Soil Organic Carbon Redistribution and Delivery by Soil Erosion in a Small Catchment of the Yellow River Basin

Abstract

Soil erosion modulates the atmospheric CO 2 level by affecting the redistribution of young biospheric organic carbon (OC bio ) and ancient petrogenic organic carbon (OC petro ) in different order streams. However, the fate of soil organic carbon (SOC) in low-order stream systems is still uncertain due to the complex influences of terrain, land uses, and anthropogenic disturbances. Here, we used the geochemical properties fingerprinting method and a radiocarbon-based two-member mixing model to clarify the source, budgets, and composition of SOC in a low-order stream catchment in the Yellow River basin. The results showed that the primary source of SOC in the catchment was agricultural activity area, which accounted for 68.5%. After vegetation restoration, the SOC delivery rate and loss rate decreased from 0.38 ± 0.06 to 0.26 ± 0.04 and 0.19 ± 0.06 to 0.14 ± 0.04 t·ha −1 ·yr −1 , respectively. The SOC mobilized by soil erosion in the source area was 1,085.8 ± 170.5 t from 1969 to 2015, and the SOC lost during the transport process was 552.9 ± 170.1 t. The lost carbon was dominated by OC bio , whereas the loss of OC petro was minimal. Soil erosion can mobilize the OC petro sequestered in terrestrial ecosystems and deliver it to a river system if it is not intercepted. The oxidation of OC petro during long-distance fluvial transport may represent a significant carbon source for atmospheric CO 2 on a geological timescale. This study contributes to our understanding of the carbon sink/source issue and quantifies the SOC budgets in stream systems.Plain Language Summary Understanding how soil erosion affects the redistribution and delivery of soil organic carbon (SOC) is essential for clarifying the source, budgets, and composition of SOC and helps us further understand the terrestrial carbon cycle. This study calculated the source of SOC based on differences in geochemical properties in different source areas. Then, we measured the radiocarbon ( 14 C) content to clarify the composition and fate of SOC during the erosion process. We found that the primary source of SOC in the catchment was the agricultural activity area and that agricultural activities and vegetation restoration were shown to significantly affect SOC redistribution. A large amount of modern organic carbon was lost during the transport process and may become an atmospheric CO 2 source over short timescales. Almost all ancient organic carbon is intercepted by the dam at the outlet. If there is no check dam, the remaining ancient organic carbon can be exported to the Yellow River and then oxidized during fluvial transport, leading to an increase in long-term atmospheric CO 2 levels. This research clarifies the influence of soil erosion on SOC redistribution and delivery and quantifies the source, budget, and composition of SOC in the low-order stream system.

Soil burial reduces decomposition and offsets erosion‐induced soil carbon losses in the Indian Himalaya

“…Soils were incubated at 20°C and maintained at 60% water holding capacity for the duration of the incubation (mean ± SEM; n = 5 at each site). Post hoc Tukey honest significant difference groups, analysed for each site by two-way ANOVA, denoted between slope position at each site that in surface soils (Anderson et al, 2020;Berhe et al, 2018;Zeng et al, 2020). The variation in field-scale budgets highlights the importance of considering geomorphic variation in erosion budgeting (Doetterl et al, 2012).…”

“…Our respiration and priming results (Figures 4–6) suggest that carbon burial reduces mineralisation contributing to the maintenance of soil carbon stocks. Furthermore, at the lower elevation site 1, where sediment also appears to have been exported beyond the field (Figure 2), erosion could be resulting in a carbon sink if there is deposition and burial elsewhere in the catchment (or at a larger scale as described by Galy et al [2007] in the net sink for the entire Himalaya), and the residence time of exported SOC is comparable to that in surface soils (Anderson et al, 2020; Berhe et al, 2018; Zeng et al, 2020). The variation in field‐scale budgets highlights the importance of considering geomorphic variation in erosion budgeting (Doetterl et al, 2012).…”

“…As well as, secondly, through physical protection from microbial mineralisation through reaggregation (Doetterl et al, 2012(Doetterl et al, , 2016Li et al, 2019). Thirdly, by the decomposition of labile or water-soluble carbon during transport leaving energy-poor carbon sources (Zeng et al, 2020). Lastly, through the preferential transport of microaggregates, with less accessible carbon sources, from monsoonal rainfall erosion (Li et al, 2019;Wang et al, 2014).…”

Characterizing Dissolved Organic Matter Across a Riparian Soil–Water Interface: Preliminary Insights from a Molecular Level Perspective

“…DOC concentrations spanned from 331 to 373 mg/kg in S-DOM and 314 to 387 mg/kg in SS-DOM, which are 2 orders of magnitude higher than those of R-DOM (1.79 to 2.07 mg/kg; assuming the density of river water is 1 kg/L) (Figure 2a,b), reinforcing that there is a large potential source of DOM to the rivers in the riparian soil. 49,50 The δ 13 C values varied from −26.1‰ to −25.4‰ in S-DOM, −24.4‰ to −24.1‰ in SS-DOM, and −27.8‰ to −27.6‰ in R-DOM, respectively (Figure 2c). The averaged δ 13 C values were consistently highest in SS-DOM, second highest in S-DOM, and lowest in R-DOM (p S-DOM vs SS-DOM = 0.006, p S-DOM vs R-DOM = 0.0009, p SS-DOM vs R-DOM = 0.00006; Figure 2d), indicating (i) a preferential release of 13 C depleted compounds from soils to the river; or (ii) a preferential in situ production of 13 C enriched compounds after soils were submerged by river water.…”

Validating the accuracy of multiple sediment fingerprinting methods

“…(2) Kruskal-Wallis H test (KW-H); and (3) stepwise discrimination function analysis (DFA) (Shi et al, 2021;Wilkinson et al, 2013;Zeng et al, 2020).…”