[Chemical forms and distribution of phosphorus in the sediment profiles of the Daliaohe River systems].

The Daliaohe river system in China has been seriously affected by long-term intensive industrial, urban and agricultural activities. The objective of this study was to determine the total phosphorus (TP) content and forms of phosphate in the sediments and investigate geochemical relationships between P forms and mineral matrix elements and P bioavailability. Four sediment profiles were taken in the Daliaohe river systems. TP content in the sediment was measured by ICP-OES and chemical forms of phosphate were measured by sequential selective extraction method. Results indicated that TP ranged from 323 to 2619 mg x kg(-1). In the sediments except 25-47 cm depth of sediment profile in the Hun river, the content of Ca bound P (Ca-P) was the highest, with more than 40% of TP. The contents of Fe bound P (Fe-P) and residual P (RES-P) were 15% to 25% of TP, while the contents of reductant soluble P (RS-P) and Al bound P (Al-P) were generally 5% to 10% of TP. However, the content of soluble and loosely bound P (S/L-P) was only less than 0.5% of TP. Huge accumulation of P in the 25-47 cm depth of the sediment profile in the Hun river led to a bigger increase in the contents of Fe-P and Al-P than Ca-P, where Al-P, Fe-P and Ca-P contents were 6.2%-23.4%, 19.6%-34.1% and 14.6%-35.6% of TP, respectively. Correlation analysis showed that sum of Fe-P and RS-P, Ca-P, and RES-P were positively correlated to Fe, Ca, and sediment organic matter (SOM) contents, respectively in the sediments except the 25-47 cm depth of sediment profile in the Hun river. In addition, TP content was positively correlated to Fe and SOM contents. The molar ratios of Fe to TP generally ranged from 20.9 to 33.9, indicating that most of sediments have capability to further retain P. Potential bioavailable P (BAP) including S/L-P, Al-P and Fe-P in the sediments was 85.43 to 1830.5 mg x kg(-1), and this part of phosphorus might pose a potential risk to the eutrophication of the Daliaohe river system and its estuary.