Effects of mangrove age on water quality and deposit sediment layer in integrated mangrove-shrimp farming systems: a case study in Mekong Delta, Vietnam

Abstract

Water quality plays a crucial role as a natural indicator in evaluating shrimp farming feasibility, closely linked to sediment characteristics. However, knowledge about how mangrove age affects water quality and sediment remains limited in mangrove-shrimp models. This study aimed to address this gap by collecting water and sediment samples from integrated mangrove-shrimp systems with three different mangrove ages in Ca Mau province, Vietnam, where Rhizophora apiculata is the dominant species in these systems. Water samples were collected twice per tide: (1) one day before water discharge for shrimp harvesting, and (2) one day after water intake into grow-out ponds. Sediment samples were taken to display sediment profiles and analyze organic matter. Linear mixed-effects models were employed to identify significant differences in water and sediment parameters among various mangrove age groups. Results indicated that mangrove age substantially affected pH, DO, N-NH₃, H₂S, and total organic carbon, but not N-NO₂, N-NO₃, N-NH₄, and TN. The first sediment layer was thickest in mangroves over 10 years old, followed by those aged 6–9 years, and thinnest in those under 5 years old. Litterfall accumulation in the bottom pond was greatest in older mangrove groups. Findings revealed significant relationships between the first sediment layer and various water parameters, emphasizing the importance of managing this layer for suitable water quality in shrimp farming. Based on linear regression, dredging is recommended if the top sediment layer is approximately 10-cm thick to maintain good water quality. Furthermore, results confirmed that water exchange enhances water quality, potentially promoting shrimp survival and productivity.