Monday paper: A dual isotope approach to isolate soil carbon pools of different turnover times


Torn, M. S., Kleber, M., Zavaleta, E. S., Zhu, B., Field, C. B., and Trumbore, S. E. 2013. A dual isotope approach to isolate soil carbon pools of different turnover times. Biogeosciences, 10, 8067-8081. DOI: 10.5194/bg-10-8067-2013.

Abstract

Soils are globally significant sources and sinks of atmospheric CO2. Increasing the resolution of soil carbon turnover estimates is important for predicting the response of soil carbon cycling to environmental change. We show that soil carbon turnover times can be more finely resolved using a dual isotope label like the one provided by elevated CO2 experiments that use fossil CO2. We modeled each soil physical fraction as two pools with different turnover times using the atmospheric 14C bomb spike in combination with the label in 14C and 13C provided by an elevated CO2 experiment in a California annual grassland. In sandstone and serpentine soils, the light fraction carbon was 21–54% fast cycling with 2–9 yr turnover, and 36–79% slow cycling with turnover slower than 100 yr. This validates model treatment of the light fraction as active and intermediate cycling carbon. The dense, mineral-associated fraction also had a very dynamic component, consisting of ∼7% fast-cycling carbon and ∼93% very slow cycling carbon. Similarly, half the microbial biomass carbon in the sandstone soil was more than 5 yr old, and 40% of the carbon respired by microbes had been fixed more than 5 yr ago. Resolving each density fraction into two pools revealed that only a small component of total soil carbon is responsible for most CO2 efflux from these soils. In the sandstone soil, 11% of soil carbon contributes more than 90% of the annual CO2 efflux. The fact that soil physical fractions, designed to isolate organic material of roughly homogeneous physico-chemical state, contain material of dramatically different turnover times is consistent with recent observations of rapid isotope incorporation into seemingly stable fractions and with emerging evidence for hot spots or micro-site variation of decomposition within the soil matrix. Predictions of soil carbon storage using a turnover time estimated with the assumption of a single pool per density fraction would greatly overestimate the near-term response to changes in productivity or decomposition rates. Therefore, these results suggest a slower initial change in soil carbon storage due to environmental change than has been assumed by simpler (one-pool) mass balance calculations.

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Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.

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Monday paper: Modelling soil organic carbon stocks in global change scenarios: a CarboSOIL application


Muñoz-Rojas, M., Jordán, A., Zavala, L. M., González-Peñaloza, F. A., De la Rosa, D., Pino-Mejias, R., and Anaya-Romero, M. 2013. Modelling soil organic carbon stocks in global change scenarios: a CarboSOIL application. Biogeosciences, 10, 8253-8268, DOI: 10.5194/bg-10-8253-2013.

Abstract

Global climate change, as a consequence of the increasing levels of atmospheric CO2 concentration, may significantly affect both soil organic C storage and soil capacity for C sequestration. CarboSOIL is an empirical model based on regression techniques and developed as a geographical information system tool to predict soil organic carbon (SOC) contents at different depths. This model is a new component of the agro-ecological decision support system for land evaluation MicroLEIS, which assists decision-makers in facing specific agro-ecological problems, particularly in Mediterranean regions. In this study, the CarboSOIL model was used to study the effects of climate change on SOC dynamics in a Mediterranean region (Andalusia, S Spain). Different downscaled climate models were applied based on BCCR-BCM2, CNRMCM3, and ECHAM5 and driven by SRES scenarios (A1B, A2 and B2). Output data were linked to spatial data sets (soil and land use) to quantify SOC stocks. The CarboSOIL model has proved its ability to predict the short-, medium- and long-term trends (2040s, 2070s and 2100s) of SOC dynamics and sequestration under projected future scenarios of climate change. Results have shown an overall trend towards decreasing of SOC stocks in the upper soil sections (0–25 cm and 25–50 cm) for most soil types and land uses, but predicted SOC stocks tend to increase in the deeper soil section (0–75 cm). Soil types as Arenosols, Planosols and Solonchaks and land uses as “permanent crops” and “open spaces with little or no vegetation” would be severely affected by climate change with large decreases of SOC stocks, in particular under the medium–high emission scenario A2 by 2100. The information developed in this study might support decision-making in land management and climate adaptation strategies in Mediterranean regions, and the methodology could be applied to other Mediterranean areas with available soil, land use and climate data.

Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.

Working for the recovery of burned soils


Fire is a natural agent that occurs in most terrestrial ecosystems. In Mediterranean areas, for example, fire is a natural agent that has contributed to shape the history of vegetation, soils, and ultimately, the landscape we know today. Also, since ancient times, men have also used fire as a tool for the management of ecosystems. As a result, the Mediterranean vegetation has developed mechanisms of adaptation to fire, but Man has contributed to the intense transformation of the original forest systems in crops, pastures and meadows and dehesas from the fifteenth century to encourage farming, sylvopastoral use of forests, and human supply.

Prescribed burn in Portugal. Photo by Vicky Arcenegui, University Miguel Hernández, Spain.
Prescribed burn in Portugal. Photo by Vicky Arcenegui, University Miguel Hernández, Spain.

In countries like Spain, the concentration of population in urban areas that began in the second half of the 20th century has led to a shift away from rural areas and declining crop and livestock pressure. The abandonment of traditional rural labors contributed to forget an efficient management of agricultural and forest resources, such as maintenance of terraces on the slopes, care of roads or forest clearing. All this, coupled with the pressures of tourism, the expansion of urban areas and other social reasons, has led to a large increase in the number and damage caused by forest fires during the 1960s, 1970s and 1980s. Since 1990, the number of forest fires has increased progressively, although affecting a lower annual total. In recent years, though the number of forest fires has declined high intensity fires are still occurring. High intensity fires occur under certain environmental conditions (high temperatures, wind and low humidity of vegetation and soil), but also due to a management of the forest environment that favors the spread of fire.

In the context of global change, scientists expect the number of high intensity wildfires increase, as well as the severity of its impact on the environment, the productive capacity and natural resources. For these reasons, scientists who study the impact of fire on soils have participated in the development of practice guidelines for the management planning burned soils that facilitate managers to decide when, where and how to act.

Soil scientists and firefighters during a prescribed burn in Sevilla. Photo by Antonio Jordán, University of Seville.
Soil scientists and firefighters during a prescribed burn in Sevilla. Photo by Antonio Jordán, University of Seville.

According to the Spanish Network Forest Fire Effects on Soils, a concern that is necessary to transfer the decision-makers that it is not always necessary to act in the post -fire, and that in many cases, both the vegetation and the soil can recover themselves in relatively short periods of time. Also, that actions cannot be the same on all systems, and the planning and management of burned areas should be based on local characteristics of the environment.

Good forest management practices should be based on scientific research. Lots of money have been used for fight against forest fires, but just to prevention activities, and scarcely for the study of their impact on soil, water and vegetation. The knowledge of the effects of fire on soil properties and the proposing and use of impact factors becomes essential when performing management decisions, restoration or prevention of the areas affected by fire.

To this end, scientists from Galicia (Forest Research Centre Lourizán, Institute of Agrobiological Research from Galicia, University of Santiago de Compostela and University of Vigo) have developed the first guide for urgent action planning against soil erosion in fire-affected forest areas. This initiative has been supported by the Spanish Government and FEDER funds of the European Union.

Guide for urgent actions against soil erosion in burned forest areas
Guide for urgent actions against soil erosion in burned forest areas

The first part of the text studies the risk of erosion and soil hydrological response after fire in Galicia, where soils, vegetation and climate are very different from neighbor regions. The second part details the urgent treatments to combat erosion risk in the post -fire, proposing methodologies for assessing the severity of fire impacts on soil and vegetation, and recommends a guide for urgent decision-making.

We hope this work, a collaboration of scientists deep and managers, help the recovery of degraded areas in a region hard hit by the effects of fire.

This post was also published simultaneously in the EGU Blog Network.

Earth System Dynamics: Soil temperature response to 21st century global warming: the role of and some implications for peat carbon in thawing permafrost soils in North America


Wisser, D., Marchenko, S., Talbot, J., Treat, C., and Frolking, S.: Soil temperature response to 21st century global warming: the role of and some implications for peat carbon in thawing permafrost soils in North America, Earth Syst. Dynam., 2, 121-138, doi:10.5194/esd-2-121-2011, 2011.

Abstract

Northern peatlands contain a large terrestrial carbon pool that plays an important role in the Earth’s carbon cycle. A considerable fraction of this carbon pool is currently in permafrost and is biogeochemically relatively inert; this will change with increasing soil temperatures as a result of climate warming in the 21st century. We use a geospatially explicit representation of peat areas and peat depth from a recently-compiled database and a geothermal model to estimate northern North America soil temperature responses to predicted changes in air temperature. We find that, despite a widespread decline in the areas classified as permafrost, soil temperatures in peatlands respond more slowly to increases in air temperature owing to the insulating properties of peat. We estimate that an additional 670 km3 of peat soils in North America, containing ~33 Pg C, could be seasonally thawed by the end of the century, representing ~20 % of the total peat volume in Alaska and Canada. Warming conditions result in a lengthening of the soil thaw period by ~40 days, averaged over the model domain. These changes have potentially important implications for the carbon balance of peat soils.

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Earth System Dynamics (ESD) is an international scientific journal dedicated to the publication and public discussion of studies that take an interdisciplinary perspective of the functioning of the whole Earth system and global change. The overall behavior of the Earth system is strongly shaped by the interactions among its various component systems, such as the atmosphere, cryosphere, hydrosphere, oceans, pedosphere, lithosphere, and the inner Earth, but also by life and human activity. ESD solicits contributions that investigate these various interactions and the underlying mechanisms, ways how these can be conceptualized, modelled, and quantified, predictions of the overall system behavior to global changes, and the impacts for its habitability, humanity, and future Earth system management by human decision making. More at Earth System Dynamics homepage.

Biogeosciences: Comparison of soil greenhouse gas fluxes from extensive and intensive grazing in a temperate maritime climate


Skiba, U., Jones, S. K., Drewer, J., Helfter, C., Anderson, M., Dinsmore, K., McKenzie, R., Nemitz, E., and Sutton, M. A.: Comparison of soil greenhouse gas fluxes from extensive and intensive grazing in a temperate maritime climate, Biogeosciences, 10, 1231-1241, doi:10.5194/bg-10-1231-2013, 2013.

Abstract

Greenhouse gas (GHG) fluxes from a seminatural, extensively sheep-grazed drained moorland and intensively sheep-grazed fertilised grassland in South East (SE) Scotland were compared over 4 yr (2007–2010). Nitrous oxide (N2O) and methane (CH4) fluxes were measured by static chambers, respiration from soil plus ground vegetation by a flow-through chamber, and the net ecosystem exchange (NEE) of carbon dioxide (CO2) by eddy-covariance. All GHG fluxes displayed high temporal and interannual variability. Temperature, radiation, water table height and precipitation could explain a significant percentage of seasonal and interannual variations. Greenhouse gas fluxes were dominated by the net ecosystem exchange of CO2 at both sites. Net ecosystem exchange of CO2 and respiration was much larger on the productive fertilised grassland (−1567 and 7157 g CO2eq m−2 yr−1, respectively) than on the seminatural moorland (−267 and 2554 g CO2eq m−2 yr−1, respectively). Large ruminant CH4 (147 g CO2eq m−2 yr−1) and soil N2O (384 g CO2eq m−2 yr−1) losses from the grazed grassland counteracted the CO2 uptake by 34%, whereas the small N2O (0.8 g CO2eq m−2 yr−1) and CH4 (7 g CO2eq m−2 yr−1) emissions from the moorland only impacted the NEE flux by 3%. The 4-yr average GHG budget for the grazed grassland was −1034 g CO2eq m−2 yr−1 and −260 g CO2eq m−2 yr−1 for the moorland.

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Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.

Solid Earth: Organic carbon stocks in Mediterranean soil types under different land uses (Southern Spain)


M. Muñoz-Rojas, A. Jordán, L. M. Zavala, D. De la Rosa, S. K. Abd-Elmabod, and M. Anaya-Romero. 2012. Organic carbon stocks in Mediterranean soil types under different land uses (Southern Spain). Solid Earth, 3, 375-386.

Abstract

Soil C sequestration through changes in land use and management is one of the sustainable and long-term strategies to mitigate climate change. This research explores and quantifies the role of soil and land use as determinants of the ability of soils to store C along Mediterranean systems. Detailed studies of soil organic C (SOC) dynamics are necessary in order to identify factors determining fluctuations and intensity of changes. In this study, SOC contents from different soil and land use types have been investigated in Andalusia (Southern Spain). We have used soil information from different databases, as well as land use digital maps, climate databases and digital elevation models. The average SOC content for each soil control section (0–25, 25–50 and 50–75 cm) was determined and SOC stocks were calculated for each combination of soil and land use type, using soil and land cover maps. The total organic C stocks in soils of Andalusia is 415 Tg for the upper 75 cm, with average values ranging from 15.9 Mg C ha−1 (Solonchaks under “arable land”) to 107.6 Mg C ha−1 (Fluvisols from “wetlands”). Up to 55% of SOC accumulates in the top 25 cm of soil (229.7 Tg). This research constitutes a preliminary assessment for modelling SOC stock under scenarios of land use and climate change.

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Solid Earth (SE) is an international scientific journal dedicated to the publication and discussion of multidisciplinary research on the composition, structure and dynamics of the Earth from the surface to the deep interior at all spatial and temporal scales. More at Solid Earth hompage.