SPATIAL AND TEMPORAL DISTRIBUTIONS OF MERCURY SPECIES AND CONTROLLING FACTORS IN HONGFENG RESERVOIR, GUIZHOU, CHINA

Abstract

The Hongfeng Reservoir was built in 1960 and is an alkaline, hyper-eutrophic and seasonal anoxic reservoir due to the contamination from domestic and industrial wastewaters. The water samples at deferent depths from two sampling sites were collected from November 2003 to September 2004 using metal clean protocols. Total Hg (THg), reactive Hg (RHg), dissolved total Hg (DHg), dissolved gaseous mercury (DGM) were measured by gold trap pre-concentration and CVAFS detection. Methyl mercury was measured by distillation followed by aqueous phase ethylation, precollection on a Tenax, isothermal gas chromatography and cold vapor atomic fluorescence detection. There was no discernible seasonal trend (about 8 rig/L) in THg concentration based on the average information developed during the four cruises except for high concentrations at bottom and water-sediment interface in May and September 2004. On the other hand, particulate mercury (PHg) and methyl mercury have discernible seasonal variability. Proportion of PHg increased from 29% in February 2004 to 50% in May 2004. In November 2003, February and May 2004 methyl mercury concentrations were relative low and increased with depth (from 0.13 to 0.40 rig/L). In September 2004, methyl mercury concentrations increased from 0.14 ng/L in the epilimnion to 0.99 ng/L in the hypolirnnion. DGM concentrations varied from 0.024 to 0.11 ng/L and decreased with depth. The concentrations of dissolve organic carbon, suspend solids, total Hg, and methyl mercury all were higher at Houwu than at Daba in spring, summer and autumn, but there were no evident differences at two sample sites in Feb.2004. This may be attributed to low temperature in winter and fishing farm's work decreased. This suggested that other pollutants such as N, P from fishing farm and other waste water at Houwu may have changed the distribution pattern of Hg in the reservoir.