Conceptual interactions through Canals between Aquaculture Ponds and a tropical lagoon

Lagoons and ponds are highly productive coastal regions with high economic value and are usually treated as independent systems in scientific studies. However, their tidal connections are often neglected. This study focuses on Chiku Lagoon (Tainan, Taiwan), a shallow, tidally driven tropical lagoon, and the surrounding aquaculture ponds, which cover approximately 36% (~39 km2) of the local land area. Here, we treat the ponds and the lagoon as a single watershed system. Tidal forcing drives water into the lagoon and its connecting aquaculture ponds, facilitating water exchange within the ponds and exporting nutrient-rich and CO2-rich waters back to the lagoon. Diel variations in temperature and biological activities are observed in both the ponds and the lagoon, while the canals and the lagoon are further influenced by tidal modulation. We propose a box-model framework to examine the complex interactions between these components under at least two scenarios: positive feedback interactions and offset interactions. We further discuss how treating ponds and lagoons as a connected system alters the interpretation of their physical and biogeochemical interactions.