Seasonal variation of heavy metals in sediment of Lake Ulansuhai, China

Sediment samples were collected from 10 sites in Lake Ulansuhai during summer and winter 2009 to reveal seasonal variations in sediment heavy metal levels. The geoaccumulation index (GI) was calculated to assess the severity of metal pollution. The GI values suggest that, in winter, the lake sediments were polluted slightly with Cu (GI = 0.66-1.34), Zn (GI = 0.59-1.35), Cr (GI = 0.49-0.82) and Pb (GI = 0.60-0.96), and moderately with Cd (GI = 1.03-4.23). The degree of pollution was higher in winter than in summer. By contrast, the degree of pollutionwas higher in summer than in winter for Hg and As. Correlation analysis can be used to identify factors influencing seasonal variations in heavy metals. The concetrations of Cu, Zn, Pb, Cr and Cd were negatively correlated with water temperature and hydrodynamic conditions, but positively correlated with organic matter concentration in the sediments and with a sediment particle size of < 63 mu m (p < 0.01). Meanwhile, Hg and As concentrations were affected by redox state and salinity. Among the metals tested, Hg and Cd posed a more serious pollution risk.