Novel insights into Pb source apportionment in sediments from two cascade reservoirs, North China

Sediments act as crucial sink and source for metal contamination in aquatic environment of reservoir systems. However, the high complexity and heterogeneity of sediments make it difficult to trace the sources of metals in reservoir sediments. As a toxic metal, how to trace anthropogenic Pb sources in sediments is important for the water quality safety, especially in reservoir. Herein, 98 sediment samples collected from the connected Panjiakou Reservoir (PJKR) and Daheiting Reservoir (DHTR) were analyzed. A novel approach for tracing anthropogenic Pb sources was established by combining the regional geochemical baseline (RGB) and Pb isotopic ratios. The results showed that the mean concentration of Pb in these two reservoirs was 44.59 mg/kg, and the RGB value of Pb was 43.77 mg/kg. Pollution assessments using RGB and enrichment factor indicated that the influence of anthropogenic Pb is greater in DHTR sediments than in PJKR sediments. Based on the RGB model, samples influenced by anthropogenic activities (SS-AA) were screened and found in the DHTR. The anthropogenic Pb contribution in DHTR SS-AA was totally 35.29%. Moreover, the mean value of ²⁰⁶Pb/²⁰⁷Pb in DHTR SS-AA (1.107 ± 0.029) was slightly lower than those of natural inputs, indicating there was a small amount of anthropogenic Pb input in DHTR. The anthropogenic Pb sources were further identified using Pb isotopic ratios (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) for DHTR SS-AA. Their apportionments were calculated with the help of the RGB model. The results showed that iron mining (20.42%) and coal combustion (14.87%) were the two main anthropogenic Pb sources. Aerosol deposition was likely the main pathway for coal combustion input. The results confirm that the proposed method of combining RGB and Pb isotopic ratios was a good attempt to trace the anthropogenic Pb sources in reservoir sediments.