Effects of ants on sandy soils in semi-arid eastern Australia .2. Relocation of nest entrances and consequences for bioturbation

The rate of bioturbation by funnel ants (Aphaenogaster barbigula) was studied on an aeolian soil in western N.S.W. Nest entrances were tagged and monitored on permanent quadrats between May 1991 and May 1993. Nest entrances remained active for approximately 9 months and, on average, changed their location twice per year. Annual bioturbation was 336 gm-2yr_1 which was equivalent to the annual development of a layer 0-28 mm thick. Bioturbation activity was poorly correlated with environmental variables. We estimate that 92% of the total volume of the soil would be removed from the profile during the construction of nest entrances within 100 years, and 100% within 200 years. This provides strong evidence that development of these soils is principally biogenic and may explain why there is little or no horizon development, or changes in particle size distribution with depth. Bioturbation is substantially greater than estimates of water erosion in these soils, suggesting that over time soil brought to the surface will lead to the development of a new layer. This deposition and subsequent incorporation of organic matter in the surface soils around the nest entrance may have consequences for enhanced nutrient development on a micro scale.