IntroductionThe ecological environment of tidal flats often changes due to tidal erosion and sedimentation. The distribution of tidal flat surface sediment is a natural reflection of the changes in the external dynamic environment, the spatial and temporal distribution pattern is of great significance.MethodsIn this study, the output structure of traditional convolutional neural network is combined with BP neural network. Meanwhile, four phases of Sentinel-2 multispectral images were collected and combined with field data from the Doulonggang tidal flat in Jiangsu Province, China, to construct the sediment composition inversion model.ResultsThe inversion accuracy was higher than 80% compared with the measured results. According to the inversion result, from 2017 to 2022, the surface sediment particle size of the tidal flat in Jiangsu varied seasonally and was coarse in summer and fine in winter. Additionally, the sediment composition tended to coarsen, showing an interannual change trend of increasing sand content and decreasing clay and silt contents.DiscussionThe above change of the sedimentary environment of the tidal flat may be caused by the decrease of fine grained sediment deposition, the introduction of exotic vegetation, the global sea level rise and the influence of human activities.
As human activity increases, coastal ecosystems are becoming increasingly vulnerable to a range of challenges. Oyster reefs are coastal ecosystems that provide habitats for a diverse range of marine species while also purifying water and providing natural coastal defense. However, because of human activity, global oyster reef areas have drastically diminished and are in grave danger. Simultaneously, it is impossible to determine the negative impact of human engineering activity on oyster reefs, due to the lack of intuitive and quantitative study methodologies. To address this issue, we applied a hydrodynamic model to analyze the impact on oyster reefs. First, we considered that human engineering activity, that is, coastal engineering, mainly affects the development of Liyashan Oyster Reefs by influencing hydrodynamics, sediment concentration, and bed-level evolution. We then applied MIKE3 to establish and validate a 3D hydrodynamic model of the southern part of the Yellow Sea around oyster reefs. Results showed that regional variations in flow velocity and suspended sediment concentration occurred in oyster reef waters, but the magnitude of these variations was limited. However, seabed elevation increased substantially in the Center Protection Area, which had a negative impact on oyster reefs. In general, our study provided a paradigm for analyzing the degree of impact on oyster reefs, showed the advantages of hydrodynamic models in quantitatively analyzing impact factors, and had reliable results.
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