Landslide and aspect effects on artificial soil organic carbon fractions and the carbon pool management index on road-cut slopes in an alpine region
Graphical abstract
Introduction
Soil organic carbon (SOC) storage has been widely considered as a promising measure for mitigating global climate change through soil carbon (C) sequestration (Huang et al., 2010). The soil C pool is sensitive to climate change and human disturbance, and its feedback can have a significant negative impact on atmospheric C emissions with soil degradation (Lal, 2002, She et al., 2014). SOC is important for soil quality and productivity, thus maintaining an adaptive SOC content is essential for mitigating global warming (Luo et al., 2011, Tang et al., 2018). Although SOC is an indicator of soil quality, some SOC fractions, such as dissolved organic carbon (DOC), easily oxidizable organic carbon (EOC), and particulate organic carbon (POC), can be used to explore even minor changes in regulating soil degradation (Bationo and Buerkert, 2001, Sainepo et al., 2018). Additionally, the carbon pool management index (CPMI) has been used as a sensitive measure to calculate the rate of change in soil C dynamics in a terrestrial ecosystem (Blair et al., 1995, Blair et al., 2006). A higher CPMI value implies that soil is being restored, improved, and maintained (Gami et al., 2009). However, the majority of previous CPMI studies have focused on agricultural lands (Chaudhary et al., 2017, Tang et al., 2018), grasslands (She et al., 2014, Qin et al., 2016, Sainepo et al., 2018) or forests (Lozano-García et al., 2016, Jasińska et al., 2019). In ecological restoration of slopes, such as roadway rock-cut slopes, these measures have largely been ignored.
Large-scale road engineering construction has led to significant soil erosion and land-sliding, resulting in a significant area of bare land in mountainous areas of China (Xiao et al., 2012). In these areas, amid concerns for the ecological environment, outside soil spray seeding (OSSS) technology has been used as an effective method to restore vegetation to bare rock-cut slopes (Gao et al., 2007, Chen et al., 2019). This process maintains slope stability by covering a metal mesh frame with artificial soil containing a mixture of humus, straw, soluble chemical fertilizer, bonding agents, water-retention agents, plant seed mixture, and backfill soil (Li et al., 2018a). However, even with the implementation of OSSS technology, deforestation and the conversion of land to other land-uses can release a large amount of C from surface soils which can inevitably affect SOC stocks (Yimer et al., 2006, Fu et al., 2018). Additionally, slope aspect can directly or indirectly affect abiotic and biotic factors, thereby contributing to C dynamics (Ai et al., 2017, Bayat et al., 2017, Bennie et al., 2008). At mid and low latitudes, mountain areas hold the highest potential for C storage (Garcia-Pausas et al., 2007). Furthermore, Lozano-García et al. (2016) highlighted that north-facing slopes had higher SOC content than other topographic aspects. Fissore et al. (2017) recorded that slope aspect and landslide occurrence were closely linked to the C cycle, and Jasińska et al. (2019) found that slope aspect significantly affected litter decomposition rate, leading to a changed SOC content. However, the majority of studies on the effects of slope aspect on soil C storage and dynamics have been undertaken in other ecosystems, such as forests (Yimer et al., 2006, Lozano-García et al., 2016, Zhu et al., 2017), grassland (Han et al., 2010, Qin et al., 2016, Fissore et al., 2017), and agricultural lands (Doetterl et al., 2012). Far less research has focused on ecological restoration in mountainous areas, especially in artificial soil systems. She et al. (2014) found that SOC estimation is affected by slope aspect in artificial grassland and Li et al. (2018b) showed that on rock-cut slopes restored at low latitudes, artificial soil quality is significantly affected by slope aspect.
Landslide occurrence is driven by topography, precipitation, and anthropogenic factors, such as road development, land-clearance on steep terrain and the service life of metal mesh used during construction (Knapen et al., 2006, Mugagga et al., 2011, Chen et al., 2015, Cheng et al., 2016, Chen et al., 2019). Landslides result in soil loss, destruction of the original vegetation and changes to soil physical and chemical properties that may cause a series of ecological and environmental problems, such as a serious decline in soil quality. Walker et al. (1996) suggested that soil organic matter (SOM) and nutrients are a limiting factor for landslide succession, and Dialynas et al. (2016) found that SOM plays a key role in the initial stage of soil formation on a landslide. Błońska et al. (2018) believed that landslides were closely linked to the C cycle and that SOM fraction can be utilized as an indicator of soil changes due to a landslide. Although previous studies have found that SOC variability is due to the nature of the landslides (for example Mugagga et al., 2011, Mai et al., 2015, Błońska et al., 2018), few studies have focused on artificial soil systems after landsliding, especially on rock-cut slopes that utilize ecological restoration techniques (such as OSSS techniques).
Chuanhuang highway (S301) is located in a typical, ecologically fragile mountainous area in western China, which is also an earthquake zone. On August 8, 2017, a magnitude 7.0 earthquake occurred in Jiuzhaigou county, Sichuan province. Located in the deep valley mountains, the earthquake triggered numerous landslides along the highway, causing highway disruption. Due to the dangerous rock-cut slope angle along the highway, damaged sections were repaired and the road was reconstructed. However, the ecological condition of the soil on the rock-cut slope has been overlooked (Cheng et al., 2018). Previous investigations have largely focused on landslide zone stability analysis (Liu et al., 2011, Cheng et al., 2018), with few studies focusing on artificial soil characteristics. Therefore, we examined artificial soil properties on a rock-cut slope using cold area highway ecological post-disaster restoration and reconstruction as a reference. Specifically, our study aims were to: (1) investigate SOC fractions and enzyme activity of artificial soil on different slope aspects to provide a scientific basis for the restoration of roadway rock-cut slopes; (2) document artificial soil nutrient changes after landslide disturbance, to improve productivity and to protect the ecological environment; and (3) describe the relationships between artificial SOC fractions and other indices and enrich knowledge of artificial soil SOC fractions in alpine areas.
Section snippets
Soil sampling sites
The study site was located on the S301, 3110–3270 m a.s.l. within the area of Jiuhuang airport, Songpan County, Sichuan province, China (32°49′ N, 103°39′ −103°40′E). The study site experiences a plateau temperate climate where the rainy season extends from May to October and the average, maximum, and minimum air temperatures in the area are 5.7 °C, 31.3 °C, and −21.0 °C, respectively. Annual average rainfall is 693.2 mm, annual average evaporation is 450 mm, and annual average wind speed is
SOC changes
On slopes not affected by a landslide, SOC was highest on the west-facing slope and declined in the order : NL-W > NL-S > NL-E > NL-N (Table 2). Furthermore, SOC for NL-W and NL-S was significantly higher (p < 0.05) than on NL-E and NL-N aspects. In contrast, there were no significant differences in SOC among four slope aspects affected by a landslide (p > 0.05).
Compared with non-landslide slopes, SOC for landslide slopes declined by 42.11% (p < 0.05) on east-facing, 66.89% (p < 0.05) on
Discussion
Our results support previous findings, indicating that artificial soil nutrients (Lozano-García et al., 2016, Li et al., 2018a, Li et al., 2018b, Jasińska et al., 2019) and soil enzyme activities (Zhang et al., 2018) can be affected by slope aspect in alpine regions, even using OSSS technology. Moreover, soil nutrients (Mugagga et al., 2011, Cheng et al., 2016, Dialynas et al., 2016, Schomakers et al., 2017) and soil enzyme activities (Błońska et al., 2018) were recorded as lower in alpine
Conclusion
Our results indicated that slope aspect had an influence on SOC, POC, EOC, TN, urease, sucrase, and consequently CPMI, but no influence on NO3–-N, NH4+-N, and DOC. Additionally, CPMI on non-landslide-east-facing slopes was the lowest, suggesting that these slopes had the worst level of management on the Chuanhuang highway. Therefore, to improve the ecological recovery of slopes, it is important to pay attention to strengthening management and maintenance of east-facing slopes during road
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported jointly by the National Key R & D Program of China (2017YFC0504903) and the National Nature Foundation (41971056).
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