Urbanisation and soil sealing:The effects on ecosystem services and soil carbon

Urban soils are increasingly being recognised for the ecosystem services they provide, including soil carbon storage. As urban populations grow, soil ecosystem services in urban areas will become increasingly important. At present, there is a lack of knowledge on the range of ecosystem services provided by urban soils compared to those provided by non-urban soils, and a broad understanding of their provision is lacking. There is increasing interest in the ecosystem service of soil carbon storage as studies have illustrated the ability of urban soils to store large amounts of carbon. In urban areas, soils are affected by urbanisation in numerous ways, including soil sealing with impervious surfaces and the addition of anthropogenic materials, such as construction rubble and waste. At present, our understanding of the effects of soil sealing and anthropogenic materials on soil carbon storage is limited. This thesis seeks to addresses these knowledge gaps by furthering our understanding of urban soil ecosystem services, with a focus on soil carbon storage in sealed soils. It presents a systematic review of urban soil ecosystem service literature followed by a survey of sealed and greenspace soils from across Manchester, UK, to investigate the effects of sealing on soil carbon. The systematic review found that supporting processes and regulating services were most commonly studied, though the multifunctionality of urban soil was being missed in research. The urban soil survey revealed that sealed soils were not always depleted of carbon and, in some cases, legacy carbon stores were present due to black carbon additions which led to carbon stocks that were comparable to, or greater than, greenspace soils. Analysis of functional soil organic matter pools suggested that the legacy carbon store did not contribute to microbially-derived mineral-associated organic matter, indicating that it did not contribute to the persistent organic carbon pool with long residence times. Analysis of deeper soils under sealed surfaces illustrated that soil history was a major controlling factor on soil carbon rather than depth, and it highlighted the importance of heterogeneity in urban soils. This thesis provides new insights into the small but growing body of work on urban and sealed soils. It contributes to our understanding of urban soil ecosystem services, carbon storage in sealed soils, and the influence of anthropogenic additions and soil history on soil functions. The findings highlight the need to include urban and sealed soil information in soil mapping, planning and construction in urban areas, and to inform best practice when managing urban soils for soil functions and ecosystem services