Characteristics of Phosphorus Fractions and Phosphate Diffusion Fluxes of Sediments in Cascade Reservoirs of the Huangbai River

Abstract

The Huangbai river, with a large phosphorite deposit in the basin upstream, is the drinking-water source of Yichang city, China, and water blooms often break out in it in present times. To investigate the internal contamination load, the distribution and vertical variation of sediment phosphorus and its fractions were analyzed. Phosphorus flux across the sediment-water surface was preliminarily analyzed in three reservoirs in the basin. The results showed that the concentration of total phosphorus (TP) decreased from the upstream to the downstream reservoirs of the basin, and the means of the TP were (8070.0±2251.4), (2681.2±1709.8), and (2656.6±1599.7) mg·kg-1, in the three reservoirs, respectively. This shows that the basin is at a highly polluted level. There were similar tendencies in the concentrations of dissolved oxygen (DO) and chlorophyll a in the surface water. The order of the phosphorus fractions was HCl-P > OP > NaOH-P in most sites. According to Fick's First Law, the flux of PO43--P across the sediment-water surface was 0.0179-0.1825 mg·(m2·d)-1, and it decreased from the upstream to the downstream reservoirs. The flux was positively related to HCl-P, OP, and TP in the high phosphorus concentration basin.