Modelling nutrient emissions from a net-cage aquaculture system in Northeastern Brazil

Aquaculture has been encouraged in Brazil in the past five decades, mainly for tilapia production. Nowadays this production rises at a rapid pace of 7.5% a year. In Brazilian reservoirs, aquaculture is permitted to occupy 1% of a lake’s surface, but this intensive fish production in net cages rises concerns about water quality. Besides, this activity is responsible for a significant biological oxygen demand, due to nutrient load, which promotes water eutrophication. In this study, four cases were investigated according to different water levels and flows, considering a 10-day production period. TELEMAC-2D was used as processor, to compute hydrodynamics and transport, and ParaView was used to visualization application. We observed higher concentrations of Nitrogen and Phosphorus (44,3 and 3,32 μg L-¹ respectively), for the low water level and flow case, which were 58% higher than for high flow, and the nutrients emitted from the source favored their increase in the downstream aquacultures. For the future it is possible to evaluate the aquaculture emissions to quantify the total nutrient accumulation for different reservoir areas, and use projections in various scenarios for decision-making and carrying capacity limit studies