11.2 Soil rehabilitation and reclamation techniques

Urban soil assessment and rehabilitation are crucial for maintaining healthy city environments. These processes involve various methods to evaluate soil quality, from visual inspections to advanced chemical tests. Understanding these techniques helps urban planners and environmentalists make informed decisions about soil health.

Rehabilitating urban soils requires a range of strategies, including physical, chemical, and biological remediation techniques. These methods can remove contaminants, improve soil structure, and restore ecosystem functions. Proper planning and implementation of these techniques are essential for successful urban soil rehabilitation projects.

Urban Soil Assessment and Rehabilitation

Methods of urban soil assessment

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• Visual soil assessment examines soil color indicating organic matter content, structure revealing aggregate stability, and presence of organic matter suggesting soil health
• Physical soil tests analyze texture determining particle size distribution, measure bulk density indicating compaction levels, and test infiltration rate assessing water movement
• Chemical soil tests measure pH influencing nutrient availability, analyze nutrient content (N, P, K) for fertility assessment, and determine heavy metal concentrations for contamination evaluation
• Biological soil tests measure soil respiration rate indicating microbial activity, assess microbial biomass reflecting soil ecosystem health, and count earthworm populations as soil quality indicators
• Remote sensing techniques utilize aerial photography for large-scale soil mapping and satellite imagery analysis for detecting soil moisture and vegetation patterns
• Soil compaction tests employ penetrometer readings measuring soil strength and cone penetration tests evaluating soil layers' resistance to pressure

Urban soil remediation techniques

• Physical remediation techniques
  • Soil washing removes contaminants using water-based solutions and surfactants
  • Soil vapor extraction removes volatile organic compounds by applying vacuum to soil
  • Thermal desorption uses heat to separate contaminants from soil particles
• Chemical remediation techniques
  • Chemical oxidation converts harmful contaminants into less toxic compounds using oxidizing agents (hydrogen peroxide)
  • Soil flushing extracts contaminants using water or other flushing solutions (chelating agents)
  • Electrokinetic remediation mobilizes contaminants using electric current through electrodes in soil
• Biological remediation techniques
  • Phytoremediation uses plants to extract (sunflowers) or stabilize contaminants in soil
  • Bioremediation utilizes microorganisms to break down pollutants (oil-eating bacteria)
• Containment techniques
  • Capping covers contaminated soil with clean material (clay, geotextiles) preventing exposure
  • Vertical barriers prevent lateral movement of contaminants using impermeable walls (slurry walls)

Soil Improvement and Rehabilitation Planning

Effectiveness of soil improvement strategies

• Organic amendments
  • Compost improves soil structure, increases water retention, and enhances nutrient content
  • Biochar enhances water retention, increases microbial activity, and sequesters carbon
• Inorganic amendments
  • Lime adjusts soil pH, improving nutrient availability for plants in acidic soils
  • Gypsum improves soil structure in clay soils, enhancing drainage and root penetration
• Bioremediation techniques
  • Mycoremediation uses fungi (oyster mushrooms) to degrade organic contaminants
  • Bacterial augmentation introduces specific bacteria to break down pollutants (PCBs)
• Soil inoculants
  • Mycorrhizal fungi enhance nutrient uptake, improve soil structure, and increase plant resilience
  • Nitrogen-fixing bacteria (Rhizobium) improve soil nitrogen content, reducing fertilizer needs
• Cover crops reduce erosion, add organic matter, and improve soil structure (clover, rye)
• Mulching conserves soil moisture, suppresses weeds, and moderates soil temperature

Planning for urban soil rehabilitation

• Site assessment involves soil testing, analyzing historical land use, and inventorying current vegetation
• Goal setting determines intended land use, establishes specific soil quality targets, and outlines rehabilitation timeline
• Constraint identification considers budget limitations, legal requirements, and logistical challenges
• Remediation strategy selection based on contaminant types, levels, time frame, and cost-effectiveness
• Soil improvement techniques include:
  1. Decompaction methods (deep ripping)
  2. Organic matter incorporation (compost addition)
  3. pH adjustment if necessary (lime application)
• Vegetation establishment plan selects native plants, determines seeding or planting methods, and develops irrigation strategy
• Monitoring and maintenance schedule includes regular soil testing, vegetation health assessment, and adaptive management approach
• Stakeholder engagement involves community in planning and implements education and outreach programs