Surface soil organic carbon accumulation in urban parks increases with urbanization intensity: a case study for Hangzhou, China

Abstract

Background and aims

Greenspace soils are a critical component of urban ecosystems, playing an essential role in delivering ecosystem services. Soil organic carbon (SOC) in these areas show considerable variability and uncertainty due to urbanization. However, it remains poorly understood how urbanization intensity and vegetation type affect greenspace SOC concentration.

Methods

This study examines how urbanization intensity (low, medium and high) and vegetation type (trees, shrubs and grasses) influence SOC concentration in urban parks in Hangzhou city, China. Urbanization intensity is measured by population, economy and urban built-up area. In addition, the response of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) in greenspace soil to urbanization intensity was also assessed in the study to further understand the stability of SOC in urban parks.

Results

Total SOC and its fractions (POC and MAOC) increased significantly in urban parks with the increase of urbanization intensity. Despite this increase, SOC did not reach saturation levels, even under high urbanization intensity. Urbanization affected SOC concentration indirectly by modifying soil total nitrogen (+ 17.1%), total phosphorus (+ 7.1%), microbial biomass carbon (+ 10.9%), microbial biomass nitrogen (+ 0.7%), clay and fine silt contents (+ 1.9%), calcium ion (+ 1.1%), and P-acquiring enzyme activity (+ 1.0%). Among SOC fractions, MAOC, rather than POC, was the dominant form along the suburb-urban gradient, with the greater increase in MAOC driving the increase in overall SOC concentration. No significant difference in total SOC was found among vegetation types, but SOC accumulation in grasses was more responsive to urbanization than in trees and shrubs.

Conclusions

Intensified urbanization leads to higher SOC concentration, particularly MAOC. These findings are crucial for quantifying the impact of urbanization on SOC in urban parks and achieving better carbon management.