Coastal wetlands facing climate change and anthropogenic activities: A remote sensing analysis and modelling application

Under high-intensity anthropogenic activities and accelerated climate change globally, estuarine and coastal wetland ecosystems (ECWEs) are facing the great challenge of surviving the destructive effects brought about by human activities and sea level rise (SLR). In this study, time-series Landsat images and object-oriented classifications were adopted to monitor the trends and status of ECWEs in the PNA (Pudong New Area) of Shanghai from 1989 to 2013. To study landward and seaward threats to the ECWEs, two types of models were employed to simulate the dynamics of the ECWEs at different time scales. A Markov Chain model and CLUE-S (Conversion of Land Use and its Effects at a Small regional extent) were used to assess the impact of anthropogenic activities on the ECWEs from the landward direction in 2025. Additionally, SLAMM (Sea Level Affecting Saltmarsh Model) was utilized to evaluate the influence of SLR on the ECWEs from the seaward direction in 2100. The results showed that (1) more than 15,000 ha of the ECWEs were lost or degraded from 1989 to 2013 and (2) most of the ECWEs were transformed into drained lands for agriculture, aquaculture, or industrial or residential use under the rapid expansion of the city. Moreover, 54% of the agricultural land was converted to built-up areas or other uses. (3) The loss of agricultural land and increase in built-up areas will continue in the short-term future (up to 2025), and the sprawl of the built-up areas will extend in every direction in the PNA. (4) As modelled by the process-based SLAMM, the landscape changes in the ECWEs will be slight due to SLR by the end of the century, rather than distinct erosion in tidal flats being caused by SLR. In summary, driven by different forces, the ECWEs will be altered greatly and threatened by the impact of human activities and SLR from landward and seaward directions. On a short-term time scale, human activities will play a more important role in the modification and evolution of the ECWEs through direct exploitation of and interference with the structure and biogeochemical processes of the ECWEs. However, on a long-term time scale, the accelerated SLR will cause the continuous narrowing of the ECWEs. Considering the blockade due to the construction of dikes along the shoreline, destructive effects will influence the ECWEs, despite the feedback among the dominant plant species, geomorphology and hydrology.