نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه علوم و مهندسی محیطزیست، دانشکده جغرافیا و علوم محیطی، دانشگاه حکیم سبزواری، سبزوار، ایران
2 گروه جغرافیای طبیعی، دانشکده علوم جغرافیایی و برنامه ریزی، دانشگاه اصفهان، اصفهان، ایران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Objective: Given the increasing and alarming trend of land cover changes-primarily driven by unsustainable development in agricultural, urban, and industrial sectors-surface water resources, particularly rivers, are facing serious threats from various pollutants. Among the most critical of these pollutants are heavy and toxic metals, which, through direct or indirect entry into the food chain, pose significant risks to human health and other living organisms. The Aras River, as a transboundary and vital water source for the northwestern provinces of Iran, is subject to such threats. Accordingly, this study aims to analyze the spatiotemporal changes in land cover and examine their relationship with variations in the concentration of heavy metals in the Aras River water. The main focus is on identifying spatial patterns of overlap between land use changes and areas of high chemical pollution, as well as assessing the potential biological risk associated with the entry of these elements into the food chain.
Methods: To analyze the trend of land cover changes from 2001 to 2024, this study used time series imagery from the MODIS sensor (product MCD12Q1). Land cover changes were extracted and analyzed for three key time periods: 2001, 2012, and 2024. Simultaneously, in order to assess the heavy metal pollution status, field sampling was conducted at 13 selected stations along the Aras River during two time periods (May and August 2024). The collected samples were prepared and acidified, and then subjected to chemical analysis using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The target metals included lead (Pb), arsenic (As), nickel (Ni), cadmium (Cd), mercury (Hg), and chromium (Cr), which were evaluated in terms of concentration, spatial distribution, and compliance with national and international standards (FAO, WHO, EPA).
Findings: The land cover analysis showed that rangelands and agricultural lands experienced the highest rate of change during the study period. The chemical analysis of water samples in May revealed that concentrations of lead, arsenic, and nickel in some stations exceeded international permissible limits. In August, despite a relative reduction in lead levels, other elements such as arsenic, cadmium, mercury, nickel, and chromium showed relatively uniform concentrations close to the biological risk threshold in most stations. Comparison with national and international standards indicated that although some metals were within the safe range for agricultural irrigation, livestock and poultry use, and aquatic organism tissue accumulation thresholds, they were deemed unsuitable for aquatic life health. Furthermore, if these resources are consumed directly or indirectly by humans through agricultural, livestock, or aquatic products, there is a potential for bioaccumulation and serious long-term toxic effects.
Conclusion: Based on the results, a significant relationship was identified between land use changes and the increase in toxic metal concentrations in water. These findings highlight the necessity of revising land management policies, imposing restrictions on the discharge of polluted effluents, and strengthening continuous water quality monitoring systems. By integrating remote sensing data with laboratory analyses, this study presents a comprehensive model for assessing the environmental impacts of land use changes, which can also be applied to other water basins across the country.
کلیدواژهها [English]
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