Assessment of available phosphorus in planted mangrove sediments in Thailand by using the Olsen extraction method

Phosphorus (P) is an essential macronutrient for plant growth, carbon sequestration, and nutrient cycling within the dynamics of mangrove ecosystems, where its bioavailability is often a limiting factor. One important factor is available P, which represents the P fraction weakly bound to minerals or organic matter that is easily consumed by plants and microbes. This available P concentrations in two sediment cores from a planted mangrove forest located in southern Thailand was investigated. The pH levels of sediment across the sites ranged from 7.13 to 7.90, indicating neutral to slightly alkaline condition, which is found to be suitable for application of the Olsen method to extract P in the sediments. Results showed that available P in sediment samples commonly decreased with increasing depth, which varied from 19.38 ± 0.06 to 47.50 ± 0.06 mg/kg P, with an average value of 28.29 ± 3.80 mg/kg P. To ensure reliability of the data, the analytical performance of the lsen extraction method (NaHCO3, pH 8.5) iscoupled with UV-Vis spectrophotometry was validated. The analytical performance of the method showed excellent linearity (R2 = 0.9980) and robust precision were %RSD 1.23–3.45% for within-day and %RSD 1.24–4.35% for between-day. Accuracy, evaluated through spike recovery ranged from 82% to 99%, indicating that the method is highly reliable. Collectively, these validation metrics indicated the effectiveness of the Olsen method as a quantitative analytical tool to determine the available P in mangrove sediment samples. This research is provided critical information on the P status in restored mangrove areas, playing a significant role of enhancing the understanding of nutrient dynamics within these ecosystems and promoting the critical potential of mangroves for supporting plant growth and blue carbon sequestration in coastal environments.