Impacts of impervious surface expansion on soil organic carbon--a spatially explicit study

Abstract

The rapid expansion of impervious surface areas (ISA) threatens soil organic carbon (SOC) pools in urbanized areas globally. The paucity of field observations on SOC under ISA (SOCISA), especially in dryland areas has limited our ability to assess the ecological impacts of ISA expansion. Based on systematically measured SOCISA (0-80 cm depth) of a dryland city, and land-use and land-cover change data derived from remotely sensed data, we investigated the magnitude and vertical/horizontal patterns of SOCISA and mapped the impact of ISA expansion on SOC storage. The mean SOCISA in the city was 5.36 ± 0.51 kg C m(-2), lower than that observed in humid cities but much higher than that assumed in many regional carbon assessments. SOCISA decreased linearly as the soil depth or the horizontal distance from the open area increased. SOCISA accounted for over half of the city's SOC stock, which decreased by 16% (primarily in the converted croplands) because of ISA expansion from 1990 to 2010. The impacts of the ISA expansion varied spatially, depending on the land- use and converted land-cover type.

Figure 1

Comparison of vertical distribution of soil organic carbon content, soil bulk density and soil organic carbon density between (a) urban impervious surface and (b) pervious surface at each layer (** and * above the error bars indicate significant differences between the soil_ISA and soil_PSA at the 0.01, 0.05 levels, respectively), and (c) the horizontal gradient of soil organic carbon from the edge of the impervious surface.

Figure 2

The land-cover types (impervious surface, urban green spaces, bare ground, and cropland) of Urumqi in 1990 (a) and 2010 (b), the expansion of impervious surface area (ISA) from 1990–2010 (c), and the carbon loss caused by ISA expansion (d). This map was generated by the one of the authors (Yan Yan) by using ArcMap (version 10.2).

Figure 3. Location of the study area (the Urumqi metropolis, Xinjiang, China) and sampling sites with photos showing the soil profiles of the impervious surface (red box 1) and the adjacent pervious surface (red box 2) in a site.

This map was generated by the one of the authors (Yan Yan) by using the ArcMap (version 10.2). The photographs in this map was taken by one of the authors (Yan Yan).