Determination of greenhouse gas fluxes using a micrometerorological method over agricultural ecosystem

Internal combustion machines started to taking the place of man power with happenning industrial revolution in 18th century. Greenhouse gases especially anthropogenic CO2 emissions that effects more harmfull on earth from these machines. Increasing of greenhouses gases concentrations blocks outgoing radiation from surface. At the same time, climate change is continuous and inevitable truth that originate from speed of rotation of the earth and cycle. Increasing of global mean temperature reveals that evaluating of greenhouse gases concentrations and reduced emisssion is needed to determine. For this reason, measurements of CO2 concentration have continued at Hawaii Island from 1950s. Therefore, determination of the carbon dioxide released to and captured from the atmosphere within the components of global carbon cycle have been searching by scientists. Researches especially over water and forest surfaces allow us to evaluate of changes CO2 and H2O fluxes. Determining of CO2, H2O and energy balance components over agricultural areas is crucial because they capture carbon dioxide from the atmosphere and release it to the atmosphere again. Evaluation of CO2 and H2O fluxes over agricultural areas becames more of global carbon budget and climate change researches. For this reason, flux networks are established to measure carbon dioxide, water vapor and energy fluxes between different terrestrial ecosystems (forests, croplands, grasslands etc.) and the atmosphere. Most of the micrometeorological systems are installed first in forests then in croplands. Most of the micrometeorological systems are installed first in forests then in croplands. The amount of micrometeorological tower sites is increasing in order to measure mass and energy fluxes above canopies. The amount of micrometeorological tower sites is increasing in order to measure mass and energy fluxes above canopies. Researches over different plants reveals that continuous measurements of whole growing vegetation period is necessary. There are many studies about greenhouse gases over different vegetations from 1990s but there are very limited studies about these issues in Turkey. It is aimed to measuring, analyzing and evaluating CO2 and H2O fluxes over winter wheat, which is an important nutritional source for Turkey. In this context, relationship between net ecosystem exchange of winter wheat farming in wide areas, straw, bare soil and meteorological factors and vegetation dynamics is determined. Changes in carbon dioxide fluxes during the two growing periods of winter wheat were measured and determined in the Thrace Region to fullfil this lack using a well accepted micrometeorological method called Eddy Covariance. For the past 20 years, the eddy-covariance technique has been widely used to measure exchange fluxes of mass and energy between ecosystems and the atmosphere. Nowadays there are about 683 operational eddy-covariance stations worldwide, organized in continental networks and contributing to the global FLUXNET network. These stations mainly concentrated in Europe, Asia, and US. Estimation of gas fluxes with the eddy-covariance technique requires the use of fast, precise gas analysers. Traditionally, high-speed gas analyzers with response rate of 10 Hz. or higher utilized for measurements of eddy covariance fluxes of carbon dioxide and water vapor are designed in open-path, closed-path, and enclosed-path configurations. There are also some assumptions of eddy covariance method. • Measurements at a point can represent an upwind area, • Measurements are done inside the boundary layer of interest, • Fetch/footprint is adequate. That means fluxes are measured only at the area of interest, • Flux is fully turbulent and most of the net vertical transfer is done by eddies, • Terrain is horizontal and uniform. Average of fluctuations is zero. Air density fluctuations , flow convergence & divergence are negligible, • Instruments can detect very small changes at very high frequency. The main requirements for instruments and data acquisition systems used for eddy covariance data are their response time to solve fluctuations up to 20 Hz. Measurements are of course never perfect because of assumptions, physical phenomena, instrumental problems, and specifics of the particular terrain or setup. Therefore, there are a number of potential flux errors, but they can be corrected. In this study; frequency response corrections, WPL (Webb-Pearman-Leuning) correction and coordinate rotation (tilt correction) have been applied to 10 Hz. time series of eddy covariance data after spike removal, high pass, low filtering effects and linear detrending. Heavy precipitation and low turbulent exchange conditions affect the eddy covariance measurements and EC produces uncorrected data. Hence, the data gaps caused by the above conditions must be filled. Here, international standard procedures have been followed. Finally, flux partitioning was applied to data set with gap. Net ecosystem exchange (NEE), gross primary production (GPP) and ecosystem respiration (Reco) values were calculated during 2012-2013 winter wheat growing season, straw for July 2013 – Decembre 2013, and bare soil for Decembre 2013 – April 2014. At night, the partitioning is simple, as Reco=NEE. During the day, the partitioning is dependent on the model used. Therefore there are substantial uncertainties associated with the resulting estimates of GEP and Reco. In the 2012 – 2013 growing period, winter wheat was planted on 1 Novembre 2012 and harvested on 31 June 2013. The eddy covariance flux measurements showed that cumulative NEE, GPP and Reco of whole growing periods, 17 months, were -502.75, 2114.50, 1611.75 gC/m2 respectively. For 2012 – 2013 growth period for winter wheat cumulative NEE, GPP, and Reco are -383,94, 1222.17, and 838.23 gC/m2, respectively. Daily means of total NEE, GPP and Reco for the whole growth period are -1.59, 5.05, and 3.46 gC/m2, succesively. Maximum of daily total NEE, GPP and Reco for the whole growing period determined 3.58, 18.74, and 8.82 gC/m2. Minimum of daily total NEE, GPP and Reco for the whole growing period evaluated -10.80, -0.20, 0.92 gC/m2, respectively. On the other hand, Gap in whole data set of NEE and GPP is 42.6%. It is also determined that 78.7% of gap at night time and 21.3% at day time. In addition, mean, maximum and minimum values of LE for winter wheat are 38.54, 479.97, -64.71 W/m2. Relationship between NEE, GPP, Reco and meteorological factors like photosynthetic photon flux density (PPFD), soil temperature, air temperature is determined. Determination coefficients (r2) between NEE and GPP is 0.93 , meteorological factors (PPFD, Tsoil, Tair) are 0.47, 0.09, 0.08. In addition, determination coefficients between GPP and meteorological factors are 0.69, 0.39, 0.35 is found. Also, determination coefficients between Reco and meteorological factors are 0.57, 0.64, 0.58 is determined. In addition to this, it is also evaluated r2 between NEE, GPP and biomass are 0.85, 0.83. Moreover, daily and growth period total reference evapotranspiration (ET0) and crop evapotranspiration (ETc) are 2.21 mm, 534.05 mm and 1.36 mm, 325.46 mm. Determination coefficient between ET0 and ETc is 0.43 Crop coefficient (kc) is calculated 0.62 for 2012 – 2013 growing period of winter wheat. Secondly, cumulative NEE, GPP, and Reco of whole straw period are -105.14, 671.92, and 566.78 gC/m2, respectively. Daily means of total NEE, GPP and Reco for straw period are -0.69, 4.39, 3.70 gC/m2. Maximum of daily total NEE, GPP and Reco for the whole growing period determined 5.34, 10.50, and 6.93 gC/m2. Minimum of daily total NEE, GPP and Reco for the whole growing period evaluated -5.40, -0.02, 1.40 gC/m2, respectively. Gap in whole data set of NEE and GPP is 41.3% and gap in night time of whole gap is 75.2% and day time gap is 24.8%. In addition average, mnimum and maximum values of LE for straw are 26.70, 167.96, and -132.69 W/m2. Relationships between NEE and meteorological factors (PPFD, Tsoil, Tair) is determined. Determination coefficients are 0.44, 0.39, and 0.58 respectively. Determination coefficients of GPP and meteorological factors are 0.75, 0.68 and 0.65. Determination coefficients of Reco and meteorological factors are 0.48, 0.38, and 0.23. Lastly, cumulative NEE, GPP, and Reco for bare soil are -13.67, 220.41, and 206.74 gC/m2, respectively. This period is between 1 December 2013 and 31 March 2014, NEE reached maximum positive value 26.82 gC/m2 on 25 January 2014. After this period, NEE started to decrease to negative value because of possible microbiological aktivities. Daily means of total NEE, GPP and Reco for bare soil period are -0.11, 1.81, 1.70 gC/m2. Maximum of daily total NEE, GPP and Reco for the whole growing period determined 2.34, 4.82, and 4.82 gC/m2. Minimum of daily total NEE, GPP and Reco for the whole growing period evaluated -3.06, -0.08, 0.00 gC/m2, respectively. Gap in whole data set of NEE and GPP is 48.5% and gap in night time of whole gap is 86.3% and day time gap is 13.7%. In addition average, mnimum and maximum values of LE for straw are 21.86, 447.11, and -141.63 W/m2. Relationships between NEE and meteorological factors (PPFD, Tsoil, Tair) is determined. Determination coefficients are 0.12, 0.06, and 0.0004 respectively. Determination coefficients of GPP and meteorological factors are 0.46, 0.03 and 0.15. Determination coefficients of Reco and meteorological factors are 0.19, 0.19, and 0.24. The results of this study show that carbon budget of winter winter wheat, which is an important nutritional source for Turkey, and also straw and bare soil was determined. This results contribute to decision makers who will apply for international meeting about climate change.