Dynamic Modeling of Nitrogen Cycling in Kappaphycus alvarezii seaweed farming in Takalar, South Sulawesi

Abstract

Abstract This study examines the nitrogen cycle within seaweed ( Kappaphycus alvarezii ) farming systems in the coastal waters of Takalar, South Sulawesi, utilizing a combination of field observations and dynamic systems modeling. Field data were employed to construct a system dynamics model using STELLA Architect 13.1. The observed data on nitrogen and seaweed biomass were used to validate the model. The model successfully replicated the observed pattern of low ammonium and high nitrate levels early in the cycle, which declined to a minimum mid-cycle and partially recovered before harvest; the associated biomass response exhibited rapid early growth, a mid-cycle slowdown, and a modest late increase. Reproducibility was notably high for nitrate (PBIAS −13.3%) and biomass (PBIAS +8.1%), while ammonium remained near detection limits and was assessed qualitatively. These findings suggest that nitrate regeneration and availability within the cycle are critical controls on farm-scale biomass accumulation and provide a validated framework for analyzing nitrogen effects on K. alvarezii production in this area.

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