Increase of methane emission linked to net cage fish farms in a tropical reservoir

Abstract

This study aimed to evaluate the influence of Nile tilapia (Oreochromis niloticus) net cage farming on methane (CH4) emission in a Brazilian tropical reservoir through the quantification of spatial and seasonal variations of diffusive and ebullitive CH4 emissions. To explain the variability of CH4 emission, a hierarchical identification of limnologic and atmospheric parameters was used. A significant increase in diffusive emissions from net cage sites (33.4 ± 54.9 mg CCH4 m−2 d−1) was observed when compared to the sites before (4.4 ± 9.4 mg CCH4 m−2 d−1) and after (6.2 ± 15.6 mg CCH4 m−2 d−1) the net cages. Also, significant increase of ebullitive emissions was also observed from the net cage sites (2,417.1 ± 2,040.7 mg CCH4 m−2 d−1) when compared to the average emissions from sites before (1.1 ± 2.1 mg CCH4 m−2 d−1) and after (88.7 ± 92.6 mg CCH4 m−2 d−1). Results showed a decrease in average CH4 emissions towards the sites after the net cages in all sampled areas which suggests that the influence of tilapia fish farming is local. The highest averages in the reservoir areas for diffusive and ebullitive CH4 emissions were observed in areas with higher production of tilapia. Finally, seasonal variation was observed on diffuse CH4 emission. High concentrations of carbon and phosphorus in water and sediment were the main drivers for increasing diffusive and ebullitive methane emissions. Our findings provide valuable information that tilapia net cage farming in reservoirs can be associated with local and dispersive increased methane emissions.