Wetland ecological index and assessment of spatial-temporal changes of wetland ecological integrity.

Long-term, quantitative, and dynamic monitoring of regional ecological integrity using remote sensing can provide powerful decision-making support for sustainable regional development. However, existing methods are unable to accurately evaluate the quality of the surface ecological integrity because they do not consider vegetation saturation and salinization of wetlands. In addition, the ecological fragility of wetlands is characterized by a high frequency of changes in ecological conditions over time, leading to a lack of directionality in the analysis of ecological changes over long time series. To accurately assess the surface ecological integrity, this study integrates environmental salinity (Baseline-based Soil Salinity Index, BSSI) and a new vegetation element (Improved Hyperspectral Image-based Vegetation Index, IHSVI), and proposes the wetland ecological index (WEI) for the ecological integrity assessment system. Combined with the annual ecological integrity assessment using the WEI, the Mann-Kendall test was used to obtain the nodes of long-term changes. The WEI-Mann Kendall (WEI-MK) framework indicates the direction of analysis and realizes clear long-term series change monitoring. In this study, we analyzed the spatial and temporal changes in ecological integrity in the Yellow River Delta from 1991 to 2020 based on the WEI-MK framework. The results showed that: 1) Compared with Remote Sensing-based Ecological Index (RSEI), the WEI improved the accuracy of wetland integrity evaluation to 89 %. The WEI also improved accuracy of assessments in other typical regions by approximately 10 %. 2) The selection of nodes based on the WEI-MK framework clarified the direction of environmental change analysis. The results show that although the quality of the terrestrial ecological environment has improved over the past 30 years in the Yellow River Delta, that of the marine ecological environment has gradually declined. In particular, the state of the marine ecological environment after 2016 should be of concern.