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Determination of errors in energy flux estimates using the bowen ratio energy balance method
Pozníková, G. ; Fischer, Milan ; Trnka, Miroslav ; Žalud, Zdeněk
The Bowen ratio energy balance method (BREB) is based on the measurement of air temperature and humidity gradients in at least two vertical levels above the surface of interest. So far, there have been a limited number of studies dealing with the footprint of the BREB. Staying conservative, many authors used the upper sensor of the BREB as a single point to determine the footprint of the BREB. In fact, the footprint of the fl uxes rather should be explained as a source area of the single point measurement carried out somewhere between the two BREB levels. It was suggested that this single point lies close to the geometrical mean of the two aero dynamical heights. However, there has still been no consensus regarding if this apparent height is fi xed or not, and if the second is true, whether it is a function of the Bowen ratio itself. Th e submitted study deals with the footprint of the BREB using several BREB experiments above various covers with diff erent fetches. Moreover, by simulating diff erent Bowen ratios between the area of interest and the contaminating area we attempt to investigate for which conditions (dry or wet) and type of transition (from drier to wetter or vice versa) the method is more sensitive to the limited fetch.
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Comparison of eddy covariance and bowen ratio energy balance method. Energy balance cloruse versus bowen ratio similarity assumption
Fischer, Milan ; Trnka, Miroslav ; Pozníková, Gabriela ; Sedlák, Pavel ; Orság, Matěj ; Kučera, J. ; Žalud, Z.
The Bowen ratio and the Monin-Obukhov similarity principles are based on the assumption that the eddy diff usivities for temperature and humidity are equal to each other under all atmospheric stratifi cations within turbulent surface boundary layer. However, several authors reported that this equality was violated under advective inversion or during the non-stationary conditions due to clouds passing by and sudden change of wind speed and direction. Th e inequality of the eddy diff usivity can lead to errors in the energy partitioning estimates by gradient techniques like the Bowen ratio energy balance (BREB) and the aerodynamical method, or methods based on residual energy balance such as the Penman-Monteith or Priestley-Taylor models. Th is study investigates two seasons of simultaneous measurement by eddy covariance (EC) and BREB above a high density poplar plantation at the Domanínek locality. Th e direct measurement of eddy diff usivities by EC is reinvestigating the validity of the long term measurement (since 2008) by BREB. Results showed unequal exchange coeffi cients with their mean 0.31 to 0.35 m2 s-1 for 2011 and 2012, respectively, favouring the transport of latent heat. Th is might be explained by the diff erent footprints of the BREB and EC methods, an undeveloped internal boundary layer or instrumental errors.
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Estimation of above ground woody biomass of SRC hybrid poplar clone J-105 in different fertilizer treatments in Czech-Moravian highland
Tripathi, A.M. ; Trnka, Miroslav ; Fischer, Milan ; Orság, Matěj ; Fajman, M. ; Marek, Michal V. ; Žalud, Zdeněk
Short rotation coppice poplar hybrid clone J-105 (Populus nigra x P. maximowiczii) is studied as an alternative source of bio-energy in the region of Czech-Moravian Highland. The plantation was established in 2001 at the locality Domanínek in the vicinity of Bystřice nad Pernštejnem (Czech Republic, 49o32’N, 16o15’E and altitude 530 m a. s. l.) where mean annual rainfall of 609 mm and mean annual temperature of 7.2oC was recorded between 1981 and 2010. The total area planted with the clone was close to 1.5 ha with total plantation area being close to 3.5 ha. The plantation with planned density of 9,216 trees ha-1was established on the former agricultural land and the length of the rotation cycle was set to 6-8 years. At the beginning of the second rotation period i.e. in spring 2009 (following winter harvest), the plantation was divided into four randomized blocks with different nutrient treatments and three replicates (4×3). These treatments comprised of application of mineral NPK fertilizer (nitrogen 305 kg ha-1, phosphorous 154 kg ha-1 and potassium 291 kg ha-1), sewage sludge (4200 kg/ha-1) and ash (1000kg ha-1) and lime (5 ton ha-1), while control was with natural nutrients content only (deposition and leaves mineralization). The objectives of the study were to estimate the above ground annual yields (based on allometry and stem inventory), the mortality and the shoot to stump ratio as the main productivity characteristics.
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Applicability of Bowen ratio energy balance method in fetch limited conditions
Pozníková, G. ; Trnka, Miroslav ; Fischer, Milan ; Orság, Matěj ; Žalud, Zdeněk
Water plays a key role in the climatic processes of the Earth. In terrestrial ecosystems the main component of water loss is evapotranspiration. One of the standard techniques used to measure evapotranspiration indirectly is the Bowen ratio energy balance method (BREB). This study focuses on the quantification of errors caused by insufficient fetch (upwind distance from the edge of investigated cover) using data from two BREB systems obtained through intensive summer 2012 campaign. The measurement took advantage of one mobile and one fixedly positioned BREB systems employed at turf grass cover from the prevailing north-west wind direction surrounded by broadleaved trees, poplar stoolbed dirty road and buildings at experimental station in Domanínek near Bystřice nad Pernštejnem. Surprisingly, the results showed no significant systematic deviation between the reference BREB with sufficient 180 m long fetch and mobile BREB positioned at fetches between 10 to 100 m. Moreover, it was not found any impact of the fetch on non-systematic errors leading to the conclusion that the fetch did not have any effect on the overall data quality and consistency. One of the explanations may be very similar response to soil moisture conditions of the selected contrasting living ecosystems and thus their similar Bowen ratios.
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The dynamics of temperature in birdboxes
Slavíková, Z. ; Žalud, Z. ; Bartošová, Lenka ; Fischer, Milan ; Trnka, Miroslav
The aim of the study was to detect the changing temperature in bird boxes of two bird species-collared flycatcher (Ficedula albicollis, T.) and great tit (Parus major, L.). The work is the result of the monitoring of nesting bird species for two years (2009 and 2010) by temperature sensors. Data was continuously recorded for several different breeding pairs with the micro-datalogers MINIKIN. Temperature sensors were fixed directly into the nest with eggs and also in the upper part of bird boxes or outside the boxes. Temperature data was then processed and analyzed. Experimental work was carried out in a floodplain forest in nature reserve Plačkův les a říčka Šatava near Vranovice, altitude: 170; latitude: 48°56´54´´; longitude: 16°35´50´´. The forest is dominated by full-grown, multi-aged canopy with no forestry management. Experimental site belongs to the same natural biogeocenoses group (i.e. Ulmi-fraxineta carpini) and to the same geobotanical group (i.e. suballiance Ulmenion of the Alnion incanae alliance). Our initial hypothesis assumed that the temperature of eggs in the nest and also the time spent in the bird boxes by both bird species (collared flycatcher and great tit) do not differ significantly. The results showed that during the period when the eggs were layed (by both bird species) the temperature were significantly however the temperature of eggs of collared flycatcher and great tit during the period of incubation were very.
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Calibration of the selected crop growth models for spring barely
Pohanková, E. ; Trnka, Miroslav ; Hlavinka, Petr ; Takáč, J. ; Kersebaum, Ch. ; Orság, Matěj ; Fischer, Milan ; Pokorný, E. ; Žalud, Zdeněk
The climate change is one of the most discussed global problems. One option how to estimate the effects of expected future climate conditions on plant production is the use of the crop growth models. Our aim was the calibration of two models (Daisy and Hermes) based on observed and measured data that were collected for spring barley (represented by cultivars Tolar and Blaník) at experimental site Bystřice nad Pernštejnem during 2011 and 2012. The onset of flowering was underestimated by an average of 1.1 and 1.6 days and maturity by 5.8 and 9.0 days using Daisy and Hermes respectively. On average Daisy systematically underestimated yields by 0.3 t/ha-1 and Hermes overestimated yields by 1.24 t/ha-1. We expect further improvement of these models estimates using the available result from the following years
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Stomatal conductance of short rotation coppice based on sap flow measurements and its response to chosen meteorological variables
Orság, Matěj ; Trnka, Miroslav ; Fischer, Milan ; Kučera, J. ; Žalud, Zdeněk
The main aim of this study was to derive stomatal conductance (gs) from sap flow measurements and explore some of possible applications of this method. Sap-flow and other meteorological variables were continuously monitored in poplar-based short rotation coppice (SRC) plantation in Bystřice nad Pernštejnem during growing season 2012. Sap flow of 8 trees was measured using heat dissipation method, then expressed as transpiration per square meter of projection area and by adding into rewritten Penman-Monteith equation the canopy conductance (gs) was obtained. Compared with direct measurements on leaf level this approach is advantageous for obtaining gs, because of integrating all leaf categories of tree or whole canopy. Further analysis also proved, that gs is strongly driven by VPD. Finally, it was found that the relationship between gs and VPD is also influenced by available soil moisture content.
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Transpiration and biomass increment in short rotation poplar coppice
Orság, Matěj ; Fischer, Milan ; Trnka, Miroslav ; Kučera, J. ; Žalud, Zdeněk
This paper deals with interaction between amount of water lost by tree transpiration and aboveground biomass increment in poplar based short rotation coppice in conditions of CzechMoravian highlands. Stem sap-flow measured on 8 poplar trees by Granier heat dissipation method was put in relation with biomass increments measured both with automated dendrometers so with manual measurements with caliper gauge. Transpiration totals ranged between 28.3–175.6 liters per tree in executed period 3.8.–31.8.2011. Above-ground biomass increments in this period varied between 30.07–519.28 g per tree and mean value of water use efficiency of all monitored trees reached 2.76 g.kg–1. Mean diurnal sap-flow total of all sampled trees was 3.25 liters. Results show that it is possible to establish relationship between transpiration totals and biomass increments (coefficient of determination R2 = 0.90) and also relationship between transpiration totals and stem diameter (R2 = 0.81). These results (especially after obtaining experimental data from spring growth conditions) can be further used for calculations of biomass increments and transpiration as scaling factors from tree level to whole stand level.
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Evapotranspiration of selected agricultural and forest species
Kučera, J. ; Urban, J. ; Trnka, Miroslav ; Fischer, Milan ; Krofta, K. ; Duffková, R.
The aim of this article is a comparison of evapotranspiration (ET) of different covers (turf grass, clover (Trifolium pratense), winter wheat (Triticum aestivum), hops (Humulus lupulus) and the high density poplar stand (J-105, Populus nigra x Populus Maximowiczii)) with the potential evapotranspiration (PET) and the general description the ET rates dynamic during the season. The second goal is to quantify the ratio of the transpiration and the whole evapotranspiration for the two contrasting cultures – the hops and poplars stand. The daily maximal sum of the grass ET reached, similarly like for the other species, up to 5–6 mm per day, which comprises 85–93 % of PET. Significantly higher ET was showed by the culture of clover. On the other hand, the lowest values were performed by the poplar stand in the first year after coppicing. The transpiration to evapotranspiration ratio resulted in 40–70 % by the hops and 80–90 % in case of the poplars.
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Water balance in short rotation poplar coppice and reference grass-plot in conditions of Czech-Moravian Highlands
Orság, Matěj ; Fischer, Milan ; Trnka, Miroslav ; Hlavinka, Petr ; Kučera, J. ; Balek, J. ; Žalud, Zdeněk
This text presents results of a study focusing on differences of water balance between two contrasting cultures - short rotation poplar coppice and grass plot in conditions of Czech-Moravian Highlands. Actual evapotranspiration (by Bowen ratio energy balance method), precipitation and soil moisture in two layers (0 – 0.45 m and 0.45 – 0.90 m) were measured on both plots during seasons 2008 – 2010. The seasonal water lost through evapotranspiration was higher for the grass (560.4 and 508 mm for grass and 523.8 and 351.8 mm for poplar during growing season 2009 and 2010 respectively), but generally the observed amounts of ETa are comparable for both cultures and within the range of values described in literature. Results of soil moisture measurements expressed as soil water availability [mm] were compared with simulations obtained from water balance model SoilClim. The model a little bit underestimated the amount of available water in the system, since based on water balance closure we suggest that there is a higher water income than was recorded from precipitation. This extra water found in observed systems may be supplied probably by lateral underground water inflow from the upper fields.
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