Nitrogen mineralization and eutrophication risks in mangroves receiving shrimp farming effluents

Nitrogen (N) inputs originated from shrimp farming effluents were evaluated for potential changes in the net N mineralization for mangrove soils from Northeastern Brazil. Our study provides notable information and assessment for the potential enhancement of N mineralization in preserved and shrimp-impacted semi-arid mangrove soils of the Jaguaribe River estuary, which is one of the largest shrimp producers of Brazil, using an analytical and daily tidal variation experimental approach. Nitrogen-rich effluents promoted a significant (pvalue < 0.001) increase of the total soil N content (1998 +/- 201 mg kg(-1)on average) compared with the preserved sites (average: 1446 +/- 295 mg kg(-1)). The effluents also increased the N mineralization in the shrimp-impacted sites (N-min: 86.6 +/- 37.5 mg kg(-1)), when compared with preserved mangroves (N-min: 56.5 +/- 23.8 mg kg(-1)). Over a daily tidal variation experiment, we found that just 30% (36.2 +/- 20.6 mg kg(-1)) of mineralized N remains stored in the soil, whereas 70% (102.9 +/- 38.8 mg kg(-1)) was solubilized in tidal waters. Therefore, the N mineralization process may trigger eutrophication by increasing N inorganic bioavailability in mangrove soils receiving N-rich effluents from shrimp ponds, which in turn might increase primary producers' activity. This approach has not been studied so far in semi-arid mangroves, where the shrimp farming activity is one of the most important economic activities.