Occurrence Form and Distribution Characteristics of Phosphorus in Surface Sediments of Typical Karst Wetlands

To explore the characteristics and risks of various forms of phosphorus in surface sediments of different wetlands in Puzhehei karst watershed. Taking Puzhehei karst watershed as the research area, surface sediments of 4 wetlands in the watershed were sampled by grab-type sediment sampler in dry, rich and flat water periods. The contents of total phosphorus (S−TP) and phosphorus forms in sediments were determined by national standard method and four-step continuous extraction method. The correlations among weakly adsorbed phosphorus (NH₄Cl−P), reducible phosphorus (BD−P), iron-aluminium bound phosphorus (NaOH−P), calcium bound phosphorus (HCl−P) and residual phosphorus were analyzed. The results showed that the distribution of S−TP in the surface sediment of Puzhehei karst basin is 506 mg/kg–846 mg/kg. For different types of wetlands, it is river wetland > swamp wetland > lake wetland > reservoir wetland. Distribution of different forms of phosphorus in surface sediments of 3 wetlands in Puzhehei karst basin except reservoir wetland was NaOH−P > residual phosphorus > BD−P > HCl−P > NH₄Cl−P, while the residual phosphorus content in reservoir wetland was higher than NaOH−P. Pearson correlation coefficient shows that the increase of S−TP content in sediment mainly comes from NaOH−P, followed by HCl−P, part of which comes from residual phosphorus. The content of total phosphorus (W−TP) and orthophosphate (SRP) in water mainly comes from residual phosphorus, S−TP and BD−P. There is little correlation between residual phosphorus and NH₄Cl−P, BD−P, NaOH−P, HCl−P, which indicates that the source of residual phosphorus is different.