Seasonal variations of phosphorus species in the Tuohe River, China. Part I. Sediments

Sediment cores were collected at an upstream site (Jintang) and a downstream site (Neijiang) in summer and winter in the Tuohe River, which is one of the five largest tributaries of the Changjiang (Yangtze) River in China. A sequential leaching procedure was applied to determine the concentrations of the different forms of solid phosphorus, including exchangeable phosphorus (Exc-P) as well as phosphorus associated with iron oxides (Fe-P), with aluminum oxides (Al-P), with apatite (Ca-P) and with the residual fraction (Res-P), as correlated with water content and total organic carbon. The seasonal variations and the vertical distributions of phosphorus species in sediments at both sampling sites demonstrated that: 1) total phosphorus (TP) in summer and winter were ranged between 1 313–2 330, 1 491–2 228 mg/kg in Jintang and 543–2 128, 603–1 175 mg/kg in Neijiang, respectively. It can predicated the pollution of TP in Jintang is serious than that in Neijiang both in summer and winter; 2) total inorganic phosphorus (TIP) was the dominant form of TP; 3) Ca-P was the main chemical forms of TIP in the sediments. Based on the profiles in sediments and bio-available phosphorus data, it revealed that bio-available phosphorus (BAP) represented only a minor portion (0.61%–3.59%) of TP, and the vertical distribution of soluble reactive phosphorus (SRP) in corresponding porewaters was more abundant in the upper layer of the sediment, which suggests that BAP may be converted to non-bioavailable phosphorus in deeper layer of the sediment of this dynamic system.