Mercury mass balance study in Wujiangdu and Dongfeng Reservoirs, Guizhou, China Xinbin Feng a, * , Hongmei Jiang a, b , Guangle Qiu a , Haiyu Yan a , Guanghui Li a , Zhonggen Li a a State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 46 Guanshui Road, Guiyang, Guizhou 550002, China b Graduate University of Chinese Academy of Sciences, Beijing 100049, China Reservoirs are the sink of total mercury but source of methylmercury to the aquatic systems. article info Article history: Received 8 December 2008 Received in revised form 4 May 2009 Accepted 6 May 2009 Keywords: Mercury methylation Methylmercury Mass balance Precipitation Reservoir abstract From October 2003 to September 2004, we conducted a detailed study on the mass balance of total mercury (THg) and methylmercury (MeHg) of Dongfeng (DF) and Wujiangdu (WJD) reservoirs, which were constructed in 1992 and 1979, respectively. Both reservoirs were net sinks for THg on an annual scale, absorbing 3319.5 g km 2 for DF Reservoir, and 489.2 g km 2 for WJD Reservoirs, respectively. However, both reservoirs were net sources of MeHg to the downstream ecosystems. DF Reservoir provided a source of 32.9 g MeHg km 2 yr 1 , yielding 10.3% of the amount of MeHg that entered the reservoir, and WJD Reservoir provided 140.9 g MeHg km 2 yr 1 , yielding 82.5% of MeHg inputs. Our results implied that water residence time is an important variable affecting Hg methylation rate in the reservoirs. Our study shows that building a series of reservoirs in line along a river changes the riverine system into a natural Hg methylation factory which markedly increases the %MeHg in the downstream reservoirs; in effect magnifying the MeHg buildup problem in reservoirs. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Reservoirs are world-widely created for various purposes including the production of hydroelectricity, irrigation, flood control, fisheries production, and recreation (The World Commis- sion on Dams, 2000). Many environmental and socio-economic consequences result from reservoir development (Dionne and Therien, 1997). Since early 1970s, scientists have observed that methylmercury (MeHg) concentrations in fish from newly created reservoirs are much elevated compared to fish from adjacent natural lakes (Smith et al., 1974; Abernathy and Cumbie, 1997; Cox et al., 1979). MeHg is produced from inorganic mercury by bacterial activity, which is enhanced by the decomposition of flooded vegetation and organic carbon in soils (Lucotte et al., 1999). From a toxicological perspective, MeHg is the most important form of Hg because it bioaccumulates in food chains and is a strong neurotoxin for human and wildlife. It is well known that reservoirs have mercury contamination problems in their fisheries that last for several decades after flooding (Bodaly et al., 1984; Verdon et al., 1991). It was recently estimated that there are now over 1.5 million km 2 of reservoir surface area globally (St Louis et al., 1994), making this a widespread environmental and socio-economic problem for populations or individuals that rely on reservoir fisheries for subsistence and fish production. Although many studies have been conducted in North America and Europe to understand the process leading to high MeHg concentrations in fish in newly created reservoirs (Kelly et al., 1997; St Louis et al., 1994; Lucotte et al., 1999; Porvari, 1998), there remains a long way to go to fully understand the mechanism. The total number of large dams in China has exceeded 50% of the total number all over the world since 1982, and the increase rate of the total number of large dams in China is much faster than that of the rest of the world (The World Commission on Dams, 2000), which is obviously due to the rapidly increasing demands for energy needs resulting from economic development. The famous ‘‘three Gorge Dam’’ will be the central concern for the Chinese scientific community in the near future in terms of the environ- mental consequences. Obviously, one of the most important issues is the possible MeHg contamination in fish. Unfortunately, studies related to mercury biogeochemical cycling in reservoirs in China are extremely limited in number, although it is reported that mercury concentrations in fish from Gezhouba Reservoir have exceeded those allowed marketing and human consumption which is 0.3 mg kg 1 in China (Jin and Xu, 1997). Southwestern China is the most abundant region for water resources in China due to distinct climate conditions. With the implementation of the ‘‘Go West’’ policy, a great number of large reservoirs have been and are being constructed along a dozen of * Corresponding author. Tel.: þ86 851 5891356; fax: þ86 851 5891609. E-mail address: fengxinbin@vip.skleg.cn (X. Feng). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2009.05.024 Environmental Pollution 157 (2009) 2594–2603