Distribution and release mechanism of heavy metals in sediments of Yelang Lake by DGT

The deposition and release of heavy metals in sediments often lead to their diffusion in lakes, especially for dispersed elements such as cadmium (Cd), which indirectly introduces pollutants into the food chain. The high rate of deposition or release of heavy metals in sediments is a problem to be solved. Southwest China is most famous in the world for the continuous distribution of karst area, for holding the largest area of bare carbonate rocks and for experiencing the strongest karst development in the world. The trace metals in 15 sites of Yelang Lake were determined by diffusive gradients in thin-films (DGT) method. The distribution and release mechanism of Cr, Ni, Cu, Cd, Zn and Pb under high geochemical backgrounds in the karst area of Guizhou Province in Southwest China were discussed. Based on the DGT concentration and pore water analysis, the distribution order of these heavy metal contents is usually upstream (SC), middle (DCB) and downstream (SW) areas of the lake, which increases during the dry season and decreases during the wet season. There was no significant difference in concentration between 0–4 and 4–8 cm depth (p < 0.05). The R values of heavy metals in the dry and wet seasons were highest with cadmium (Cd) and lowest with chromium (Cr) and lead (Pb). The results of the metal geo-accumulation index (Igₑₒ) and the potential ecological risk index are highest on Cd and lowest on Cr. The mean concentrations of Cr, Cd, Zn, Ni (DCB, SW), Pb (SC, DCB) and Cu (SC) are between the corresponding threshold effect level and the probable effect level, and the average potential ecological risk is ranked in descending order of Cd > Pb > Zn > Cu > Ni > Cr. These three areas are at medium risk levels and the potential ecological risks increases from upstream to downstream. The deposition rate of heavy metals in Yelang Lake sediment was higher than the release rate and the ecological risk from heavy metals was relatively low. Since Cd is the main ecological risk factor in the lake, more attention needs to be given to Cd contamination in the Yelang Lake basin of the karst area.