Effect of Sodium Nitrate Treatment on Water and Sediment Quality in Laboratory and Pond Studies

Sodium nitrate (NaNO3) has been widely used in shrimp aquaculture ponds as a fertilizer, a water quality enhancer and a bottom soil oxidant. This study was conducted to determine whether or not treatment with sodium nitrate can improve water quality, bottom soil condition, phytoplankton abundance and community structure and fish yield in freshwater channel catfish ponds. The study consisted of a pond study and a laboratory study. In the pond study, sodium nitrate was applied at 2 mg/L NO3--N at 2-week intervals to rectangular ponds of 400-m2 water surface area stocked with 400 channel catfish Ictalurus punctatus fingerings and 10 grass carp Ctenopharyngodon idella. Water quality, phytoplankton communities, sediment condition and fish production were compared between triplicate treatment and control ponds. The results showed that catfish production and survival rate did not differ (P>0.1) between treated and control ponds. There were higher mean concentrations of nitrate nitrogen, total nitrogen, soluble reactive phosphorus, total phosphorus, turbidity and chlorophyll a in sodium nitrate-treated ponds than in control ponds (P0.1). There were also no differences in pH and organic matter concentration of sediment (P>0.1) between control and treated ponds. However, application of sodium nitrate caused a decline in redox potential between the beginning and the end of grow-out period in sediment (P<0.1), and upon draining, sediment in treated ponds was lighter colored than that of control ponds. This suggests that nitrate treatment enhanced oxidation at the sediment surface. In the laboratory study, sodium nitrate was further investigated to determine if it would influence redox potential, denitrification rate, and the rate of organic matter decomposition when added to sediment. Results revealed no differences (P>0.05) in redox potential and organic matter concentration in sediment treated with 0 to 32 mg/kg of NO3--N. There was no increase in denitrification (P>0.05) in sediment to which nitrate was applied at 0 to 10 mg/L to the water. Dissolved oxygen declined at similar rates in water samples held in BOD bottles and treated with 0 to 8 mg/L NO3--N. Nitrate and ammonium also were compared as nitrogen source for phytoplankton. Uptake rate of ammonium by green algae was greater than that of nitrate. However, diatom and blue-green algae communities appeared to use both forms of nitrogen

Dynamics of soil properties and pathogen levels in Pacific white shrimp ponds during a production cycle: Implications for aquaculture management

Abstract This study examines the temporal and spatial variations in soil properties and microbial populations in Pacific white shrimp ponds throughout a production cycle in Phuket Province, southern Thailand, aiming to refine shrimp farming methodologies and enhance pond soil management. We collected soil samples from four ponds across two aquaculture sites at six different stages of the production cycle—Before Sediment Flushing (BSF), After Sediment Flushing (ASF), and during each month of the four‐month cycle (M1 to M4). These samples were analyzed from both central and peripheral pond zones at three soil depths (0–5 cm, 5–10 cm, and 10–15 cm). The results indicated negligible variation in soil characteristics and microbial loads across all stages. Nevertheless, a significant finding was the fluctuation in levels of easily decomposable organic matter (EDOM), which is critical for maintaining soil and water quality and affects both shrimp growth and disease incidence. EDOM levels decreased to their lowest after ASF, then progressively increased, reaching a peak at M4 (p < 0.05). The study suggests that effective sediment flushing post‐cultivation not only mitigates the accumulation of deleterious residues, but also reduces the necessity for prolonged pond desiccation, thereby offering a sustainable strategy to maintain the ecological balance of shrimp ponds over successive farming cycles