|
|
The Bowen Ratio/Energy Balance method and detailed temperature profile measurements to improve data quality control
Pozníková, Gabriela ; Fischer, Milan ; Orság, Matěj ; Trnka, Miroslav ; Žalud, Zdeněk
Water plays a key role in the functionality and sustainability of ecosystems. In light of predicted climate change, research should focus on the water cycle and its individual components. The main component of water balance driving water from ecosystems is evapotranspiration (ET). One standard method for measuring ET is the Bowen Ratio/Energy Balance (BREB) method. It is based on the assumption that water vapour and heat are transported by identical eddies with equal efficiency. When using the BREB method, we assume that the profiles of temperature and air humidity are ideally logarithmic or at least consistent. Since the BREB method is usually based on measurements of temperature and humidity at only two heights, it is difficult to verify whether this assumption has been fulfilled. Potential profile inconsistencies are more likely for temperature because the sensible heat flux changes its sign more often and negative latent heat flux is not physically possible during positive sensible heat flux. We therefore conducted a field experiment using a 4-mhigh measurement mast with 20 thermocouples for detailed measurement of air temperature profiles above different covers, e.g. grassland, spring barley, and poplar plantations. Our main objective was to investigate the basic assumptions of the BREB method, i.e. the temperature profile’s consistency under various weather conditions. To be more specific, we aimed to investigate whether inflexion points occurred within the temperature profile and if so when.
|
|
|
Long-term productivity of short rotation coppice under decreased soil water availability
Orság, Matěj ; Fischer, Milan ; Tripathi, Abishek ; Žalud, Zdeněk ; Trnka, Miroslav
Wood, in fact, is the unsung hero of the technological revolution that has brought us from a stone and bone culture to our present age (Perlin 1991). Given its high-energy content and versatile use, biomass in the form of wood has been used for energy purposes for millennia. The production and use of woody biomass resources has been expanding around the world. The main drivers of its use as a source of energy are diversification and mitigation of energy related greenhouse gas emissions through partial substitution for fossil fuels. An alternative to sourcing wood biomass from natural forests is short rotation woody coppice. Its productivity is largely dependent on the environment in terms of climatic conditions. Especially drought is the main constraint on woody biomass production and involves serious economic consequences. For that reason, our field experiment was designed to evaluate the impact of decreased soil water availability on productivity of a poplar based short rotation coppice plantation over multiple growing seasons during 2011–2014. Aboveground biomass productivity of treatments with and without throughfall exclusion was assessed within this study. Our results show a systematic decline in the productivity of the plots subjected to decreased soil water availability by 30% in 2011, 20% in 2012, 49% in 2013, and 51% in 2014 compared to control plot. Aboveground biomass productivity ranged from 8.8 to 9.9 t dry matter ha−1 year−1 for the control treatment and 4.5 to 8.0 t dry matter ha−1 year−1 for the treatment with throughfall exclusion.On average, the throughfall exclusion treatment exhibited 47% less productivity than control treatment had over the entire study period.
|
|
|
Leaf area index development and radiation use efficiency of a poplar short rotation coppice culture
Tripathi, Abishek ; Fischer, Milan ; Trnka, Miroslav ; Orság, Matěj ; Vanbeveren, S. ; Marek, Michal V.
Leaf area index (LAI) is the most appropriate parameter for analyzing canopy structure and crop productivity. LAI and radiation use efficiency (RUE) were estimated to evaluate the productivity of a short rotation coppice culture of a poplar clone. RUE was calculated as the ratio between total aboveground woody biomass and available photosynthetic active radiation (PAR) accumulated during one growing season. Prior to coppicing, LAI reached a maximum value of 7.3 (in 2009), whereas the maximum LAI after coppicing was 6.8 (in 2012). The maximum RUE reached prior to coppicing was 0.25 g mol−1 (in 2009), while after coppicing it was 0.20 g mol−1 (in 2012), which did not represent a significant difference (p > 0.05).
|
|
|
Poplar-based short rotation coppice under artificially induced drought stress
Orság, Matěj ; Fischer, Milan ; Trnka, Miroslav ; Žalud, Zdeněk
The main aim of this study was to evaluate the diff erences in chosen microclimatological and ecophysiological variables between two types of experimental plots with diff erent levels of available soil water within a poplar-based (Populus nigra × P. maximowiczii) short rotation coppice plantation (SRC) during summer 2012. Diversity of sap fl ow, stomatal conductance and biomass increment were monitored between two treatments during the growing season of 2012. Th ere are 3 pairs of experimental plots under research. Each pair comprises a control plot and a neighbouring plot, equipped with a roof system, draining 40 % of the incoming rain water away (the water reduced plot). Our results show that a 40 % reduction in through-fall resulted in a 26 % reduction in transpiration and a 27 % reduction in stomatal conductance over the four month study period, which led to a statistically signifi cant (p = 0.03) deceleration of above-ground biomass accumulation at the plots with water-reduced treatment.
|
|
|
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.
|
|
|
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.
|
guest ::
