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To understand the mercury (Hg) pollution level and the corresponding ecological risk in agricultural watershed of the Three Gorges Reservoir region, a typical watershed, Wangjiagou, located in Fuling, where is in interior zones of the Three Gorges Reservoir region, was selected as the study object. Meanwhile, ArcGIS geo-statistics module was conducted for investigation of the Hg contents and distribution characteristics in soils of different land use types including dry land, farmland, woodland and settlements. Also the corresponding Hg pollution level and ecological risk were assessed. The results suggested that soil Hg contents in this watershed ranged from 9.47 to 94.57 microg x kg(-1), and the mean value was (34.23 +/- 16.23) microg x kg(-1). Higher Hg contents in surfaces of soils were observed in woodland, followed by farmland and settlement. The lowest was found in dry land. Surfaces of soils significantly showed Hg accumulation, and an obvious inverse correlation between soil Hg contents and soil depths was also observed in this study. Additionally, geo-statistics analysis showed a weak spatial correlation of soil Hg contents in this watershed, indicating the spatial distribution of soil Hg in this watershed was mainly influenced by several natural factors such as atmospheric wet-dry deposit, vegetation coverage and topography, instead of anthropogenic interference. Overall confirmative soil Hg pollution was not found in this watershed, which showed a very low pollution index (-0.08), but a moderate potential ecological risk still existed (the ecological risk index was 57), of which woodland had the highest potential risk. The total capacity of Hg in this watershed was 25.39 kg, among which dry land accounted for 69%.

The temporal and spatial distribution of mercury (Hg) in four different sources of stream (aquaculture wastewater, bare land, forestry land and agro-forestry land) and well water of an agro-forestry and livestock compound watershed in the Three Gorge Reservoir region was studied during the period from March 2013 to March 2014. The total mercury (THg) concentrations ranged 9.95-15.26 ng x L(-1) with an average of (11.95 +/- 1.87) ng x L(-1), and the THg concentration decreased in the order of bare land > aquaculture wastewater> forestry land > agro-forestry land > well water. The total methylmercury (TMeHg) concentrations ranged 0.120-0.441 ng x L(-1) with an average of (0.232 +/- 0.099) ng x L(-1), and the TMeHg concentration decreased in the order of aquaculture wastewater > agro-forestry land > forestry land > bare land > well water. THg and TMeHg in well water were both dominated by the dissolved fraction, whereas for other sources of stream, the particulate phase accounted for the major fraction of THg and TMeHg. The THg concentrations in winter and spring were significant higher than those in summer and fall, however, no obvious seasonal trend of TMeHg distribution was observed. Comprehensive analysis showed human activities and weather conditions such as air temperature and precipitation etc. were the main reasons for the difference of temporal and spatial distribution of THg and TMeHg.

The distribution of mercury (Hg) in four different water bodies (streams, pond, precipitation and wells) of a small typical agricultural watershed in the Three Gorges Reservoir region was studied during the period from November 2011 to September 2012. Total mercury (THg) and methylmercury (TMeHg) concentrations ranged from 1.12 ng x L(-1) to 64.04 ng x L(-1) and from 0 (undetected) to 4.24 ng x L(-1), with an average of (13.54 ± 10.55) ng x L(-1) and (0.22 ± 0.42) ng x L(-1), respectively. Particulate mercury (PHg) accounted for a major fraction of THg in these four water bodies, whereas for TMeHg dissolved fraction dominated in wells and streams, but not in pond and precipitation. An obvious spatial pattern of Hg distribution was observed with THg concentration in the order of precipitation > pond > streams > wells and streams > pond > precipitation > wells for TMeHg. The THg temporal distribution showed that THg concentrations in cold season were higher than that in warm season, but the temporal distribution of TMeHg varied with the water types. Comprehensive data analysis found that wet deposition was a significant source of Hg in this agricultural watershed and the particulate transport was the main way for Hg and MeHg transport in this watershed. In addition, surface runoff was an important process for Hg contribution from watershed to the Three Gorges Reservoir, but played a minor role for TMeHg load to the reservoir.