Abstract
The widespread use of reclaimed water has alleviated the water resource crisis worldwide, but long-term use of reclaimed water for irrigation, especially in agricultural countries, might threaten the soil environment and further affect groundwater quality. An in-situ experiment had been carried out in the North China Plain, which aimed to reveal the impact of long-term reclaimed water irrigation on soil properties and distribution of potentially toxic elements (As, Cd, Cr, Hg, Zn and Pb) in the soil profile as well as shallow groundwater. Four land plots were irrigated with different quantity of reclaimed water to represent 0, 13, 22 and 35 years’ irrigation duration. Pollution Load Index (PLI) values of each soil layer were calculated to further assess the pollution status of irrigated soils by potentially toxic elements (PTEs). Results showed that long-term reclaimed water irrigation caused appreciable increase of organic matter content, and might improve the soil quality. High soil organic matter concentrations conduced to high adsorption and retention capacity of the soils toward PTEs, which could reduce the risk of PTEs leaching into deep layers or shallow groundwater. Highest levels of Cr, Pb and Zn were observed at 200–240 cm and 460–500 cm horizons in plots. Longer irrigation time (35 years and 22 years) resulted in a decreasing trend of As, Cd, Hg, Pb and Zn in lower part of soil profiles (>540 cm) compared with that with 13-years’ irrigation years. Long-term reclaimed water irrigation still brought about increases in concentrations of some elements in deep soil layer although their content in soils and shallow groundwater was below the national standard. Totally speaking, proper management for reclaimed water irrigation, such as reduction of irrigation volume and rate of reclaimed water, was still needed when a very long irrigation period was performed.
Highlights
Water scarcity continues to be a major crisis in many regions in the world
Field experimental sites in this study were located at the Long-River reclaimed water irrigation area (LRRWIA), in Daxing district (Figure 1a), Int
Reclaimed water used as irrigation water could provide soils with nutrients and organic matter, improving soil fertility and crop production
Summary
Water scarcity continues to be a major crisis in many regions in the world. An estimated 700 million people are facing water shortages in 43 countries [1,2], such as India, the State of California in the US, the North China Plain and other similar arid and semi-arid areas [3,4,5]. Overuse and extensive exploitation of groundwater have led to water shortage issues and frequent drought events [5,6], which promote reclaimed water reuse worldwide [7]. Reclaimed water is a stable water source which can contribute a huge quantity of nutrients [8,9] and its reuse in agriculture can significantly increase crop production [10]. It was estimated in a report that about 20 million ha of farmland was irrigated with reclaimed water and the amount would increase dramatically in the few decades due to the intensive water crisis [11]. Electrical conductivity (EC) would increase but the soil capacity of holding nutrient elements would reduce [14]
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