فصلنامه
نوع مقاله : مقالات پژوهشی
نویسندگان
1 دانشگاه فردوسی مشهد
2 گروه علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه شیراز، شیراز، ایران
کلیدواژهها
عنوان مقاله English
نویسندگان English
Introduction
Lake desiccation is a major environmental concern in arid and semi-arid regions. The exposed lakebeds resulting from this process can become important sources of wind-blown dust and may facilitate the transport of heavy metals (HMs) to surrounding ecosystems. Previous studies have largely focused on determining HM concentrations in soils, sediments, and airborne dust, whereas less attention has been paid to quantifying HM transport by wind erosion from dried lakebeds. Since the amount of HMs transported depends on both their concentrations in sediment and the quantity of sediment mobilized by wind, HM flux provides a more comprehensive measure of their potential transport. Therefore, this study aimed to assess the potential for HM transport from the dried lakebeds of Kaftar, Tashk, and Parishan in Fars Province, southern Iran, by determining HM concentrations, enrichment ratios (ERs), and HM fluxes using a portable wind tunnel.
Materials and Methods
Three dried lakebeds, including Kaftar, Tashk, and Parishan, in Fars Province, southern Iran, were selected as representative dust-source areas. At each lakebed, three independent wind-tunnel experiments were conducted at separate locations on surfaces without crusts to account for spatial heterogeneity. A surface soil sample (0–5 cm) was collected from each experimental location. Some physical and chemical properties of the soil samples, including soil texture, pH, electrical conductivity (EC), and organic carbon content, were determined using standard laboratory procedures.
Wind erosion experiments were performed using a portable wind tunnel at a constant wind velocity of 14 m s⁻¹, measured at a height of 0.25 m above the soil surface, for 10 min. After each experiment, wind-eroded sediments were collected, and the mean weight diameter (MWD) of both lakebed soils and transported sediments was determined. Concentrations of nickel (Ni), lead (Pb), and cadmium (Cd) in the soil and wind-eroded sediment samples were measured by atomic absorption spectrophotometry following aqua regia digestion. Sediment fluxes, HM fluxes, and ERs were then calculated.
Statistical analyses included one-way ANOVA followed by Duncan’s multiple range test to compare variables among lakebeds, paired t-tests for Cd, and Wilcoxon signed-rank tests for Ni and Pb to compare lakebed soils with wind-eroded sediments. Linear regression was used to examine relationships between HM concentrations in lakebed soils and wind-eroded sediments. All analyses were performed using IBM SPSS Statistics 27, with statistical significance set at P < 0.05.
Results and Discussion
The results revealed considerable differences among the three dried lakebeds in terms of wind erosion rate and HM transport potential. Sediment fluxes in Kaftar (1.64 g m⁻² s⁻¹) and Tashk (1.56 g m⁻² s⁻¹) were significantly higher than that in Parishan (0.86 g m⁻² s⁻¹), with no significant difference between Kaftar and Tashk. In both lakebed soils and wind-eroded sediments, HM concentrations followed the order Ni > Pb > Cd. Although the mean weight diameter (MWD) of wind-eroded sediments was lower than that of the corresponding lakebed soils, enrichment ratios (ERs) for all three elements were below unity (ER < 1), indicating lower HM concentrations in wind-eroded sediments than in lakebed soils. The relative patterns of ER values varied among elements and lakebeds. Cadmium consistently exhibited higher ER values than Pb (0.49–0.53 vs. 0.24–0.26), whereas Ni had the highest ER in Kaftar (0.65) and Parishan (0.56). In Tashk, however, where the Ni concentration in lakebed soils was substantially lower than in the other lakebeds, the Ni ER decreased to 0.30, falling below that of Cd (0.53). These patterns suggest that the relative enrichment of HMs in wind-eroded sediments varies among elements and lakebeds and may reflect differences in their geochemical characteristics and interactions with soil particles. Strong positive linear relationships were observed between HM concentrations in lakebed soils and wind-eroded sediments for Ni (R² = 0.98), Pb (R² = 0.94), and Cd (R² = 0.87). High R² values indicate that HM concentrations in lakebed soils largely explained their concentrations in wind-eroded sediments.
Heavy metal fluxes exhibited patterns different from those of sediment fluxes. Ni, Pb, and Cd fluxes ranged from 0.22 to 3.82, 0.07 to 0.23, and 0.05 to 0.11 mg m⁻² min⁻¹, respectively. Although sediment fluxes were statistically similar between Kaftar and Tashk, Ni and Pb fluxes were significantly higher in Kaftar, whereas Cd flux reached its highest value in Tashk. These findings demonstrate that HM transport depends on both the amount of sediment transported and the metal concentrations within the transported sediments, highlighting the importance of considering both factors simultaneously when assessing HM transport.
Conclusion
The dried lakebeds of Parishan, Kaftar, and Tashk can act as potential sources of Ni, Pb, and Cd through wind erosion, although transport patterns differed among elements and lakebeds. The lower MWD of wind-eroded sediments and ER values below unity indicated that sediment transport did not result in relative HM enrichment. HM flux, integrating sediment flux and HM concentration, provided a comprehensive measure of HM transport and can help prioritize lakebeds for dust monitoring. These findings are limited to surfaces without crusts and should be further evaluated under a wider range of wind velocities in future studies.
کلیدواژهها English
