Effects of Flue Gas Desulfurization (FGD) Gypsum on Desalination of Reclaimed Tidal Flat Soil

Soil desalination of reclaimed tidal land by natural processes of rain washing and plant community succession needs several decades. Using flue gas desulfurization (FGD) gypsum as soil amendments can accelerate this natural process of desalination to within a couple of years by replacing exchangeable sodium (Na⁺) with calcium ions (Ca²⁺). Field experiments in a reclaimed tidal land located at Chongming Island of Yangtze River Delta had been conducted with FGD gypsum at rates equivalent to 0, 15, 30, 45, 60 t/hm² since 2011. The results showed that under the condition of 1 050 mm annual precipitation and two years after FGD gypsum treatment, the desalination effect of top soil (0-30 cm) was significant, and degree of soil alkalization measured as exchangeable sodium percentage (ESP) decreased by 53%. Species number and coverage of herbaceous plants increased with increasing rates of FGD gypsum (P＜0.05). Instead of dominated species reed, some halophytic herbs like Suaeda glauca, Herba taraxaci, Artemisia lavandulaefolia, and even non-halophytic Medicago sativa and Alternanthera philoxeroides were found in the 1 m×1 m quadrats. Survival rates of woody plants on higher FGD gypsum treatments were also significantly higher than that of controls (P＜0.05). It is expected that safe levels of FGD gypsum can be applied effectively to remediate saline soil of reclaimed tidal lands on a large scale.