An integrated land-sea framework for assessing coastal wetland ecological quality and the impact of Spartina alterniflora expansion: A case study from the eastern coast of China

Coastal wetlands are vital in mitigating climate change through sequestering carbon, maintaining biodiversity and regulating flood storage capacity. Therefore, the ecological environmental quality (EEQ) assessment of coastal wetlands holds significant scientific value. In recent decades, the rapid expansion of Spartina alterniflora (S. alterniflora) has constantly nibbled away at the living space of native vegetation, leading to the long-term far-reaching impacts on the EEQ of coastal wetlands. However, the high vegetation coverage of S. alterniflora can interfere with assessment based on traditional remote sensing ecological index (RSEI), which also tends to mask water bodies, limiting its applicability in water-dominated coastal wetland landscape. In this study, an integrated assessment framework that combines the biodiversity-enhanced RSEI (RSEI-BD) with the remote sensing-based water ecological index (RSWEI) were proposed to enabling a comprehensive evaluation of EEQ dynamics and ecological impacts under the influence of S. alterniflora expansion. The results showed that the median value of EEQ across four study periods was 0.42, 0.55, 0.53, and 0.62, with the overall ecological condition exhibiting a trend of recovery. The expansion of S. alterniflora exhibited dual impacts on EEQ: areas where its invasion led to degradation accounted for 12.94 % of the total degraded regions, while areas showing ecological improvement within invaded zones comprised 3.03 % of the total improved areas. This study provides a methodological approach for remote sensing-based coastal wetland EEQ assessment, and valuable insights on the effectiveness of ecological conservation and remediation practices, and sustainable management of coastal wetlands ecosystems.