Urban soils
Urban soils are unique because they are often profoundly altered by human activity, resulting in distinct physical, chemical, and biological properties that differ significantly from natural soils. Their primary defining characteristics include extreme spatial variability, compaction, contamination with human-made materials, and modified nutrient cycles.
Urban soils are often forgotten about in both research and soil quality monitoring programmes, but we depend on them for a range of purposes, just like we do soils used for food production.
Urban soils mitigate stormwater flows, provide food, and facilitate shade provision and temperature moderation by allowing trees to grow. There are many reasons we should value our urban soils.
Beneficial functions of urban soils
Urban soils provide a wide variety of essential ecosystem services that are vital for the sustainability and livability of cities. These functions help regulate the urban environment, support life, and provide a foundation for human activity.
The beneficial functions of urban soils include:
- Water Regulation and Flood Mitigation
- Climate Change Mitigation and Regulation
- Pollutant Filtration and Detoxification
- Support for Biodiversity and Habitats
- Support for Vegetation and Food Production
- Physical and Cultural Support
- Human Health and Well-being
To take advantage of these functions, communities are implementing green infrastructure practices, such as rain gardens and using compost amendments, to improve the health and functionality of degraded urban soils.
Threats to urban soils
Just like any other soil, urban soils have many beneficial properties, and we rely on them for a myriad of purposes, including flood protection, food production, shade provision, and recreation.
It's often forgotten that urban soils exist, including in soil quality monitoring and research. Urban soils are incredibly undervalued, in fact, people often pay to dump them in landfill - despite their vital role in environmental services.
Urban soils face multiple threats, including soil sealing, soil disposal, and contamination.
Relevant topics and projects
Manaaki Whenua – Landcare Research has extensive experience in urban soils. Our research focuses on understanding and mitigating the impacts of urban development on soil functions and promoting sustainable urban planning.
Key areas of our work include:
- Hydrological properties: Impact of how modern "cut/fill" developments impact on soil water storage and permeability.
- Policy and guidance: Our findings inform policy discussions, including a report by the Parliamentary Commissioner for the Environment that called for greater protections for urban soil to safeguard vital environmental services. We have also developed the first-ever New Zealand guide for managing "surplus" or excavated soil and sediments, promoting a circular economy approach.
- Urban ecology and design: Our work extends to urban ecology, developing approaches to integrate indigenous nature and biodiversity into urban design, including trials with green roofs and biodiverse subdivisions.
- Data and mapping: We provide soil information and mapping data (S-map Online) used by councils and stakeholders for better land-use planning and decision-making, covering a range of land uses including urban areas.
Our work emphasizes that soils are a critical part of nature-based solutions for urban challenges like stormwater management and climate change resilience.