soil - Lublin

AERATION AND CLIMATIC GLOBAL CHANGE
Stępniewski W., Stępniewska Z.
INTRODUCTION
The list of greenhouse gases comprises water vapor, carbon dioxide, methane,
nitrous oxide and others. Total greenhouse effect is evaluated to be about 32 o C. Of
this about 20 o C is caused by the presence of water vapor in the atmosphere, 7 o C by
carbon dioxide, 2.4 o C by ozone, 1,4 o C - by nitrous oxide, and 0.8 o C by methane
(Kożuchowski and Przybylak, 1995). The present day concern about global warming
is caused by expected further increase of the global temperature by 2-4 o C during
21 century. Talking about interrelation between soil aeration and global warming
usually methane and nitrous oxide are taken into consideration. However, this
relationship is also valid for water vapor and carbon dioxide.
WATER VAPOR
Water vapor pressure in the atmosphere is not related directly to soil aeration
status. However, anoxic conditions in soil occur predominantly in wetlands, which
generate higher humidity in the atmosphere. Thus the presence of wetlands should
increase the temperature through elevated humidity of atmospheric air.
CARBON DIOXIDE
Carbon dioxide is the second important greenhouse gas. Under natural conditions
its primary source was the respiration of soil (assessed at present to be about
60 Pg of C), of plants and animals (also about 60 Pg of C), while its essential sink
was the photosynthesis (121 Pg C) (Lal, 2002). The equilibrium between them has
been modified by anthropogenic emission presented in Table 1. The total organic C
pool in soil is assessed as 1550 Pg, atmospheric C pool as 750 Pg and pool in biota
– as 610 Pg (Lal, 2002). Change of soil carbon pool by 1 Pg is equivalent to 0.47
ppm change in the atmospheric CO 2 (Lal, 2002).
Availability of oxygen is of primary importance for the process of organic matter
mineralization due to microbial respiration. The rate of annual increase of the
atmospheric pool of carbon dioxide is 0.4% and the residence time is 50-200 years.
Anoxic conditions in wetlands lead to reduction of respiration rate and to net carbon
accumulation in soil. This, in turn, leads to reduction of its amount in the atmosphere.
However it should be kept in mind that in anoxic wetlands part of the
assimilated carbon is returned to the atmosphere in the form of methane, which is
much more active radiatively (see further). Thus the net effect of wetlands is the
increase of the global temperature because the methane evolved and the increased
humidity of the atmosphere prevail over the accumulation of organic carbon under
such conditions.
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