Water Quality Model for Mariculture Management

In marine fish farms located in subtropical eutrophic coastal waters, the dissolved oxygen (DO) level is often intimately related to algal growth dynamics. For effective mariculture management, a simple, tractable model that can elucidate the dependence of water quality on the important hydrographic, meteorological, and ecological parameters is required. A quasisteady water quality model is formulated herein to predict the long-term (seasonal) average concentrations of phytoplankton, organic nitrogen, dissolved inorganic nitrogen, and potential dissolved oxygen drop (PDOD) for fish farms located in weakly flushed tidal embayments. The fish culture zone is treated as a completely mixed nitrogen-limited system in which algal carbon is decomposed and nutrients regenerated continuously. The model assumes Monod-growth type relations for algal growth and nutrient uptake and incorporates algal settling and respiration, and tidal flushing. Using realistic estimates of light and temperature limiting factors and kinetic rate coefficients, model predictions of seasonally averaged water quality and qualitative features are well supported by field data.