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[Vertical Distribution Profiles and Release Potential of Mainstream Column Sediments in the Three Gorges Reservoir After Impoundment to 175 m].

To investigate the vertical distribution characteristics of phosphorus in the main stream sediments of the Three Gorges Reservoir (TGR), column sediment samples were collected from 5 sites in October 2010, and sediment particle size, organic matter contents, and mineral compositions were analyzed. Investigation of the contribution rate of phosphorus released from column sediments in the TGR was also conducted. The results show that the sediment pH is between 7.3-7.8. The mainstream column sediment is mainly constituted by silt and clay, which account for 49.4%-78.6% and 20.6%-50.6% of total sediments, while sand represents less than 4.4%. Median grain size of each sampling site presented a phased increase or decrease trend. The organic matter content was between 12.94 g·kg-1 and 53.43 g·kg-1, and it tended to slightly increase from upstream to downstream. The C/N ratio in the sediment was between 4.00 and 11.64, and organic matter content was mainly affected by terrigenous input. Total phosphorus (TP) content was between 861.86 mg·kg-1 and 1024.54 mg·kg-1, and it exhibited negligible change in vertical distribution. There is no obvious enrichment phenomenon of phosphorus for column sediment. The major component of sediment TP is calcium bound phosphorus (Ca-P, 47.83%-73.90%), and there are various trends for phosphorus distribution in different sampling sites. Exchangeable phosphorus (Ex-P), aluminum-bound phosphorus (Al-P), and iron-bound phosphorus (Fe-P) in the 0-4 cm surface sediment of each sampling sites was relatively high. For most sampling sites, no obvious change of phosphorus fractions in 16-20 cm of sediment was detected. Bioavailable phosphorus (the sum of Ex-P, Al-P, and Fe-P) accounted for 2.78%-7.05% of TP, indicating that bioavailability of phosphorus in the column sediments is low. The contents of bioavailable phosphorus and organic matter were significantly and positively correlated (P<0.05, N=50). The distribution and transformation of organic matter will affect the migration and transformation of sediment phosphorus in the TGR.