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Baihua reservoir experienced serious Hg contamination from the inflow river named Dongmen river from 1971 to 1997(Yan et al.,2008).Than a large amount of particles with high mercury concentration have been washed into Baihua reservoir led to high mercury pollution was recorded in the corresponding sediment layers.The Dongmen river was dredged in 2008 to remove the secondary pollution source of mercury for Baihua reservoir.However,deposited mercury may be released from the sludge during the coarse operation of dredging project.To evaluate the release of mercury during the dredge process,four representative sites from upstream to downstream were sampled.The sampling location were as follows: S1(26°38′16.38″N,106°29′19.35″E),S2(26°37′47″N,106°29′41″E),S3(26°38′02″N,106°29′39″E),S4(26°38′21″N,106°29′40″E).The DHg(dissolved mercury)measurement in pore water was based on the method provided by Hou(2004).The average DHg concentration are 13.0,38.2,12.3,14.2,36.9 and 27.8 ng/L for 1-3 cm,4-6 cm,7-9 cm,10-12 cm,13-15 cm and 15-18 cm interval,respectively.Two peaks of the DHg concentration were respectively presented at 4-6 cm and 13-18 cm interval in four pore water profiles(Figure 1).Since the sediment accumulation was 0.17g?cm-2a-1 as reported by Wang(2000),the 4-6 cm interval is correspond to the year between 2006 and 2009,and the 13-18 cm interval is correspond to the year between 1971 and 1997.The continuous mercury discharge from the chemical plant led to the high Hg concentration in 13-18 cm interval.It is also reasonable to consider that the high Hg concentration in 4-6 cm interval was resulted in the dredge project.More mercury may be abruptly flowed into Baihua reservoir during the operation of the dredge project.The DHg in pore water shows a downward trend from S1 to S3.However,the DHg in S4 shows higher concentration.The result demonstrated that the diffusion effect plays a small role in reducing concentration of mercury.Further efforts are needed to better understand the release of mercury after dredging in the inflow river.