Coupled controls of climate, lithology and land use on dissolved trace elements in a karst river system

Abstract

As an important factor affecting water quality, dissolved trace element (DTE) is not well studied in the karst region. Here, eighteen DTEs were analyzed to investigate their contents, seasonal-spatial variations, sources and controlling factors, and to evaluate water quality and health risks in a karst river system (Chishui River, southwestern China). The results showed that dissolved trace element concentrations (DTECs) in this river were at a relatively low level compared with other Chinese rivers. Except for Cr, Ni, Sr and U, other DTEs had a higher median concentration in the wet period than in the dry period. Water quality and health risk assessments indicated that the water quality in this river had no extensive heavy metal pollution, and the DTECs were below the hazard level. Correlation analysis and principal component analysis identified that Al, Co, Cu, Li, Mn, Ni, U, Mo, Sb and Sr were mainly derived from natural sources, while As, Ba, Cr, Ga, Pb, Rb, V and Zn were dominated by anthropogenic sources. Carbonate and urban land distributions control the DTECs of river waters, indicated by correlations of DTECs with coverage of carbonate and urban land within the draining area. Further analyses found that for mono-lithological sub-catchments with low urban land coverage, the water samples from carbonate catchments had a higher concentration of Co, Cr, Ni, U, Mo, Li and Sr and a lower concentration of Ga, Pb, Sb, Cu, As, Rb, V, Mn, Zn, Al and Ba than the water samples from silicate catchments. These differences would be changed with the increasing of urban land coverage in mono-lithological sub-catchments, suggesting that the impacts of urban land on DTEs are not limited to As and Rb indicated by correlation analyses. Seasonal changes in contents of DTEs and in their correlations with analyzed factors reflect the regulations of seasonal hydrologic conditions. This study highlights that the DTECs of river waters in the Chishui River basin, a region with low level of urbanization, are significantly related to urban land distribution. Future urban planning and watershed management need consider the impacts of urbanization on the DTEs and water quality in rivers in karst areas.