Abstract: This study analyzed the content of total phosphorus (TP) in the sediments of major Chinese tidal flats. It found that the northern flats, separated by the Zhejiang Cixi sampling site, showed low TP content in the surficial and core samples of the Liaoning Liao River delta (0.046%±0.013% surficial, 0.047%±0.015% core) and the Shandong Qingdao mud flats (0.047%±0.009%; 0.055%±0.008%). The average TP in the rest of the northern flats, such as Tianjin Hangu, the Yellow River delta, Jiangsu Yancheng, Shanghai Chongming Dongtan, and Cixi, varied from 0.051% to 0.070%, the highest level in the 12 tidal flats. Except for the Xiamen Jiulong River and Guangdong Pearl River flats (0.051%～0.070%), the TP content values were found to be lower in the southern flats, especially in Fuzhou Minjiang, Gangxi Yingluo Bay, and Hainan Dongzhaigang (0.019%～0.041%). The high TP in the northern flats can be attributed to fluvial sediments carried by high discharge rivers. At the site of high measured TP values, large amounts of Ca-P also were detected (4.16～9.56 μmol g^-1). The concentration of Fe-P in the core samples was lower than the surficial samples. The tidal flats of Hangu, Qindao and Jiulong River exhibited the highest Fe-P levels. Two consecutive and non-consecutive incubation experiments showed various self-release velocities of TP. In the consecutive incubations, the largest release velocity occurred in the Jiulong River delta (0.927±0.312 μmol kg^-1h^-1). The non-consecutive experiments showed a significant increasing trend of TP release velocities in 11 tidal flats, except for the Liao River delta (P<0.01). Among the sites, the Hangu, displayed the highest TP release velocity (1.437±0.325 μmol kg^-1h^-1).

Key words: total phosphorus, phosphorus fractionation, internal loading of phosphorus