Vejetasyon yüzeyindeki sera gazı (CO2) değişiminin mikrometeorolojik yöntem ile belirlenmesi
Determination of the greenhouse gas (CO2) exchange on the vegetation surface by micrometeorological method
Yazar: MERVE KIZIL  AYDIN
Danışman: PROF. DR. LEVENT ŞAYLAN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Meteoroloji Mühendisliği Ana Bilim Dalı / Atmosfer Bilimleri Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: Meteoroloji = Meteorology
Dizin: Bitki örtüsü = Vegetation ; Eddy akımları = Eddy currents ; Mikrometeoroloji = Micrometeorology ; Sera gazı = Greenhouse gases

Özet:
Son yıllarda iklim değişikliği ve bunun etkileri tüm dünya tarafından dikkat çekmeye başlamıştır. Gezegenimizin ortalama sıcaklığının artması, kutuplarda bulunan buzulların erimesi ve buna bağlı olarak su seviyesinin yükselmesi, önceye göre daha fazla yıkıcı iklim olaylarının yaşanması ve mevsimlerin kayması insanların iklim değişikliğinin gerçekleşmeye başladığını fark etmelerini sağladı. Bu olayların önüne geçebilmek adına iklim değişikliğinin sebepleri araştırmaları arttı ve en büyük sebeplerinden birisinin sera gazlarının kontrolsüz artışı olduğuna kanaat getirildi. 
İnsan nüfusunun artışı, kontrolsüz fosil yakıt kullanımı, ormanların ve tarım arazilerinin yok edilmesi gibi etkenler sera gazlarının atmosferdeki konsantrasyonunun yükselmesine sebep olmaktadır. Atmosferde biriken bu sera gazları, atmosferdeki ışınım geçirimini azaltarak dünyada sera gazı etkisine yol açmaktadır. Bilim insanları bu olayların önüne geçebilmek için çalışmalar ve araştırmalar yapmaktadırlar. Aynı zamanda, ülkeler de kendi üzerlerine düşen görevi yaparak yıllık sera gazı emisyonlarını hesaplayıp, sera gazı azaltım eylem planlamalarını hazırlamaktadır. 
Sera gazı azaltım çalışmalarını planlamadan önce, ilk olarak sera gazı miktarının doğru hesaplanması gerekmektedir. Bu tezde, ülkemizde önemli bir tarım bitkisi olan yonca bitkisinin Eddy kovaryans yöntemi kullanılarak sera gazı emisyon/yutak kapasitesi incelenmiştir. Aynı zamanda alana ait meteorolojik parametrelerin ve bitki gelişiminin takibi de yapılmış ve bu değişkenler ile karbon akıları arasındaki ilişki belirlenmiştir.
Yonca bitkisi, bulunduğu alan içerisinde 3-4 yıl kalabilen ve bir yıl içerisinde birden çok hasat edilebilen bir bitkidir. Bu çalışmada yonca bitkisi Ekim 2018'de ekilmiş olup, karbon akı ölçümleri 18 Aralık 2020-12 Nisan 2022 tarihleri arasında yapılmıştır. Yonca bitkisi üzerinde, günlük ortalama GPP, Reco ve NEE değerleri sırasıyla 4.29, 3.63 ve -0.66 g C/m2 olarak hesaplanmıştır. Çalışma sonucunda, toplam GPP, Reco ve NEE değerleri sırasıyla 1747.50, 2065.98 ve -318.49 g C/m2'dir. NEE'nin negatif olması, yonca bitkisinin çalışma süresince arasında bir yutak kapasitesi olduğu, yani atmosferden karbon indirdiği anlamına gelmektedir.
Yonca bitkisinin karbon akıları ile meteorolojik ve bitki gelişim parametreleri arasındaki ilişkiyi tespit edebilmek adına yoncanın her bir gelişim dönemi için ayrı ayrı belirlilik katsayıları hesaplanmıştır. Meteorolojik değişkenler için hesaplanan belirlilik katsayısı değerlerinin oldukça düşük olmaları sebebiyle, hava sıcaklığı, toprak sıcaklığı ve global radyasyon ile karbon akıları arasında bir ilişki tespit edilememiştir. Bitki gelişim parametreleri için hesaplanan belirlilik katsayılarında ise, ilişkilerin 0.62 ile 0.88 arasında değiştiği, fakat NEE ile LAI ve bitki gövde boyu arasındaki ilişkinin düşük olduğu görülmektedir.
Yonca bitkisinin karbon akıları hakkında küresel çapta yapılmış olan çalışmalar çok sınırlıdır. Bu çalışmanın küresel ve ulusal çapta, yonca bitkisinin karbon bütçesini belirlemek ve bu karbon akılarının hangi değişkenlerden etkilendiğini anlayabilmek açısından katkı sağlaması hedeflenmektedir.

Abstract:
In recent years, the climate change and its effects have started to attract attention all over the world. This changes increase the average temperature of our planet, the melting of the glaciers at the poles and the corresponding rise in the water level, the occurrence of more destructive climate events than before, and the shifting of the seasons made people realize that climate change is taking place. In order to prevent these events, research on the causes of climate change has increased and it has been concluded that one of the biggest reasons is the uncontrolled increase in greenhouse gases.
Factors such as the increase of the human population, the uncontrolled use of fossil fuels, the destruction of forests and agricultural lands cause the concentration of greenhouse gases in the atmosphere to increase. These greenhouse gases accumulating in the atmosphere cause greenhouse gas effect in the world by reducing the radiation transmission in the atmosphere. Scientists conduct studies and researches to prevent these events. At the same time, countries do their part by calculating their annual greenhouse gas emissions and preparing their greenhouse gas reduction action plans.
The researchers divided the greenhouse gas inventory calculations into sectors. These sectors are gathered under 5 main headings as energy, industrial processes, waste sector, agriculture, land use, land use change and forestry. Since the agricultural sector includes livestock and agricultural lands, it meets the most basic nutritional needs of people. In terms of food safety, the agricultural sector has a very small place in the mitigation action plans. For this reason, rather than developing greenhouse gas reduction strategies in the agricultural sector, it is more important to determine the greenhouse gas emission/sink capacity of each parameter in this sector.
In this thesis, the greenhouse gas emission/sink capacity of the alfalfa plant, which is an important agricultural plant in our country, was investigated by using the Eddy covariance method. At the same time, meteorological parameters of the area and plant growth were followed and the relationship between these variables and carbon fluxes was determined.
The study was carried out on a 2.5 ha alfalfa field in Kırklareli Atatürk Soil Water and Agricultural Meteorology Research Institute. Alfalfa plant can stay in the area for 3-4 years and can be harvested more than once in a year. In this study, alfalfa plant was planted in October 2018 and carbon flux measurements were made between 18 December 2020 and 12 April 2022. 
Eddy covariance method was used in the study. Eddy covariance method measures CO2 and H2O fluxes in the environment with open type infrared CO2/H2O gas analyzer and 3 dimension sonic anemometer instruments. If there is not enough turbulence, the data is considered incorrect and removed from the data set. Secondly, if there is precipitation in the area or if water droplets have accumulated on the gas analyzer, the measurements made by the device will be inaccurate and these data should be discarded. In addition, data with high frequency, that is, rapid change, will also be erroneous, so these data are also discarded. After that, often the vertical axis (w-axis) cannot be positioned perpendicular to the mean flow lines when placing the sonic anemometer.. For this reason, the wind of the w-axis will mix with the winds of the other axes. To correct these errors, coordinate correction is applied to the data. Finally, there is the effect of temperature and water vapor fluctuations in the measurement of CO2 and H2O flux, WPL correction is applied to compensate for these effects. After these corrections ended, the data became more meaningful, but gaps occurred in the data set due to discarded data. These gaps were filled with the method called "gap filling" and an uninterrupted and error-free carbon flux data set was obtained.
The carbon fluxes of the plant were examined under 3 main headings, these are: gross primary production (GPP), ecosystem respiration (Reco) and net ecosystem exchange (NEE). Average daily GPP, Reco and NEE values on alfalfa plant were calculated as 4.29, 3.63 and -0.66 g C/m2, respectively. As a result of the study, the total GPP, Reco and NEE values are 1747.50, 2065.98 and -318.49 g C/m2, respectively. A negative NEE means that the alfalfa plant has a sink capacity during the study period, that is, it reduces carbon from the atmosphere.
The plant was harvested six times in 2021 and entered the dormant period between mid-November 2021 and March 2022. With the rising temperatures in March, it came out of the dormant period and started to develop again. In summary, the alfalfa plant had seven growth periods (6 in 2021 and 1 in 2022) and one dormant period between the measurement dates. During the study period, since the alfalfa was harvested six times, the above-ground biomass of the plant, LAI, and the plant stem length decreased continuously. Therefore, just after the harvest dates, photosynthesis and respiration values decreased. Due to favorable meteorological conditions, the plant developed again in a short time, but was re-harvested as the plant developed. In order to minimize the effects of these continuous fluctuations between carbon flux values with meteorological and plant growth parameters, these relations were calculated according to the development periods. 
The relationship between carbon fluxes (GPP, Reco and NEE) with meteorological variables was calculated. In the first place, the coefficients of determination between carbon fluxes with air temperature (Ta) were determined. The coefficients of determination calculated between Ta and carbon fluxes changed from 0.04 to 0.54 for GPP; from 0 to 0.79 for Reco; from 0.01 to 0.57 for NEE. Then, the coefficients of determination between carbon fluxes and soil temperature were determined. The coefficients of determination calculated between soil temperature and carbon fluxes are between 0.1 and 0.68 for GPP; between 0.02 and 0.87 for Reco; between 0.04 and 0.56 for NEE. Finally, the coefficients of determination between carbon fluxes and global solar radiation (Rg) were determined. The coefficients of determination calculated between Rg and carbon fluxes are weak. Since the coefficient of determination values calculated for meteorological variables are quite low, a good relationship could not be determined between air temperature, soil temperature and global radiation with carbon fluxes.
Additionally, the relationship between carbon fluxes and plant growth was also examined, and the coefficients of determination for growth periods were calculated between carbon fluxes with above-ground biomass, leaf area index (LAI) and plant stem height. Initially, the coefficients of determination calculated for the above-ground biomass are between 0.29 and 1 for GPP; between 0.09 and 0.96 for Reco; between 0.02 and 1 for NEE. Then, the coefficients of certainty calculated for LAI varied from 0.65 to 0.98 for GPP; from 0.55 to 0.99 for Reco; from -0.98 to 0.98 for NEE. Furthermore, the coefficients of determination calculated for plant stem height are between 0.49 and 1 for GPP; between 0.45 and 0.93 for Reco; between -0.50 and 1 for NEE. In the specificity coefficients calculated for the plant growth parameters, it is seen that the relationships vary from 0.62 to 0.88, but the relationship between NEE and LAI and plant stem height is low. 
In the calculation of each coefficient of determination, it is striking that the values for the dormant period are quite low. The relationship between carbon fluxes and plant growth could be expected to be higher than the coefficients of determination given above. After the last harvest on November 16, 2021, the plant continued to grow for a while and plant development continued. However, after a short time, the plant entered the dormant period with the cooling of the weather. The plant's height, leaf area index and biomass decreased as the plant was affected by cold and entered the dormant period. This has lead to the fact that the relationship of the plant's dormancy period is quite low. If the relationship of the plant's dormancy periods are not taken into account, the average certainty coefficients will be higher.
Global studies on the carbon fluxes of alfalfa plant are very limited. More studies are needed in order to understand, interpret and predict the changes in carbon fluxes of alfalfa plants. It is aimed that this study will contribute to determining the carbon budget of the alfalfa plant on a global and national scale and to understand which variables are affected by these carbon fluxes. With the longer duration of the studies and the different meteorological conditions in different areas, the amount of carbon that these and similar plants emission/sink into our atmosphere can be determined more effectively.