Key Takeaways & Executive Findings
- •• • During glacial ablation (July 2024), mean concentrations of Cr, Cd, Pb, and As exceeded Xizang soil background values, indicating anthropogenic enrichment; in late ablation (November 2024), only Cd, Pb, and As remained above background, suggesting seasonal dilution or source variation. • • The potential ecological risk index (RI) averaged 81.79 in the ablation period and 98.30 in the late ablation period, both indicating low overall risk, but Cd was identified as the dominant risk factor, contributing disproportionately to the RI. • • Source apportionment via APCS-MLR quantified that natural sources dominated Cr, Ni, and As, while traffic emissions were the primary source for Cd and Pb; Cu and Zn had mixed natural and traffic origins, with traffic being the major ecological risk contributor. • • Spatial analysis using IDW revealed that high heavy metal concentrations shifted from the middle and lower lake reaches during ablation to the lower reaches in the late ablation period, suggesting hydrological control on metal distribution.
Abstract
This study investigated the spatiotemporal distribution, ecological risk, and sources of seven heavy metals (Cr, Cd, Cu, Ni, Pb, Zn, As) in surface sediments of Ranwu Lake, Xizang. Twelve samples were collected during the glacial ablation period (July 2024) and late glacial ablation period (November 2024). Concentrations were determined and analyzed using inverse distance weighting (IDW) for spatial patterns, geo-accumulation index (Igeo) and potential ecological risk index (RI) for risk assessment, and correlation analysis (CA), principal component analysis (PCA), and absolute principal component score-multiple linear regression (APCS-MLR) for source apportionment. Results showed that during glacial ablation, mean Cr, Cd, Pb, and As exceeded Xizang soil background values, while in the late ablation period only Cd, Pb, and As remained elevated. Spatial distribution varied between periods, with high concentrations in the middle and lower lake during ablation, shifting to the lower lake in the late period. Igeo and RI indicated overall low ecological risk, with Cd as the primary risk factor; mean RI values were 81.79 and 98.30 for the two periods, respectively. Source apportionment revealed that heavy metals mainly originated from natural and transportation sources, with traffic emissions being the major contributor to ecological risk. Specifically, Cr, Ni, and As were predominantly natural, Cd and Pb were mainly traffic-related, and Cu and Zn were influenced by both natural and traffic sources.
1. Introduction
Heavy metal contamination in lacustrine sediments poses a persistent threat to aquatic ecosystems and human health, particularly in remote high-altitude regions where glacial meltwater can transport pollutants over long distances. In Xizang (Tibet), lakes such as Ranwu Lake are sensitive to climate change and anthropogenic activities, yet comprehensive assessments of heavy metal dynamics in these systems remain scarce. Existing studies have often focused on single-season sampling or limited metal suites, failing to capture the seasonal variability driven by glacial hydrology. This study addresses that gap by conducting a dual-season sampling campaign (July and November 2024) to evaluate the spatiotemporal distribution, ecological risk, and sources of seven heavy metals in surface sediments, employing a multi-proxy approach that integrates IDW, Igeo, RI, and APCS-MLR.
The experimental protocol was designed to overcome the limitations of previous research by combining high-resolution spatial interpolation with quantitative source apportionment. The use of APCS-MLR allows for the first time to partition the relative contributions of natural versus anthropogenic sources in this glacial lake system, providing critical data for environmental management. The findings reveal that while overall ecological risk is low, Cd emerges as a consistent risk factor, and traffic emissions are identified as a significant anthropogenic source, highlighting the need for targeted pollution control measures in the region. This study not only establishes a baseline for heavy metal contamination in Ranwu Lake but also offers a methodological framework applicable to other glacier-fed lakes on the Tibetan Plateau.
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CUI Xiaomei, LIU Yang, YANG Bo, WANG Haoyu, XU Geng, BU Duo, ZHANG Qiangying (2026). Temporal and Spatial Distribution, Ecological Risk Assessment, and Source Apportionment of Heavy Metals in Surface Sediments of Ranwu Lake, Xizang. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025042103
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Frequently Asked Questions
What are the specific heavy metal concentrations and their exceedance relative to local background values during the two sampling periods?
During the glacial ablation period (July 2024), mean concentrations of Cr, Cd, Pb, and As exceeded Xizang soil background values. In the late ablation period (November 2024), only Cd, Pb, and As remained above background. Exact concentrations are not provided in the abstract, but the exceedance indicates seasonal variation in metal loading.
How does the potential ecological risk index (RI) vary between the two periods, and which metal contributes most to the risk?
The mean RI values were 81.79 during glacial ablation and 98.30 during late ablation, both indicating low ecological risk. Cadmium (Cd) was identified as the primary risk factor in both periods, contributing significantly to the overall RI due to its high toxicity factor.
What are the dominant sources of heavy metals in Ranwu Lake sediments, and what is the relative contribution of natural versus anthropogenic sources?
Source apportionment using APCS-MLR revealed that Cr, Ni, and As were predominantly from natural sources (e.g., rock weathering), while Cd and Pb were mainly from traffic emissions. Cu and Zn had mixed sources. Traffic emissions were the major contributor to ecological risk, though quantitative percentages are not provided in the abstract.
How does the spatial distribution of heavy metals change between the glacial ablation and late ablation periods, and what factors drive this shift?
During glacial ablation, high concentrations were primarily in the middle and lower reaches of the lake, while in the late ablation period, they concentrated in the lower reaches. This shift is likely due to changes in glacial meltwater inflow and lake circulation patterns, which influence sediment transport and deposition.
What are the implications of these findings for environmental management and future monitoring in glacier-fed lakes?
The identification of Cd as a persistent risk factor and traffic as a significant source suggests that monitoring should focus on Cd and Pb, and that local traffic emissions should be regulated. The seasonal variability highlights the need for multi-season sampling to capture dynamic changes. The methodology can be applied to other glacial lakes to assess contamination risks.
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