Dryland, calcareous soils store (and lose) more near-surface organic carbon than previously thought
Journal of Geophysical Research: Earth Surface
Wiley-Blackwell / American Geophysical Union
©2016. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Dryland, calcareous soils store (and lose) significant quantities of near-surface organic carbon
Semiarid ecosystems are susceptible to changes in dominant vegetation which may have significant implications for terrestrial carbon dynamics. The present study examines the distribution of organic carbon (OC) between particle size fractions in near-surface (0–0.05 m) soil and the water erosion-induced redistribution of particle-associated OC over a grass-shrub ecotone, in a semiarid landscape, subject to land degradation. Coarse (>2 mm) particles have comparable average OC concentrations to the fine (<2 mm) particles, accounting for ~24–38% of the OC stock in the near-surface soil. This may be due to aggregate stabilization by precipitated calcium carbonate in these calcareous arid soils. Critically, standard protocols assuming that coarse fraction particles contain no OC are likely to underestimate soil OC stocks substantially, especially in soils with strongly stabilized aggregates. Sediment eroded from four hillslope scale (10 × 30 m) sites during rainstorm events was monitored over four annual monsoon seasons. Eroded sediment was significantly enriched in OC; enrichment increased significantly across the grass-shrub ecotone and appears to be an enduring phenomenon probably sustained through the dynamic replacement of preferentially removed organic matter. The average erosion-induced OC event yield increased sixfold across the ecotone from grass-dominated to shrub-dominated ecosystems, due to both greater erosion and greater OC enrichment. This erosional pathway is rarely considered when comparing the carbon budgets of grasslands and shrublands, yet this accelerated efflux of OC may be important for long-term carbon storage potentials of dryland ecosystems.
This research was conducted while A.M. Cunliffe was in receipt of a NERC Doctoral Training grant (NE/K500902/1) and was supported by the NSF Long Term Ecological Research Program at the Sevilleta National Wildlife Refuge (DEB-1232294) This research was conducted while A.M.C. was in receipt of a NERC Doctoral Training grant (NE/ K500902/1) and was supported by the NSF Long Term Ecological Research Program at the Sevilleta National Wildlife Refuge (DEB-1232294). L.T. was supported by travel bursaries from the University of Sheffield, the Worshipful Company of Farmers, and the Royal Society Dudley Stamp Memorial Fund Award. We are grateful to John Buffington, Jon Pelletier, and two anonymous reviews whose suggestions greatly improved upon earlier versions of this paper.
Vol. 121, No. 4, pp. 684–702