## 3 Results and Discussion
### Preprocessing of Gas Monitoring Data
#### 3.3.2 Change of Harmful Gas Concentration with Density of _Limnoperna fortunei_
When the number density of _Limnoperna fortunei_ was 0.5-1.5 \(\times\) 10\({}^{4}\) mussels/m\({}^{2}\), the release concentration of H\({}_{2}\)S was maintained at a low level throughout the whole process of spoilage, and the maximum concentration was not more than 0.3221 mg/m\({}^{3}\). When the density of _Limnoperna fortunei_ reached 2.5 \(\times\) 10\({}^{4}\) mussels/m\({}^{2}\), the release concentration of H\({}_{2}\)S increased exponentially, with the density increasing from 0.7552 to 5.0946 mg/m\({}^{3}\). In general, the median H\({}_{2}\)S concentration increased with the increase in _Limnoperna fortunei_ density, which may be related to the early release of H\({}_{2}\)S in f _Limnoperna fortunei_. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Density (\(\times\)10\({}^{4}\)** & & & **R\({}^{2}\)** & **Serial Number** \\
**Mussels/m\({}^{2}\))** & & & & \\ \hline
0.5 & \(C_{H_{2}S}=-17.33+7.17+24.37t^{-1}-1.65t^{2}-18.59t^{-2}+0.20t^{3}+7.07t^{-3}- 0.01t^{4}-1.06t^{-4}\) & 98.55\% & Equation (20) \\
1.0 & \(C_{H_{2}S}=-20.61+11.26t+21.05t^{-1}-3.31t^{2}-11.33t^{2}+0.49t^{3}+2.84t^{-3 }-0.03t^{4}-0.25t^{-4}\) & 98.20\% & Equation (21) \\
1.5 & \(C_{H_{2}S}=-105.84+37.75t+178.28t^{-1}-7.92t^{2}-172.44t^{-2}+0.90t^{3}+86.9 8t^{-3}-0.04t^{4}-17.62t^{-4}\) & 98.80\% & Equation (22) \\
2.0 & \(C_{H_{2}S}=-64.52+36.33t+69.70t^{-1}-11.80t^{2}-45.44t^{-2}+2.16t^{3}+16.37t^{ -3}-0.20t^{4}\) & 99.95\% & Equation (23) \\
2.5 & \(C_{H_{2}S}=-132.70+62.68t+1726.92t^{-1}-184.56t^{2}-1351.13t^{-2}+32.64t^{3}+ 577.83t^{-3}-\) & 99.46\% & Equation (24) \\
3.0 & \(C_{H_{2}S}=1816.59-679.02t-3098.72t^{-1}+161.26t^{2}+3300.02t^{-2}-23.50t^{3}- 2169.67t^{-3}+1.92t^{4}+\) & 99.75\% & Equation (25) \\
779.70t^{-4}-0.07t^{5}-118.27t^{-5}\) & & & \\
35 & \(C_{H_{2}S}=-112.59+51.34t+158.60t^{-1}-13.59t^{2}-139.81t^{-2}+1.90t^{3}+68. 57t^{-3}-0.11t^{4}\) & 99.76\% & Equation (26) \\  & \(-14.09t^{4}\) & & \\
4.0 & \(C_{H_{2}S}=-2425.00+1240.72t+2944.31t^{-1}-393.83t^{2}-2148.75t^{-2}+75.23t^{3}+ 860.06t^{-3}-\) & 99.86\% & Equation (27) \\
4.5 & \(C_{H_{2}S}=99.40-47.25t-109.47t^{-1}+12.81t^{2}+59.08t^{-2}-1.82t^{3}-12.44t^{- 3}+0.11t^{4}\) & 99.86\% & Equation (28) \\
5.0 & \(C_{H_{2}S}=-26.37+21.86t+16.28t^{-1}-7.87t^{2}-4.86t^{-2}+1.34t^{3}+0.51t^{-3}- 0.09t^{4}\) & 99.84\% & Equation (29) \\
5.5 & \(C_{H_{2}S}=-23.43+17.18t+15.44t^{-1}-4.94t^{2}-4.32t^{-2}+0.64t^{3}+0.28t^{-3 }-0.03t^{4}\) & 99.66\% & Equation (30) \\
6.0 & \(C_{H_{2}S}=694.4t-34.29t-66.68t^{-1}+9.97t^{2}+29.54t^{-2}-1.52t^{3}-4.89t^{-3 }+0.09t^{4}\) & 99.973\% & Equation (31) \\
6.5 & \(C_{H_{2}S}=-1042.09+575.54t+1143.17t^{-1}-189.92t^{2}-736.72t^{-2}+36.67t^{3}+ 254.11t^{-3}-3.82t^{4}-\) & 99.89\% & Equation (32) \\
7.0 & \(C_{H_{2}S}=-8.73+15.54t-6.06t^{-1}-5.66t^{2}+6.79t^{-2}+0.87t^{3}-1.60t^{-3}-0. 05t^{4}\) & 99.95\% & Equation (33) \\ \hline \hline \end{tabular}  
In the table, \(C_{i}\) is the concentration of H\({}_{2}\)S, mg/m\({}^{3}\); \(t\) is the time out of water, d.  
\end{table} 
Table 5: H\({}_{2}\)S release concentration equation of _Limnoperna fortunei_ with different densities. Figure 11: The change of NH\({}_{3}\) concentration under different densities of _Limnoperna fortunei_.