The Study On Temporal Variation And Impact Factors Of Carbon Flux Between Urban Ecosystem And Atmosphere In Changsha

Influenced by the increasing of greenhouse gas emissions, the global temperature increase gradually, and there have a global climate warming. The increasing close relation of human and city makes the urban ecosystem play an important role in the global change. Yet urban ecosystem has gradually become an important source of carbon dioxide in the atmosphere. The existed researches on urban ecosystem CO2 flux were mainly concentrated in Europe and the United States, Japan and other developed countries in globe. But compared with the relative uniform underlying surface of terrestrial ecosystems such as forest, grassland wetland and farmland ecosystems these researches are still less. Based on the eddy correlation technology which acquire the continuous observation of urban ecosystem carbon flux and the factors associated with the carbon cycle from 2012 to 2014 in Changsha, this articles take an urban ecosystem as the research object. And then analysis the variable characteristics of carbon flux and its impact factors of the urban ecosystem. The main conclusions are as follows:a. The pitch angle after double rotation (DR) or triple rotation (TR) and the roll angle after TR transformation, are both have a great changes in amplitude and an obvious directivity. The figure of pitch and roll angle which after planar fit (PF) transformation is fixed. The measured value of vertical mean velocity is non-vanishing, the vertical mean velocity which after DR and TR are zero, and the vertical mean velocity which after PF transformation decrease significantly than the measured value of vertical mean velocity and is non-vanishing. The coherence of Carbon flux which after PF transformation (Fc_PF) and carbon flux which is measured (Fc_measured) is similar with the coherence of Carbon flux which after DR transformation (Fc_DR) and Fc_measured. Therefore, Planar fit is most suitable this research station.b. The temperature present a variable characteristics of single wave. The maximum monthly mean temperature appeared in July, and the minimum monthly mean temperature appeared in January or February. The monthly distribution of rainfall is very uneven, but it mainly concentrated in the first half of the year. The maximum monthly amount of precipitation appeared in May or June, and the minimum monthly amount of precipitation appeared in October or December. Photosynthetically active radiation (PAR) have a similar annual variation with temperature. The maximum monthly amount of PAR appeared in July, and the minimum monthly amount of PAR appeared in January or February, it has a large extent of variation of annual.c. Carbon flux have an obvious variable characteristics of diurnal and seasonal. Carbon flux are positive value in daytime and varies weakly at night, in the daytime carbon flux mostly are negative value and the mutative extent of it is gently increasing. The duration of negative value of carbon flux vary with the seasons. The diurnal variation of carbon flux has a "double peak valley" characteristics, the peak value affected by human activities and the valley value affected by environmental factors. Over the course of a year, carbon flux present a multiple change trend, the minimum of it generally appear in the summer, the maximum of it is associated with anthropogenic discharge and lack in regularity.d. The response of carbon flux to its environmental factors related to time scales. On day and month scale, carbon flux with air temperature present a relationship of negative correlation. On day scale, carbon flux with PAR present a relationship of logarithmic function, and on month scale the relationship is quartic polynomial function. Carbon flux with wind speed present a relationship of cubic polynomial function. Carbon flux with wind direction present a relationship of sine. The distribution of different types of underlying surface can affect the carbon flux, the wind direction in the range of 1-180°, the carbon source is greater than the carbon sink, he wind direction in the range of 180-360°, the carbon sink is greater than the carbon source.