Sedimentary nutrients in the mainstream and its five tributary bays of a large subtropical reservoir (Three Gorges Reservoir, China)

In order to analyze the distribution pattern of the sediment nitrogen and phosphorus of the Three Gorges Reservoir (TGR), the mainstream of TGR and five tributary bays in Hubei province were observed from October 2005 to July 2006. The spatial and seasonal dynamics of the sediment total nitrogen (TNsed) and total phosphorus (TPsed), the relationship between the mainstream and tributary, and the sediment nutrients' effect to the surface water were analyzed. The results showed that, concentrations of TNsed ranged from 0.27 to 2.04 mg/g, and TPsed fluctuated between 0.17 and 1.21 mg/g. Both of the maximum of TNsed and TPsed appeared in the Xiangxi Bay (the longest bays studied), 1.09 and 0.90 mg/g respectively. No significant spatial differences were found among different sites in other bays (p > 0.05). For seasonal dynamics of TPsed, only the difference in the Yuanshui Bay between spring and summer was significant (p < 0.05). For TNsed, significant differences existed among different seasons in most bays, especially between autumn and other seasons. Cluster analysis based on the surface water nutrients and sediment nutrients indicated that the influence range of the mainstream to the surface water ranged from 10.7 to 15.1 km, while the length of the influence range to the sediment was about 5.34 km. Results of the correlation analysis showed that the internal loading in Hubei province of TGR has not caused a significant effect on the surface water in a large spatial scale, although the influence was significant in some shallow regions.