Lateral transport of soil carbon and land−atmosphere CO ₂ flux induced by water erosion in China

Abstract

Soil erosion by water impacts soil organic carbon stocks and alters CO 2 fluxes exchanged with the atmosphere. The role of erosion as a net sink or source of atmospheric CO 2 remains highly debated, and little information is available at scales larger than small catchments or regions. This study attempts to quantify the lateral transport of soil carbon and consequent land−atmosphere CO 2 fluxes at the scale of China, where severe erosion has occurred for several decades. Based on the distribution of soil erosion rates derived from detailed national surveys and soil carbon inventories, here we show that water erosion in China displaced 180 ± 80 Mt C·y −1 of soil organic carbon during the last two decades, and this resulted a net land sink for atmospheric CO 2 of 45 ± 25 Mt C·y , equivalent to 8-37% of the terrestrial carbon sink previously assessed in China. Interestingly, the "hotspots," largely distributed in mountainous regions in the most intensive sink areas (>40 g C·m ), occupy only 1.5% of the total area suffering water erosion, but contribute 19.3% to the national erosion-induced CO 2 sink. The erosion-induced CO 2 sink underwent a remarkable reduction of about 16% from the middle 1990s to the early 2010s, due to diminishing erosion after the implementation of large-scale soil conservation programs. These findings demonstrate the necessity of including erosion-induced CO 2 in the terrestrial budget, hence reducing the level of uncertainty.land−atmosphere CO 2 flux | soil carbon displacement | water erosion | national scale T errestrial ecosystems are a net sink of anthropogenic CO 2 globally (1, 2) but can be net sources or sinks regionally [e.g., Northeast Region of China (3)]. Knowledge of the distribution, magnitude, and variability of land carbon fluxes and underlying processes is important both for improving model-based projections of the carbon cycle and for designing ecosystem management options that effectively preserve carbon stocks and enhance carbon sinks. Despite considerable efforts made by the research community, the mechanisms governing uptake or release of carbon from land ecosystems are still poorly quantified (4).Soil erosion occurs naturally but is accelerated by human cultivation of the landscape, and modifies CO 2 exchange (5) between the soil and atmosphere. Soil erosion destroys the physical protection of carbon in soil aggregates and accelerates decomposition, inducing a net CO 2 source. Continuous erosion over a long period can destabilize carbon in deeper soil horizons and trigger its decomposition e.g., as conditions of temperature and moisture become more favorable (6, 7). Soil erosion also decreases nutrient availability and reduces soil water holding capacity, affecting ecosystem productivity (8) with feedback to the ecosystem carbon balance. However, because only a fraction of eroded carbon is lost to the atmosphere, the rest may be lost to streams and rivers and eventually delivered to marine ecosystems or deposited in the landscape. With the fine and light soil particles p...

Impact of Water-Induced Soil Erosion on the Terrestrial Transport and Atmospheric Emission of Mercury in China

“…17 The database was created based on two detailed national survey data sets of water erosion in 1995–1996 and 2010–2012. These two national surveys combined remote-sensing images and field survey data to provide the spatial distribution of water erosion for a total of 2359 counties in China in the two periods.…”

“…The surface soil THg concentration data (0–20 cm) from these databases were used in this study because THg usually accumulates in the surface soil, and soil erosion happens mainly in this layer. 17,25 …”

“…34 The flux of THg released into streams was derived using the following equations, as used in previous studies: 8,17 …”

“…40–42 However, there is still a lack of studies on the case of Hg(0) emissions to the atmosphere from surface soil in the erosion impacted area caused by water erosion on a large scale. While Wang et al provided a comprehensive estimation of the emission of Hg(0) from natural surfaces in China based on mechanistic models, 25 we further quantified the contribution of Hg(0) emissions from the erosional area from erosion to the total emissions of Hg(0) in the surface soil in China, using the approach outlined below: 17,39 …”

Global soil organic carbon removal by water erosion under climate change and land use change during AD 1850–2005

“…Some studies coupled process-oriented soil erosion models with carbon turnover models calibrated for specific micro-catchments on timescales of a few decades to a millennium, (Billings et al, 2010;Van Oost et al, 2012;Nadeu et al, 2015;Wang et al, 2015a;Zhao et al, 2016;Bouchoms et al, 2017). Other studies focused on the application of parsimonious erosion-SOC-dynamics models using the Revised Universal Soil Loss Equation (RUSLE) approach together with sediment transport methods at regional or continental spatial scales (Chappell et al, 2015;Lugato et al, 2016;Yue et al, 2016;Zhang et al, 2014). However, the modeling approaches used in these studies apply erosion models that still require many variables and data input that is often not available at the global scale or for the past or the future time period.…”