Ecological remediation of waste resources by comprehensive afforestation utilization in mudflat ecosystem

The ecological rehabilitation engineering out of the coastal mudflat ecosystem was accomplished principally by virescence. However, the lack of proper soil resources for reformation of the coastal mudflat was the primary difficulty. Artificial soil mounds composed of three solid wastes (dredged sediments, caustic sludge, and coal ash) were constructed and afforested. The waste properties and the effects of the unnatural soil on tree growth, desalination, pH value, biomass, microbial community, and toxic metals were investigated in the next couple of years. After four growing seasons, salt content was reduced to the threshold for salt-sensitive plants and the pH value remained stable (below 8.30). The total biomass of the tree-shrub-herb community, which was composed of Fraxinus pennsylvanica Marsh, Populus tomentosa Carr, Robinia pseudoacacia Linn, Loniccra macckii. Maxim, Tamarix chinensis Lour, and Medicago sativa L, was above 31.92thm(-2). The survival, tree height, diameter, and biomass of these plants varied significantly across plant species. The number of colony-forming units (CFU) per gram of dry artificial soil was significantly higher than foreign soil and coastal solonchak at 0-40cm deep. The concentrations of Hg, Cr, Cd, As and Pb in leachates and the artificial soil were below nationally accepted norms. The results show that the comprehensive afforestation utilization in Tianjin coastal ecosystem could solve the problems of solid waste pollution and the damage to nearby ecosystem as well as reducing the cost of rehabilitations.