Effects of soil drying and wetting-drying cycles on the availability of heavy metals and their relationship to dissolved organic matter

Abstract

Purpose Variation in soil moisture content can change metal availability. However, the effects of soil drying during wetting-drying cycles on metal availability have been little investigated. Metal availability to an imposed sink can be assessed by the diffusive gradients in thin film (DGT) technique. The purpose of this study was therefore to investigate the effects of the soil drying processes and previous soil moisture contents on metal availability using DGT. Materials and methods Two metal-polluted agricultural soils with contrasting pH (one acid and one calcareous) were collected from agricultural fields and were repeatedly phytoextracted with a Zn/Cd hyperaccumulator. Both soils, with and without phytoextraction, were subjected to two soil drying processes, i.e. drying from flooded conditions to 50 % maximum water holding capacity (WHC) and drying from 100 to 30 % WHC. Changes in metal availability induced by changing soil water moisture were examined using DGT.Results and discussion In acid soils, the availability of cadmium (Cd), zinc (Zn) and nickel (Ni) (but not copper) increased with drying from saturation to 50 % WHC. Drying soil from 100 to 30 % WHC had weak or no significant effects on available metals. Availabilities of Cd, Ni and Zn correlated well with available Al for both drying conditions. In calcareous soil, a decreasing trend of metal availability with soil drying from saturation to 50 % WHC or from 100 to 30 % WHC was found. Soils were also subjected to different wetting-drying cycles prior to drying. In acid soil, available copper (Cu) was correlated with dissolved organic carbon (DOC). Available Cd, Ni and Zn were correlated with available Al and increased with soil wetting-drying cycles in phytoextracted soil, but not in nonremediated soil. In calcareous soil, available Cu and Ni were correlated well with DOC and were higher with long dry periods. However, available Cd and Zn were lower in soils dried from the cycle of saturation to 50 % WHC. Conclusions The results indicate that soil water regimes can be manipulated to alleviate soil metal availability, but they must be tailored to individual metals and different soil types, and soil moisture content before drying should be considered when dried soils are used for evaluation of metal availability.

The Release and Migration of Cr in the Soil under Alternating Wet–Dry Conditions

“…This increase could be attributed to short-term wet–dry cycles that enhance the release of heavy metals in the soil. Changes in soil moisture during wet–dry cycles in rainfall leaching increase the content of water-soluble organic carbon (DOC), facilitating the migration of heavy metals [ 25 ]. Previous research has explored longer dry periods (45 days) in which, during the leaching–drying–re-leaching process, a significant release of Cr into the soil occurred [ 40 ].…”

“…Under wet–dry alternation leaching patterns, the release of heavy metals in the soil and the speciation of heavy metals are influenced. Wet–dry alternation alters soil aeration and moisture content and, consequently, controls the effectiveness of heavy metal elements in the soil, as well as the content of soluble organic carbon (DOC) in the soil [ 25 ]. The structure and activity of microbial communities are also significantly affected by natural wet–dry alternations [ 26 ].…”

Using Native Woody Plants for Phytomanagement of Urban Technosols Contaminated by Wood Pole Preservatives

“…The objective was to simulate the natural phenomenon caused by the alternation of anaerobic and aerobic conditions in the field. [33] This phenomenon was replicated on a reduced time scale by alternating the wetting and drying stages, following methodologies described by USPA and Li et al [28,34] The soil was wetted four times with tap water to 50% of water retention capacity. Wetting was followed by a 72 h drying phase at ambient temperature.…”

Phytoremediation of Heavy Metals and PAHs in Alkaline Slag Fill at a Wet Meadow Site

“…Among the variables, soil pH is the most important as it controls the solubility of metal hydroxides, carbonates and phosphates (Clemente et al, 2003;Carrillo -González et al, 2006). Soil moisture regime can also affect the transformation rate of heavy metals (Zheng and Hang 2011;Li et al 2015). The latter study found that when the factors, high pH and wettingdrying cycles are combined, the available fractions of metals decrease.…”