Nutrient Mass Balances in Intensive Shrimp Ponds with a Sludge Removal Regime: A Case Study in the Tam Giang Lagoon, Central Vietnam

Abstract

Understanding the sources and sinks of nutrients is of significant importance for better management of pond water quality and the environmental impact of aquaculture. The objective of the present study was to estimate the nutrient mass balances of four intensive shrimp (Litopenaeus vannamei) ponds in Tam Giang Lagoon, Central Vietnam, using a sludge management regime. The nutrient budgets were calculated based on the sources and sinks of nutrients in the ponds over a period of 49 d. The input sources of N and P were mainly shrimp feed, which accounted for more than 90%. Shrimp harvesting was the largest sink of N (37.5%), but not of P (18.3%). Almost 30.4% N and 16.9% P of input were not accounted for the measured losses. While the smallest proportion of N (18.9%) was retained in sludge, the largest amount of P was accumulated in sludge (53.2%). The farm was operated without water exchange, so ponds gained only 1.9% N and 4.2% P from water intake. The pond lost about 13.2% N and 11.6% P from discharge water. Production of 1 kg shrimp needed 84.9 g N and 26.1 g P from total input sources and discharged 47.3 g N and 16.0 g P to the environment. Environmental losses of nutrients were lower or intermediate, when the loads were expressed in both kg/ha/cycle and kg of N or P per ton of shrimp produced. Furthermore, the environmental impacts of aquaculture are controlled from the system.