Factors controlling spatial variation in soil aggregate stability in a semi-humid watershed
Introduction
Soil aggregates are the basic units of soil structure formed naturally by soil particles (Li et al., 2020; Xu et al., 2020). The stability of soil aggregates can affect soil ability to support ecosystem functions, including food production, flood control, pollution prevention and climate change mitigation. This is achievable through the impact of soil aggregates on a wide range of soil processes such as compaction, aeration, germination and rooting, water flux, solute transport, storage and stabilization of organic carbon, nutrient adsorption, biological activity and crusting (Ayoubi et al., 2012; Besalatpour et al., 2014, 2013; Rivera and Bonilla, 2020; Wang et al., 2019; Wu et al., 2016; Yu et al., 2020). Soil aggregate stability (SAS) is also a key determinant of soil erodibility and is an input parameter in spatially-distributed soil erosion models (Ayoubi et al., 2018; Shi et al., 2020). However, SAS has a high degree of spatial heterogeneity at different scales (Annabi et al., 2017; Bird et al., 2007). A good understanding of the controls on spatial variation in SAS is critical for accurately predicting soil erosion across landscapes and development of effective management strategies for sustainable ecosystem functions (Annabi et al., 2017).
There are vast studies on the effects of environmental factors on SAS. Studies have shown that SAS is not only affected by soil intrinsic properties such as soil texture (Dimoyiannis, 2012; Lado et al., 2004; Zuo et al., 2019), water retention (He et al., 2018) and organic carbon content (Abiven et al., 2009; Six et al., 1998; Yu et al., 2020), but also by external factors such as topography (Le Bissonnais et al., 2002; Zádorová et al., 2011), vegetation (Ilay and Kavdir, 2018; Wang et al., 2019), land use and associated management practices (Ayoubi et al., 2012, 2020; Okolo et al., 2020; Wang et al., 2018; Zhao et al., 2017). For example, clay particles are efficient for aggregation due to their large specific surface area, high cation exchange capacity and therefore high physicochemical interaction activity (Amézketa, 1999). Soil organic matter (SOM), as the main binding agent in aggregate formation, can increase SAS by promoting the formation of organic-mineral assemblages and forming hydrophobic coatings around aggregates (Vogelmann et al., 2017; Yu et al., 2017). Vegetation can improve SAS through root network connectivity, root-soil adhesion and root biochemistry (Li et al., 2020). As determinants of flow velocity and surface runoff generation, topographic attributes such as slope and aspect are strongly correlated with SAS (Le Bissonnais et al., 2002). Management practices (e.g., tillage) associated with land use affect SAS through mechanical weakening and breaking up of aggregate structures (Wacha et al., 2018). Although strong correlations exist between SAS and these environmental factors, the relative importance of these factors in terms of driving the variation in SAS is not entirely clear. This is because most studies have focused on the effects of individual factors on SAS rather than their interactive effects.
In fact, some of these influencing factors are interlinked. In addition to direct effects, they also exert indirect effects on SAS. For example, vegetation can indirectly affect soil SAS through soil property dynamics such as the fixation and decomposition of SOM (Wang et al., 2019, 2016b; Zhao et al., 2017). Topography can affect a series of eco-hydrological processes involving the movement and fate of soil water and particles, spatial allocation of vegetation cover and land use; all of which in turn affect SAS (Le Bissonnais et al., 2002; Wang et al., 2013; Zádorová et al., 2011). Therefore, it is essential to consider the interaction effects of the factors in order to better understand the variation in SAS, based on exhaustive spatial surveys of SAS and comprehensive environmental characteristics. The need for such information is increasing in hydrological modeling at watershed scales as basic units on which management practices are built.
Chinese Loess Plateau (CLP) is one of the most severely eroded areas in the world as it is characterized by loose loess soil, steep topography, heavy summer rainstorm and inappropriate land management (Zhang et al., 2019). Since the 1950s, a variety of measures have been implemented by the Chinese government to control soil erosion and restore vegetation on the plateau (Xin et al., 2016). The “Grain for Green” (GFG) project launched in 1999 is one of the most important programs in recent time that converts steep-slope croplands and wastelands into grasslands, shrublands and forests (Deng et al., 2019). The highly complex landscape is suitable for systematic investigation of the effects of environmental factors on SAS. Studies have been conducted on spatial variation in SAS in relation to land use (Wang et al., 2018; Wei et al., 2012), vegetation cover (Wang et al., 2019; Zhu et al., 2017) and vegetation succession (Cheng et al., 2015; Yao et al., 2019) in the region. However, little work has been done on spatial variation in SAS and the driving factors (direct or indirect) at watershed scale. This is because of the high cost and time-consuming efforts associated with studying SAS. The specific objectives of this study were to: i) investigate the level and spatial variation in SAS across an entire watershed; ii) assess the importance of major factors relative to spatial variation in SAS; and iii) elucidate the structural cause–effect relationships of SAS and the major factors.
Section snippets
Study area
This study was conducted in ShuangChaGou watershed (1.1 km2), located in Luochuan County, Shaanxi province, China (Fig. 1a). The study area has a warm temperate and semi-humid continental monsoon climate with mean annual precipitation of 622 mm. The precipitation is concentrated over summer (July to September) and mostly occurs in the form of storm. The mean annual temperature is 9.2 °C, with accumulated temperature above 10 °C of 3040 °C. The mean annual sunshine hours is 2552 h, with mean
SAS indices statistics and distribution
The descriptive statistical parameters for the soil aggregate fractions and SAS indices are given in Table 1. The aggregates were dominated by small macroaggregates for both soil depths, with averages of 41.2 and 38.1 % at the 0–10 cm and 10–20 cm depths, respectively. Microaggregates (29.1 and 30.4 %) and <0.053 mm fractions (24.2 and 26.7 %) accounted for the second and third highest proportions in the bulk soil, while large macroaggregates (5.6 and 4.8 %) was the lowest proportion. For the
SAS in the watershed
The watershed is characterized by low SAS. The soil MWD ranges were 0.33–1.87 and 0.27–1.75 mm for the 0–10 and 10–20 cm soil depths, respectively (Table 1). This is consistent with the results of other studies (0.22–2.84 mm) on CLP (Wang et al., 2019, 2018; Wei et al., 2012; Zhu et al., 2017). According to the classification criteria developed by Le Bissonnais (1996) — MWD < 0.4 mm is classed as very unstable, 0.4–0.8 mm as unstable, 0.8–1.3 mm as medium, 1.3–2.0 mm as stable and > 2.0 mm as
Conclusions
At the watershed scale, SAS was affected by various factors, including soil, topography, vegetation and land use. This had a potential effect on the formation of soil aggregates and the processes of breakdown. Soil intrinsic properties, primarily soil texture and SOC, were more important in controlling the variation in SAS. Topographic attributes such as TWI and altitude, can also affect SAS either by direct impacts or by indirect impacts through influencing soil property dynamics such as SOC
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 research was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (No. XDB40020203), the National Natural Science Foundation of China (No. 41971045), and the Youth Innovation Promotion Association CAS. We sincerely thank the anonymous reviewers for their valuable assistance in improving the manuscript.
References (61)
- et al.
The effects of organic inputs over time on soil aggregate stability – a literature analysis
Soil Biol. Biochem.
(2009) - et al.
Spatial variability of soil aggregate stability at the scale of an agricultural region in Tunisia
Catena
(2017) - et al.
Soil aggregation and organic carbon as affected by topography and land use change in western Iran
Soil Tillage Res.
(2012) - et al.
Estimating wet soil aggregate stability from easily available properties in a highly mountainous watershed
Catena
(2013) - et al.
Multi-scale variability in soil aggregate stability: implications for understanding and predicting semi-arid grassland degradation
Geoderma
(2007) - et al.
Soil aggregation and intra-aggregate carbon fractions in relation to vegetation succession on the Loess Plateau, China
Catena
(2015) - et al.
Land-use changes driven by’ Grain for Green’ program reduced carbon loss induced by soil erosion on the Loess Plateau of China
Glob. Planet. Change
(2019) - et al.
Geochemical characterization of the Luochuan loess-paleosol sequence, China, and paleoclimatic implications
Chem. Geol.
(1996) - et al.
Soil aggregate stability improves greatly in response to soil water dynamics under natural rains in long-term organic fertilization
Soil Tillage Res.
(2018) - et al.
Depth-dependent response of soil aggregates and soil organic carbon content to long-term elevated CO2 in a temperate grassland soil
Soil Biol. Biochem.
(2018)
Microaggregate stability and storage of organic carbon is affected by clay content in arable Luvisols
Soil Tillage Res.
Colloidal iron and organic carbon control soil aggregate formation and stability in arable Luvisols
Geoderma
Physical and chemical protection in hierarchical soil aggregates regulates soil carbon and nitrogen recovery in restored perennial grasslands
Soil Biol. Biochem.
The role of biology in the formation, stabilization and degradation of soil structure
Geoderma
Mapping soil organic matter using the topographic wetness index: a comparative study based on different flow-direction algorithms and kriging methods
Ecol. Indic.
Predicting soil aggregate stability using readily available soil properties and machine learning techniques
Catena
Soil microaggregate size composition and organic matter distribution as affected by clay content
Geoderma
A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics
Soil Tillage Res.
Soil moisture influences sorptivity and water repellency of topsoil aggregates in native grasslands
Geoderma
Regional-scale variation and distribution patterns of soil saturated hydraulic conductivities in surface and subsurface layers in the loessial soils of China
J. Hydrol.
Estimating the influence of related soil properties on macro- and micro-aggregate stability in ultisols of south-central China
Catena
Aggregate stability and associated organic carbon and nitrogen as affected by soil erosion and vegetation rehabilitation on the Loess Plateau
Catena
Using soil aggregate stability and erodibility to evaluate the sustainability of large-scale afforestation of Robinia pseudoacacia and Caragana korshinskii in the Loess Plateau
For. Ecol. Manage.
Spatial variations of aggregate stability in relation to sesquioxides for zonal soils, South-central China
Soil Tillage Res.
Spatial variability in soil organic carbon and its influencing factors in a hilly watershed of the Loess Plateau, China
Catena
Carbon stabilization in aggregate fractions responds to straw input levels under varied soil fertility levels
Soil Tillage Res.
Response of aggregate associated organic carbon, nitrogen and phosphorous to re-vegetation in agro-pastoral ecotone of northern China
Geoderma
Spatial analysis of soil aggregate stability in a small catchment of the Loess Plateau, China: I. Spatial variability
Soil Tillage Res.
The coupling effects of soil organic matter and particle interaction forces on soil aggregate stability
Soil Tillage Res.
Importance of soil interparticle forces and organic matter for aggregate stability in a temperate soil and a subtropical soil
Geoderma
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2022, Journal of Cleaner ProductionCitation Excerpt :Hills and mountains are the dominant landforms in the southern part of our study area and account for 80% of Fujian Province (Zhu et al., 2021a), so the main land use was forest in the south of the study area (Fig. 1d). Stable macro-aggregates tend to form when more SOM serves as a binding agent and when anthropogenic activities in forests are absent (Fig. 3 and S1) (Zhang et al., 2021). The central part of our study area is also covered by hills and mountains (>70%), and farmland, including dry land and irrigated paddy fields, is sporadically distributed on plains.