László Haszpra

Productivity, Respiration, and Light-Response Parameters of World Grassland and Agroecosystems Derived From Flux-Tower Measurements

Abstract Grasslands and agroecosystems occupy one-third of the terrestrial area, but their contribution to the global carbon cycle remains uncertain. We used a set of 316 site-years of CO2 exchange measurements to quantify gross primary productivity, respiration, and light-response parameters of grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. We analyzed data from 72 global flux-tower sites partitioned into gross photosynthesis and ecosystem respiration with the use of the light-response method (Gilmanov, T. G., D. A. Johnson, and N. Z. Saliendra. 2003. Growing season CO2 fluxes in a sagebrush-steppe ecosystem in Idaho: Bowen ratio/energy balance measurements and modeling. Basic and Applied Ecology 4:167–183) from the RANGEFLUX and WORLDGRASSAGRIFLUX data sets supplemented by 46 sites from the FLUXNET La Thuile data set partitioned with the use of the temperature-response method (Reichstein, M., E. Falge, D. Baldocchi, D. Papale, R. Valentini, M. Aubinet, P. Berbigier, C. Bernhofer, N. Buchmann, M. Falk, T. Gilmanov, A. Granier, T. Grünwald, K. Havránková, D. Janous, A. Knohl, T. Laurela, A. Lohila, D. Loustau, G. Matteucci, T. Meyers, F. Miglietta, J. M. Ourcival, D. Perrin, J. Pumpanen, S. Rambal, E. Rotenberg, M. Sanz, J. Tenhunen, G. Seufert, F. Vaccari, T. Vesala, and D. Yakir. 2005. On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm. Global Change Biology 11:1424–1439). Maximum values of the quantum yield (α  =  75 mmol · mol−1), photosynthetic capacity (Amax  =  3.4 mg CO2 · m−2 · s−1), gross photosynthesis (Pg,max  =  116 g CO2 · m−2 · d−1), and ecological light-use efficiency (εecol  =  59 mmol · mol−1) of managed grasslands and high-production croplands exceeded those of most forest ecosystems, indicating the potential of nonforest ecosystems for uptake of atmospheric CO2. Maximum values of gross primary production (8 600 g CO2 · m−2 · yr−1), total ecosystem respiration (7 900 g CO2 · m−2 · yr−1), and net CO2 exchange (2 400 g CO2 · m−2 · yr−1) were observed for intensively managed grasslands and high-yield crops, and are comparable to or higher than those for forest ecosystems, excluding some tropical forests. On average, 80% of the nonforest sites were apparent sinks for atmospheric CO2, with mean net uptake of 700 g CO2 · m−2 · yr−1 for intensive grasslands and 933 g CO2 · m−2 · d−1 for croplands. However, part of these apparent sinks is accumulated in crops and forage, which are carbon pools that are harvested, transported, and decomposed off site. Therefore, although agricultural fields may be predominantly sinks for atmospheric CO2, this does not imply that they are necessarily increasing their carbon stock.

Regional carbon dioxide fluxes from mixing ratio data

We examine the atmospheric budget of CO2 at temperate continental sites in the Northern Hemisphere. On a monthly time scale both surface exchange and atmospheric transport are important in determining the rate of change of CO2 mixing ratio at these sites. Vertical differences between the atmospheric boundary layer and free troposphere over the continent are generally greater than large-scale zonal gradients such as the difference between the free troposphere over the continent and the marine boundary layer. Therefore, as a first approximation we parametrize atmospheric transport as a vertical exchange term related to the vertical gradient of CO2 and the mean vertical velocity from the NCEP Reanalysis model. Horizontal advection is assumed to be negligible in our simple analysis. We then calculate the net surface exchange of CO2 from CO2 mixing ratio measurements at four tower sites. The results provide estimates of the surface exchange that are representative of a regional scale (i.e. ∼106 km2). Comparison with direct, local-scale (eddy covariance) measurements of net exchange with the ecosystems around the towers are reasonable after accounting for anthropogenic CO2 emissions within the larger area represented by the mixing ratio data. A network of tower sites and frequent aircraft vertical profiles, separated by several hundred kilometres, where CO2 is accurately measured would provide data to estimate horizontal and vertical advection and hence provide a means to derive net CO2 fluxes on a regional scale. At present CO2 mixing ratios are measured with sufficient accuracy relative to global reference gas standards at only a few continental sites. The results also confirm that flux measurements from carefully sited towers capture seasonal variations representative of large regions, and that the midday CO2 mixing ratios sampled in the atmospheric surface layer similarly capture regional and seasonal variability in the continental CO2 budget.

Measuring system for the long-term monitoring of biosphere/atmosphere exchange of carbon dioxide

We describe an ongoing program being carried out in Hungary to investigate the role of the temperate continental region in the global carbon cycle. Carbon dioxide mixing ratios are continuously monitored at 10, 48, 82, and 115 m above the ground on a television transmitter tower, and the atmosphere/surface exchange of CO2 is measured by eddy covariance at 82 m. The region surrounding the tower is typical of rural areas of central Europe, with agricultural fields, forest patches, and small villages. We first describe the layout and the operation of the measuring system designed for the continuous, unattended monitoring of the vertical distribution of CO2 mixing ratio in the lowest 115 m of the atmosphere based on a Li-Cor model 6251 infrared gas analyzer (IRGA). It provides vertical profile data with a temporal resolution of 8 min. Next, we discuss the measuring system for long-term, continuous monitoring of the biosphere/atmosphere exchange of CO2. The eddy correlation system is based on a Li-Cor model 6262 fast-response IRGA and a Gill ultrasonic anemometer running at 4 Hz sampling frequency. Results are to illustrate the performance of the systems. Among others, they show the occasional accumulation of CO2 in the boundary layer in the Carpathian Basin during winter and the diurnal variation of the vertical distribution of CO2 mixing ratio in summer. A simple method based on similarity theory to calculate vertical fluxes from vertical gradients is presented, which can be used to fill the data gaps that inevitably occur during long-term eddy correlation measurements. The present study confirms the feasibility of the long-term tall-tower CO2 flux and mixing ratio measurements.

On the representativeness of carbon dioxide measurements

On the basis of the measurements at two monitoring sites located close to each other (220 km) in plain regions in Hungary, the representativeness of low-elevation continental CO 2 measurements is estimated. It is shown that under such conditions only the measurements carried out in the early afternoon hours can be considered as regionally representative for the CO 2 content of the planetary boundary layer (PBL). Filtering the data in this way, it is calculated that the characteristic CO 2 mixing ratio in the PBL may be about 2.5 ppm higher over this part of Europe than at the Mauna Loa Observatory (National Oceanic and Atmospheric Administration), Hawaii.

A recent build‐up of atmospheric CO2 over Europe. Part 1: observed signals and possible explanations

We analysed interannual and decadal changes in the atmospheric CO2 concentration gradient (ΔCO2) between Europe and the Atlantic Ocean over the period 1995–2007. Fourteen measurement stations are used, with Mace-Head being used to define background conditions. The variability of ΔCO2 reflects fossil fuel emissions and natural sinks activity over Europe, as well as atmospheric transport variability. The mean ΔCO2 increased by 1–2 ppm at Eastern European stations (∼30% growth), between 1990–1995 and 2000–2005. This built up of CO2 over the continent is predominantly a winter signal. If the observed increase of ΔCO2 is explained by changes in ecosystem fluxes, a loss of about 0.46 Pg C per year would be required during 2000–2005. Even if severe droughts have impacted Western Europe in 2003 and 2005, a sustained CO2 loss of that magnitude is unlikely to be true.We sought alternative explanations for the observed CO2 build-up into transport changes and into regional redistribution of fossil fuel CO2 emissions. Boundary layer heights becoming shallower can only explain 32% of the variance of the signal. Regional changes of emissions may explain up to 27% of the build-up. More insights are given in the Aulagnier et al. companion paper.

Modelling photochemical air pollutant formation in Hungary using an adaptive grid technique

A regional air quality model has been developed that describes the transport and chemical transformation of photochemical oxidants across Central Europe using an adaptive gridding method to achieve high spatial resolution. High-resolution emission inventories for Budapest and Hungary were utilised. The air pollution episode in August 1998 was modelled using a fixed coarse grid (mesh size 70 km) a fixed fine grid (17.5 km) and an adaptive, variable sized (from 17.5 to 70 km) grid. The fine and the adaptive grid models provided similar results, but the latter required 50% longer computing time. High ozone concentrations appeared downwind of Budapest and the plume extended up to about 150 km from the city at 17.00 on the simulated day. The simulation results were compared with ozone concentrations measured at the K-puszta and Hortobagy monitoring stations.

Atmospheric greenhouse gases: The Hungarian perspective

List of authors 1. Introduction (Haszpra, L.) Part I - Atmospheric trends and fluctuations 2. History and sites of atmospheric greenhouse gas monitoring in Hungary (Haszpra, L., Barcza, Z., Szilagyi, I.) 3. Trends and temporal variations of major greenhouse gases at a rural site in Central Europe (Haszpra, L., Barcza, Z., Szilagyi, I., Dlugokencky, E., Tans, P.) 4. Regional climate change and fluctuations as reflected in the atmospheric carbon dioxide concentration (Haszpra, L., Barcza, Z.) Part II - Measurements and estimations of biosphere-atmosphere exchange of greenhouse gases 5. Methodologies (Farkas, Cs., Alberti, G., Balogh, J., Barcza, Z., Birkas, M., Czobel, Sz., Davis, K. J., Fuhrer, E., Gelybo, Gy., Grosz, B., Kljun, N., Koos, S., Machon, A., Marjanovic, H., Nagy Z., Peresotti, A., Pinter, K., Toth, E., Horvath, L.) 6. Grasslands (Nagy, Z., Barcza, Z., Horvath, L., Balogh, J., Hagyo, A., Kaposztas, N., Grosz, B., Machon, A., Pinter, K.) 7. Forests (Marjanovic, H., Alberti, G., Balogh, J., Czobel, Sz., Horvath, L., Jagodics, A., Nagy, Z., Ostrogovic, M. Z., Peressotti, A., Fuhrer, E.) 8. Arable lands (Toth, E., Barcza, Z., Birkas, M., Gelybo, Gy., Zsembeli, J., Bottlik, L., Davis, K. J., Haszpra, L., Kern, A., Kljun, N., Koos, S., Kovacs, Gy., Stingli, A., Farkas, Cs.) Part III - Modeling of biosphere-atmosphere exchange of greenhouse gases 9. Models and their adaptation (Somogyi, Z., Hidy, D., Gelybo, Gy., Barcza, Z., Churkina, G., Haszpra, L., Horvath, L., Machon, A., Grosz, B.) 10. Grasslands (Hidy, D., Machon, A., Haszpra, L., Nagy, Z., Pinter, K., Churkina, G., Grosz, B., Horvath L., Barcza, Z.) 11. Forests (Somogyi Z.) 12. Arable lands (Grosz, B., Gelybo, Gy., Churkina, G., Haszpra, L., Hidy, D., Horvath, L., Kern, A., Kljun, N., Machon, A., Pasztor, L., Barcza, Z.) 13. Model Based Biospheric Greenhouse Gas Balance of Hungary (Barcza, Z., Bondeau, A., Churkina, G., Ciais, Ph., Czobel, Sz., Gelybo, Gy., Grosz, B., Haszpra, L., Hidy, D., Horvath, L., Machon, A., Pasztor, L., Somogyi, Z., Van Oost, K.) Part IV - Greenhouse gas emissions and removals in Hungary based on IPCC methodology 14. Long term trends and country specific methodologies (Kis-Kovacs, G., Lovas, K., Nagy, E., Tarczay, K.) 15. Terrestrial biosphere (Somogyi, Z., Borka, Gy., Lovas, K., Zsembeli, J.) 16. Energy production, industrial processes and waste management Subject index

Effect of the soil wetness state on the stomatal ozone fluxes over Hungary

A coupled Eulerian photochemical reaction-transport model and a detailed ozone dry deposition model have been utilised for the estimation of stomatal ozone fluxes over Hungary. Ozone concentrations were modelled on an unstructured triangular grid using a method of lines approach to the solution of the reaction−diffusion−advection equations describing ozone formation, transport and deposition. The model domain covers Central-Europe including Hungary, which was located at the centre of the domain and covered by a high resolution nested grid. The dry deposition velocity of ozone was calculated based on the aerodynamic, quasi-laminar boundary layer and canopy resistance. The effect of soil water content on the stomatal ozone flux was analysed. The stomatal ozone flux calculations were performed for two cases, with and without taking into account the effect of the soil moisture stress on the ozone deposition. The meteorological data were generated by the ALADIN meso-scale limited area numerical weather prediction model. It was found that