Phosphorus accumulation and sorption characteristics of P-enriched soils in the Dian Lake basin, southwestern China

PURPOSE: The eutrophication of the Dian Lake is very serious. Phosphorus (P)-enriched soils in the southern basin can contribute significantly to the overall P loads in the Dian Lake. The objective of the present study was to investigate the distribution of P fractions and the P sorption properties in the P-enriched soils along the Chai river, southern of the Dian Lake. The information is essential to understanding P discharge from the intensively cropped field to waterways. MATERIALS AND METHODS: Soil samples were collected in five sites located along the Cha river at the southern part of the basin of the Dian Lake, southwestern China, from the upstream cropped fields to the estuary buffer, respectively. Soil total phosphorus (TP), inorganic P fractions, organic carbon (SOC), N, pH, and particle size distribution were quantified. Phosphorus sorption was modeled with the simple Langmuir equations. RESULTS AND DISCUSSION: Total P, loosely bound, and non-occluded inorganic P (Pi) concentrations at all soil depths (0–80 cm) were significantly higher in the upstream Ferrisols than that in the downstream Gleysols of the Chai river. However, the occluded Pi concentrations were significantly higher in the Gleysols than that in the Ferrisols. Phosphorus in the 0–80 cm soil profile of both Ferrisol and Gleysols are largely dominated by Ca-bound Pi (47–79%). The higher sorption maximum (Sₘₐₓ), binding energy (k), and equilibrium buffering capacity (PEBC) and lower zero equilibrium P concentration (EPC₀) over all sampling depths were observed in the Gleysols than that in the Ferrisols. The increase of Sₘₐₓ, k, and PEBC and decrease of EPC₀ as sampling depth increased suggest that there might be fewer P losses via leaching process both in the upstream and downstream areas of the Chai river. CONCLUSIONS: It is evident from this study that the upstream areas is actually acting as a source for dissolved P, whereas the downstream areas is acting as a sink. Moreover, management options to reduce P losses in land runoff may therefore be a more effective way to minimizing eutrophication risk in the P-enriched area.