Orginal articleSoil erosion progression under rill and gully erosion processes and its effect on variations of mechanisms controlling C mineralization ratio
Introduction
Detachment and transportation of soil particles by overland flow are the most important causes of land degradation in water erosion-prone environments that significantly affect the global carbon cycle in terrestrial ecosystems (Mohseni and Salar, 2021). Different stages of linear erosion development, such as rilling and gullying, can irreversibly damage the soil aggregate properties (Smith et al., 2001; Chaplot et al., 2005; Su et al., 2010). Soil aggregate is recognized as a major factor protecting the SOC against decomposition and mineralization by soil microbial respiration (Quijano et al., 2019). The progression of water erosion patterns from rill to gully erosion significantly affects the level of soil aggregate degradation (physiochemical indicators such as particles size distribution, geometric mean diameter, mean weight diameter, and labile components of SOC, including dissolved SOC and microbial biomass carbon) (Six et al., 2000; Nael et al., 2004), and thereby stimulates changes in the biochemical mechanisms controlling the OC mineralization ratio within the original soils eroded by the rill and gully erosion processes.
The rill and gully have recognized as two stages of erosion progression that different driving forces encourage the appearance and development of these erosional landforms (Jiang et al., 2019). The rill erosion process occurs due to the concentration of the flow into small channels that their depth is less than 10 cm. In this condition, the concentrated flow forces detached particles from the walls and at the bottom of the rill. Rill head-cut migration and sidewall expansion affected by the overland flow encourage the development of rill channels into the ephemeral gullies that are larger than rills (in terms of length and width) and smaller than classical gullies. Finally, classical gullies are referred to the stage of channel development where land is taken out of the production. In this type of erosion, gullies cannot be removed by tillage operation. Rill and ephemeral gully erosion are the transitional phases to irreversible states of soil erosion (i.e. classical gullies). Therefore, geo-conservation and restoration efforts in these stages can help to prevent the occurrence of such irreversible transitions.
In initial erosion stages, such as the rill erosion process, labile OC-rich topsoil-layer strongly removes by raindrop energy (Owens et al., 2002; Mueller-Nedebock et al., 2016). Rill head-cut migration and sidewall expansion affected by the overland flow encourage the development of rill channels into the gully, causing the degradation of a larger amount of OC-rich topsoil that is combined with deeper horizons poor in OC (Bryan, 2000; Nadeu et al., 2011). These conditions weaken the aggregate structural stability in the original soils eroded by the gullies compared with the rill erosion (Schiettecatte et al., 2008). Therefore, variability in the depth of the soil layer eroded by the different erosion stages significantly affects the quantity of labile components of SOC and the characteristics of soil aggregates, which can be considered as the indicators for evaluating the soil degradation levels (Su et al., 2010) in the original soils influenced by the rill and gully erosion processes. These conditions can be responsible for variability in mechanisms controlling the level of SOC vulnerability to microbial respiration under the different erosion patterns.
To date, many studies have focused on the role of different water erosion stages such as interrill, rill, and gully erosion in SOC cycling (Roose et al., 2006; Zhang et al., 2006; Kuhn et al., 2009; Huang et al., 2010; Hemelryck et al., 2010; Nadeu et al., 2011; Cantón et al., 2014; Jiang et al., 2019; Quijano et al., 2019). The majority of studies in this field investigated the impacts of water erosion patterns on the dynamics of SOC during sediment transport and deposition processes. These studies showed that different erosion processes could cause a preferential accumulation of SOC in deposited sediments. However, the fate of the original soils eroded by the rill and gully erosion processes and their function on the physical and biochemical soil properties controlling the vulnerability level of SOC to microbial mineralization have been extensively neglected.
In this study, we illustrate the impact of different erosion stages, including the rill and gully erosion processes, on the relationship pattern between the C mineralization ratio and the physiochemical soil characteristics in the original soils eroded by these processes. We employed a conceptual approach incorporating an empirical model (multiple linear stepwise regressions) and our field survey data to evaluate the following objectives: 1) the effect of soil erosion progression (rill and gully erosion processes) on the level of soil aggregate degradation (indicators such as particle size distribution, geometric mean diameter, mean weight diameter, and labile components of OC), and 2) how the progression of soil erosion patterns affects variations of biochemical mechanisms controlling the C mineralization ratio within the original soils eroded by the rill and gully.
Section snippets
Study region
The studied region is part of the Gorgan plain located in Golestan province, northern Iran (Fig. 1). The gradient of study region forms a slope of 20 % located in elevation of 550 m.a.s.l. The studied area's climate is arid (aridity index of 0.19) with a mean annual temperature of ∼17°C. The average annual precipitation of the region exhibits a significant gradient from 750 mm close to the Alborz Mountains to 200 mm toward the Turkmen Steppe (Rahimzadeh et al., 2019). Rangeland is the dominant
Variability in soil degradation level under rill and gully erosion processes
The statistical results illustrated significant differences of the physiochemical soil characteristics between the different erosion patterns (Tables 2 and 3). As shown in Table 2 and Fig. 2, the macro-aggregates (> 0.25 mm) and fine fractions (< 0.05 mm) did not show any statistically significant differences (P > 0.05) between the different erosion patterns. However, the greater value (P < 0.05) of micro-aggregates (0.05-0.25 mm) was observed in the original soils eroded by the rill erosion.
Discussion
Despite extensive research on the role of different water erosion stages, such as interrill, rill, and gully erosion processes, in organic carbon cycling within deposited sediments (Schiettecatte et al., 2008; Kuhn et al., 2009; Huang et al., 2010; Nadeu et al., 2011; Cantón et al., 2014; Jiang et al., 2019; Quijano et al., 2019), there is no dedicated study showing the impact of the progression of soil erosion on the fate of the eroded soils and its function on the physical and biochemical
Conclusions
The present study quantified the impact of the rill and gully erosion processes on biochemical mechanisms controlling the C mineralization ratio. Despite the labile components of organic carbon were considerably higher in the original soils eroded by the rill erosion, the C mineralization ratio significantly became lower in the rill soils compared with the gully soils. This can probably be explained by the impact of the interaction between the aggregate stability indicators and DOC on the
Declaration of Competing Interest
None declared.
Ethical statement
Authors state that the research was conducted according to ethical standards.
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2023, CatenaCitation Excerpt :The lowest stability of soil macroaggregates and microaggregates at the gully bottoms can be related to water transport capacity at the sides of the drainage line. Flow can stimulate variations in the physical and biochemical properties of the soil that control the mineralization of organic carbon and weaken the structural stability of aggregates (Mohseni and Hosseinzadeh, 2021). High flow triggers undermining and tunneling, a feature observed in the study site, especially at locations with curves in the drainage line; the strong flow decreases soil resistance to erosion and increases gully depth (Martínez-Casasnovas et al., 2004; Rienks et al., 2000).