RESUMO
In recent years, carbon emission research has been receiving increasing attention. China has put forward the strategic goal of achieving a carbon emission peak by 2030. Hence this research is very important for the measurement of greenhouse gas emissions in China. CO2 and CH4 fluxes from a paddy field in the middle-lower Yangtze Plain in China were analyzed based on the eddy covariance technique. The CO2 flux showed an "U" curve during the observation period, with an average flux of -3.33 µmol·(m2·s)-1, which was a sink. Negative values appeared at the tillering stage, and the minimum was shown at the heading period. The CH4 flux trend was roughly opposite to the that of the CO2 flux, which first increased and then decreased. It raised rapidly during the tillering and jointing stages and then dropped rapidly from the peak to the trough during the booting stage, and only a slight increase was found in the blooming stage. The maximum flux[0.40 µmol·(m2·s)-1] appeared at the beginning of the booting stage and the end of the jointing stage, and the average flux was 0.11 µmol·(m2·s)-1. The CO2 flux was positive at night and negative during the day. It decreased from 07:00 and reached a minimum around 13:00 at -16.01 µmol·(m2·s)-1. The CH4 flux was low at night and high during the daytime. It increased at 06:00 and reached a peak around 14:00, at approximately 0.16 µmol·(m2·s)-1. An exponential correlation was found between air temperature and CH4 flux. The vapor pressure deficit showed a linear correlation with CH4 flux. The response of environmental factors on CO2 fluxes and CH4 fluxes on a diurnal scale was greater than that on a seasonal scale, and the daytime response was greater than that at night. CH4 flux decreased significantly with the increase in CO2 flux on the diurnal scale, but the correlation was not obvious on the seasonal scale. The increased CH4 flux slowed down after fertilizing.
Assuntos
Gases de Efeito Estufa , Carbono , Dióxido de Carbono/análise , China , Gases de Efeito Estufa/análise , Metano/análise , Óxido Nitroso/análise , Estações do AnoRESUMO
The relationship between the structure and function of forest ecosystems is the main intere-sts in the research area of forest ecology and management. However, over complex terrains in particular, these studies had been challenged as uneasy tasks due to the limitations in the forest survey and measurement techniques and other supporting technologies. Chinese Academy of Sciences (CAS) funded "Multi-Tower LiDAR/ECFlux Platform for Monitoring the Structure and Function of Secondary Forest Ecosystems" (Multi-Tower Platform, MTP) as a field station network corner-stone research infrastructure project, which was completed by Qingyuan Forest CERN (Chinese Ecosystem Research Network). In a distinctively-bounded and monitored-outlet watershed, the MTP was integrated by light detection and ranging (LiDAR) scanners, eddy covariance (EC) flux instrument systems, whole- and sub-watershed hydrology station network, long-term forest plot arrays, and live data center. Using LiDAR scanning, the MTP can get cloud data for holographic information on canopy structure. The EC-flux instrument system and hydrology station network along with forest plot arrays could ensure the reliability of water and carbon observations over this complex terrain, which allows to verify the studies on flux measurement technologies and methods, as well as to understand the processes of ecohydrology and CO2 exchange between forest ecosystem and the atmosphere. Further, we can also assess the primary ecosystem services, including water conservation and carbon sequestration. All the data from "tower-station" were streamed through wireless network, which would facilitate data monitoring, management, and sharing. There are three tasks of MTP team: 1) defining innovative methods and descriptors to quantify three-dimensional forest structure; 2) developing theories and techniques to measure CO2/H2O fluxes and other trace gases over complex terrains; 3) understanding the relationship between structure and function of forest ecosystems, providing information and rationales for forest management practices to assure broad and sustainable benefits from forests.
Assuntos
Ecossistema , Árvores , Atmosfera , Florestas , Reprodutibilidade dos TestesRESUMO
The open-path CO2/H2O analyzer that is currently widely used in the eddy covariance (EC) system possesses a surface heating effect, which may influence the accuracy of the eddy-flux measurements. Taking the open-path EC system in the temperate deciduous forest of the Maoershan Ecosystem Research Station as a case, we assessed the heating effect of the open-path CO2/H2O ana-lyzer (Li-7500) with fine-wire thermocouples and tested the applicability of Burba's equations. The results indicated that between April 23 and May 28 in 2016, the daytime air temperature in the mid-optical-path of the Li-7500 was on average 0.2 â higher than the ambient air temperature, while the nocturnal temperature was almost equal, with the peak of the heating often occurring in the morning transition period and at noon or in the early afternoon. The diurnal variation in the heating effect on the sensible heat flux (HS,HE) estimated from the simple linear-fitting models in the fourth method by Burba (BurbaLF) was overall a rectangle-like wave, whereas that from the multiple regression models (BurbaMR) showed a weak mono-peak shape. Compared with direct mea-surements (K079) with the K-type fine-wire thermocouples (with a 0.079 mm diameter of single bare wire) and the HS,HE modeled with two fine-wire thermocouples (K079Model), the estimated HS,HE with the BurbaLF and BurbaMR varied little in the daytime with a lower but wider daytime-peak (20 W·m-2), a sharp transition between daytime and nighttime, and a typical nocturnal va-lue of ï¼ 5 W·m-2. The peak values of HS,HE estimated from the K079 and K079Model could be higher than 40 W·m-2, and the values at night fluctuated around zero. The sensible heat flux in the optical-path of the Li-7500 was increased by 13.6% during the daytime. The value of the daytime heating effect on the CO2 turbulent flux (Fc,HC) estimated from the K079 and K079Model was averaged about 0.5 mg CO2·m-2·s-1, twice of the value estimated previously. Compared with the direct measurements, the Burba equations underestimated the Fc,HC around the noon due to the inadequate HS,HE, but overestimated the Fc,HC in the morning, the late afternoon and the night because of over-corrections of HS,HE, resulting in an overall overestimate of Fc,HC. These findings validated that both K079 and K079Model methods can be used to estimate the Fc,HC.