Climate-dependent topographic effects on pyrogenic soil carbon in southeastern Australia

Xiang Wang, Jonathan Sanderman, Kyungsoo Yoo

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Abstract

The interactive effects of climate and topography on the composition, distribution and storage of soil organic carbon (SOC) remain unclear. This is particularly true for pyrogenic carbon (PyC) which is considered long-lasting in soil environments. With a goal to characterize how PyC responds to climate-dependent erosion and deposition processes, two hillslopes from SE Australia, differing in climate (MAP: 549 vs. 815 mm) and vegetation but with similar topography were selected for this study. We examined the colluvial soils that include A and B horizons on eroding (convex) and depositional (convergent) areas within each hillslope. Mid-infrared measurements with a partial least squares regression model were adopted to quantify the size and distribution of SOC fractions (i.e., particulate organic carbon (POC) fraction, humus organic carbon (HOC) and resistant organic carbon (ROC; representing PyC fraction) along the two hillslopes. These SOC fractions were examined with respect to climate, topographic position and soil depth. Total SOC was dominated by HOC (44 to 88%) followed by PyC (7 to 37%) and POC (0 to 37%). Effects of topography on inventories of PyC were more strongly expressed in the drier hillslope (eroding vs. depositional: 0.39 vs. 1.73 kg m −2 ) than the wetter hillslope (eroding vs. depositional: 1.14 vs. 2.46 kg m −2 ), which also illustrates that climatic effects on soil PyC differ between eroding and depositional hillslope areas. In contrast, relative contributions of PyC to SOC showed less systematic variation with topography (6.9–36.8% in eroding soils vs. 6.9–37.3% in depositional soils) and climate (6.9–36.8% at drier site vs. 6.9–37.3% at wetter site), which together with other laboratory and field data suggest that erosion may not preferentially transport PyC over other organic carbon forms or that erosional PyC flux may not be large enough to alter SOC concentration and distribution into fractions. Our results highlight the importance of considering topography in understanding SOC pools in general and PyC specifically under different climates.

Original languageEnglish (US)
Pages (from-to)121-130
Number of pages10
JournalGeoderma
Volume322
DOIs
StatePublished - Jul 15 2018

Fingerprint

topographic effect
soil carbon
organic carbon
climate
carbon
hillslope
soil organic carbon
soil
topography
particulate organic carbon
humus
erosion
carbon footprint
carbon flux
B horizons
A horizons
soil depth
edaphic factors
carbon sinks
least squares

Keywords

  • Climate
  • Erosion
  • Hillslope
  • Pyrogenic carbon
  • Soil carbon
  • Topography

Cite this

Climate-dependent topographic effects on pyrogenic soil carbon in southeastern Australia. / Wang, Xiang; Sanderman, Jonathan; Yoo, Kyungsoo.

In: Geoderma, Vol. 322, 15.07.2018, p. 121-130.

Research output: Contribution to journalArticle

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abstract = "The interactive effects of climate and topography on the composition, distribution and storage of soil organic carbon (SOC) remain unclear. This is particularly true for pyrogenic carbon (PyC) which is considered long-lasting in soil environments. With a goal to characterize how PyC responds to climate-dependent erosion and deposition processes, two hillslopes from SE Australia, differing in climate (MAP: 549 vs. 815 mm) and vegetation but with similar topography were selected for this study. We examined the colluvial soils that include A and B horizons on eroding (convex) and depositional (convergent) areas within each hillslope. Mid-infrared measurements with a partial least squares regression model were adopted to quantify the size and distribution of SOC fractions (i.e., particulate organic carbon (POC) fraction, humus organic carbon (HOC) and resistant organic carbon (ROC; representing PyC fraction) along the two hillslopes. These SOC fractions were examined with respect to climate, topographic position and soil depth. Total SOC was dominated by HOC (44 to 88{\%}) followed by PyC (7 to 37{\%}) and POC (0 to 37{\%}). Effects of topography on inventories of PyC were more strongly expressed in the drier hillslope (eroding vs. depositional: 0.39 vs. 1.73 kg m −2 ) than the wetter hillslope (eroding vs. depositional: 1.14 vs. 2.46 kg m −2 ), which also illustrates that climatic effects on soil PyC differ between eroding and depositional hillslope areas. In contrast, relative contributions of PyC to SOC showed less systematic variation with topography (6.9–36.8{\%} in eroding soils vs. 6.9–37.3{\%} in depositional soils) and climate (6.9–36.8{\%} at drier site vs. 6.9–37.3{\%} at wetter site), which together with other laboratory and field data suggest that erosion may not preferentially transport PyC over other organic carbon forms or that erosional PyC flux may not be large enough to alter SOC concentration and distribution into fractions. Our results highlight the importance of considering topography in understanding SOC pools in general and PyC specifically under different climates.",
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