over decades, even though annual variations are on the order of millimetres.\n\nSpectral indices EVI (Enhanced Vegetation Index) and LSWI (Land Surface Water Index) are derived from red, near‑infrared, and microwave bands of satellite sensors. EVI is sensitive to photosynthesis and vegetation density, whereas LSWI detects surface water and soil moisture. The combined ELR = EVI/LSWI highlights areas where vegetation is active but water is limited, typical of high‑elevation zones. Conversely, ELD = EVI‑LSWI emphasizes transitions between vegetation and water, useful for identifying flood fronts.\n\nResults show a significant reduction in above‑ground biomass (≈‑30 % in H, ≈‑45 % in L) and a loss of soil organic carbon (≈‑20 % in H, ≈‑35 % in L) with a 0.5 m SLR increase. Plant species diversity, measured by Shannon index, rises by 12 % in L, suggesting that wetter conditions favor opportunistic species. The decline in LAI (≈‑15 % in H, ≈‑25 % in L) indicates smaller or fewer leaves, likely a physiological response to water stress.\n\nThese dynamics have implications for coastal management: carbon and nitrogen loss reduces the delta’s capacity as a nutrient sink, while increased plant diversity may alter marine food webs. Using ELR and ELD as rapid indicators enables real‑time monitoring of meta‑ecosystem transformations, providing valuable data for mitigation plans and the designation of protected areas in the face of climate change.