# From Feed to Fish--Nutrients' Fate in Aquaculture Systems
## 3 Results
### Nutrient Output in Fishponds
#### 3.4.3 Gas Efflux, Ammonia Volatilization and Denitrification  
Out of the twenty-three papers reviewed, eight focused on evaluating the nutrient release through gas efflux. Five studies have examined the nitrogen efflux, while only three assessed the carbon efflux. Other than respiration, carbon gaseous fluxes, such as CO\({}_{2}\) and CH\({}_{4}\), were often neglected in the past, as they were perceived to have minimal impact on the pond's carbon budget at the time [38]. Within the examined literature, nitrogen gas forms were quantified through denitrification and ammonia volatilization, while diffusive and ebullitive pathways were utilized to measure nitrogen (N\({}_{2}\)) and carbon compound emissions (Table 8). Despite the relevance of N\({}_{2}\)O for climate change, the quantification was not found in the assessed papers. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Reference** &
\begin{tabular}{c} **Pond** \\ **Hydrology** \\ \end{tabular} & **C (\%)** & **kg ha\({}^{-1}\) d\({}^{-1}\)** & **N (\%)** & **kg ha\({}^{-1}\) d\({}^{-1}\)** & **P (\%)** & **kg ha\({}^{-1}\) d\({}^{-1}\)** \\ \hline
[27] & Flushed & n.r. & n.r. & 5 & 0.4 & 0.4 & 0.01 \\
[28] & n.r. & n.r. & n.r. & 14 & 0.3 & n.r. & n.r. \\
[29] & n.r. & n.r. & n.r. & 8 & 0.1 & 33 & 0.3 \\
[30] & Not flushed & n.r. & n.r. & 0.2 & 3.2 & 0.3 & 1.1 \\
[31] & Flushed & 0.8 & 0.05 & 7.3 & 0.6 & 4.5 & 0.06 \\
[32] & Flushed & n.r. & n.r. & n.r. & n.r. & 13 & 0.01 \\
[36] & Flushed & n.r. & n.r. & 76 & 1.3 & 55 & 0.1 \\
[35] & Flushed & n.r. & n.r. & 13 & 1.3 & 9 & 0.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: _Cont._ \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Reference** & **Pathway** & **C (\%)** & **kg ha\({}^{-1}\) d\({}^{-1}\)** & **N (\%)** & **kg ha\({}^{-1}\) d\({}^{-1}\)** \\ \hline
[16] & Respiration & 26 & 62 & n.r. & n.r. \\
[21] & Diffusion + ebullition & n.r. & n.r. & 32 & 1.2 \\
[24] & Diffusion & n.r. & n.r. & 0.3 & 0.01 \\  & Ebullition & n.r. & n.r. & 52 & 2 \\  & Diffusion CO\({}_{2}\) & 1.4 & 0.4 & n.r. & n.r. \\
[25] & Diffusion CH\({}_{4}\) & 0 & 0.01 & n.r. & n.r. \\  & Ebullition CO\({}_{2}\) & 0.2 & 0.1 & n.r. & n.r. \\  & Ebullition CH\({}_{4}\) & 1.3 & 0.3 & n.r. & n.r. \\
[28] & NH\({}_{3}\) volatilization & n.r. & n.r. & 12.5 & 0.25 \\
[30] & Denitrification & n.r. & n.r. & 17 & 0.34 \\
[30] & NH\({}_{3}\) volatilization & n.r. & n.r. & 0.8 & 0.1 \\
[31] & NH\({}_{3}\) volatilization & n.r. & n.r. & 2.7 & 0.25 \\
[38] & Respiration & 40 & 20 & n.r. & n.r. \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Contribution of gas efflux to the outputs of carbon and nitrogen and its rates (kg ha\({}^{-1}\) d\({}^{-1}\)). Values shown in the table are the mean of the values reported in the assessed papers. n.r. : not reported. Ammonia volatilization and denitrification were assumed to be negligible, hence not quantified in manured ponds, and were associated with very low concentrations of nitrate, nitrite, and total ammonia in the pond water [29]. In polyculture, aerated carp ponds (_Channa arguss_ and _Hypothalmichthys nobilis_), ammonia volatilization contributed less than 1% of the outputs [30]. Also, low contribution (<3%) was also found in _Micropretus salmoides_ aerated ponds [31]. Ammonia volatilization contribution to the budget was higher (12.5%) in _Ictalurus punctatus_, and together with denitrification (17% of the outputs), the gas efflux was the second major nitrogen output in this study [28]. When considering both N\({}_{2}\) diffusion and ebullition in integrated ponds of _Orechromis niloticus_, they collectively accounted for 32% of the total outputs [21]. However, a clearer understanding of each contribution emerged when the efflux pathways were reported separately. It was evident that diffusion played a minor role compared to ebullition, which alone constituted 52% of the total outputs in _Colossoma macropomum ponds_[24].