Soil Carbon Cycle

COS 19-2: Transformations of pine forest-derived dissolved organic matter in a temperate zone soil

by Megan Mobley

Storm pulses and varying sources of hydrologic carbon export from a mountainous watershed

by Christopher Shope

Geophysical evidence for the lateral distribution of free phase gas at the peat basin scale in a large northern peatland

by Andrew Parsekian

A comparison of 1D vertical models of biogenic gas content within a northern peatland from common mid-point and cross-borehole GPR

by Andrew Parsekian

Near‐saturation dielectric properties of peat soil with entrapped free‐phase gas determined using ground penetrating radar

by Andrew Parsekian

DIELECTRIC PROPERTIES OF PEAT WITH BIOGENIC FREE PHASE GAS

by Andrew Parsekian

Isotopes in pyrogenic carbon: a review

by Philippa Ascough

Co-authored with M. I. Bird.
Published in Organic Geochemistry, Volume 42, Issue 12, January 2012, Pages 1529-1539 (Organic Isotopes in Soil)

Pyrogenic carbon (PC; also known as biochar, charcoal, black carbon and soot) derived from natural and anthropogenic... more Pyrogenic carbon (PC; also known as biochar, charcoal, black carbon and soot) derived from natural and anthropogenic burning plays a major, but poorly quantified, role in the global carbon cycle. Isotopes provide a fundamental fingerprint of the source of PC and a powerful tracer of interactions between PC and the environment. Radiocarbon and stable carbon isotope techniques have been widely applied to studies of PC in aerosols, soils, sediments and archaeological sequences, with the use of other isotopes currently less developed. This paper reviews the current state of knowledge regarding (i) techniques for isolating PC for isotope analysis and (ii) processes controlling the carbon (13C and 14C), nitrogen, oxygen, hydrogen and sulfur isotope composition of PC during formation and after deposition. It also reviews the current and potential future applications of isotope based studies to better understand the role of PC in the modern environment and to the development of records of past environmental change.

Labile carbon and other soil quality indicators in two tillage systems during transition to organic agriculture

by David Lewis

David Bruce Lewis, Jason P. Kaye, Randa Jabbour, and Mary E. Barbercheck
Renewable Agriculture and Food Systems (2011) 26:342–353

Weed management is one of the primary challenges for producers transitioning from conventional to organic agriculture.... more Weed management is one of the primary challenges for producers transitioning from conventional to organic agriculture. Tillage and the use of cover crops are two weed control tactics available to farmers transitioning to organic management, but little is known about their interactive effects on soil quality during the transition period. We investigated the response of soils to tillage and initial cover crop during the 3-year transition to organic in a cover crop–soybean (Glycine max)–maize (Zea mays) rotation in the Mid-Atlantic region of the USA. The tillage treatment contrasted full, inversion tillage with moldboard plowing (FT) versus reduced tillage with chisel plowing (RT). The cover crop treatment contrasted annual versus mostly perennial species during the first year of the rotation. The experiment was initiated twice (Start 1 and Start 2), in consecutive years in adjacent fields. By the end of the experiment, labile carbon, electrical conductivity, pH and soil moisture were all greater under RT than under FT in both starts. Soil organic matter and several other soil attributes were greater under RT than under FT in Start 1, but not in Start 2, perhaps owing to differences between starts in initial field conditions and realized weather. Soil attributes did not differ between the two cover crop treatments. Combining our soils results with agronomic and economic analyses on these plots suggests that using RT during the organic transition can increase soil quality without compromising yield and profitability.

Biogeochemical cycling of carbon, phosphorus, and trace metals

by Jennifer Stern

Biological and physical influences on the carbon isotope content of CO2 in a subalpine forest snow pack

by Sean Schaeffer

Bowling, DR, WJ Massman, SM Schaeffer, SP Burns, RK Monson, and MW Williams (2009)

Biogeochemistry. doi:10.1007/s10533-008-9233-4

Seasonal and episodic moisture controls on plant and microbial contributions to soil respiration

by Sean Schaeffer

Mariah S. Carbone, Christopher J. Still, Anthony R. Ambrose, Todd E. Dawson, A. Park Williams, Claudia M. Boot, Sean M. Schaeffer, Joshua P. Schimel

Oecologia (2011) 167:265–278

Bioenergy systems, soil health and climate change

by Brendan George

Chapter in a recent book "Soil health and climate change" edited by B.P. Singh, A.L. Cowie & K.Y. Chan (Springer).
http://www.springer.com/life+sciences/agriculture/book/978-3-642-20255-1

Currently fossil fuels supply most of the world’s energy needs, in processes that move carbon from geologic pools to... more Currently fossil fuels supply most of the world’s energy needs, in processes that move carbon from geologic pools to the  atmosphere. In 2007, use of fossil fuels released an estimated 28.8 Gt of carbon dioxide equivalent (CO2-e) into the atmosphere (International Energy Agency 2009). The increasing atmospheric concentration of carbon dioxide (CO2) and other greenhouse gases (GHGs) influences climate (Solomon et al. 2007), and this process may be accentuated if climate and
carbon cycle feedback loops continue to develop (Friedlingstein 2008; Gregory et al. 2009).

It is generally accepted that we need to move to a “low-carbon future” with reduced reliance on fossil fuels for energy. Bioenergy can play a significant role, meeting some of our energy needs while reducing carbon emissions and even sequestering significant amounts of carbon. While there is the potential for
bioenergy systems to provide very significant amounts of energy across the world (Bauen et al. 2010), intensifying production systems and changing land use and land management to produce biomass may impact on soil health and soil carbon in
particular (Lal et al. 2003). The question of how bioenergy systems should be managed to achieve optimal outcomes is not yet clearly resolved (e.g. Blanco-Canqui 2010; Cowie et al. 2006; Delucchi 2010; Lal et al. 2003). And while bioenergy systems, if thoughtfully designed, can contribute to mitigating climate change, we also need to consider some of the issues in adapting to climate change to sustain production.

This chapter reviews some of the current work and expectations for the improved management of bioenergy systems that not only produce significant amounts of biomass but maintain or improve soil health.

A pedogenic goethite record of soil CO2 variations as a response to soil moisture content

by Erik Gulbranson

Alkali Extraction of Archaeological and Geological Charcoal: Evidence for Diagenetic Degradation and Formation of Humic Acids

by Philippa Ascough

Co-authored with M.I. Bird, S. Francis and T. Lebl
doi:10.1016/j.jas.2010.08.011

Charcoal forms a crucial source of archaeological and palaeoenvironmental data, providing a record of cultural... more Charcoal forms a crucial source of archaeological and palaeoenvironmental data, providing a record of cultural activities, past climatic conditions and a means of chronological control via radiocarbon (14C) dating. Key to this is the perceived resistance of charcoal to post-depositional alteration, however recent research has highlighted the possibility for alteration and degradation of charcoal in the environment. An important aspect of such diagenesis is the potential for addition of exogenous “humic acids’ (HA), to affect the accuracy of archaeological and palaeoenvironmental reconstructions based upon chemical analyses of HA-containing charcoal. However the release of significant quantities of HA from apparently pristine charcoals raises the question whether some HA could be derived via diagenetic alteration of charcoal itself. Here we address this question through comparison of freshly-produced charcoal with samples from archaeological and geological sites exposed to environmental conditions for millennia using elemental (C/H/O) and isotopic (δ13C) measurements, Fourier Transform Infrared Spectroscopy (FTIR) and proton Liquid-State Nuclear magnetic Resonance (1H-NMR). The results analyses show that the presence of highly carboxylated and aromatic alkali-extractable HA in charcoal from depositional environments can often be attributable to the effects of post-depositional processes, and that these substances can represent the products of post-depositional diagenetic alteration in charcoal.

Evidence for bias in C and N concentrations and δ13C composition of terrestrial and aquatic organic materials due to pre-analysis acid preparation techniques

by Chris Brodie

Chemical Geology. 282, 67 - 83.

Lead Author: Dr. Chris Brodie (Durham University, UK; Hong Kong University, Hong Kong)

Co-Authors: Prof. Melanie Leng (NIGL, UK), Dr. James Casford (Durham University, UK), Christopher Kendrick (NIGL, UK), Dr. Jeremy Lloyd (Durham University, UK), Dr. Zong Yongqiang (Hong Kong University, Hong Kong), Prof. Michael Bird (James Cook University, Australia).

ABSTRACT:
This study is the first systematic comparison of the effect of acid treatment methods on the... more ABSTRACT:
This study is the first systematic comparison of the effect of acid treatment methods on the reliability of organic carbon [C] and nitrogen [N], and carbon isotope (δ13C) values on a range of terrestrial and aquatic, modern and geological environmental materials. We investigated the 3 most common methods; (i) acidification followed by sequential deionised water rinses (“rinse method”); (ii) acidification in silver capsules (“capsule method”); and (iii) acidification by exposure to an acid vapour (“fumigation method”). We also investigated the effect of sample size and capsule type (silver and tin) on C/N ratio and δ13C values. We find (i) %C, %N, C/N and δ13C showed significant within and between method variability; (ii) disproportionate and non-linear offsets of %C, %N and C/N values after acidification within and between methods and within and between sample materials; (iii) that alterations in %C did not necessarily manifest themselves in shifts in δ13C, and vice-versa; (iv) small (~ 90 μg C) sample sizes showed consistent overestimations and inaccuracies after acidification; (v) The effect of capsule type was not significant on most samples, but did show a notable effect on our aquatic materials, generally increasing %C and %N, and producing depleted δ13C values. These findings raise cause for concern on the interpretative nature of C/N ratios and their support for carbon isotope values. The comparability between laboratories (different preparation methods) and environmental settings (amount, type and nature of OM) are also likely to be problematic. We conclude that the response of C and N concentrations in organic matter to acid treatment in environmental materials is neither negligible nor systematic.

Keywords: δ13C; C/N ratio; Method comparison; Rinse method; Capsule method; Fumigation method; environmental reconstruction

Herbivore Effects on Above-and Belowground Plant Production and Soil Nitrogen Availability In the Trans-Himalayan Shrub-Steppes

by Sumanta Bagchi

Oecologia 164:1075-1082. (2010)

Large mammalian herbivores may have positive, neutral, or negative effects on annual net aboveground plant production... more Large mammalian herbivores may have positive, neutral, or negative effects on annual net aboveground plant production (NAP) in different ecosystems, depending on their indirect effects on availability of key nutrients such as soil N. In comparison, less is known about the corresponding influence of grazers, and nutrient dynamics, over annual net belowground plant production (NBP). In natural multi-species plant communities, it remains uncertain how grazing influences relative allocation in the above- and belowground compartments in relation to its effects on plant nutrients. We evaluated grazer impacts on NAP, NBP, and relative investment in the above- and belowground compartments, alongside their indirect effects on soil N availability in the multiple-use Trans-Himalayan grazing ecosystem with native grazers and livestock. Data show that a prevailing grazing intensity of 51% increases NAP (+61%), but reduces NBP (−35%). Grazing also reduced C:N ratio in shoots (−16%) and litter (−50%), but not in roots, and these changes coincided with increased plant-available inorganic soil N (+23%). Areas used by livestock and native grazers showed qualitatively similar responses since NAP was promoted, and NBP was reduced, in both cases. The preferential investment in the aboveground fraction, at the expense of the belowground fraction, was correlated positively with grazing intensity and with improvement in litter quality. These results are consistent with hypothesized herbivore-mediated positive feedbacks between soil nutrients and relative investment in above- and belowground compartments. Since potentially overlapping mechanisms, such as N mineralization rate, plant N uptake, compositional turnover, and soil microbial activity, may contribute towards these feedbacks, further studies may be able to discern their respective contributions.

Introduced Grazers Can Restrict Potential Soil Carbon Sequestration Through Impacts on Plant Community Composition

by Sumanta Bagchi

Ecology Letters 13: 959-968. (2010)

Grazing occurs over a third of the earth’s land surface and may potentially influence the storage of 109 Mg year^−1 of... more Grazing occurs over a third of the earth’s land surface and may potentially influence the storage of 109 Mg year^−1 of greenhouse gases as soil C. Displacement of native herbivores by high densities of livestock has often led to overgrazing and soil C loss. However, it remains unknown whether matching livestock densities to those of native herbivores can yield equivalent soil C sequestration. In the Trans-Himalayas we found that, despite comparable grazing intensities, watersheds converted to pastoralism had 49% lower soil C than watersheds which retain native herbivores. Experimental grazer-exclusion within each watershed type, show that this difference appears to be driven by indirect effects of livestock diet selection, leading to vegetation shifts that lower plant production and reduce likely soil C inputs from vegetation by c. 25 gC m^−2 year^−1. Our results suggest that while accounting for direct impacts (stocking density) is a major step, managing indirect impacts on vegetation composition are equally important in influencing soil C sequestration in grazing ecosystems.