Conceptualization and validation of a dynamic model for the simulation of nitrogen transformations and fluxes in fish ponds

Abstract

Nitrogen is a key element in aquatic environments and an important pond management variable. In aquaculture systems, nitrogen accumulation eventually leads to a deterioration of the system. The interactions between various N-species are complex and difficult to integrate. Modelling can improve our ability to evaluate this complex system. This paper integrates existing knowledge about nitrogen transformations in fish ponds into a model that calculates the amount of various N-compounds in the water column and in the sediment. The model is also used to gain insight into the relative importance of transformation processes between the various N-compounds. The model was divided into three modules: fish, phytoplankton and sediment-water. The fish module is based on physiological and bio-energetic principles. The phytoplankton dynamics module is based on physico-chemical principles of alga growth. The water-sediment module is based on the bacterial transformations and chemical fluxes of N-species across the water-sediment interface. Relationships and parameters were taken from the literature, except for a few parameters that were estimated by fitting model predictions to observed data. The model was implemented in Turbo Pascal (7.0) using a fixed time step of 1 h and it was calibrated using a set of data from an earthen fish pond stocked with Colossoma macropomum. The validation was performed using data from earthen ponds stocked with Oreochromis niloticus. The difference between the calibrated and validated model was related to the fish species. All concentrations of the various N-species present were simulated well, except the N retained in organic matter in the sediment (average relative error −0.34). Sensitivity analysis revealed that the concentrations of inorganic-N compounds, both in the water column and in the sediment, are more affected by changes in specific parameters included in the fish and phytoplankton modules than other forms of nitrogen in the pond. The model works well, except for organic matter accumulation in the sediment. Further research should concentrate on a better understanding of the bottom organic matter dynamics, to make the model a more comprehensive predictive tool.

A simulation model for nitrogen retention in a papyrus wetland near Lake Victoria, Uganda (East Africa)

“…Diffusion of dissolved nutrients across the watersludge interface and the sludge-sediment interface was modelled with an equation based on Fick's second law (Jiménez-Montealegre et al 2002). For example Eq.…”

Nitrogen budget in integrated aquaculture systems with Nile tilapia and Amazon River prawn

“…This allows identifying the destination of supplied resources and, thus, changes practices to enhance the system efficiency. Nitrogen is a key element because it is essential for animal nutrition and for the control of environment pollution (Jimenez-Montealegre et al 2002). A quantitative understanding of nitrogen budget is a prerequisite to achieve waste reduction (Mariscal-Lagarda and PaezOsuna 2014) and decrease the chemical fertilizer dependency (Fernando and Halwart 2000).…”

Is integrated multitrophic aquaculture the solution to the sectors’ major challenges? – a review

“…In the last decades, there has been a growing need to better understand and optimise aquaculture performance, flow rates and transformations of toxic compounds in aquaculture production systems (Jim enez-Montealegre et al 2002). Thus, dynamic modelling has been developed towards the use of models for analysis and simulation of aquacultures (Wik et al 2009).…”