Tidal–Diurnal Interactions and Nitrogen Dynamics: Integrating Variability into Sustainable Brackishwater Pond Management

Abstract

Water quality is a fundamental determinant of aquaculture success, shaping growth, health, and survival of cultured species. In traditional pond irrigation systems, tidal-driven variability alters physicochemical conditions, creating risks of stress, reduced productivity, and mortality. Understanding tidal influence is vital for designing adaptive and sustainable management strategies. This study investigated water quality dynamics in Sawohan Village, Sidoarjo, Indonesia, across a freshwater–brackish–saline gradient. Sampling was conducted under spring and neap tides during both daytime and nighttime. Parameters measured included pH, salinity, dissolved oxygen (DO), alkalinity, nitrate, nitrite, and ammonia, analyzed with descriptive and inferential statistics. Results showed that tidal phase and sampling time were key regulators of variability. DO and alkalinity displayed significant diel fluctuations, while salinity and nitrate reflected tidal mixing and freshwater inflows. Nitrate and nitrite are below the threshold set by the quality standard during nighttime neap tides, posing ecological risks. Nitrite occasionally surpassed safe limits, particularly in saline ponds during neap tides, suggesting incomplete nitrification under oxygen-limited conditions. Overall, findings demonstrate that tidal–diurnal interactions strongly influence nitrogen dynamics and water quality stability. Incorporating tidal variability into aquaculture management can improve ecological resilience, mitigate nitrogen-related risks, and support sustainable productivity in coastal environments.