Nitrate, ammonium, and phosphate patterns from mangrove sediment cores near extensive aquaculture areas in the Red River Delta, Vietnam

Mangroves are an important ecosystem in the coastal zone, acting as a natural filter and trapping system of nutrients and pollutants exported from continental environments. The high loading of nutrients in mangrove forests may lead to increasing tree mortality rates, altered forest structure, and biodiversity degradation. In the present study, we analyzed sediment grain size, organic matter content, ammonium, nitrate, and phosphate in sediment cores from different mangrove stands to determine factors influencing nutrient dynamics in mangrove forests in the Red River Delta, Vietnam. Research results showed that the sedimentary organic matter content varied between 5.54 to 8.56%, with an average value of 7.10 ± 0.94%. The nutrient concentrations in mangrove sediment ranged from 0.925 to 32.278 mg/kg, 0.236 to 7.24 mg/kg, and 0.047 to 9.124 mg/kg for ammonium, nitrate, and phosphate, respectively. Nutrient concentrations in the top layer of sediment cores decrease gradually with increasing distance from aquaculture ponds, highlighting the impact of aquaculture discharge on nutrient dynamics in coastal areas. Organic matter and nutrient concentrations were highest in the surface layer (0–20 cm depth), declining steadily between 20–50 cm, with minimal variation from 50–100 cm in depth of sediment cores. The present study results suggested that aquaculture activities and mangrove stands significantly influence nutrient dynamics in mangrove sediments. Ongoing monitoring is necessary to determine the long-term impacts of aquaculture on mangrove forests and adjacent coastal ecosystems.