Concentration, Health Risk, and Hydrological Forcing of Heavy Metals in Surface Water Following Water-Sediment Regulation of the Xiaolangdi Dam in the Yellow River

Abstract

Water and sediment regulation aimed at aquatic ecosystems and preserving reservoir capacity to minimize the negative consequences of dams can fundamentally change the distribution of heavy metals (HMs) in the reservoir and downstream reaches. However, the effects of water and sediment regulation on variation in HMs are still poorly understood. In this study, the variations in concentration, contamination, human health risk, potential sources, and influencing factors of the metalloid As and HMs (Cr, Hg, Ni, Pb, and Zn) in surface water in the reservoir and the downstream reach of the Xiaolangdi Dam (XLD) following the operation of the water-sediment regulation scheme (WSRS) were determined. These results indicate that HM concentrations in the two post-WSRS seasons were much lower than the water quality standards, but were significantly increased over time due to the trapping effects of the XLD (p < 0.05, except for Zn). However, As concentration in the reservoir was significantly lower than that observed in downstream reaches, likely due to anthropogenic input from agricultural activities. Meanwhile, HM concentrations varied with distance to the dam, which displayed a distinct accumulation closer to the dam in the post-WSRS II season. The contamination of HMs, the carcinogenic risk of exposure to As, and the noncarcinogenic risks associated with exposure to Hg, Ni, Pb, and Zn via the direct ingestion pathway of drinking water were all within acceptable levels following the WSRS, but increased over time. The carcinogenic risk of Cr in the post-WSRS II season was at an unacceptably high level, particularly at sites near the dam. Hydrological characteristics (water level and flow rate) were the dominant factors in determining the distribution of HMs. These results can provide new insight for a better understanding of the variations in HMs following the water and sediment regulation practices, and guide future management in regulating the trapping effects of dams.

Keywords: health risk; heavy metals; hydrological forcing; trapping effect; water-sediment regulation.

Figure 1

Location of the study area and sampling sites in the Xiaolangdi Reservoir (S1–S5) and the downstream reach (S6–S11) in the middle and lower reaches of the Yellow River.

Figure 2

Concentrations of As (a), Cr (b), Cu (c), Ni (d), Pb (e), and Zn (f) in relation to distance above and below the Xiaolangdi Dam in the post-WSRS I and post-WSRS II seasons.

Figure 3

Contamination of heavy metals in surface water of the Xioalangdi Reservoir and the downstream reach following the WSRS.

Figure 4

Carcinogenic risk of As (a) and Cr (b) and Non-carcinogenic risk of Hg (c), Pb (d), Ni (e), and Zn (f) in surface water of the Xiaolangdi Reservoir and the downstream reach in the post-WSRS I and II seasons. The dashed line shows the unacceptable limit for the carcinogenic risks. The non-carcinogenic risks were all far below the unacceptable limit. The diamond marker stands for outliers.

Figure 5

Potential sources of HMs in surface water in the XLD Reservoir and its downstream reach following the WSRS in the post-WSRS I (a,c) and II (b,d) seasons, based on PMF (a,b) and HCA (c,d).

Figure 6

Biplot from redundancy analysis (RDA) showing the relationship between hydrological characteristics and heavy metal concentrations in surface water in the Xiaolangdi Reservoir and its downstream reach. Inlet, Reservoir, Outlet, HYK, and JHT represent sample sites located near the inlet (S1 and S2), reservoir (S3, S4, and S5), outlet (S6 and S7), Huayuankou (S8 and S9), and Jihetan stations (S10 and S11), respectively. I and II represent the post-WSRS I and post-WSRS II seasons, respectively. The environmental variables include water level (WL), flow rate (FR), pH, dissolved oxygen (DO), and electrical conductivity (EC).