Free water productivity measurements in leaky mariculture ponds

The rate of net organic productivity in experimental shrimp mariculture ponds was determined via free water methods for each hour over a two month period in late summer 1985. Automated measurements of pH and temperature served as the basis for development of a mass balance budget for dissolved inorganic carbon. Pond surface area and volume changed with depth in a complex but predictable fashion. The seepage rate, which is a quantitatively important term in the inorganic carbon budget, was determined with the salt mass balance. Seepage rates averaged 136–182 mm day⁻¹ (23–37% of pond volume per day). Close agreement between evaporation rates, independently determined from water budgets for each of the four adiacent ponds, demonstrated that the calculated seepage rates were accurate. All four ponds were net producers of organic matter despite the fact that three of the four received additions of allochthonous organic matter. Net productivity averaged 14–65 mmol C m⁻² day⁻¹.