The volumetric water content of the soil was greatest when the
water table was 15 cm below the soil surface, and decreased as the
water table lowered (Fig. 4). The CO2 concentration was greater in deeper soil (Fig. 5) and, for any given depth, was greatest when the
water table was 15 cm below the soil surface and decreased as the
water table lowered. The highest CO2 concentration was 3.5% at
the depth of 20 cm when the water table was 15 cm below the soil
surface. In contrast, the O2 concentration was lower in deeper soil
(Fig. 6) and, for any given depth, was lowest when the water table
was 15 cm below the soil surface and increased as the water table
lowered. The lowest O2 concentration was 17.2% at the depth of
20 cm when the water table was 15 cm below the soil surface.