Supplementary material to "Geogenic organic carbon in terrestrial sediments and its contribution to total soil carbon"

Soil carbon is an important component of the global carbon cycle with an estimated pool of soil organic carbon of about 1500 Gt. There are few estimates of the pool of inorganic carbon, but it is thought to be approximately 50% of the organic carbon pool. There is no detailed study on the estimation of the soil carbon pool for Australian soils.In order to quantify the carbon pools and to determine the extent of spatial variability in the organic and inorganic carbon pools, 120 soil cores were taken down to a depth of 0.90 m from a typical cotton field in northern NSW. Three cores were also taken from nearby virgin bushland and these samples were used as paired samples. Each soil core was separated into 4 samples, i.e. 0–0.15, 0.15–0.30, 0.30–0.60, and 0.60–0.90 m. Soil organic carbon was determined by wet oxidation and inorganic carbon content was determined using the difference between total carbon and organic carbon, and confirmed by the acid dissolution method. Total carbon was measured using a LECO CHN analyser. Soil organic carbon of the field constituted 62% (0–0.15 m), 58% (0.15–0.30 m), 60% (0.30–0.60 m), and 67% (0.60–0.90 m) of the total soil carbon. The proportion of inorganic carbon in total carbon is higher than the global average of 32%. Organic carbon content was relatively higher in the deeper layers (>0.30�m) of the studied soils (Vertosols) compared with other soil types of Australia. The carbon content varied across the field, however, there was little correlation between the soil types (grey, red, or intergrade colour) and carbon content. The total soil carbon pool of the studied field was estimated to be about 78 t/ha for 0–0.90 m layer, which was approximately 58% of the total soil carbon in the soil under nearby remnant bushland (136 t/ha). The total pool of carbon in the cotton soils of NSW was estimated to be 44.8 Mt C, where organic carbon and inorganic carbon constitute 34.9 Mt C and 9.9 Mt C, respectively. Based on the results of a limited number of paired sites under remnant vegetation, it was estimated that about 18.9 Mt of C has been lost from Vertosols by cotton cropping in NSW. With more sustainable management practices such as conservation tillage and green manuring, some of the lost carbon can be resequestered, which will help to mitigate the greenhouse effect, improve soil quality and may increase crop yield.

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Estimates of soil organic carbon stocks in central Canada using three different approaches

Canadian Journal of Forest Research ◽

10.1139/x01-122 ◽

2002 ◽

Vol 32 (5) ◽

pp. 805-812 ◽

Cited By ~ 47

Author(s):

J S Bhatti ◽

M J Apps ◽

C Tarnocai

Keyword(s):

Surface Layer ◽

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Carbon ◽

Soil Depth ◽

Peat Soil ◽

Regression Line ◽

Organic C ◽

Soil C ◽

Total Soil

This study compared three estimates of carbon (C) contained both in the surface layer (030 cm) and the total soil pools at polygon and regional scales and the spatial distribution in the three prairie provinces of western Canada (Alberta, Saskatchewan, and Manitoba). The soil C estimates were based on data from (i) analysis of pedon data from both the Boreal Forest Transect Case Study (BFTCS) area and from a national-scale soil profile database; (ii) the Canadian Soil Organic Carbon Database (CSOCD), which uses expert estimation based on soil characteristics; and (iii) model simulations with the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2). At the polygon scale, good agreement was found between the CSOCD and pedon (the first method) total soil carbon values. Slightly higher total soil carbon values obtained from BFTCS averaged pedon data (the first method), as indicated by the slope of the regression line, may be related to micro- and meso-scale geomorphic and microclimate influences that are not accounted for in the CSOCD. Regional estimates of organic C from these three approaches for upland forest soils ranged from 1.4 to 7.7 kg C·m2 for the surface layer and 6.2 to 27.4 kg C·m2 for the total soil. In general, the CBM-CFS2 simulated higher soil C content compared with the field observed and CSOCD soil C estimates, but showed similar patterns in the total soil C content for the different regions. The higher soil C content simulated with CBM-CFS2 arises in part because the modelled results include forest floor detritus pool components (such as coarse woody debris, which account for 412% of the total soil pool in the region) that are not included in the other estimates. The comparison between the simulated values (the third method) and the values obtained from the two empirical approaches (the first two methods) provided an independent test of CBM-CFS2 soil simulations for upland forests soils. The CSOCD yielded significantly higher C content for peatland soils than for upland soils, ranging from 14.6 to 28 kg C·m2 for the surface layer and 60 to 181 kg C·m2 for the total peat soil depth. All three approaches indicated higher soil carbon content in the boreal zone than in other regions (subarctic, grassland).

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Geogenic organic carbon in terrestrial sediments and its contribution to total soil carbon

SOIL ◽

10.5194/soil-7-347-2021 ◽

2021 ◽

Vol 7 (2) ◽

pp. 347-362

Author(s):

Fabian Kalks ◽

Gabriel Noren ◽

Carsten W. Mueller ◽

Mirjam Helfrich ◽

Janet Rethemeyer ◽

...

Keyword(s):

Organic Carbon ◽

Sediment Cores ◽

Sedimentary Rocks ◽

Loess Soil ◽

Soil Mass ◽

Strong Increase ◽

Large Contribution ◽

Red Sandstone ◽

Total Soil ◽

Terrestrial Sediments

Abstract. Geogenic organic carbon (GOC) from sedimentary rocks is an overlooked fraction in soils that has not yet been quantified but influences the composition, age, and stability of total organic carbon (OC) in soils. In this context, GOC is the OC in bedrock deposited during sedimentation. The contribution of GOC to total soil OC may vary, depending on the type of bedrock. However, no studies have been carried out to investigate the contribution of GOC derived from different terrestrial sedimentary rocks to soil OC contents. In order to fill this knowledge gap, 10 m long sediment cores from three sites recovered from Pleistocene loess, Miocene sand, and Triassic Red Sandstone were analysed at 1 m depth intervals, and the amount of GOC was calculated based on 14C measurements. The 14C ages of bulk sedimentary OC revealed that OC is comprised of both biogenic and geogenic components. The biogenic component relates to OC that entered the sediments from plant sources since soil development started. Assuming an average age for this biogenic component ranging from 1000–4000 years BP (before present), we calculated average amounts of GOC in the sediments starting at 1.5 m depth, based on measured 14C ages. The median amount of GOC in the sediments was then taken, and its proportion of soil mass (g GOC per kg−1 fine soil) was calculated in the soil profile. All the sediments contained considerable amounts of GOC (median amounts of 0.10 g kg−1 in Miocene sand, 0.27 g kg−1 in Pleistocene loess, and 0.17 g kg−1 in Red Sandstone) compared with subsoil OC contents (between 0.53 and 15.21 g kg−1). Long-term incubation experiments revealed that the GOC appeared comparatively stable against biodegradation. Its possible contribution to subsoil OC stocks (0.3–1.5 m depth) ranged from 1 % to 26 % in soil developed in the Miocene sand, from 16 % to 21 % in the loess soil, and from 6 % to 36 % at the Red Sandstone site. Thus, GOC with no detectable 14C content influenced the 14C ages of subsoil OC and may partly explain the strong increase in 14C ages observed in many subsoils. This could be particularly important in young soils on terrestrial sediments with comparatively low amounts of OC, where GOC can make a large contribution to total OC stocks.

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Geogenic organic carbon in terrestrial sediments and its contribution to total soil carbon

10.5194/soil-2020-34 ◽

2020 ◽

Author(s):

Fabian Kalks ◽

Gabriel Noren ◽

Carsten Mueller ◽

Mirjam Helfrich ◽

Janet Rethemeyer ◽

...

Keyword(s):

Organic Carbon ◽

Sediment Cores ◽

Sedimentary Rocks ◽

Loess Soil ◽

Red Sandstone ◽

Total Soil ◽

Incubation Experiments ◽

Terrestrial Sediments ◽

Plant Sources

Abstract. Geogenic organic carbon (GOC) from sedimentary rocks is an overlooked fraction in soils that has not been quantified yet, influencing the composition, age and stability of total organic carbon (OC) in soils. In this context GOC is referred to as the OC in bedrocks deposited during sedimentation. However, the contribution of GOC to total soil OC varies with the type of bedrock. So far studies investigating the contribution of GOC derived from different terrestrial sedimentary rocks to soil OC contents are missing. In order to fill this gap, we analysed 10 m long sediment cores at three sites recovered from Pleistocene Loess, Miocene Sand and Triassic Red Sandstone and calculated the amount of GOC based on 14C measurements. 14C ages of bulk sedimentary OC revealed that OC represents a mixture of biogenic and geogenic components. Biogenic refers to OC that entered the sediments recently from plant sources. All sediments contain considerable amounts of GOC (median amounts of 0.10 g kg−1 at the Miocene Sand, 0.27 g kg−1 at the Pleistocene Loess and 0.17 at Red Sandstone) in comparison to subsoil OC contents (between 0.53–15.21 g kg−1). Long-term incubation experiments revealed that this GOC seemed to be comparatively stable against biodegradation. Its possible contribution to subsoil OC stocks (0.3–1.5 m depth) is ~ 2.5 % in soil developed in the Miocene Sand, ~ 8 % in the Loess soil and ~ 12 % at the Red Sandstone site. Thus GOC having no detectable 14C contents influences 14C ages of subsoil OC and thus may partly explain the strong 14C ages increase observed in many subsoils. This is particularly important in soils on terrestrial sediments with comparatively low amounts of OC, where GOC can considerably contribute to total OC stocks.

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Soil organic carbon dynamics jointly controlled by climate, carbon inputs, soil properties and soil carbon fractions

Global Change Biology ◽

10.1111/gcb.13767 ◽

2017 ◽

Vol 23 (10) ◽

pp. 4430-4439 ◽

Cited By ~ 86

Author(s):

Zhongkui Luo ◽

Wenting Feng ◽

Yiqi Luo ◽

Jeff Baldock ◽

Enli Wang

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Properties ◽

Soil Carbon ◽

Carbon Dynamics ◽

Carbon Fractions ◽

Soil Organic Carbon Dynamics ◽

Soil Carbon Fractions

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Long-Term Nitrogen Addition Decreases Soil Carbon Mineralization in an N-Rich Primary Tropical Forest

Forests ◽

10.3390/f12060734 ◽

2021 ◽

Vol 12 (6) ◽

pp. 734

Author(s):

Xiankai Lu ◽

Qinggong Mao ◽

Zhuohang Wang ◽

Taiki Mori ◽

Jiangming Mo ◽

...

Keyword(s):

Microbial Biomass ◽

Organic Carbon ◽

Tropical Forest ◽

Soil Carbon ◽

Tropical Forests ◽

Carbon Mineralization ◽

N Deposition ◽

Soil Carbon Mineralization ◽

N Additions

Anthropogenic elevated nitrogen (N) deposition has an accelerated terrestrial N cycle, shaping soil carbon dynamics and storage through altering soil organic carbon mineralization processes. However, it remains unclear how long-term high N deposition affects soil carbon mineralization in tropical forests. To address this question, we established a long-term N deposition experiment in an N-rich lowland tropical forest of Southern China with N additions such as NH4NO3 of 0 (Control), 50 (Low-N), 100 (Medium-N) and 150 (High-N) kg N ha−1 yr−1, and laboratory incubation experiment, used to explore the response of soil carbon mineralization to the N additions therein. The results showed that 15 years of N additions significantly decreased soil carbon mineralization rates. During the incubation period from the 14th day to 56th day, the average decreases in soil CO2 emission rates were 18%, 33% and 47% in the low-N, medium-N and high-N treatments, respectively, compared with the Control. These negative effects were primarily aroused by the reduced soil microbial biomass and modified microbial functions (e.g., a decrease in bacteria relative abundance), which could be attributed to N-addition-induced soil acidification and potential phosphorus limitation in this forest. We further found that N additions greatly increased soil-dissolved organic carbon (DOC), and there were significantly negative relationships between microbial biomass and soil DOC, indicating that microbial consumption on soil-soluble carbon pool may decrease. These results suggests that long-term N deposition can increase soil carbon stability and benefit carbon sequestration through decreased carbon mineralization in N-rich tropical forests. This study can help us understand how microbes control soil carbon cycling and carbon sink in the tropics under both elevated N deposition and carbon dioxide in the future.

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Can Agricultural Management Induced Changes in Soil Organic Carbon Be Detected Using Mid-Infrared Spectroscopy?

Remote Sensing ◽

10.3390/rs13122265 ◽

2021 ◽

Vol 13 (12) ◽

pp. 2265

Author(s):

Jonathan Sanderman ◽

Kathleen Savage ◽

Shree Dangal ◽

Gabriel Duran ◽

Charlotte Rivard ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Carbon ◽

Diffuse Reflectance Spectroscopy ◽

Low Cost ◽

Soil Survey ◽

Mid Infrared ◽

Mir Spectroscopy ◽

Induced Changes ◽

Carbon Change

A major limitation to building credible soil carbon sequestration programs is the cost of measuring soil carbon change. Diffuse reflectance spectroscopy (DRS) is considered a viable low-cost alternative to traditional laboratory analysis of soil organic carbon (SOC). While numerous studies have shown that DRS can produce accurate and precise estimates of SOC across landscapes, whether DRS can detect subtle management induced changes in SOC at a given site has not been resolved. Here, we leverage archived soil samples from seven long-term research trials in the U.S. to test this question using mid infrared (MIR) spectroscopy coupled with the USDA-NRCS Kellogg Soil Survey Laboratory MIR spectral library. Overall, MIR-based estimates of SOC%, with samples scanned on a secondary instrument, were excellent with the root mean square error ranging from 0.10 to 0.33% across the seven sites. In all but two instances, the same statistically significant (p < 0.10) management effect was found using both the lab-based SOC% and MIR estimated SOC% data. Despite some additional uncertainty, primarily in the form of bias, these results suggest that large existing MIR spectral libraries can be operationalized in other laboratories for successful carbon monitoring.

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Topography Influences Management System Effects on Total Soil Carbon and Nitrogen

Soil Science Society of America Journal ◽

10.2136/sssaj2008.0392 ◽

2009 ◽

Vol 73 (6) ◽

pp. 2059-2067 ◽

Cited By ~ 28

Author(s):

S. Senthilkumar ◽

A. N. Kravchenko ◽

G. P. Robertson

Keyword(s):

Soil Carbon ◽

Management System ◽

Carbon And Nitrogen ◽

Soil Carbon And Nitrogen ◽

Total Soil

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Subsoil organic carbon turnover is dominantly controlled by soil properties in grasslands across China

10.5194/egusphere-egu21-2413 ◽

2021 ◽

Author(s):

Yuehong Shi ◽

Xiaolu Tang ◽

Peng Yu ◽

Li Xu ◽

Guo Chen ◽

...

Keyword(s):

Climate Change ◽

Organic Carbon ◽

Soil Properties ◽

Soil Carbon ◽

Carbon Turnover ◽

Area Index ◽

Important Indicator ◽

Environmental Controls ◽

Biogeochemical Models ◽

Soc Stock

<p>Soil carbon turnover time (&#964;, year) is an important indicator of soil carbon stability, and a major factor in determining soil carbon sequestration capacity. Many studies investigated &#964; in the topsoil or the first meter underground, however, little is known about subsoil &#964; (0.2 &#8211; 1.0 m) and its environmental drivers, while world subsoils below 0.2 m accounts for the majority of total soil organic carbon (SOC) stock and may be as sensitive as that of the topsoil to climate change. We used the observations from the published literatures to estimate subsoil &#964; (the ratio of SOC stock to net primary productivity) in grasslands across China and employed regression analysis to detect the environmental controls on subsoil &#964;. Finally, structural equation modelling (SEM) was applied to identify the dominant environmental driver (including climate, vegetation and soil). Results showed that subsoil &#964; varied greatly from 5.52 to 702.17 years, and the mean (&#177; standard deviation) subsoil &#964; was 118.5 &#177; 97.8 years. Subsoil &#964; varied significantly among different grassland types that it was 164.0 &#177; 112.0 years for alpine meadow, 107.0 &#177; 47.9 years for alpine steppe, 177.0 &#177; 143.0 years for temperate desert steppe, 96.6 &#177; 88.7 years for temperate meadow steppe, 101.0 &#177; 75.9 years for temperate typical steppe. Subsoil &#964; significantly and negatively correlated (p < 0.05) with vegetation index, leaf area index and gross primary production, highlighting the importance of vegetation on &#964;. Mean annual temperature (MAT) and precipitation (MAP) had a negative impact on subsoil &#964;, indicating a faster turnover of soil carbon with the increasing of MAT or MAP under ongoing climate change. SEM showed that soil properties, such as soil bulk density, cation exchange capacity and soil silt, were the most important variables driving subsoil &#964;, challenging our current understanding of climatic drivers (MAT and MAP) controlling on topsoil &#964;, further providing new evidence that different mechanisms control topsoil and subsoil &#964;. These conclusions demonstrated that different environmental controls should be considered for reliable prediction of soil carbon dynamics in the top and subsoils in biogeochemical models or earth system models at regional or global scales.</p>

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