Phosphorus Environmental Risk Assessment in Wetland Soil

At the interface between agricultural fields and water bodies there are wetlands constituted by hydromorphic soils. Our hypothesis is that hydromorphic soil acts a P sink and the P buffer capacity increases over time. To test our hypothesis, we apply tools to evaluate the P environmental risk via i) maximum phosphorus adsorption capacity (PMAC); ii) environmental soil phosphorus thresholds (P-threshold); iii) soil phosphorus storage capacity (SPSC) in hydromorphic soil (Histosol) and a non-hydromorphic soil (Cambisol) under application of mineral P. The PMAC was estimated by the Langmuir model in soil samples collected at four depths (0–10, 10–20, 20–40 and 40–60 cm). Soil samples were incubated for 30, 60 and 120 days with mineral P equivalent to 0, 25, 50, 75 and 100% of the PMAC. The P-threshold was determined from the degree of phosphorus saturation (DPS), estimated using PMAC and Fe + Al extracted with Mehlich-1. The SPSC was obtained from the 0–60 cm depth using the DPS% M1(CMAP) . The PMAC values ranged from 2321 to 3539 mg kg −1 with higher values in the Histosol compared to the Cambisol. The Histosol presented a P-threshold of 19% DPS (609 mg kg −1 ), while in the Cambisol it was 24% DPS (582 mg kg −1 of P Mehlich-1). According to the SPSC tool, the soil acted as a source of P when P Mehlich-1 exceeded 887 mg kg −1 in Histosol, while in Cambisol it was 773 mg kg −1 . Overall, the P buffering capacity was higher in the Histosol, indicating the importance of preserving wetlands for water quality. Graphical Abstract