Air‐Filled Porosity as a Key to Reducing Dissolved Arsenic and Cadmium Concentrations in Paddy Soils. Issue 3 (1st May 2018)

• Record Type: Journal Article
• Authors: Nakamura, Ken; Katou, Hidetaka; Suzuki, Katsuhiro; Honma, Toshimitsu
• Is Part Of: Journal of Environmental Quality. Volume 47:Issue 3(2018)
• Page Start: 496
• Page End: 503
• Publication Date: 2018-05-01
• Subjects: Agricultural ecology -- Periodicals; Environmental engineering -- Periodicals; Pollution -- Periodicals; 630
• DOI: 10.2134/jeq2017.09.0385
• Languages: English
• ISSNs: 0047-2425

Abstract

Abstract : Simultaneous suppression of rice ( Oryza sativa L.) uptake of As and Cd is challenging because these toxic elements are immobilized under contrasting redox conditions. Given the notion that oxygen diffusion governs redox conditions in temporarily drained paddy soil, we assume that the key to simultaneous suppression of dissolved As and Cd concentrations is air‐filled porosity (AFP) of soil. The objectives of this study were to reveal relationships between AFP and dissolved As and Cd concentrations in paddy soils and to identify the optimum water management, in terms of AFP, for simultaneous reduction of As and Cd. Dissolved As and Cd concentrations were determined in soil cores collected at different depths and times during rice growing seasons. Dissolved As concentrations were appreciable (>3 µg L −1 ) only when AFP was below a threshold value of 0.04 to 0.10 m 3 m −3, suggesting that dissolved As was rapidly immobilized once AFP exceeded the threshold value on drainage. Dissolved Cd concentrations were roughly proportional to AFP, with higher concentrations associated with lower soil pH. Although dissolved As concentrations tended to be low in soil samples with high dissolved Cd concentrations and vice versa, both concentrations were low when AFP was slightly above the threshold value for As immobilization. The results suggest that dissolved As and Cd can be simultaneously kept at low levels by appropriate water management practices that produce AFP slightly above the threshold value for As immobilization. Core Ideas: Dissolved As and Cd in paddy soil respond to changes in air‐filled porosity (AFP). Dissolved As was appreciable only when AFP was below a threshold value. The increase in dissolved Cd with AFP upon drainage was a slowly continuing process. Slightly above the threshold AFP, both dissolved As and Cd were at low levels. AFP is easier to predict than Eh, serving as a guide to optimal water management.