Mikrometeorolojik Yöntemlerle Bitkilerin Enerji Akılarının Belirlenmesi

Abstract

Dünya nüfusundaki artış, biyolojik ve ekolojik yaşam ile tarımsal ve endüstriyel üretim aktivitelerinde ihtiyaç duyulan su miktarında artışa sebep olmaktadır. İklim değişikliği, tek su kaynağı olan yağışın küresel dağılımı üzerinde etkiler yaratmaktadır. Bu dağılım bölgeye bağlı olarak kuraklık veya sel gibi doğal afetlere sebep olabilmektedir. Bu nedenle insanlık için her bir su damlası daha da önemli hale gelmektedir. Atmosfer bilimlerinin temelleri enerji ve su dengesi üzerine kuruludur. Enerji dengesi bileşenleri değiştirilebilir parametreler olmamasına karşın, su dengesi bileşenleri müdahaleye açık ve değiştirilebilir parametrelerdir. Bu noktada su kayıplarının belirlenmesi ve kontrolü önem arz etmektedir. Ekosistemde su kayıplarının ana bileşeni evapotranspirasyondur. Enerji ve su dengesinin en önemli ve ortak bileşeni olan evapotranspirasyon, kara ve su yüzeylerinden oluşan buharlaşma ve bitkilerden meydana gelen terleme ile atmosfere gönderilen toplam su miktarı olarak tanımlanır ve yüzey – atmosfer etkileşimi ile oluşur. Dünya genelinde kullanımda olan ve evapotranspirasyonun belirlenmesi amacıyla kullanılan birçok teknik bulunmaktadır. Mikrometeorolojik bir yöntem olan Bowen Oranı Enerji Dengesi (BREB) yöntemi enerji akılarının dolaylı ölçümünde sıklıkla kullanılan; net radyasyon, toprak ısı akısı ile iki farklı seviyede sıcaklık ve nem ölçümü temeline dayanan, dayanıklı ve düşük maliyetli bir yöntemdir. Evapotranspirasyonun ölçümünde kullanılan bir diğer mikrometeorolojik yöntem ise Eddy Kovaryans (EC) yöntemidir. Yöntem, çok geniş alanlarda dahi birçok gazın atmosfer ile yeryüzü arasındaki taşınımını atmosferik sınır tabakada ölçebilen, üç boyutlu rüzgâr hızı ve gaz yoğunluğu ölçümüne dayalı bir sistemdir. Penman – Monteith (PM) ise evapotranspirasyonun hesaplanmasında kullanılan denklemlerden biridir. Penman – Monteith eşitliğinin FAO yaklaşımı ise, PM temeline dayanan ve referans evapotranspirasyonun belirlenmesi amacıyla yaygın olarak kullanılan yöntemdir. Bu çalışmada BREB, EC ve PM yöntemleri, ülkemizin kuzeybatısındaki Kırklareli ili sınırları içerisinde hizmet vermekte olan Atatürk Toprak, Su ve Tarımsal Meteoroloji Araştırma İstasyonu’na ait deneme alanında kışlık buğday bitkisinin enerji akılarını ve gerçek evapotranspirasyon değerini belirlemek amacıyla kullanılmıştır. Ayrıca PM metodunun FAO yaklaşımı kullanılarak referans evapotranspirasyon belirlenmiştir. Ayrıca buğday bitkisi ekili alanda aerodinamik ve yüzey iletkenlik değeri ile ayrışma katsayısı hesapları yapılmıştır. Elde edilen sonuçlara göre, bölgede buğday bitkisinin ekim tarihi olan 9 Ekim 2009 tarihinden hasat tarihi 6 Temmuz 2010’a kadar oluşan gerçek evapotranspirasyon değeri BREB yöntemi ile 465.3 mm, EC yöntemi ile 344.1 mm ve PM eşitliği ile 392.6 mm olarak belirlenmiştir. Bölgede evapotranspirasyonun en fazla Mayıs ayında gerçekleştiği tespit edilmiştir. Aynı dönemde referans evapotranspirasyon 843.8 mm olarak hesaplanmıştır. Aerodinamik iletkenlik, yüzey iletkenliği ve ayrışma katsayısı değerleri sırasıyla 13.7 mm/sn, 38.9 mm/sn ve 0.84 olarak belirlenmiştir.

The growth in world population increases the demand of water for biological and ecological life, agricultural and industrial production activities. The only source of water is precipitation and global climate change affects the distribution of precipitation in the world. Distribution of precipitation may result in natural disasters like droughts and floods depending on the region. Thus every water drop is getting more and more important for human being. The fundamentals of atmospheric sciences rely on energy and water balance and every atmospheric system is controlled by the overall balance of energy and water. Energy balance is a natural and irreversible system and mostly cannot be affected by outside sources. On the other hand, water balance is composed of changeable components and exposed to intervention that makes it more crucial. At this point, determination and control of water loss are being much more significant. Main component of water loss is evapotranspiration in terrestrial ecosystem. Evapotranspiration, the most important and common component of energy and water balance, is defined as the sum of evaporation and plant transpiration from the Earth’s land and ocean surfaces to the atmosphere and composed of land – atmosphere interaction. In order to determine evapotranspiration rate, there are several measurement and calculation techniques in use around the world. Accurate measurements of the vertical transfer of mass and energy on the land surface are necessary to understand the various components of hydrological cycle. The two most commonly used methods to measure evapotranspiration rates are the Bowen Ratio Energy Balance and Eddy Covariance methods. Both methods are suitable when a number of requirements, mostly with respect to terrain topography and homogeneous fetch extension, are fulfilled. Furthermore, meteorological variables can be used to calculate evapotranspiration rates. Penman – Monteith combination equation is the most frequently used method for this purpose. As a matter of fact that lysimeters are used to measure evapotranspiration directly on the ground, but this technique is very expensive and difficult to use in forest and cultivated area. The Bowen Ratio Energy Balance (BREB) is a micrometeorological method often used to estimate energy fluxes (latent heat, sensible heat fluxes) cause of simplicity, robustness, and affordability. It is an indirect measurement method based on the measurements of net radiation, soil heat flux, temperature and humidity of air at two different levels. The partitioning of available energy between sensible and latent heat can usually obtained by BREB method. The errors associated with BREB method should be analyzed to determine analytically the reliable values of Bowen ratio, latent heat and sensible heat fluxes. The Eddy Covariance (EC) method is one of the most accurate, direct and defensible approaches available to date for measurements of gas fluxes and monitoring of gas emissions from areas with sizes ranging from a few hundred to millions of square meters. It is a key atmospheric measurement technique to measure and calculate vertical turbulent fluxes within atmospheric boundary layers. This technique consists of direct and very fast measurements of actual gas transport by a three dimensional wind speed in real time in situ. The covariance is calculated between the fluctuating component of the vertical wind and the fluctuating component of gas concentration. The measured flux is proportional to the covariance. Main challenge of this method is the shear complexity of system design, implementation and processing the large volume of data. The method is mathematically complex and requires a lot of care for setting up and processing data. Penman – Monteith (PM) combined equation is based on the measurements of net radiation, soil heat flux, wind speed, air temperature and humidity. FAO approach of the Penman – Monteith equation needs the same parameters of the Penman – Monteith equation to calculate reference evapotranspiration. The two methods are the most popular methods among the empirical formulas. This study was carried out in the research area of Ataürk Soil, Water and Agricultural Meteorology Research Station in the Kirklareli city locates in the northwest part of Turkey. The Bowen Ratio Energy Balance and Eddy Covariance methods were employed to measure latent heat and sensible heat fluxes of winter wheat during the growing period of October 2009 – July 2010. In addition to these methods, Penman – Monteith equaiton was performed to estimate actual evapotranspiration. Also, reference evapotranspiration was calculated by using FAO approach of Penman – Monteith equation. Moreover, aerodynamic and surface conductances and decoupling coefficient values were calculated for the first time at this region as a part of this study. Micrometeorological variables were measured continuously and 30 minutes time interval used for BREB calculation, 10 Hz time interval used for EC measurements. Then daily values were calculated for BREB and EC. PM calculation was made on daily basis, too. Furthermore, the relationships among BREB, EC and PM results were compared with correlation analysis. BREB approach can be only used under appropriate atmospheric conditions to evaluate the fluxes; that means data should have compatibility with laws of atmospheric motion. In order to find out appropriate data, a data filtration method was applied to the output of calculation based on 30 minutes time interval. Daily average micrometeorological measurements represented that the mean air temperature value was 11.5°C within the range of -13.2°C and 38.4°C with the standart deviation of 7.2°C, mean relative humidity value was 79% within the range of 26% and 100% with the standart deviation of 10.1%, mean wind speed value was 1.8 m/s with the maximum value of 9.7 m/s and standart deviation of 1.5 m/s, mean global solar radiation was 222 W/m2 with the maximum value of 539 W/m2 and standart deviation of 132.4 W/m2, mean net radiation was 61.7 W/m2 within the range of 263.1 W/m2 and -31.9 W/m2 with the standart deviation of 126.5 W/m2, average soil heat flux was -1.5 within the range of -27.7 W/m2 and 25.0 W/m2 with the standart deviation of 8.8 W/m2 during the experiment period. The total precipitation was 560.8 mm over the growing season and winter wheat was not irrigated during the growing period. Daily maximum value of precipitation was 33.9 mm and it’s average was 2.1 mm with the standart deviation of 5.1 mm. The wettest month was February with the total precipitation amount of 112.2 mm. The minimum monthly total precipitation was 11.9 mm in May. Results showed that total evapotranspiration amounts estimated by BREB, PM and EC were 465.3 mm, 392.6 mm, 344.1 mm respectively. Daily average of actual evapotranspiration was calculated as 1.72 mm by BREB, 1.27 mm by EC, 1.45 mm by PM. Maximum values of actual evapotranspiration estimated by BREB, EC and PM were 5.89 mm, 4.34 mm, 5.97 mm respectively. Monthly evapotranspiration reached to the maximum value in May with the value of 141 mm for BREB, 79.5 mm for EC, 99 mm for PM. Monthly minimum evapotranspiration was calculated for December and January. Total water loss was 23 mm for BREB, 37.7 mm for EC, 18.8 mm for PM between December 1 to January 31. The correlation analysis of BREB, EC and PM approaches demonstrated that good correlation was found between daily evapotranspiration data of BREB and EC (R2 = 0.71). Also BREB and PM have a good relationship (R2 = 0.71). A weak relationship was found between EC and PM (R2 = 0.51). By using BREB method, the daily average of latent heat was estimated as 137.7 W/m2 within the range of 1.1 W/m2 and 404.6 W/m2 with the standart deviation of 97.1 W/m2 and daily average sensible heat flux was 40.8 W/m2, ranging from 0.1 W/m2 to 280.2 W/m2 with the standart deviation of 42.4 W/m2. Results also showed that daily average β value was 0.33 ranging from 0.01 to 2.89 with the standart deviation of 0.40 during the experiment period. This result indicated that approximately 75% of the available energy was used for latent heat of evaporation and 25% was used for sensible heat in the experimental area. Reference evapotranspiration value was calculated as 844 mm by using FAO – 56 PM equation. Daily average reference evapotranspiration was 3.11 mm within the range of 0.2 mm and 11.7 mm (σ = 2.3 mm). The reference evapotranspiration calculation indicated that monthly maximum total reference evapotranspiration value was found in June as 185.2 mm, in May as 173.5 mm and minimum total reference evapotranspiration was estimated in December as 35.4 mm, in January as 44.6 mm. The average aerodynamic conductance value was calculated as 13.7 mm/s within the range of 1.5 mm/s and 76.1 mm/s (σ = 10.4 mm/s). The aerodynamic conductance showed a positive trend during the experiment period. The average surface conductance of winter wheat was determined as 38.9 mm/s within the range of 7.1 mm/s and 300 mm/s (σ = 33.6 mm/s). Surface conductance values indicated that there was a positive trend during the experiment period. Decoupling coefficient value determined as 0.84 with the highest value of 0.99, lowest value of 0.61 (σ = 0.08). The decoupling coefficient indicated that evapotranspiration was strongly controlled by surface conductance in the research area. In conclusion, agrometeorological and EC station were set up and required parameters were collected over a cultivated area. Actual evapotranspiration was measured and calculated by using three different and mostly used methods for winter wheat in the Thrace Region. The relationships among three methods were determined as well. Additionally, reference evapotranspiration, aerodynamic and surface conductance and decoupling coefficient were estimated for first time for winter wheat in Turkey.