Dynamic Modeling of Nitrogen Cycling in Kappaphycus alvarezii seaweed farming in Takalar, South Sulawesi
Jamaluddin Fitrah Alam*, Nita Rukminasari, Asmi Citra Malina, Amanda Pricella Putri, Andi Alya Yusriyyah, Nur Halizah Roebetho, Putri Sakinah Resman, Rahmat Pratama

Faculty of Marine Science and Fisheries, Hasanuddin University, Makassar, Indonesia

Abstract

This study investigates the nitrogen cycle within seaweed (Kappaphycus alvarezii) farming systems in the coastal waters of Takalar, South Sulawesi, through a combination of field observations and dynamic systems modeling. Field data were collected over a 45-day cultivation cycle, encompassing weekly measurements of ammonium (NH4), nitrate (NO3), environmental parameters (temperature, dissolved oxygen, current velocity), and biomass growth. Specific Growth Rate (SGR) was calculated to assess productivity under varying nitrogen conditions. These empirical datasets were used to construct a system dynamics model using STELLA Architect 13.1, integrating nutrient inputs (e.g., river runoff, domestic effluents), nitrogen uptake rates by seaweed, and relevant transformation pathways (e.g., nitrification, denitrification). Model validation was performed through behavior reproduction, employing RMSE and NSE as key metrics. The resulting model provides a quantitative framework to examine nitrogen availability and its influence on biomass productivity. This approach enables scenario testing for optimized cultivation strategies under constrained nitrogen regimes, supporting precision aquaculture and sustainable nutrient management in tropical coastal systems.

Keywords: Nitrogen cycling, seaweed farming, system dynamics, nutrient uptake, Kappaphycus alvarezii

Topic: Sustainable Aquaculture and Fisheries