Document Type : Original Article
Authors
Department of Construction and Water Management, Science and Research Unit, Islamic Azad University, Tehran, Iran
10.22034/iwm.2026.2077942.1253
Abstract
Extended Abstract
Introduction: Contamination of water resources by heavy metals, due to their high persistence, bioaccumulation potential, and toxic effects, is considered to be one of the serious challenges for sustainable water resources management in urban-industrial watersheds. The Karaj watershed, because of its population density, industrial and agricultural activities, is among the areas prone to this type of contamination. However, a comprehensive assessment of the spatial distribution and environmental status of heavy metals in the water resources of this watershed has received less attention. Therefore, the overall aim of this study is to spatially analyze and assess the risk of heavy metals in the groundwater resources of the Karaj watershed in order to provide management strategies for sustainable water resources development.
Materials and methods: Water samples were collected from 22 monitoring stations distributed across the Karaj watershed, covering the upstream, midstream, and downstream reaches. Sampling and analyses were conducted in collaboration with the Alborz Province Water and Wastewater Company. Concentrations of Arsenic (As), Nickel (Ni), and Chromium (Cr) were determined using standard methods recommended by the World Health Organization (WHO) and the Iranian National Standards (ISIRI 1053). Geographic coordinates of sampling points were recorded using GPS devices. To assess the spatial variability of metal concentrations, the Inverse Distance Weighting (IDW) interpolation method was applied in the ArcGIS environment. Three pollution indices were used to quantify the contamination levels: (1) the single-factor Pollution Index (PI), (2) the Heavy Metal Pollution Index (HPI), and (3) the Contamination Degree (Cd). The results of these indices were compared with the permissible limits of WHO and ISIRI standards. Statistical analyses were conducted using descriptive statistics and correlation analysis to evaluate the relationships among metals and identify potential pollution sources.
Results and Discussion: The concentrations of As, Ni, and Cr in all sampling sites were below the permissible limits of the WHO and ISIRI drinking water standards. Spatial interpolation maps revealed that the concentration gradients of heavy metals were generally uniform across the watershed, with slightly elevated values near agricultural and urban zones the downstream of the Karaj River. The calculated pollution indices indicated low contamination risk in all sampling locations: the maximum PI values were below 1, the mean HPI was significantly lower than the critical value of 100, and the Cd index approached zero. These findings suggest that the water quality in the Karaj watershed is within a safe range with respect to heavy metal pollution. The spatial uniformity of contamination patterns reflects the absence of major point-source pollution, implying that the detected concentrations primarily result from natural geochemical processes and limited non-point sources. The integration of GIS-based spatial analysis with pollution indices proved effective for identifying potential vulnerable zones and for supporting watershed-scale environmental management.
Conclusion: This study demonstrated that the levels of As, Ni, and Cr in the Karaj watershed remain within acceptable limits, indicating that heavy metal pollution do not currently pose a significant environmental threat. The results confirm that the combined use of IDW spatial interpolation and pollution indices provides a powerful tool for evaluating the environmental quality of water resources at a watershed scale. The main conclusions are as follows:
1. All measured heavy metal concentrations were below international and national permissible limits, confirming the good water quality status of the Karaj watershed.
2. Spatial patterns of heavy metals were relatively homogeneous, with no significant point-source pollution detected.
3. The calculated indices (PI, HPI, and Cd) consistently indicated minimal contamination, supporting the sustainable use of water resources in the region.
The methodology adopted in this study can serve as a reference model for other Iranian watersheds facing similar environmental challenges.
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