Soil organic carbon in soils of the northern permafrost zones: Information status and challenges

Agriculture and Agri-Food CanadaSummerland, British Columbia

Scott Smith and Bert VandenBygaart

Presentation to FAO SOC SymposiumRome, March 22, 2017

Outline

1. Introduction- why is this important2. The nature of SOC in permafrost-affected soils3. The challenges of quantifying SOC in permafrost-

affected soils4. Information products available5. Recommendations

Schuur and Hugelius (2016) Terrestrial Carbon Cycle. Arctic Report Card.

Northern permafrost zones soils contain up to 1800 Pg C m-2 to a depth of 100 cm, half of all terrestrial SOC, double amount in atmosphere.

Warming conditions promote microbial conversation of permafrost C into the greenhouse gases CO2 and CH4

Overall tundra appears to be releasing net carbon to the atmosphere

The magnitude and timing of greenhouse gas emissions from these regions and their impact on changing climate remain highly uncertain

Source: Zubrzycki et al. 2014

The nature of SOC in permafrost-affected soils

In the northern high-latitude regions, soil formation is governed by a number of unique cryogenic processes (such as frost heave, cryoburbation and thermokarst formation) .

The roles of cold temperatures and ice formation are extremely important for organic matter accumulation and re-distribution in soils.

These processes can cause extreme variability in the size and distribution of SOC stocks, particularly in soils underlain by permafrost (i.e. Cryosols).

Permafrost is by definition ground that does not thaw during the summer, under these conditions soils may contain large volumes of ice.

Figure source Mishra 2013

The nature of SOC in permafrost-affected soils

Source: Bockheim J G 2007 Importance of cryoturbation in redistributingorganic carbon in permafrost-affected soils Soil Sci. Soc. Am.J. 71 1335–42:

The nature of SOC in permafrost-affected soils

Source: Zubrzycki et al. 2014

Cryoturbation processes mix and bury SOC

Source: Ping et al. 2015

Active layer

Earth Hummock

Ice Wedges

Source: Ping et al. 2010

Non-cryoturbated Cryoturbated

• It has been estimated that 19% of the soil area of the permafrost region (3.6 million km2) is cryoturbated. (Mishray et al 2013)

• The impact of these features on the heterogeneity of SOC stocks needs to be considered when upscaling to regional scale databases.

The amount of data is small relative to that available in other regions of the world primarily due to logistical difficulties, extreme working conditions, and the cost involved with accessing remote areas.

The soils in permafrost regions are under sampled, both spatially and vertically, especially below the active layer

Existing databases vary considerably in terms of sampling depth and protocols, analytical methods, and the overall reliability of the data (Hugelius and Kuhry 2009,Hugelius et al 2013).

Source: Mishra et al 2013; Vitharana et al 2015

Significant risks for biased conclusions exist due to inadequate and uneven distributions of SOC profile observations in permafrost regions.

The Challenges in Quantifying SOC in Cryosolic Soils

Permafrost regions hold between 1400 and 1850 Pg of SOC to a depth of over 300 cm, twice the mass of carbon found in the atmosphere and almost half of all global soil carbon ,

Stocks of SOC 0 - 30 cm are estimated at 200 Pg m-2,

Stocks of SOC 0 - 100 cm is estimated at 500 Pg m-2

Source: Hugelius et al. (2013)

(1778 pedons for a 18.8 x 106 km2 land area).

The NCSCD was developed by an international working group composed of the best cryopedologists from all northern countries particularly Canada, US and Russia

SOC values scaled-up from pedons to landscape using component listings from legacy soil survey maps

Grid cell published at 1 km2

Figure 1. Inconsistencies in SOC stocks (to 1 m depth) between observation-based (Northern Circumpolar Soil Carbon Database) and baseline ESM estimates calculated from the mean values in four CMIP5 models

Source: Mishra et al2013

Hengl, T., Mendes de Jesus, J., Heuvelink, G. B.M., Ruiperez Gonzalez, M., Kilibarda, M. et al. (2017) SoilGrids250m: global gridded soil information based on Machine Learning. PLOS ONE 12(2): e0169748

Hengl T, de Jesus JM, MacMillan RA, Batjes NH, Heuvelink GBM, et al. (2014) SoilGrids1km — Global Soil Information Based on Automated Mapping. PLoS ONE 9(8): e105992. doi:10.1371/journal.pone.0105992

Predictive (digital) mapping using pedon inputs up-scaled spatially using multivariate statistics.Reports on a full set of soil attributes not just SOC

Soil Grids 250m is currently undergoing validation in Canada, including the permafrost region

Major constraint for both datasets in the northern circumpolar region is lack of data

RecommendationsAs with organic (peat) soils, Cryosolic soils should be reported at both the 0 -30 cm and 0-100 cm depth intervals due to the abundance of subsurface SOC

Both information products represent the best current data available for the permafrost region – different methods and different expertise

It is unlikely there will be the time or enough new data to create better data products for high latitude regions the FAO GSOC map…..so..

Countries should examine both data products and incorporate these into their national maps as they best see fit.

Thank you for your attention

Source: Swanson et al. 2000

High-latitude terrestrial ecosystems are key components in the global carbon cycle. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify stocks of soil organic carbon (SOC) in the northern circumpolar permafrost region (a total area of 18.7 × 106 km2). The NCSCD is a geographical information system (GIS) data set that has been constructed using harmonized regional soil classification maps together with pedon data from the northern permafrost region. Previously, the NCSCD has been used to calculate SOC storage to the reference depths 0–30 cm and 0–100 cm (based on 1778 pedons). It has been shown that soils of the northern circumpolar permafrost region also contain significant quantities of SOC in the 100–300 cm depth range, but there has been no circumpolar compilation of pedon data to quantify this deeper SOC pool and there are no spatially distributed estimates of SOC storage below 100 cm depth in this region. Here we describe the synthesis of an updated pedon data set for SOC storage (kg C m−2) in deep soils of the northern circumpolar permafrost regions, with separate data sets for the 100–200 cm (524 pedons) and 200–300 cm (356 pedons) depth ranges.

The Northern Circumpolar Soil Organic Carbon Database

Hugelius, G., Tarnocai, C., Broll, G., Canadell, J. G., Kuhry, P., and Swanson, D. K.: The Northern Circumpolar Soil Carbon Database: spatially distributed datasets of soil coverage and soil carbon storage in the northern permafrost regions, Earth Syst. Sci. Data, 5, 3-13, doi:10.5194/essd-5-3-2013, 2013.

The nature of SOC in permafrost-affected soils

Surface carbon is buried by various processes including these common to all soil

But in permafrost regions buried carbon is disrupted by cryogenic processes and ultimately preserved through freezing

Sources: Chaoprichaa and Marín-Spiottaa, 2013;

Machine learning from existing pedon data