Changes in soil organic carbon stocks by urbanization

Soils accumulate about 1500-2000 Pg (1015 g) C, providing the largest stock in terrestrial ecosystems (Swift, 2001; Janzen, 2004). Historically, soil organic carbon (SOC) is a widely accepted indicator of soil quality. For example, SOC depletion is used as a basic indicator of soil degradation (Nortcliff, 2002; Bastida et al., 2008). The shift in recent decades from traditional agricultural attitudes of soil as a substrate for food production to its role in essential ecological processes and functions highlighted the importance of soil carbon stocks and fluxes (Bolin et al., 1979; Kovda and Rozanov, 1988). Carbon 62sequestration, for example, is an important process to mitigate climate change (IPCC, 2001; Lal, 2004; Janzen, 2004), whereas soil respiration is the largest biogeochemical carbon efflux into the atmosphere, contributing to climate change (Raich et al., 2002; Schulze, 2006). Soil microbial carbon indicates the soil’s performance as a habitat for microorganisms. Soil microbial communities contribute to biodiversity and gene reservoirs (Andrews et al., 2004; Blum, 2005; Dobrovolsky and Nikitin, 2012). The relation between soil microbial carbon and microbial respiration defines the microbial metabolic coefficient, which is widely accepted as a relevant indicator of the state of microbial soil communities and ecosystem disturbance (Anderson and Domsch, 1985; Dilly et al., 2003; Bastida et al., 2006). Many studies classifying and assessing soil functions acknowledge the role of SOC (e.g., BBodSchG, 1998; Karlen et al., 2003; Andrews et al., 2004; Blum, 2005; Dobrovolsky and Nikitin, 2012; Table 3.1). Although reviewed approaches to classify soil functions differ in terms of definitions and labels of each function, their total number, and the classification’s major purpose, they all consider SOC as an important parameter: up to two thirds of the soil functions are directly or indirectly related to SOC stocks. The recently emerged concept of ecosystem services (ESs; MA, 2003) expands the analysis of environmental properties, processes, and functions with human economic benefits (de Groot, 1992; Costanza et al., 1997). Although soil services are considered part of ESs (Breure et al., 2012), SOC directly or indirectly affects many specific ESs, including soil fertility maintenance, food production, and climate regulation (MA, 2003; TEEB, 2010). Currently, most of the carbon assessments focus on natural (forest/meadows) and agricultural ecosystems (e.g., Islam and Weil, 2000; Valentini et al., 2000; Hamilton et al., 2002; Cruvinel et al., 2011; Fromin et al., 2012). Much less, however, is known about the effect of urbanization on soil carbon stocks and fluxes. © 2018 by Taylor & Francis Group, LLC.