Phosphorus speciation in wetland sediments of Zhujiang (Pearl) River Estuary, China

Phosphorus fractions and adsorption-release characteristics of sediments in the Zhujiang (Pearl) River estuary wetland were investigated. Results showed that the total phosphorus (TP) content in surface sediments ranged from 648.9 mg/kg to 1064.0 mg/kg; inorganic phosphorus (IP) was the major fraction of TP and ranged from 422.5 mg/kg to 643.9 mg/kg. Among the inorganic phosphorus, the main fractions were phosphorus bound to Al and Fe (Fe/Al-P), and calcium-bound phosphorus (Ca-P), accounting for 23%–42% and 21%–67% of IP, respectively. The vertical distribution of TP contents were significantly positive correlated with organic phosphorus (Org-P) and Fe/Al-P contents. The bio-available phosphorus contents in vertical sediments varied from 128.6 mg/kg to 442.9 mg/kg, mainly existed in Fe-Al/P fraction, and increased from the bottom to top sediments. The transport of phosphorus in sediment-water interface was controlled by the soil characteristics. The active Fe and Al content was considered as the main factor that determines adsorption capacity in vegetated marsh wetland. The P buffering capacity of the sediments in vegetated marsh wetland was greater than that in mudflat wetland. The potential risk of eutrophication in the study area is high. Reducing terrestrial phosphorus discharge and preventing the sediment Fe/Al-P release to the interstitial water are the possible solutions to reduce the risk of eutrophication in estuary wetlands, and planting vegetation in estuary wetland can also reduce the release of phosphorus in surface sediment.