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Three different, state-of-the-art biogeochemical models are adapted in order to quantify the carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) exchanges between arable lands and the atmosphere. Biome-BGC and MOD17 are validated using the long-term measurement results from Hegyhátsál tall tower site (Western Hungary). After a simple bias correction, it was found that Biome-BGC is capable to describe the net ecosystem exchange (NEE) of Hungarian arable lands. The model is used to estimate the net primary production (NPP) and the net biome production (NBP) in the vicinity of the tall tower for the period of 1997–2008. The validation of MOD17 shows that the model is suitable to describe the gross primary production (GPP) of arable lands, although the model has limitations in years with higher precipitation amount. Introducing a new method MOD17 is downscaled to 250 m resolution, which is close to the size of agricultural parcels in the region. The downscaling helps us to better understand the biogeochemical processes of individual parcels with different crop cultivars. The DNDC model is parameterized using country-specific fertilizer input and climate data to provide estimates of the N2O and CH4 emissions for different crop cultivars. Sensitivity analysis was performed to find the most important parameters needed for accurate emission estimation. The results show that N2O emission is highly variable for the different crop types, and it has significant contribution to the GHG balance of arable lands. Methane has bidirectional fluxes and arable lands were generally net sinks of CH4 in the study period (2002–2004). [ABSTRACT FROM AUTHOR]

Fluxes of carbon dioxide, methane, nitrous oxide, and carbon stocks were measured at selected Hungarian forests and at a Croatian stand 120 km far from the Hungarian border. Annual carbon balance for Hungarian forests was also determined. Carbon stock of dendromass in selected Hungarian beech, hornbeam-pedunculate oak, and Turkey oak forests was between 191 and 292 t C ha−1 in 2003–2005. The total carbon stock (dendromass and soil) of Hungarian forests is estimated to be 377 MtC (1991–2000), and the annual carbon uptake of dendromass is 6.9 MtC. According to the measurements and estimations, the gross primary production (GPP) in 2008–2009 at Jastrebarsko pendunculate oak forest was 1,428 and 1,633 g C m−2 year−1, while ecosystem respiration of CO2 was 1,044 and 1,049 gC m−2 year−1, yielding a net ecosystem exchange (NEE) of −384 and −584 g C m−2 year−1, respectively. Net primary production (NPP) of Hungarian forests (1991–2000) was 377 g C m−2 year−1 (246 g C m−2 year−1 excluding leaves) part of which is released back to the atmosphere by heterotrophic respiration and harvest. Comparison of CO2 sinks using forest inventory approach (and not considering carbon storage in durable wood products) of Hungary΄s forest (2.26 t CO2 ha−1 year−1) and pedunculate oak forests in Croatia (4.57 t CO2 ha−1 year−1) gives a good agreement considering differences between forests and management practice. However, flux measurements from Jastrebarsko indicate that forests are probably much stronger sink. The share of the other greenhouse gases (CH4 and N2O) to the greenhouse balance between atmosphere and forest ecosystem (expressed in CO2 equivalent) is negligible in lowland forests of Bodrogköz region (average uptake of CH4 of 0.03 t CO2-eq ha−1 year−1 and emission of N2O of 0.05 t CO2-eq ha−1 year−1). However, for the forests in Mátra mountain region, emissions of N2O are not negligible with 0.61 and 0.83 t CO2-eq ha−1 year−1 for spruce plantation and sessile oak-hornbeam forest, respectively. Due to the lack of long-term observations, these results have to be regarded as first approximations. [ABSTRACT FROM AUTHOR]