Soil Physico-Chemical Properties Change Across an Urbanity Gradient in Berlin

James Whitehead,Anne Hiller,Stefan Hempel,Moritz Von Der Lippe,Matthias C Rillig

doi:10.3389/fenvs.2021.765696

Abstract

In this study the impacts of urbanity on physical soil properties were explored by measuring water stable aggregates, combined particle size, infiltration rate and hydrophobicity across an urban gradient. The use of a gradient allowed for the relative importance of different environmental drivers to be assessed. We sampled 54 sites across Berlin and used a pre-existing database of environmental variables to extract three main axes of variation relating to urbanity, soil nutrient content, and heavy metal content. These axes, along with site age, were used to explore the drivers of changes in physical properties across an urban landscape. The percentage of water stable aggregates was found to decrease with urbanity, whilst infiltration rate was found to increase. Hydrophobicity did not appear to be influenced by urbanity but interacted with both infiltration rate and water stable aggregates. Combined particle sizes in the soil were found to increase with urbanity. Our findings provide evidence for urbanity being an important driver of variation in physico-chemical soil properties, which has implications for the provision of ecosystem services by these soils.

Highlights

Since the middle of the 20th Century, the global urban population has been rapidly increasing, from 751 million individuals in 1950 to an estimated 4.2 billion in 2018, which accounts for roughly 55% of the total global population (United Nations, 2018)
It was found that axis 1 scores were significantly higher for new sites than old sites (Wilcoxon rank sum W 623, FIGURE 3 | Relationships between soil parameters versus PCA axes and site age (N New, O Old). (A) WSA% vs. PCA axes (B) WSA% vs. Age (C) mean weight diameter (MWD) vs. PCA axes (D) MWD vs. Age (E) Infiltration Rate vs. PCA axes (F) Infiltration Rate vs. Age
A reduction in WSA% with increasing urbanity has implications for urban soil biodiversity due to the important role that bacteria and fungi (Lehmann et al, 2017), in particular arbuscular mycorrhizal fungi (Lehman et al, 2020), play in aggregate formation, a reduction in WSA% in urban soils may be a result of reduced microbial activity

Summary

Introduction

Since the middle of the 20th Century, the global urban population has been rapidly increasing, from 751 million individuals in 1950 to an estimated 4.2 billion in 2018, which accounts for roughly 55% of the total global population (United Nations, 2018). It has been estimated that whilst less than 0.5% of total global land surface is covered in built-up urban developments, this small percentage represented a total of 0.5 million km at the turn of the last century (Goldewijk et al, 2010), estimates vary (Potere and Schneider, 2007). These urban ecosystems provide services to their inhabitants but are often hotspots for global change factors such as increased temperature (Arnfield, 2003), salinisation (Equiza et al, 2017), and the presence of pollutants such as heavy metals (Plyaskina and Ladonin, 2009). Urban landscapes have previously been associated with generally high levels of compaction (Lehmann and Stahr, 2007), this may only be true in localised areas of high intensity usage (Edmondson et al, 2011)

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Results

Discussion

Conclusion