Comment on bg-2022-1

Jakob Wallinga

doi:10.5194/bg-2022-1-rc1

Abstract

Abstract. The acceleration of erosion, transport, and burial of soil organic carbon (OC) by water in response to agricultural expansion represents a significant perturbation of the terrestrial C cycle. Recent model advances now enable improved representation of the relationships between sedimentary processes and OC cycling, and this has led to substantially revised assessments of changes in land OC as a result of land cover and climate change. However, surprisingly a consensus on both the direction and magnitude of the erosion-induced landâatmosphere OC exchange is still lacking. Here, we show that the apparent soil OC erosion paradox, i.e., whether agricultural erosion results in an OC sink or source, can be reconciled when comprehensively considering the range of temporal and spatial scales at which erosional effects on the C cycle operate. We developed a framework that describes erosion-induced OC sink and source terms across scales. We conclude that erosion induces a source for atmospheric CO2 when considering only small temporal and spatial scales, while both sinks and sources appear when multi-scaled approaches are used. We emphasize the need for erosion control for the benefits it brings for the delivery of ecosystem services, but cross-scale approaches are essential to accurately represent erosion effects on the global C cycle.

Highlights

We show that the apparent soil C erosion paradox, i.e., whether agricultural erosion results in a C sink or source, can be reconciled when comprehensively considering the range 15 of temporal and spatial scales at which erosional effects on the C cycle operate
The model shows that C stocks in stores along the LOAC are not necessarily in equilibrium with the erosional disturbance and it is critical to consider the dynamic phases of both C recovery at sites of erosion and C destabilization in sedimentary environments
The time since agricultural disturbance and the residence times of 150 C in sedimentary environments are critical factors to consider. Considering all these processes This reconciles the apparent soil C erosion paradox by showing that both major source and sink terms for atmospheric C are simultaneously induced by erosion

Summary

Introduction

Soil erosion has been identified as the biggest threat to global food security (Amundson et al, 2015). This realization led to the notion of a win-win situation whereby soil conservation practices that reduce soil erosion result in healthier soils, but that an additional and large C sink could be obtained by halting the large source term associated with pre-conservation agricultural soil erosion (Koch et al, 2013; Lal, 2003, 2019; Ran et al, 2014, 2018; Worrall et al, 2016) This notion was 30 challenged by other studies that suggested a different pathway for the eroded C (Berhe et al, 2007; Harden et al, 1999; Van Oost et al, 2007; Smith et al, 2001; Stallard, 1998). We conceptualize the effects of the contributing erosional (sub-)processes across time and space using decay functions (see methods)

Transport in runoff and rivers

SOC recovery after erosion

SOC burial

Discussion and conclusion

Methods

Findings

Method Data Mod Data Mod