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Soil conservation is of global importance, as accelerated soil erosion by human activity is a primary threat to ecosystem viability. However, the significance and role of soil conservation in reshaping landscape carbon (C) accounting has not been comprehensively integrated in the terrestrial C sink. Here, we present the first integrated assessment of the modified terrestrial C sink and aquatic C transport due to soil conservation for the semiarid Chinese Loess Plateau (CLP), the world's most vulnerable region to soil erosion. We show a surprisingly low terrestrial‐aquatic C transfer that offset the terrestrial net ecosystem productivity by only 7.5%, which we attribute to the effective implementation of soil conservation practices. Despite the highest soil erosion, the semiarid CLP acts as effective C sink at 43.2 ± 22.6 g C m−2 year−1, which is comparable to temperate forest in absorbing atmospheric CO2. Moreover, C burial in reservoirs has created an additional anthropogenic C sink of 2.9 ± 1.1 g C m−2 year−1. Our findings indicate that effective soil conservation can significantly increase landscape C sequestration capacity. The co‐benefits of soil conservation in erosion control and C sequestration have important implications for policy makers in other regions undergoing increasing erosion intensity to pursue environmental sustainability. Plain Language Summary: Aquatic export of terrestrial carbon (C) plays a significant role in modulating the magnitude of terrestrial C sink. Previous estimates of terrestrial C sink may be overestimated because not all C losses across heterogeneous landscapes are accurately determined and properly accounted for. This is particularly possible for catchments with high erosion and terrestrial‐aquatic C transfer potential. Meanwhile, soil conservation can greatly modify landscape C sequestration capacity. Thus, a more comprehensive assessment of net landscape C budget is needed that integrates aquatic export of terrestrial C while considering the role and significance of soil conservation. For the Chinese Loess Plateau in semiarid climates that once characterized the world's high soil erosion rate, we show a surprisingly low aquatic C transfer that offset the terrestrial C sink by only 7.5%, due largely to successful soil conservation in the past decades. Our findings suggest that effective implementation of soil conservation practices can substantially reduce terrestrial‐aquatic C transfer and enhance the landscape C sequestration capacity. Key Points: The magnitude of terrestrial‐aquatic C transfer in influencing landscape‐scale C balance on the Chinese Loess Plateau (CLP) is assessedThe low reduction of terrestrial C sink by terrestrial‐aquatic C transfer on the CLP is largely due to soil conservationEffective implementation of soil conservation can substantially reduce terrestrial‐aquatic C transfer and enhance landscape C sink capacity [ABSTRACT FROM AUTHOR]

Purpose: Soil erosion drastically perturbs the global carbon cycle, and splash erosion is the first critical stage of soil erosion by water. Thus, studying the soil organic carbon (SOC) dynamic caused by splash erosion is essential. Methods: Simulated rainfall splash experiments were conducted on three cultivated soils with different SOC contents (black soil, purple soil, and red soil) to investigate the dynamics of SOC related to splash erosion, and the splash distance was 0–5, 5–10, 10–17, 17–28, 28–40 cm, respectively. Results: SOC was unevenly distributed and enriched in different-sized aggregates. The enrichment ratio of SOC (EROC) was basically greater than 1 and increased as the splash distance increased. Moreover, the variation of EROC differed from that in the aggregate enrichment ratio (ERA), and the EROC in large macroaggregates (> 0.5 mm) decreased with increasing ERA. The weight proportion of SOC mobilization with different-sized aggregates was consistent with the mass percentage of aggregates. Specifically, there was a significant positive exponential relationship between SOC mobilization and the aggregate mass of the greatest proportion, indicating that the mobilization of SOC was mainly affected by the aggregate mass of the greatest proportion. Conclusions: Our findings indicated that SOC migration can be realized by aggregates transport under splash erosion, indicating that improving soil structure will help to reduce SOC migration and even loss. [ABSTRACT FROM AUTHOR]

Soil erosion modulates the atmospheric CO2 level by affecting the redistribution of young biospheric organic carbon (OCbio) and ancient petrogenic organic carbon (OCpetro) 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 OCbio, whereas the loss of OCpetro was minimal. Soil erosion can mobilize the OCpetro sequestered in terrestrial ecosystems and deliver it to a river system if it is not intercepted. The oxidation of OCpetro during long‐distance fluvial transport may represent a significant carbon source for atmospheric CO2 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 (14C) 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 CO2 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 CO2 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. Key Points: Agricultural activities and vegetation restoration have impacted the sediment and erosion‐induced redistribution of soil organic carbonA large amount of soil organic carbon was lost during the transport process, and the lost carbon was dominated by biospheric organic carbonThe petrogenic organic carbon exported from the low‐order stream may become a carbon source on a geological timescale [ABSTRACT FROM AUTHOR]

• Splash erosion affected the redistribution of soil particles and SIC. • The redistribution of splashed material and SIC varied with soil type. • SIC had sorting and enrichment characteristics. Splash erosion caused by raindrops is the first stage of water erosion that detaches and transports soil particles. As an important component of soil particles, soil inorganic carbon (SIC) contains little information on its redistribution during splash erosion. In this study, two soils, purple soil and loess, were selected and placed in a soil tray with a diameter of 20 cm at the center of a splash tray, and a rainfall simulator was used to simulate three raindrop energies in experiments to investigate the migration of soil particles and SIC. The results showed differences in the amount and selective migration of splashed material between the soils, which was evident in the obvious sorting of the particle size of purple soil with distance and the insignificant change of loess soil. The SIC sorting characteristic performed differently in the two soils, that is, the SIC content of purple soil increased with particle size, while that of loess was the opposite. The enrichment and depletion of SIC during splash erosion varied with soil type, and differed from the general enrichment of soil organic carbon (SOC). The SIC enrichment ratio (ER IC) of purple soil was generally > 1, whereas the ER IC values of loess were < 1. In addition, multiple linear regression (MLR) models were established to predict the SIC content of splashed material. Rainfall splash plays an important role in SIC migration and may further affect the carbon cycle. These preliminary results provide a basis for further study of SIC response to rainfall splash. [ABSTRACT FROM AUTHOR]

• Seasonal and diel CO 2 emissions in a hard-water reservoir show temporal variability. • Inputs of dissolved inorganic carbon play a central role in sustaining the p CO 2. • Nocturnal fluxes are higher than daytime fluxes due largely to aquatic metabolism. • Episodic weather events reverse the diel pattern and cause higher daytime fluxes. • Using daytime measurements alone would underestimate the daily efflux by 9–25%. Reservoirs represent a key component of the global carbon cycle. However, estimates of carbon dioxide (CO 2) emissions from reservoirs remain poorly constrained due to the absence of spatially and temporally resolved measurements. We performed high-resolution monitoring of CO 2 emissions (F CO2) in a semiarid hard-water reservoir to examine its seasonal and diel variability. Our results suggest that dissolved inorganic carbon input plays a central role in sustaining the surface water CO 2 partial pressure (p CO 2), which varies from 1076 to 4587 μatm. Although the reservoir is moderately to highly productive throughout the year, it is a net CO 2 source with F CO2 values in the range of 308–1753 mg C m−2 d–1. This high CO 2 efflux indicates that productive waters are not necessarily CO 2 sinks. Both p CO 2 and F CO2 exhibit clear seasonal and diel patterns. Surface water p CO 2 is highest in March and presents a consistent diurnal/nocturnal pattern with the daytime p CO 2 6–13% lower than the nighttime p CO 2. High CO 2 efflux is observed during the ice-thaw period, indicating the release of CO 2 that was accumulated during the winter. CO 2 effluxes are typically higher during the nighttime driven by aquatic metabolism, but episodic weather events (e.g., rainfall and strong winds) can significantly enhance CO 2 emissions and even reverse the diel pattern. Our study also shows that using only daytime measurements to estimate daily CO 2 emissions would underestimate it by 9–25%. Hence, future global assessments should incorporate CO 2 emissions from hard-water reservoirs and account for their seasonal and diel variability. [ABSTRACT FROM AUTHOR]