Small-scale spatial variation in soil CO 2 concentration in a natural carbon dioxide spring and some related plant responses

Abstract

Small-scale spatial and temporal distribution of soil CO 2 within the natural CO 2 spring (mofette) field Stavešinci (NE Slovenia) was studied. By using an infrared gas-analyser, gas measurements were performed measuring soil CO 2 in a regular sampling grid (depth 20 cm, resolution 0.5 m) in an area of 60 m 2. The measurements were performed at different times of the year, in May (20) 2002 and in November (10 and 17) and December (4) 2003. To illustrate the small-scale spatial variability of soil CO 2 concentration, the data were interpolated by the inverse distance third power moving average method. The main geothermal exhalation spots were marked and the gaseous environment of different parts of the mofette area was described. One third of the plot was strongly enriched in CO 2 with median CO 2 concentration ranging from 21.3% to 30.9% in four samplings. The measurements revealed a clear patchy pattern of soil CO 2 enrichment. Drastic changes of soil CO 2 concentrations over a short distance indicate limited lateral diffusion in the silty-clay mofette soil. The spatial patterns of soil gases can be regarded as fairly constant over longer periods of time as revealed by a comparison of consecutive samplings. The growth of Solidago gigantea in the studied area was followed and clear negative correlations have been proved when plant height and leaf chlorophyll content were compared to soil CO 2 concentration. The Spearman rank correlation coefficient for average plant height and average soil [CO 2] was r = − 0.69, and for leaf chlorophyll content and soil [CO 2] was r = − 0.76. Our study showed that the relation between the gaseous environment and plant response at the natural CO 2 springs could be efficiently explained on the basis of soil [CO 2].