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Soil carbon and climate change: from the Jenkinson effect to the compost-bomb instability

by on July 14, 2011

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Soil carbon and climate change: from the Jenkinson effect to the compost-bomb instability

C. M. Luke, P. M. Cox

First generation climate–carbon cycle models suggest that climate change will suppress carbon accumulation in soils, and could even lead to a net loss of global soil carbon over the next century. These model results are qualitatively consistent with soil carbon projections published by Jenkinson almost two decades ago. More recently there has been a suggestion that the release of heat associated with soil decomposition, which is neglected in the vast majority of large-scale models, may be critically important under certain circumstances. Models with and without the extra self-heating from microbial respiration have been shown to yield significantly different results. The present paper presents a mathematical analysis of a tipping point or runaway feedback that can arise when the heat from microbial respiration is generated more rapidly than it can escape from the soil to the atmosphere. This ‘compost-bomb instability’ is most likely to occur in drying organic soils with high porosity covered by an insulating lichen or moss layer. However, the instability is also found to be strongly dependent on the rate of global warming. This paper derives the conditions required to trigger the compost-bomb instability, and discusses the relevance of these to the concept of dangerous rates of climate change. On the basis of simple numerical experiments, rates of long-term warming equivalent to 10°C per century could be sufficient to trigger compost-bomb instability in drying organic soils.

However, all current global climate–carbon cycle models ignore a potentially important soil biological heating term that could change this situation radically.

Source Wiley

Soil Science: Sometimes terms which refer to branches of soil science, such as pedology (formation, chemistry, morphology and classification of soil) and edaphology (influence of soil on organisms, especially plants), are used as if synonymous with soil science. The diversity of names associated with this discipline is related to the various associations concerned. Indeed, engineers, agronomists, chemists, geologists, geographers, ecologists, biologists, microbiologists, sylviculturists, sanitarians, archaeologists, and specialists in regional planning, all contribute to further knowledge of soils and the advancement of the soil sciences.

Soil scientists have raised concerns about how to preserve and soil and arable land in a world with a growing population, possible future water crisis, increasing per capita food consumption, and land degradation.

Source Soil Science

Soil respiration refers to the production of carbon dioxide when soil organisms respire. This includes respiration of plant roots, the rhizosphere, microbes and fauna.

Soil respiration is a key ecosystem process that releases carbon from the soil in the form of CO2. CO2 is acquired from the atmosphere and converted into organic compounds in the process of photosynthesis. Plants use these organic compounds to build structural components or respire them to release energy. When plant respiration occurs below-ground in the roots, it adds to soil respiration. Over time, plant structural components are consumed by heterotrophs. This heterotrophic consumption releases CO2 and when this CO2 is released by below-ground organisms, it is considered soil respiration.

The amount of soil respiration that occurs in an ecosystem is controlled by several factors. The temperature, moisture, nutrient content and level of oxygen in the soil can produce extremely disparate rates of respiration. These rates of respiration can be measured in a variety of methods. Other methods can be used to separate the source components, in this case the type of photosynthetic pathway (C3/C4), of the respired plant structures.

Soil respiration rates can be largely effected by human activity. This is because humans have the ability to and have been changing the various controlling factors of soil respiration for numerous years. Global climate change is composed of numerous changing factors including rising atmospheric CO2, increasing temperature and shifting precipitation patterns. All of these factors can effect the rate of global soil respiration. Increased nitrogen fertilization by humans also has the potential to effect rates over the entire Earth.

Soil respiration and its rate across ecosystems is extremely important to understand. This is because soil respiration plays a large role in global carbon cycling as well as other nutrient cycles. The respiration of plant structures releases not only CO2 but also other nutrients in those structures, such as nitrogen. Soil respiration is also associated with positive feedbacks with global climate change. Positive feedbacks are when a change in a system produces response in the same direction of the change. Therefore, soil respiration rates can be effected by climate change and then respond by enhancing climate change.

Source Soil Respiration

Oceanographer: Nitrous Oxide Emitting Aquatic ‘Dead Zones’ Contributing To Climate Change  “When suboxic waters (oxygen essentially absent) occur at depths of less than 300 feet, the combination of high respiration rates, and the peculiarities of a process called denitrification can cause N2O production rates to be 10,000 times higher than the average for the open ocean.

Source Pedology erosion weathering during the PETM

Related Soil ScienceSoil RespirationMagnetic Death StarMagnetiteOrogenWeatheringErosionDecompositionErosion and tectonicsPETM Paleocene Eocene Thermal MaximumAprubt CC – Runaway CCEpeirogenic movementLithosphereGeomorphologySedimentology –  PedologyStructural geology – GeochemistryHypoxiaOrographySiltation

  1. The Rate of Permafrost Carbon Release Under Aerobic and Anaerobic Conditions and its Potential Effects on Climate

    Recent observations suggest that permafrost thaw may create two completely different soil environments: aerobic in relatively well-drained uplands and anaerobic in poorly-drained wetlands. The soil oxygen availability will dictate the rate of permafrost carbon release as carbon dioxide (CO2) and as methane (CH4), and the overall effects of these emitted greenhouse gases on climate. The objective of this study was to quantify CO2 and CH4 release over a 500-day period from permafrost soil under aerobic and anaerobic conditions in the laboratory and to compare the potential effects of these emissions on future climate by estimating their relative climate forcing. We used permafrost soils collected from Alaska and Siberia with varying organic matter characteristics and simultaneously incubated them under aerobic and anaerobic conditions to determine rates of CO2 and CH4 production. Over 500 days of soil incubation at 15°C, we observed that carbon released under aerobic conditions was 3.9 to 10.0 times greater than anaerobic conditions. When scaled by greenhouse warming potential to account for differences between CO2 and CH4, relative climate forcing ranged 1.5-7.1. Carbon release in organic soils was nearly 20 times greater than mineral soils on a per gram soil basis, but when compared on a per gram carbon basis deep permafrost mineral soils showed a similar carbon release rates as organic soils for some soil types. This suggests that permafrost carbon may be very labile but that there are significant differences across soil types depending on the processes that controlled initial permafrost carbon accumulation within a particular landscape. Overall, our study showed that, independent of soil type, permafrost carbon in a relatively aerobic upland ecosystems may have a greater effect on climate as compared to a similar amount of permafrost carbon thawing in an anaerobic environment, despite the release of CH4 that occurs in anaerobic conditions.

  2. The Root of the Problem
    New research suggests that the flow of carbon through plants to underground ecosystems may be crucial to how the environment responds to climate change.

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  1. Methane release and Runaway Climate Change « The Climax

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