Eurasian steppes cover a vast area of about 8·10 6 km 2 , of which a fraction between 60% and 70%... more Eurasian steppes cover a vast area of about 8·10 6 km 2 , of which a fraction between 60% and 70% was converted to agricultural use in the past, and have been poorly investigated in respect with the exchanges of CO 2 with the atmosphere while they could play a relevant role in the carbon uptake located over the northern hemisphere lands at temperate latitudes. In particular, old agricultural fields abandoned after 1990 in former Soviet Union could contribute actively to the sequestration of atmospheric carbon, since after land use change they tend to restore the original stock of carbon of steppe ecosystems, that went partly lost with the agricultural use of the land. This study provides a quantitative characterization of the carbon pools, of the patterns of carbon allocation within the ecosystems, of the CO 2 exchanges between the biosphere and the atmosphere, as well as of the response of CO 2 fluxes to environmental drivers of true bunchgrass steppes and neighbouring old agricultural fields hosting different temporal stages of recovering grassland located in the Republic of Hakasia and in the Republic of Tuva (Russian Federation). Within about 40 years, cultivations caused a loss of organic carbon not lower than 46%-52% in respect with the level of steppes (average carbon sotck: 140.9 tCha -1 in Hakasia and 45.5 tCha -1 in Tuva) and affected both the soil organic carbon pool, 80-92% of the lost carbon, and the belowground biomass pool for the remaining part. The biomass carbon stock of steppes of Hakasia and Tuva was found to be stored mainly in the belowground pool, with a proportion ranging 88-94%, due to the highly developed root system of perennial species. In old agricultural fields, belowground biomass was still predominant but the share of biomass found in the aboveground pool, from 12% to 42%, was larger than in steppes. The assessment of net primary productivity (NPP) at sites of Hakasia by different biometric methods ranged between 6.0 ad 13.1 t d.m. ha -1 , and organicated carbon was allocated primarily to the root system, with a fraction varying between 70% and 90% for both steppe and old field ecosystems. CO 2 fluxes at ecosystem scale were monitored by eddy covariance technique over three stages of an old field succession in Hakasia represented by an early stage (5 years since land use change), an intermediate stage (10 years) and a mature stage (steppe). Yearly CO 2 exchange estimates disclosed all the sites to act as carbon sinks, with a strenght declining from the early stage (2.1 tC ha -1 ) to the steppe ecosystem (1.1 tC ha -1 ). Also the amounts of carbon assimilated by photosynthesis (GPP) and released to the atmosphere through ecosystem respiration (R eco ) decreased over the stages of the succession, yielding the observed trend in the net ecosystem productivity (NEP). The steppe ecosystem, even if characterized by lower carbon assimilation than old field ecosystems, displayed a less pronounced reduction of the photosynthetic process in response to extreme high air temperature and air dryness conditions, maintaining its efficiency in carbon uptake. The steppe ecosystem was also found resilient to disturbances since after a fire burst before the onset of the growing season, it showed an enhanced carbon sequestration that could completely offset the amount of carbon lost from the burnt biomass. The carbon budget of the true steppe, estimated additionally using the ecological inventory methodology based on the difference between net primary productivity and heterotrophic respiration (NEP=NPP-Rh), agreed with the result obtained with the micrometeorological technique. The spatialization of the carbon balance observed at sites in the steppe region of the Republic of Hakasia, to assess the magnitude of the sink of steppes and old fields ecosystems in the Russian Federation, suggests a carbon sequestration of 0.17 PgC yr -1 .
The progress in the understanding of the carbon exchange between forests and the atmosphere has b... more The progress in the understanding of the carbon exchange between forests and the atmosphere has been dramatic over the last few years, yet largely based on observations of middle-aged or mature stands in the temperate and boreal region while quite a few studies report on the temporal dynamics of carbon balance in forest stand chronosequences taking into account the effect of forest management (Law et al., 2003; Kowalski et al., 2003; Kolari et al, 2004; Zha et al., 2009). In order to quantify the temporal variability of CO2 fluxes at ecosystem level following coppicing, we analyze eddy covariance data of a deciduous oak (Quercus cerris L.) coppice forest in central Italy (Roccarespampani, VT) collected over two differently aged forest stands in the period 2000-2006 and covering most of the rotation period (0-6; 11-15 years). Data processing was performed evenly for whole data-set according to the CarboEurope database standard (Papale et al., 2006). The inter-annual variability and s...
The performance of eight fast-response methane (CH 4 ) gas analysers suitable for eddy covariance... more The performance of eight fast-response methane (CH 4 ) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions. The moderate CH 4 fluxes observed at the location, of the order of 25 nmol m −2 s −1 , provided a suitable signal for testing the instruments' performance.
Springer Environmental Science and Engineering, 2012
This chapter considers the current state of Siberian terrestrial ecosystems, their spatial distri... more This chapter considers the current state of Siberian terrestrial ecosystems, their spatial distribution, and major biometric characteristics. Ongoing climate change and the dramatic increase of accompanying anthropogenic pressure provide different but mostly negative impacts on Siberian ecosystems. Future climates of the region may lead to substantial drying on large territories, acceleration of disturbance regimes, deterioration of ecosystems, and positive feedback to global warming. The region requires urgent development and implementation of strategies of adaptation to, and mitigation of, negative consequences of climate change.
The carbon dioxide (CO 2 ) exchange of five different peatland systems across Europe with a wide ... more The carbon dioxide (CO 2 ) exchange of five different peatland systems across Europe with a wide gradient in land use intensity, water table depth, soil fertility and climate was simulated with the process oriented CoupModel. The aim of the study was to find out whether CO 2 fluxes, measured at different sites, can be explained by common processes and parameters or to what extend a site specific configuration is needed. The model was calibrated to fit measured CO 2 fluxes, soil temperature, snow depth and leaf area index (LAI) and resulting differences in model parameters were analyzed. Finding site independent model parameters would mean that differences in the measured fluxes could be explained solely by model input data: water table, meteorological data, management and soil inventory data.
Springer Environmental Science and Engineering, 2012
This chapter provides observational evidence of climatic variations in Siberia for three time sca... more This chapter provides observational evidence of climatic variations in Siberia for three time scales: during the past 10,000 years, during the past millennium prior to instrumental observations, and for the past 130 years during the period of large-scale meteorological observations. The observational evidence is appended with the global climate model projections for the twenty-fi rst century based on the most probable scenarios of the future dynamics of the major anthropogenic and natural factors responsible for contemporary climatic changes. Historically, climate of Siberia varied broadly. It was both warmer and colder than the present. However, during the past century, it became much warmer; the cold season precipitation north of 55°N increased, but no rainfall increase over most of Siberia has occurred. This led to drier summer conditions and to increased possibility of droughts and fi re weather. Projections of the future climate indicate the further temperature increases, more in the cold season and less in the warm season, signi fi cant changes in the
Simulating biogenic carbon fluxes in Siberia is difficult, because the growing season is short an... more Simulating biogenic carbon fluxes in Siberia is difficult, because the growing season is short and the transitions between the seasons are fast. At the start of the growing season, when the snow has melted, the soil is still frozen. The melt water therefore either runs off quickly in non-flat terrain, or waterlogs the soil in flat terrain. Consequently, the soil moisture content during soil thawing tends to the extremes, either very wet or towards dry. This 'bi-modal' behaviour of soil moisture at the start of the growing season is difficult to capture by vegetation models. Consequently, the carbon fluxes and transpiration rates are either too much limited by anticipated water stress, or too little limited during waterlogging. We present here a method to improve the simulated soil moisture in a vegetation model, SiBCASA (Schaefer et al., 2008) by assimilating remotely sensed soil moisture into the SiBCASA. We use the blended active and passive microwave soil moisture data se...
This article presents a new parameterization of the global vegetation organizing carbon and hydro... more This article presents a new parameterization of the global vegetation organizing carbon and hydrology in dynamic ecosystems (ORCHIDEE) model, modifying the assimilation, allocation, and phenology processes for a steppe ecosystem. It aims 1) to improve the modeled growth primary production (GPP) based on both in situ CO 2 flux measurements and remote-sensing data of the fraction of absorbed photosynthetic radiation, and 2) to evaluate how GPP improvement results in better-modeled fluxes for ecosystem respiration, net ecosystem exchange, and latent heat. This new parameterization leads to a realistic annual GPP (comparable to the data within 10%), and a realistic seasonal variability of GPP (R 2 5 0.80). Further, we found that improving GPP into ORCHIDEE immediately brings ecosystem respiration and net ecosystem exchange fluxes into better agreement with the eddy-covariance data, both on seasonal but also on interannual time scales. This result suggests that the response of this steppe ecosystem to interannual climate variations can be well reproduced from the response to seasonal variation, and that biotic effects are not interannual. This indicates the potential ability to reproduce climate-induced changes in the carbon balance of steppes with the use of a generic process-oriented vegetation model such as ORCHIDEE.
1] At a semiarid steppe site located in the SE of Spain, relatively large CO 2 emissions were mea... more 1] At a semiarid steppe site located in the SE of Spain, relatively large CO 2 emissions were measured that could not be attributed to the ecosystem activity alone. Since the study site was located in a tectonically active area, it was hypothesized that a part of the measured CO 2 was of geologic origin. This investigation included a survey of soil CO 2 efflux, together with carbon isotope analyses of the CO 2 in the soil atmosphere, soil CO 2 efflux (i.e., Keeling plots), groundwater and local thermal springs. These measurements confirmed the hypothesis of degassing from geologic sources. In areas with local faults and ancient volcanic structures, soil CO 2 efflux rates were significantly higher (i.e., up to 6.3 and 1.4 mmol CO 2 m À2 s À1 ) than measurements in a comparable site that was some distance from fault sites (means of 1.0 and 0.43 mmol CO 2 m À2 s À1 in March and June, respectively). The CO 2 concentration in the soil atmosphere at the eddy covariance site reached 0.14% v/v at 0.70 m soil depth with a 13 C-enriched isotopic composition (d 13 C from À10.2‰ to À16.6‰), consistent with the isotopic composition of the soil CO 2 efflux estimated by Keeling plots (i.e., À16.6‰). 13 C-enriched CO 2 also occurred in local aquifers, and there was evidence of degassing from deep crust and mantle at regional scale by the helium isotopic ratio in spring waters located about 30 km (R/Ra: 0.12) and 200 km (R/Ra: 0.95) NW of the eddy covariance site. This study highlights the importance of considering CO 2 sources of geologic origin when assessing the net ecosystem carbon balance of sites that may possibly be affected by circulation of such CO 2 -rich fluids.
Despite the advance in our understanding of the carbon exchange between terrestrial ecosystems an... more Despite the advance in our understanding of the carbon exchange between terrestrial ecosystems and the atmosphere, semiarid ecosystems have been poorly investigated and little is known about their role in the global carbon balance. We used eddy covariance measurements to determine the exchange of CO 2 between a semiarid steppe and the atmosphere over 3 years. The vegetation is a perennial grassland of Stipa tenacissima L. located in the SE of Spain. We examined diurnal, seasonal and interannual variations in the net ecosystem carbon balance (NECB) in relation to biophysical variables. Cumulative NECB was a net source of 65.7, 143.6 and 92.1 g C m À2 yr À1 for the 3 years studied, respectively. We separated the year into two distinctive periods: dry period and growing season. The ecosystem was a net source of CO 2 to the atmosphere, particularly during the dry period when large CO 2 positive fluxes of up to 15 lmol m À2 s À1 were observed in concomitance with large wind speeds. Over the growing season, the ecosystem was a slight sink or neutral with maximum rates of À2.3 lmol m À2 s À1 . Rainfall events caused large fluxes of CO 2 to the atmosphere and determined the length of the growing season. In this season, photosynthetic photon flux density controlled day-time NECB just below 1000 lmol m À2 s À1 . The analyses of the diurnal and seasonal data and preliminary geological and gas-geochemical evaluations, including C isotopic analyses, suggest that the CO 2 released was not only biogenic but most likely included a component of geothermal origin, presumably related to deep fluids occurring in the area. These results highlight the importance of considering geological carbon sources, as well as the need to carefully interpret the results of eddy covariance partitioning techniques when applied in geologically active areas potentially affected by CO 2 -rich geofluid circulation.
Direct measurements of CO 2 and water vapour of regenerating forests after fire events (secondary... more Direct measurements of CO 2 and water vapour of regenerating forests after fire events (secondary succession stages) are needed to determine the role of such disturbances in the biome carbon and water cycles functioning. An estimation of the extension of burnt areas is also required in order to quantify NBP (net biome productivity), a variable that includes large-scale carbon losses (such as fire) bypassing heterotrophic respiration.
Steppe ecosystems represent an interesting case in which the assessment of carbon balance may be ... more Steppe ecosystems represent an interesting case in which the assessment of carbon balance may be performed through a cross validation of the eddy covariance measurements against ecological inventory estimates of carbon exchanges .
Recent studies have highlighted the need to consider geological carbon sources when estimating th... more Recent studies have highlighted the need to consider geological carbon sources when estimating the net ecosystem carbon balance (NECB) of terrestrial ecosystems located in areas potentially affected by geofluid circulation. We propose a new methodology using physical parameters of the atmospheric boundary layer to quantify the CO 2 coming from deep ground origin in a steppe ecosystem located in the SE of Spain. Then, we compared published NECB estimates at the site with seasonal patterns of soil CO 2 efflux and biological activity measured by satellite images over a 2-year period (2007/2008). The alpha grass ecosystem was a net carbon source (93.8 and 145.1 g C m -2 year -1 , in 2007 and 2008, respectively), particularly as a result of large amounts of carbon released over the dry period that were not related to biological activity. While the highest ecosystem CO 2 emission rates were measured over the dry period (reaching up to 15 lmol m -2 s -1 ), soil CO 2 efflux rates (ca. 0.5 lmol m -2 s -1 ) and plant productivity were minimal during this period. After using a linear relationship between NECB and wind speed for different stability conditions and wind sectors, we estimated the geological flux F GEO (217.9 and 244.0 g C m -2 in 2007 and 2008, respectively) and subtracted it from the NECB to obtain the biological flux F BIO (-124.0 and -98.9 g C m -2 in 2007 and 2008, respectively). We then partitioned F BIO into gross primary productivity and ecosystem respiration and proved that, after removing F GEO , ecosystem respiration and soil CO 2 efflux followed E. Pegoraro: Deceased.
Recent updated estimates of the carbon balance of European forests based on a suite of ecological... more Recent updated estimates of the carbon balance of European forests based on a suite of ecological inventories and models confirmed their active role as sink (Ciais at al. 2008, Luyssaert et al. 2010), determined primarily by the management applied in the last decades with wood removals being lower than Net Primary Productivity (NPP). Eddy covariance (EC) continuous measurements of CO2
The progress in the understanding of the carbon exchange between forests and the atmosphere has b... more The progress in the understanding of the carbon exchange between forests and the atmosphere has been dramatic over the last few years, yet largely based on observations of middle-aged or mature stands in the temperate and boreal region while quite a few studies report on the temporal dynamics of carbon balance in forest stand chronosequences taking into account the effect
Eurasian steppes cover a vast area of about 8·10 6 km 2 , of which a fraction between 60% and 70%... more Eurasian steppes cover a vast area of about 8·10 6 km 2 , of which a fraction between 60% and 70% was converted to agricultural use in the past, and have been poorly investigated in respect with the exchanges of CO 2 with the atmosphere while they could play a relevant role in the carbon uptake located over the northern hemisphere lands at temperate latitudes. In particular, old agricultural fields abandoned after 1990 in former Soviet Union could contribute actively to the sequestration of atmospheric carbon, since after land use change they tend to restore the original stock of carbon of steppe ecosystems, that went partly lost with the agricultural use of the land. This study provides a quantitative characterization of the carbon pools, of the patterns of carbon allocation within the ecosystems, of the CO 2 exchanges between the biosphere and the atmosphere, as well as of the response of CO 2 fluxes to environmental drivers of true bunchgrass steppes and neighbouring old agricultural fields hosting different temporal stages of recovering grassland located in the Republic of Hakasia and in the Republic of Tuva (Russian Federation). Within about 40 years, cultivations caused a loss of organic carbon not lower than 46%-52% in respect with the level of steppes (average carbon sotck: 140.9 tCha -1 in Hakasia and 45.5 tCha -1 in Tuva) and affected both the soil organic carbon pool, 80-92% of the lost carbon, and the belowground biomass pool for the remaining part. The biomass carbon stock of steppes of Hakasia and Tuva was found to be stored mainly in the belowground pool, with a proportion ranging 88-94%, due to the highly developed root system of perennial species. In old agricultural fields, belowground biomass was still predominant but the share of biomass found in the aboveground pool, from 12% to 42%, was larger than in steppes. The assessment of net primary productivity (NPP) at sites of Hakasia by different biometric methods ranged between 6.0 ad 13.1 t d.m. ha -1 , and organicated carbon was allocated primarily to the root system, with a fraction varying between 70% and 90% for both steppe and old field ecosystems. CO 2 fluxes at ecosystem scale were monitored by eddy covariance technique over three stages of an old field succession in Hakasia represented by an early stage (5 years since land use change), an intermediate stage (10 years) and a mature stage (steppe). Yearly CO 2 exchange estimates disclosed all the sites to act as carbon sinks, with a strenght declining from the early stage (2.1 tC ha -1 ) to the steppe ecosystem (1.1 tC ha -1 ). Also the amounts of carbon assimilated by photosynthesis (GPP) and released to the atmosphere through ecosystem respiration (R eco ) decreased over the stages of the succession, yielding the observed trend in the net ecosystem productivity (NEP). The steppe ecosystem, even if characterized by lower carbon assimilation than old field ecosystems, displayed a less pronounced reduction of the photosynthetic process in response to extreme high air temperature and air dryness conditions, maintaining its efficiency in carbon uptake. The steppe ecosystem was also found resilient to disturbances since after a fire burst before the onset of the growing season, it showed an enhanced carbon sequestration that could completely offset the amount of carbon lost from the burnt biomass. The carbon budget of the true steppe, estimated additionally using the ecological inventory methodology based on the difference between net primary productivity and heterotrophic respiration (NEP=NPP-Rh), agreed with the result obtained with the micrometeorological technique. The spatialization of the carbon balance observed at sites in the steppe region of the Republic of Hakasia, to assess the magnitude of the sink of steppes and old fields ecosystems in the Russian Federation, suggests a carbon sequestration of 0.17 PgC yr -1 .
The progress in the understanding of the carbon exchange between forests and the atmosphere has b... more The progress in the understanding of the carbon exchange between forests and the atmosphere has been dramatic over the last few years, yet largely based on observations of middle-aged or mature stands in the temperate and boreal region while quite a few studies report on the temporal dynamics of carbon balance in forest stand chronosequences taking into account the effect of forest management (Law et al., 2003; Kowalski et al., 2003; Kolari et al, 2004; Zha et al., 2009). In order to quantify the temporal variability of CO2 fluxes at ecosystem level following coppicing, we analyze eddy covariance data of a deciduous oak (Quercus cerris L.) coppice forest in central Italy (Roccarespampani, VT) collected over two differently aged forest stands in the period 2000-2006 and covering most of the rotation period (0-6; 11-15 years). Data processing was performed evenly for whole data-set according to the CarboEurope database standard (Papale et al., 2006). The inter-annual variability and s...
The performance of eight fast-response methane (CH 4 ) gas analysers suitable for eddy covariance... more The performance of eight fast-response methane (CH 4 ) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions. The moderate CH 4 fluxes observed at the location, of the order of 25 nmol m −2 s −1 , provided a suitable signal for testing the instruments' performance.
Springer Environmental Science and Engineering, 2012
This chapter considers the current state of Siberian terrestrial ecosystems, their spatial distri... more This chapter considers the current state of Siberian terrestrial ecosystems, their spatial distribution, and major biometric characteristics. Ongoing climate change and the dramatic increase of accompanying anthropogenic pressure provide different but mostly negative impacts on Siberian ecosystems. Future climates of the region may lead to substantial drying on large territories, acceleration of disturbance regimes, deterioration of ecosystems, and positive feedback to global warming. The region requires urgent development and implementation of strategies of adaptation to, and mitigation of, negative consequences of climate change.
The carbon dioxide (CO 2 ) exchange of five different peatland systems across Europe with a wide ... more The carbon dioxide (CO 2 ) exchange of five different peatland systems across Europe with a wide gradient in land use intensity, water table depth, soil fertility and climate was simulated with the process oriented CoupModel. The aim of the study was to find out whether CO 2 fluxes, measured at different sites, can be explained by common processes and parameters or to what extend a site specific configuration is needed. The model was calibrated to fit measured CO 2 fluxes, soil temperature, snow depth and leaf area index (LAI) and resulting differences in model parameters were analyzed. Finding site independent model parameters would mean that differences in the measured fluxes could be explained solely by model input data: water table, meteorological data, management and soil inventory data.
Springer Environmental Science and Engineering, 2012
This chapter provides observational evidence of climatic variations in Siberia for three time sca... more This chapter provides observational evidence of climatic variations in Siberia for three time scales: during the past 10,000 years, during the past millennium prior to instrumental observations, and for the past 130 years during the period of large-scale meteorological observations. The observational evidence is appended with the global climate model projections for the twenty-fi rst century based on the most probable scenarios of the future dynamics of the major anthropogenic and natural factors responsible for contemporary climatic changes. Historically, climate of Siberia varied broadly. It was both warmer and colder than the present. However, during the past century, it became much warmer; the cold season precipitation north of 55°N increased, but no rainfall increase over most of Siberia has occurred. This led to drier summer conditions and to increased possibility of droughts and fi re weather. Projections of the future climate indicate the further temperature increases, more in the cold season and less in the warm season, signi fi cant changes in the
Simulating biogenic carbon fluxes in Siberia is difficult, because the growing season is short an... more Simulating biogenic carbon fluxes in Siberia is difficult, because the growing season is short and the transitions between the seasons are fast. At the start of the growing season, when the snow has melted, the soil is still frozen. The melt water therefore either runs off quickly in non-flat terrain, or waterlogs the soil in flat terrain. Consequently, the soil moisture content during soil thawing tends to the extremes, either very wet or towards dry. This 'bi-modal' behaviour of soil moisture at the start of the growing season is difficult to capture by vegetation models. Consequently, the carbon fluxes and transpiration rates are either too much limited by anticipated water stress, or too little limited during waterlogging. We present here a method to improve the simulated soil moisture in a vegetation model, SiBCASA (Schaefer et al., 2008) by assimilating remotely sensed soil moisture into the SiBCASA. We use the blended active and passive microwave soil moisture data se...
This article presents a new parameterization of the global vegetation organizing carbon and hydro... more This article presents a new parameterization of the global vegetation organizing carbon and hydrology in dynamic ecosystems (ORCHIDEE) model, modifying the assimilation, allocation, and phenology processes for a steppe ecosystem. It aims 1) to improve the modeled growth primary production (GPP) based on both in situ CO 2 flux measurements and remote-sensing data of the fraction of absorbed photosynthetic radiation, and 2) to evaluate how GPP improvement results in better-modeled fluxes for ecosystem respiration, net ecosystem exchange, and latent heat. This new parameterization leads to a realistic annual GPP (comparable to the data within 10%), and a realistic seasonal variability of GPP (R 2 5 0.80). Further, we found that improving GPP into ORCHIDEE immediately brings ecosystem respiration and net ecosystem exchange fluxes into better agreement with the eddy-covariance data, both on seasonal but also on interannual time scales. This result suggests that the response of this steppe ecosystem to interannual climate variations can be well reproduced from the response to seasonal variation, and that biotic effects are not interannual. This indicates the potential ability to reproduce climate-induced changes in the carbon balance of steppes with the use of a generic process-oriented vegetation model such as ORCHIDEE.
1] At a semiarid steppe site located in the SE of Spain, relatively large CO 2 emissions were mea... more 1] At a semiarid steppe site located in the SE of Spain, relatively large CO 2 emissions were measured that could not be attributed to the ecosystem activity alone. Since the study site was located in a tectonically active area, it was hypothesized that a part of the measured CO 2 was of geologic origin. This investigation included a survey of soil CO 2 efflux, together with carbon isotope analyses of the CO 2 in the soil atmosphere, soil CO 2 efflux (i.e., Keeling plots), groundwater and local thermal springs. These measurements confirmed the hypothesis of degassing from geologic sources. In areas with local faults and ancient volcanic structures, soil CO 2 efflux rates were significantly higher (i.e., up to 6.3 and 1.4 mmol CO 2 m À2 s À1 ) than measurements in a comparable site that was some distance from fault sites (means of 1.0 and 0.43 mmol CO 2 m À2 s À1 in March and June, respectively). The CO 2 concentration in the soil atmosphere at the eddy covariance site reached 0.14% v/v at 0.70 m soil depth with a 13 C-enriched isotopic composition (d 13 C from À10.2‰ to À16.6‰), consistent with the isotopic composition of the soil CO 2 efflux estimated by Keeling plots (i.e., À16.6‰). 13 C-enriched CO 2 also occurred in local aquifers, and there was evidence of degassing from deep crust and mantle at regional scale by the helium isotopic ratio in spring waters located about 30 km (R/Ra: 0.12) and 200 km (R/Ra: 0.95) NW of the eddy covariance site. This study highlights the importance of considering CO 2 sources of geologic origin when assessing the net ecosystem carbon balance of sites that may possibly be affected by circulation of such CO 2 -rich fluids.
Despite the advance in our understanding of the carbon exchange between terrestrial ecosystems an... more Despite the advance in our understanding of the carbon exchange between terrestrial ecosystems and the atmosphere, semiarid ecosystems have been poorly investigated and little is known about their role in the global carbon balance. We used eddy covariance measurements to determine the exchange of CO 2 between a semiarid steppe and the atmosphere over 3 years. The vegetation is a perennial grassland of Stipa tenacissima L. located in the SE of Spain. We examined diurnal, seasonal and interannual variations in the net ecosystem carbon balance (NECB) in relation to biophysical variables. Cumulative NECB was a net source of 65.7, 143.6 and 92.1 g C m À2 yr À1 for the 3 years studied, respectively. We separated the year into two distinctive periods: dry period and growing season. The ecosystem was a net source of CO 2 to the atmosphere, particularly during the dry period when large CO 2 positive fluxes of up to 15 lmol m À2 s À1 were observed in concomitance with large wind speeds. Over the growing season, the ecosystem was a slight sink or neutral with maximum rates of À2.3 lmol m À2 s À1 . Rainfall events caused large fluxes of CO 2 to the atmosphere and determined the length of the growing season. In this season, photosynthetic photon flux density controlled day-time NECB just below 1000 lmol m À2 s À1 . The analyses of the diurnal and seasonal data and preliminary geological and gas-geochemical evaluations, including C isotopic analyses, suggest that the CO 2 released was not only biogenic but most likely included a component of geothermal origin, presumably related to deep fluids occurring in the area. These results highlight the importance of considering geological carbon sources, as well as the need to carefully interpret the results of eddy covariance partitioning techniques when applied in geologically active areas potentially affected by CO 2 -rich geofluid circulation.
Direct measurements of CO 2 and water vapour of regenerating forests after fire events (secondary... more Direct measurements of CO 2 and water vapour of regenerating forests after fire events (secondary succession stages) are needed to determine the role of such disturbances in the biome carbon and water cycles functioning. An estimation of the extension of burnt areas is also required in order to quantify NBP (net biome productivity), a variable that includes large-scale carbon losses (such as fire) bypassing heterotrophic respiration.
Steppe ecosystems represent an interesting case in which the assessment of carbon balance may be ... more Steppe ecosystems represent an interesting case in which the assessment of carbon balance may be performed through a cross validation of the eddy covariance measurements against ecological inventory estimates of carbon exchanges .
Recent studies have highlighted the need to consider geological carbon sources when estimating th... more Recent studies have highlighted the need to consider geological carbon sources when estimating the net ecosystem carbon balance (NECB) of terrestrial ecosystems located in areas potentially affected by geofluid circulation. We propose a new methodology using physical parameters of the atmospheric boundary layer to quantify the CO 2 coming from deep ground origin in a steppe ecosystem located in the SE of Spain. Then, we compared published NECB estimates at the site with seasonal patterns of soil CO 2 efflux and biological activity measured by satellite images over a 2-year period (2007/2008). The alpha grass ecosystem was a net carbon source (93.8 and 145.1 g C m -2 year -1 , in 2007 and 2008, respectively), particularly as a result of large amounts of carbon released over the dry period that were not related to biological activity. While the highest ecosystem CO 2 emission rates were measured over the dry period (reaching up to 15 lmol m -2 s -1 ), soil CO 2 efflux rates (ca. 0.5 lmol m -2 s -1 ) and plant productivity were minimal during this period. After using a linear relationship between NECB and wind speed for different stability conditions and wind sectors, we estimated the geological flux F GEO (217.9 and 244.0 g C m -2 in 2007 and 2008, respectively) and subtracted it from the NECB to obtain the biological flux F BIO (-124.0 and -98.9 g C m -2 in 2007 and 2008, respectively). We then partitioned F BIO into gross primary productivity and ecosystem respiration and proved that, after removing F GEO , ecosystem respiration and soil CO 2 efflux followed E. Pegoraro: Deceased.
Recent updated estimates of the carbon balance of European forests based on a suite of ecological... more Recent updated estimates of the carbon balance of European forests based on a suite of ecological inventories and models confirmed their active role as sink (Ciais at al. 2008, Luyssaert et al. 2010), determined primarily by the management applied in the last decades with wood removals being lower than Net Primary Productivity (NPP). Eddy covariance (EC) continuous measurements of CO2
The progress in the understanding of the carbon exchange between forests and the atmosphere has b... more The progress in the understanding of the carbon exchange between forests and the atmosphere has been dramatic over the last few years, yet largely based on observations of middle-aged or mature stands in the temperate and boreal region while quite a few studies report on the temporal dynamics of carbon balance in forest stand chronosequences taking into account the effect
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Papers by Luca Belelli Marchesini