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Diurnal variations and vertical distribution of δ13C, and concentration of atmospheric and soil CO2 in a meadow site, SE Poland

Szaran J., Dudziak A., Trembaczowski A., Niezgoda H., Hałas S.

Geological Quarterly

2005

Vol. 49, No. 2

135--144

We provide the results of 24-hour observations made in a meadow site located in a small river valley in Central Europe. Samples of atmospheric air were taken from three horizons: near the soil (0.05 m), in the grass (0.5 m) and above the meadow (2 m) at two-hour intervals. At the same time, samples of soil air were collected from two horizons: -0.1 and -0.5 m. We have found a variation of δ¹³C above the ground from -6‰ during the day to -20‰ late at night accompanied by variations in CO₂ concentration from 270 ppm during the day, to various levels late at night at different heights above the ground. The maximum concentration was 1430 ppm at the ground level. The correlation coefficient between δ¹³C and reciprocal of concentration was the highest (R2 = 0.984) for the samples collected 2 m above the ground, the regression line clearly indicating CO₂ mixing from the two sources: atmospheric and biogenic reservoirs. The intercept of the mixing line yields δC = -23.0‰ for the biogenic CO₂. In contrast, the diurnal variations in the soil were relatively small, δ¹³C varied from -21.6 to -23.4‰, while CO₂ concentration from 4300 to 8200 and from 24 700 to 34 500 ppm at depths of 0.1 m and 0.5 m respectively, which is less than 2-fold. Small diurnal variations are characteristic of dry soils, where δ^13C is weakly correlated with CO₂ concentration (in our case R2 was 0.30 and 0.54, respectively).

Respiration and assimilation processes reflected in the carbon isotopic composition of atmospheric carbon dioxide

Szaran J., Niezgoda H., Trembaczowski A.

Nukleonika

2002

Vol. 47,suppl.1

59-61

This paper presents diurnal variations of concentration and carbon isotopic composition of atmospheric carbon dioxide caused by respiration and assimilation processes. Air samples were collected during early and late summer in 1998 in unpolluted area (village Guciow located near the Roztocze National Park, SE Poland) in three different environments: uncultivated field on a hill, a meadow in the Wieprz river valley and a forest. The effect is very strong during intensive vegetation growth on a sunny day and clear night. The largest diurnal variations in atmospheric CO2 concentration and its carbon isotopic composition in June above the meadow were about 480 ppm and 10‰, respectively.