## 3 Results
### Spatial Distribution of the Soil-Sediment pH  
The average pH value of the soil in the study area was 5.1, which is acidic, reflecting the leaching of base ions, such as K, Na, Ca and Mg, and the enrichment of acid ions, such as H and Al. The average pH of the sediment was 7.3, which is neutral and is largely from the acceptance of terrestrial salt ions, reflecting the sediment's enrichment process.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \multirow{2}{*}{**Index**} & **Clay** & **Silt** & **Sand** & **\textless{0.031 mm}** & **0.031\(-\)0.053 mm** & **0.053\(-\)0.25 mm** & **0.25\(-\)1 mm** & **1\(-\)2 mm** \\ \cline{3-10}  & & (\%) & (\%) & (\%) & (\%) & (\%) & (\%) & (\%) \\ \hline \multirow{4}{*}{Terrestrial soil} & max & 448.22 & 85.2 & 65.2 & 83.4 & 90.1 & 9.8 & 51.5 & 40.3 \\  & min & 5.27 & 16.6 & 12.8 & 14.8 & 19.7 & 4.4 & 5.2 & 0.0 \\  & average value & 56.26 & 48.5 & 39.0 & 51.5 & 54.1 & 7.4 & 23.3 & 14.1 \\  & standard deviation & 108.58 & 17.0 & 14.3 & 17.0 & 17.7 & 1.7 & 9.7 & 10.1 \\  & coefficient of variation & 1.93 & 0.4 & 0.4 & 0.3 & 0.3 & 0.2 & 0.4 & 0.7 \\ \hline \multirow{4}{*}{Lagoon sediment} & max & 467.50 & 73.6 & 64.2 & 96.7 & 83.1 & 19.4 & 59.8 & 79.4 \\  & min & 8.49 & 3.3 & 3.1 & 26.4 & 4.3 & 0.3 & 2.7 & 0.0 \\  & average value & 62.75 & 50.8 & 46.2 & 49.2 & 60.7 & 9.9 & 17.3 & 11.6 \\  & standard deviation & 118.89 & 20.0 & 18.1 & 20.0 & 23.3 & 5.3 & 14.1 & 20.9 \\  & coefficient of variation & 1.89 & 0.4 & 0.4 & 0.4 & 0.4 & 0.5 & 0.8 & 1.8 \\ \hline \multirow{4}{*}{Bar soil} & max & 448.22 & 56.6 & 51.8 & 81.4 & 66.5 & 9.8 & 30.3 & 40.3 \\  & min & 15.91 & 18.6 & 15.1 & 43.4 & 21.6 & 4.4 & 15.2 & 7.7 \\  & average value & 127.11 & 43.2 & 36.2 & 56.8 & 50.1 & 8.3 & 20.6 & 16.4 \\  & standard deviation & 214.12 & 17.1 & 15.4 & 17.1 & 19.8 & 2.6 & 6.9 & 15.9 \\  & coefficient of variation & 1.68 & 0.4 & 0.4 & 0.3 & 0.4 & 0.3 & 0.3 & 1.0 \\ \hline \multirow{4}{*}{Oceanic sediment} & max & 541.03 & 68.0 & 62.3 & 100.0 & 80.6 & 11.4 & 94.5 & 67.5 \\  & min & 12.31 & 0.0 & 0.0 & 32.0 & 0.0 & 0.4 & 6.9 & 1.1 \\  & average value & 244.43 & 15.7 & 14.2 & 84.3 & 18.3 & 3.2 & 43.2 & 29.8 \\  & standard deviation & 204.87 & 23.4 & 21.3 & 23.4 & 27.5 & 3.7 & 39.3 & 30.0 \\  & coefficient of variation & 0.84 & 1.5 & 1.5 & 0.3 & 1.5 & 1.2 & 0.9 & 1.0 \\ \hline \multirow{4}{*}{Region of interest} & max & 706.85 & 85.2 & 68.7 & 100.0 & 90.1 & 12.0 & 51.5 & 85.6 \\  & min & 5.27 & 0.0 & 0.0 & 14.8 & 0.0 & 0.5 & 3.2 & 0.0 \\ \cline{1-1}  & average value & 237.63 & 28.8 & 23.4 & 72.6 & 32.4 & 4.9 & 19.8 & 41.2 \\ \cline{1-1}  & standard deviation & 205.46 & 26.4 & 21.7 & 25.0 & 29.0 & 3.3 & 10.8 & 29.1 \\ \cline{1-1}  & coefficient of variation & 0.86 & 0.91 & 0.93 & 0.34 & 0.90 & 0.68 & 0.55 & 0.71 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Soil–sediment texture characteristics.  
From the distribution point of view, as shown in Figure 3c, the soil pH in the western land area was the lowest and slightly acidic, the pH value in the sea area east of the sand bar was the second highest and neutral and the pH value in the northeastern sea area was the highest. The values ranged from acidic to neutral and exhibited transitional characteristics. Overall, the pH difference in the study area reflected the enrichment and migration process of base ions.