Engineering assessment of water quality correlationsfor passive aquaponic systems in tropical environments

Abstract

This study presents an engineering-oriented correlation analysis of water quality variables—pH, temperature, and dissolved oxygen (DO)—in a passive aquaponic system integrating red tilapia (Oreochromis spp.) and lettuce (Lactuca sativa) under tropical outdoor conditions. Environmental data were collected at 45-minute intervals over three months using embedded sensors and a microcontroller-based data logger. Pearson, Spearman, and Kendall correlation coefficients were applied to evaluate linear and monotonic relationships among variables. The results indicate a moderate, statistically significant positive correlation between pH and DO (r = 0.566, p < 0.001), and a weaker but still significant correlation between temperature and DO (r = 0.420, p < 0.001). No significant relationship was found between pH and temperature (r = 0.081, p = 0.271). These findings demonstrate that natural environmental dynamics can support acceptable water quality levels without active aeration or control systems. The correlation structure obtained may inform the design of low-cost, energy-efficient monitoring frameworks and decision-support tools for aquaponic systems in resource-constrained or offgrid environments.