► We present the development of the Biome-BGC model to improve its performance in herbaceous ecosystems. ► Phenology representation and soil hydrology were improved, and drought-related processes ...were implemented. ► Management modules were also included in the model. ► The performance of the model was evaluated using eddy covariance-based measurement data.
Apart from measurements, numerical models are the most convenient instruments to analyze the carbon and water balance of terrestrial ecosystems and their interactions with changing environmental conditions. The process-based Biome-BGC model is widely used to simulate the storage and flux of water, carbon, and nitrogen within the vegetation, litter, and soil of unmanaged terrestrial ecosystems. Considering herbaceous vegetation related simulations with Biome-BGC, soil moisture and growing season control on ecosystem functioning is inaccurate due to the simple soil hydrology and plant phenology representation within the model. Consequently, Biome-BGC has limited applicability in herbaceous ecosystems because (1) they are usually managed; (2) they are sensitive to soil processes, most of all hydrology; and (3) their carbon balance is closely connected with the growing season length. Our aim was to improve the applicability of Biome-BGC for managed herbaceous ecosystems by implementing several new modules, including management. A new index (heatsum growing season index) was defined to accurately estimate the first and the final days of the growing season. Instead of a simple bucket soil sub-model, a multilayer soil sub-model was implemented, which can handle the processes of runoff, diffusion and percolation. A new module was implemented to simulate the ecophysiological effect of drought stress on plant mortality. Mowing and grazing modules were integrated in order to quantify the functioning of managed ecosystems. After modifications, the Biome-BGC model was calibrated and validated using eddy covariance-based measurement data collected in Hungarian managed grassland ecosystems. Model calibration was performed based on the Bayes theorem. As a result of these developments and calibration, the performance of the model was substantially improved. Comparison with measurement-based estimate showed that the start and the end of the growing season are now predicted with an average accuracy of 5 and 4 days instead of 46 and 85 days as in the original model. Regarding the different sites and modeled fluxes (gross primary production, total ecosystem respiration, evapotranspiration), relative errors were between 18–60% using the original model and 10–18% using the developed model; squares of the correlation coefficients were between 0.02–0.49 using the original model and 0.50–0.81 using the developed model.
To evaluate the damaging effect of tropospheric ozone on vegetation, it is important to evaluate the stomatal uptake of ozone. Although the stomatal flux is a dominant pathway of ozone deposition ...onto vegetated surfaces, non-stomatal uptake mechanisms such as soil and cuticular deposition also play a vital role, especially when the leaf area index
L
A
I
<
4
. In this study, we partitioned the canopy conductance into stomatal and non-stomatal components. To calculate the stomatal conductance of water vapour for sparse vegetation, we firstly partitioned the latent heat flux into effects of transpiration and evaporation using the Shuttleworth–Wallace (SW) model. We then derived the stomatal conductance of ozone using the Penman–Monteith (PM) theory based on the similarity to water vapour conductance. The non-stomatal conductance was calculated by subtracting the stomatal conductance from the canopy conductance derived from directly-measured fluxes. Our results show that for short vegetation (
LAI
=
0.25) dry deposition of ozone was dominated by the non-stomatal flux, which exceeded the stomatal flux even during the daytime. At night the stomatal uptake of ozone was found to be negligibly small. In the case of vegetation with
L
A
I
≈
1
, the daytime stomatal and non-stomatal fluxes were of the same order of magnitude. These results emphasize that non-stomatal processes must be considered even in the case of well-developed vegetation where cuticular uptake is comparable in magnitude with stomatal uptake, and especially in the case of vegetated surfaces with
L
A
I
<
4
where soil uptake also has a role in ozone deposition.
Vessel wall enhancement (VWE) in contrast-enhanced magnetic resonance imaging (MRI) is a potential biomarker for intracranial aneurysm (IA) risk stratification. In this study, we investigated the ...relationship between VWE features, risk metrics, morphology and hemodynamics in 41 unruptured aneurysms. We reconstructed the IA geometries from MR angiography and mapped pituitary stalk-normalized MRI intensity on the aneurysm surface using an in-house tool. For each case, we calculated the maximum intensity (CR
) and IA risk (via size and the rupture resemblance score (RRS)). We performed correlation analysis to assess relationships between CR
and IA risk metrics (size and RRS), as well as each parameter encompassed in RRS, i.e. aneurysmal size ratio (SR), normalized wall shear stress (WSS) and oscillatory shear index. We found that CR
had a strong correlation (Pearson correlation coefficient, PCC = 0.630) with size and a moderate correlation (PCC = 0.472) with RRS, indicating an association between VWE and IA risk. Furthermore, CR
had a weak negative correlation with normalized WSS (PCC = -0.320) and a weak positive correlation with SR (PCC = 0.390). Local voxel-based analysis showed only a weak negative correlation between normalized WSS and contrast-enhanced MRI signal intensity (PCC = -0.240), suggesting that if low-normalized WSS induces enhancement-associated pathobiology, the effect is not localized.
Data on net ecosystem exchange (NEE) dynamics and carbon balance of a dry, extensively managed sandy grassland, as measured in Hungary in the years 2003 and 2004 are reported. The grassland was a ...weak source of carbon in 2003 (80
g
C
m
−2), owing to the exceptionally hot and dry conditions while it was a strong sink in 2004 (−188
g
C
m
−2), when the amount of precipitation was considerably exceeding the 10 years average. Gross primary production (GPP) values in 2003 and 2004 were 584 and 1112
g
C
m
−2, respectively, while ecosystem respiration (
R
eco) values were 663 and 924
g
C
m
−2 for these 2 years. GPP declined more than
R
eco due to drought and heat wave effects in 2003 than in 2004. The ratio between net sink and net source days were 0.55 and 1.11 for 2003 and 2004, respectively. The average of daily NEE sums during source periods did not differ between the 2 years (0.796 and 0.777
g
C
m
−2
day
−1), while for the sink periods the average of daily NEE sums were strongly different (−0.836 and −1.677
g
C
m
−2
day
−1, for 2003 and 2004). The main difference between the years was found in late winter source activity associated with low temperatures (2003), the degree of summer drought and the absence (2003) or presence (2004) of autumn regrowth. As sink activity potentially may occur in the period April–June, the amount of winter–early spring precipitation proved to be decisive to the carbon balance of the grassland and was much less in 2003 than in 2004. Significant source activity was found during droughts in each year contributing up to 50% to the total source activity. While in the favourable periods the assimilation and respiration components were correlated, significant ecosystem respiration not coupled to current photosynthesis was responsible for large part of the source activity of the grassland. Good correlations were found between satellite derived normalized difference vegetation index (NDVI) and broadband NDVI (NDVI
b) values in both years. The relation between GPP and the NDVI
b index was significantly different between the main growth periods (April–June) of the 2 years, while it was statistically not significant during the autumn regrowth period (2004).
There is a need for long-term data on N
2
O emission in Central Europe to provide a thorough understanding of the variability of the emission processes as affected by different biotic and abiotic ...drivers. It could be helpful for national greenhouse gas inventories and also for revealing potential ways of mitigation. In order to describe temporal variability of soil N
2
O emission under varying key conditions, a field experiment was carried out at a cropland site on loamy and clay loamy Chernozems in Central Hungary. Dynamics of N
2
O emissions were observed bi-weekly during a two-year-long study (November 2017–November 2019) using a static closed chamber–gas chromatographic method. Additional variables, including soil water content, soil temperature, leaf area index, vegetation index and net ecosystem exchange of CO
2
were also measured. Besides, a laboratory pot experiment was conducted focusing on the role of soil water content, N fertilizer, and plant presence on soil N
2
O emissions. Average field N
2
O emissions during the study period varied between 0.27 and 29.94 µg N m
–2
h
−1
with the largest emission peaks measured following the freeze-thaw cycle during wintertime. Additional N
2
O emission peaks were observed following applications of N fertilizer and at high soil water content. Significant positive correlations were found between field N
2
O emission and both soil water content and vegetation index. In contrast, a negative relationship was found between N
2
O emission and soil temperature. Similar pattern was observed in the pot experiment with a significant positive correlation between N
2
O emissions and soil water content when neither soil nitrate content nor temperature were limiting for microbial denitrification. In addition, a significant correlation between N
2
O emission and fertilizer rate was revealed at the soil water content higher than 30% both in bare and planted soil. However, variations in soil N
2
O emission among the treatments were not significantly correlated with plant presence, but a partial positive effect was observed when the soil water content was higher than 30% and samples were treated with 150 kg ha
–1
N. Based on the measured N
2
O emission from both field and lab experiments and its relationship with the different drivers, it can be concluded that soil N
2
O emission was strongly influenced by soil water content and N fertilizer rates and plant presence could moderately modify these responses.
An automated open system for measurement of soil CO2 efflux (Rsc) was developed and calibrated against known fluxes. The system was tested in the field, while estimating soil respiration ...simultaneously by the gradient method (Rsg) at a dry, sandy grassland site (Bugac, Hungary). Ecosystem respiration (Rego) was measured using the eddy covariance technique. The small chamber size (5 cm in diameter) made it possible to use the chambers in vegetation gaps, thereby avoiding the necessity of removing shoots and disturbing the spatial structure of vegetation and the upper soil layer. Low air flow rates associated with small chamber volume and chamber design allowed the overpressure range to stabilize between 0.05–0.12 Pa. The correlation between ecosystem and soil CO2 efflux rates as measured by the independent methods was significant, Reco rates were similar or even lower than Rsc in the low flux (up to 2 μmol CO2 m−2 s−1) range but the differences were within the uncertainty limits for the two fluxes. Rsc from trenched and non-trenched plots amounted to 16 % and 44 % of Reco, respectively. The gradient method showed both up and downward CO2 fluxes originating from the main rooting zone after rains. Diffusive retardation played a smaller role than CO2 production considering the soil air CO2 concentration increase after rains in a given layer. Downward fluxes within the soil profile amounted to 15 % of the simultaneous upward fluxes and to ~7.6 % of the total (upward) effluxes during the 3-month study. The upper 5 cm soil layer contributed to ~50 % of the total soil CO2 efflux. Downward fluxes are expected to seriously affect (1) the Reco vs. temperature response functions and (2) the net ecosystem exchange of CO2 (NEE) vs. photon flux density response functions, therefore potentially affecting the gap filling procedures and to lead to a situation (3) when the measured surface and the real time ecosystem fluxes will necessarily differ in the short term. Simultaneous measurements of Reco and soil CO2 effluxes may reveal the timing and magnitude of the decoupling, thereby contributing to decreasing uncertainty associated with eddy flux measurements over flat terrains. While the correlations between CO2 effluxes measured by independent systems are strong, Rsg was generally larger than Rsc or Reco, mainly due to overestimation of effective diffusivity in the soil.
The aim of this work is to estimate the net N balance (deposition - emission) between the atmosphere and a semi-arid, semi-natural grassland (Bugac station, Central Hungary, CarboEurope IP, ...NitroEurope IP level 3 site). Dry deposition of N compounds has been determined by the inferential method, based on continuous monitoring of NO₂ gas and daily 24-hour concentration measurements of HNO₃ vapour, NH₃ gas, and NH₄⁺ and NO₃⁻ particles, using dry deposition velocities from the literature, measured above surfaces with the same characteristics as Bugac station. The bi-directional flux of NH₃ within the atmosphere and the canopy (excluding soil emission) has also been estimated by the inferential method. Wet deposition of nitrate and ammonium ions was calculated on the basis of daily precipitation sampling and concentration measurements of nitrate and ammonium ions. To estimate the soil-atmosphere exchange of different gaseous N forms (N₂, NO, N₂O, NH₃), the DNDC model was used as validated by the chamber measurements of NO and N₂O soil emission fluxes. Soil emissions of NO and N₂O have been determined by dynamic and static soil chamber methods, respectively. The measurement and modelling activity covers a complete year. Using the measured and modelled data, the calculated N balance at Bugac station between August 2006 and July 2007 is estimated at -8.8 kg N ha⁻¹ year⁻¹ (deposition) as a sum of the deposition and emission terms (-10.4 and 1.6 kg N ha⁻¹ year⁻¹, respectively). Due to the warm and dry weather during the examined period, wet fluxes were substantially lower than usual, which may also have altered the regular yearly course of dry deposition and emission.
▶ The optimum soil wetness for N
2O production was between 40 and 50% for sandy soil. ▶ N
2O flux for sandy soil in dry and wet years were 0.80 and 0.74
kg
N
ha
−1
yr
−1. ▶ Grazing (sandy soil, 50–80 ...cows/km
2) enhanced emission by 4–18% in dry–wet years. ▶ Above loess soil 100
kg
N
ha
−1
yr
−1 fertilizer results in emission factor of 0.26%. ▶ Irrigation of loess soil enhanced the soil N
2O flux by 70% in dry year.
Nitrous oxide (N
2O) is emitted into the atmosphere in substantial quantities as an intermediate product of mainly denitrification processes and soil nitrification. N
2O emission from Hungarian sandy and loess type soils has been measured between August 2002 and December 2004. The effects of soil parameters and different farming activities (grazing exclusion, irrigation and mineral fertilization) on the rate of emission were investigated. Soil N
2O efflux was determined by measuring the accumulation of N
2O in 10 parallel small (
V
=
400
cm
3,
A
=
80
cm
2) static chambers. Samples were taken with evacuated tubes followed by gas chromatography–mass spectrometry analysis. Emission from sandy grassland under extensive farming proved to be negligible below soil temperature of 5
°C, the mean fluxes at
t
soil
>
10
°C and
t
soil
<
10
°C were differing significantly (15.4 and 1.7
μg
N
m
−2
h
−1, respectively). N
2O efflux was linked to temperatures up to
t
soil
=
20
°C, while at higher soil temperatures a decrease of efflux was observed. The optimum soil wetness (WFPS, water-filled pore space) for N
2O production was between 40 and 50% for this sandy soil. The annual sum of efflux for control plots in dry (2003) and wet (2004) years was almost the same (0.80 and 0.74
kg
N
ha
−1
yr
−1, respectively), probably due to the fact that in dry year soil wetness is lower than the optimum, and vice versa, in a wet year the high WFPS did not favoured N
2O production. Grazing (50–80 cows per km
2) enhanced emission by 4–18% in dry and wet years, respectively. Around 6% of total atmospheric deposition (13.8
kg
N
ha
−1
yr
−1) was transformed into N
2O and emitted into the atmosphere from the sandy soil. A two-year fertilization experiment above loess soil (August 2002–July 2004, with regular precipitation amount during the period) resulted in an emission factor of 0.26% as a consequence of applying 100
kg
N
ha
−1
yr
−1 ammonium nitrate mineral fertilizer in April, each year. Average fluxes were 1.13 and 0.90
kg
N
ha
−1
yr
−1 above fertilized and control plots, respectively. Monoliths from loess soil were used to study the effect of irrigation on N
2O fluxes. In contrast to sandy soil there were detectable soil fluxes below 5
°C. N
2O production increases with soil temperature until 15–20
°C above which lower emissions were detected. The optimum wetness for N
2O production in loess soil was around 30–40 WFPS but above 70–80% (up to saturation) other, yet unexplained maximum was observed. Irrigation enhanced the soil flux by 70% in the dry year (2003), when measured fluxes were 1.56 and 0.92
kg
N
ha
−1
yr
−1 on irrigated and control plots, respectively.
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