Engineering assessment of water quality correlations for 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’s r, Spearman’s rs, and Kendall’s τ were applied to evaluate linear and monotonic relationships among variables. The results indicate a moderate, statistically significant positive correlation between pH and DO (Pearson’s r = 0.566, p < 0.001), and a weaker but still significant positive correlation between temperature and DO (Pearson’s r = 0.420, p < 0.001). The latter contrasts with the expected inverse trend in closed systems, suggesting compensatory biological processes in passive tropical environments. No significant relationship was found between pH and temperature (Pearson’s 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 off-grid environments.