Mercury and methylmercury concentrations in two newly constructed reservoirs in the Wujiang River, Guizhou, China

Abstract

We studied the distribution of different mercury species in two newly created reservoirs (Hongjiadu [HJD] and Suofengying [SFY] Reservoir) within the Wujiang River, Guizhou Province, China. These reservoirs were sampled four times between January, 2007, and November, 2007. Water, soil, and fish tissue samples were collected and analyzed for organic (methylmercury) and total Hg. Dissolved organic carbon (DOC) content in water was measured as well. In both reservoirs, the DOC concentration was low (range 0.5-4.9 mg/L). Organic matter content in soil collected near the bank of both reservoirs was also low (range 0.4-6.9%). The total MeHg level did not increase significantly with depth in water column, nor did it exhibit a pronounced spatial pattern moving from upstream to the dam. The total MeHg level did not increase significantly with depth in water column, nor did it exhibit a pronounced spatial pattern moving from upstream to the dam. The total Hg content in fish tissue was on average 0.044 mg/kg wet weight, which is a very low content in an international comparison. It is suggested that the studied reservoirs were not active sites of net Hg methylating. Low levels of organic matter (OM) may constrict the evolution of the bulk Hg methylation process occurring in flooded soil. Therefore, we hypothesize that newly constructed reservoirs in the karstic region of Southwest China appear to be much less beset by the problems of MeHg pollution that have been reported for corresponding reservoirs in North America and Europe. However, further research is required to verify this finding.

Eutrophication in the newly built Laohutan Reservoir during the initial impoundment period: the role of nutrient loading

“…With the relatively low anti-interference ability and little ecological stability, the new reservoir cannot have enough strong self-purification or water environmental bearing capacities to purify the input nutrients. Then, the large inputs of nutrients accelerated the growth of algae, especially cyanobacteria and the weak new reservoirs ecosystem cannot maintain the ecological balance (Smith et al 1999;Yao et al 2011;Smayda 2008).…”

“…These fragile and unstable ecosystems accelerate water environment deterioration. Some new reservoirs even show eutrophication during the first impoundment (Camargo et al 2005;Yao et al 2011). So does the nutrient loading play a role in eutrophication as important as it does in mature reservoirs?…”

Synthesis of current data for Hg in areas of geologic resource extraction contamination and aquatic systems in China

“…The Baihua Reservoir, which has a recent history of Hg pollution caused by waste water discharges from the Guizhou organic chemical plant (GOCP), utilising metallic Hg as a catalyst to produce acetic acid, exhibited high levels of total-Hg in the water body and in underlying sediments (Feng et al, 2003c(Feng et al, , 2004dHou et al, 2004;Yan et al, 2005). In a comparison between an up to 30 years old reservoir (Wujiangdu Reservoir) and newly constructed ones (Hongjiadu and Suofengying Reservoirs), the latter category exhibits slightly lower MMHg concentrations (Yao et al, 2011). He et al (2008a) conducted a long-term monitoring study of the Hg load in inflows and the outflow of the Hongfeng Reservoir and found a good comparison concerning the MMHg concentration in the flows with the exception for the summer period when the MMHg level in the outflow was up to 6 times higher than that in inflows ( Fig.…”

“…Louis et al, 2004). In Guizhou, the area flooded after establishment of a new reservoir generally consisted of farmlands with a meagre organic matter content (1.9% to 4.1% for the Hongjiadu and Suofengying reservoirs (Yao et al (2011)). Hence, the limited access to fresh organic material may curb the establishment of active environments for biomethylation.…”

“…Concerning the elevated Hg levels observed in fish from North America and northern Europe, Lucotte et al (1999) suggested that the decomposition of flooded organic matter (OM), which generates favourable conditions for bacterial methylation of inorganic Hg to MMHg, could be the primary driving process underlying high MMHg in fish. It is evident that the conditions in newly constructed Chinese reservoirs with comparatively different type and low availability of organic matters are not in favour of net in-situ methylation (Meng et al, 2010b;Yao et al, 2011;Larssen, 2010). Another important factor is that the most common fish species in Chinese reservoirs are herbivorous species, which grow fast and have a limited time to bioaccumulate MMHg before being consumed.…”