## 4 Discussion  
### Correlations among Different Forms of Nitrogen in the Soil-Sediment  
1. Total nitrogen and organic nitrogen  
Total nitrogen in soil and sediment can generally be divided into inorganic nitrogen and organic nitrogen. In different regions, the content of each form of nitrogen and the proportions of the total nitrogen have great differences. Figure 4a shows that, overall, the soil-sediment organic nitrogen and total nitrogen contents in the lagoon of the Samet Inland Sea were significantly and positively correlated, and the correlation between the two was more similar in different soil-sediment samples. Tables 3-5 support this result, and organic nitrogen was the main component of total nitrogen in the soil and sediment. 2. Total nitrogen and inorganic nitrogen  
The relationship between total nitrogen and inorganic nitrogen is complex among the different soil-sediment samples. Table 6 shows that, overall, the contents of inorganic nitrogen and total nitrogen in the soil-sediment samples from the inland sea lagoon were positively correlated, but the correlation was not strong. This was probably because the inorganic nitrogen proportion of the total nitrogen was small, and the inorganic nitrogen content in aquatic sediments was lower than that in terrestrial soils. According to Figure 4c, the total nitrogen in the sediment was positively correlated with the ammonium content. Although the nitrogen and ammonium contents in the soil were also positively correlated, the correlation was not strong. The competition ability for ammonium ions in the sediment was weak, so it was challenging to desorb ammonium, and ammonium could be preserved in the sediment. Figure 4d shows that the total nitrogen in the soil was positively correlated with nitrate, and the total nitrogen in the sediment was also positively correlated with nitrate. Be-cause the grain size of the soil is coarser than that of sediment, the aeration was good, nitrification was easy to carry out and ammonium was easily oxidized to nitrate and nitrite. Figure 4e shows that the total nitrogen was positively correlated with the nitrite in the sediment, the total nitrogen was negatively correlated with the nitrite in the soil and the nitrite in the sediment was more abundant than that in the soil. This may be because the studied waters are mainly in a reducing environment, and in an anaerobic sedimentary environment, nitrate is easily reduced to nitrite. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & **pH** & \begin{tabular}{c} **Organic** \\ **Matter** \\ \end{tabular} & **CCE** & **Clay** & \begin{tabular}{c} **Total** \\ **Nitrogen** \\ \end{tabular} & \
\begin{tabular}{c} **Organic** \\ **Nitrogen** \\ \end{tabular} &
\begin{tabular}{c} **Inorganic** \\ **Nitrogen** \\ \end{tabular} & **Ammonium** & **Niltrate** & **Niltrate** \\ \hline pH & 1.00 & & & & & & & & & \\ organic matter & \(-\)0.42 & 1.00 & & & & & & & & \\ CEC & \(-\)0.37 & 0.693 ** & 1.00 & & & & & & & \\ clay & \(-\)0.28 & 0.06 & 0.28 & 1.00 & & & & & & \\ total nitrogen & \(-\)0.37 & 0.34 & 0.36 & 0.12 & 1.00 ** & 1.00 & & & & \\ organic nitrogen & \(-\)0.37 & 0.33 & 0.35 & 0.12 & 1.000 ** & 1.00 & & & & \\ inorganic nitrogen & \(-\)0.24 & 0.42 & 0.35 & 0.33 & \(-\)0.04 & \(-\)0.05 & 1.00 & & & \\ ammonium & \(-\)0.32 & 0.832 ** & 0.517 * & 0.01 & \(-\)0.14 & \(-\)0.15 & 0.47 & 1.00 & & \\ nitrate & \(-\)0.23 & 0.39 & 0.33 & 0.33 & \(-\)0.03 & \(-\)0.05 & 0.999 ** & 0.43 & 1.00 & \\ nitrite & \(-\)0.03 & 0.05 & 0.05 & 0.31 & \(-\)0.02 & \(-\)0.04 & 0.795 ** & 0.14 & 0.794 ** & 1.00 \\ \hline \hline \end{tabular}  
* At the 0.05 level (two-tailed), the correlation is significant. ** At the 0.01 level (two-tailed), the correlation is significant.  
\end{table} 
Table 3: Correlation analysis of the basic physical and chemical properties of inland soil and nitrogen forms (25 samples).