Sedimentary record of metal elements in the Dashiwei sinkhole section of Bailang underground river, Guangxi 

In this work, the concentration of metal elements and sediment organic matter (SOM) in sediment cores of the Dashiwei sinkhole section from the Bailang underground river has been studied, and the pollution history of the river basin from 1932 to 2007 has been reconstructed by combining the 210Pb dating and historical records. The results show that concentrations of main toxic heavy metals Cd and Hg in the sediment cores are high, which are 3.4 and 0.6 times than the soil background values of Guangxi, respectively, even more than 11.2 and 2.7 times of the soil background value throughout China, respectively. On the whole, the distributions of heavy metal elements have a similar increase tendency in the sediment cores. The vertical distribution of metal elements in the sediment cores shows that metal element pollution in the underground river were associated with many events in history, such as peasant movement, the war of AntiJapanese, Great Leap Forward age, the early stage of reform and opening up , and the rapid development of economy. Especially，the vertical variation of Ca and Mg in the sediment core records indicates that a new construction climax has begun in this karst mountain area since 1983. Correlation and clustering analyses show that, (1) Cr and Pb came mainly from natural environment, (2) Cu, Ni, Zn, As and MgO originated from natural environment and artificial sources, (3) Cd, Hg, Mn, CaO and SOM stemmed from artificial pollution sources. Correlation analysis with polycyclic aromatic hydrocarbons suggests that part of Zn, Cd and As came from coal combustion. In a nutshell, metal elements in the sediment cores better recorded pollution history of the Bailang underground river.