Irrigation with water from Beni Haroun reservoir (Algeria) changed soil physicochemical properties and increased the availability of metallic trace elements in croplands

Abstract

The Beni Haroun Dam (BHD), situated in the province of Mila, Algeria, stands as the largest dam within the country, facilitating the irrigation of approximately 40,000 ha of agricultural lands characterized by sub-humid and semi-arid climates. Over time, the water within this reservoir has experienced an escalation in contamination, primarily attributed to its role as a major recipient of diverse municipal and industrial effluents, both treated and untreated. Consequently, mounting apprehensions regarding the potential migration of pollutants to irrigated soils have surfaced. The primary aim of this investigation was to assess the levels of contamination by mineral elements and heavy metals present in agricultural soils irrigated by waters originating from BHD. A total of 48 soil samples were systematically collected from 12 distinct sites, comprising 10 irrigated areas and 2 control sites, each spanning depths of 0, 10, 20, and 30 cm. Then subjected to chemical characterization, including the total quantification of minerals (Ca²⁺, Mg²⁺, Na⁺, K⁺), and heavy metals (Cd²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cr³⁺ and Fe³⁺). as well as the determination of cation exchange capacity (CEC), exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR) as well as soil texture. This study indicated that irrigating with dam waters increased the soil exchangeable cations in comparison to the control one: Ca²⁺ (21.99 ± 3.65 meq 100 g⁻¹), Mg²⁺ (10.53 ± 1.94 meq 100 g⁻¹), Na⁺ (10.08 ± 1.78 meq 100 g⁻¹), K⁺ (2.81 ± 0.8 meq 100 g⁻¹), and enhanced soil characteristics: CEC (25.2 ± 5.55), ESP (41.69 ± 11.21) and SAR (2.51 ± 0.43). In terms of percentage of enrichment, the mineral elements are classified as follows: Na⁺ > Ca²⁺ > K⁺ > Mg²⁺. The metal contents in irrigated soils were also higher but remained less than the recommended international limits. They are classified as follows: Fe³⁺ > Zn²⁺ > Pb²⁺ > Cr³⁺ > Cu²⁺ > Cd²⁺. The soils under investigation are deemed susceptible to salinization, sodification, and contamination with prolonged irrigation. Such conditions pose potential risks to human health should vegetable crops absorb these metals. Therefore, it is recommended to implement adequate drainage measures, emphasizing surface drainage, and to conduct regular monitoring for the accumulation of salt and sodium.