The Variety Of The Apparent CO₂ Flux In The Bare Intertidal Zone

The research on the apparent CO2 flux in the bare intertidal zone which is an important compose of an especial kind of wetland is of consequence. Understanding the variety of the apparent CO2 flux in the bare intertidal zone and the influence from the environmental factors correctly is one of the important complementarities for the research on intertidal carbon cycle. Using a Li-8100 automated soil CO2 flux system (Licor, Lincoln, Nebraska, USA), this work observed the apparent CO2 flux from the sedinment to the atmosphere in situ in the bare intertidal zone in northern China for the first time. According to the long-term observation on the apparent CO2 flux from the sedinment to the atmosphere in the bare sandy intertidal zone in the Laoshan Mountain Scenic Area, Qingdao, sum up the variety of the apparent CO2 flux as follows: during the daytime in the spring, summer and the autumn, the apparent CO2 flux between the sediment and the atmosphere gradually increased as tide ebbed, reached the maximum when the tide reached its lowest ebb and remained at the maximum during the flood tide; however, during the daytime in the winter, the apparent CO2 flux between the sediment and the atmosphere was low in both the ebb tide and the flood tide without obvious variety because the sediment temperature was lower; the apparent CO2 flux between the sediment and the atmosphere was low without obvious variety in the evening because the he sediment temperature was lower in the evening than in the daytime and decreased at all times in the evening. In addition, according to the observation at different position in the same intertidal zone(in the Laoshan Mountain Scenic Area, Qingdao), the apparent CO2 flux in the middle of the intertidal zone>the apparent CO2 flux at the top of the intertidal zone>the apparent CO2 flux at the bottom of the intertidal zone. It was shown that the daytime variety of the apparent CO2 flux between the sediment and the atmosphere in the Qingdao bay and Jiaozhou bay was the same as that in the Laoshan Mountain Scenic Area, Qingdao.Tide, sediment redox potential and temperature were the main environmental factors impacting the apparent CO2 flux from intertidal sediments to the atmosphere. The tide mainly impacted the apparent CO2 flux in the daytime ebb tide; the sediment redox potential didn't only impact the rate in which the apparent CO2 flux changed with the height to tide in the daytime ebb tide but also impacted the average apparent CO2 flux in the daytime flood tide when the sediment redox potential was low; the sediment temperature impacted the average apparent CO2 flux in the daytime flood tide when the sediment redox potential was high, in addition, the low sediment temperaure induced to the low apparent CO2 flux in the evening.Observing the total apparent CO2 flux from the sediment to the atmosphere in the daytime needs lots of time because of the obvious daytime vaiety of the apparent CO2 flux. This work summed up the method which can be used to estimate the total daytime apparent CO2 flux with a few of data based on the variety of the apparent CO2 and the influnce from environment factors. The linear regression between the estimated and measured apparent CO2 fluxes was y= 0.9353x+0.0872(R2 = 0.75).The monthly variety of the daytime average apparent CO2 flux was obvious, and redox potential and temperature were two main factors impacting the diurnal apparent CO2 flux from intertidal sediments to the atmosphere. When the redox potential was below 300 mv, the redox potential was the key factor controlling apparent CO2 flux while the impact of temperature was limited; when redox potential ranged from 300 to 500 mv, both redox potential and temperature were main factors regulating the variation in apparent CO2 flux, with more important role of temperature than redox potential; when the redox potential was above 500 mv, the apparent CO2 flux was high because both the redox potential and temperature were high, while the impact of the variation in redox potential at this high value on apparent CO2 flux was limited, thus leaving temperature variation the sole important influencing factor. Thus, the higher the redox potential and temperature are, the higher the apparent CO2 flux from sandy intertidal sediment to the atmosphere. The equation F = ( aEh + R0 ') ekT including both the redox potential and temperature based on Van't Hoff equation could estimate the the daytime average apparent CO2 flux better. In this equation, F is the daytime average apparent CO2 flux, a is the rate in which the apparent CO2 flux changes with redox potential, Eh is the redox potential at the depht of 1cm, R0'is the apparent CO2 flux at 0℃and 0mv, k is a canstant and can be used to calculate Q10, T is the temperature at the depth of 1cm.