Vertical soil water movement in a tropical rainforest catchment in northeast queensland

Abstract

In a tropical rainforest catchment, shallow piezometers respond almost instantaneously to rainfall, but the dominant groundwater recharge mechanisms are not well understood. To improve understanding, the downward movement of soil water on a runoff plot was traced using tritiated water injected at 0.20 m below the surface which marks the lower boundary of active subsurface storm flow. The tritium pulse was translated slowly down the profile, apparently dominated by interstitial piston flow on the lines described by Zimmermann's theoretical model. This recharge mechanism accounted for about 35 per cent of rainfall or 50 per cent of throughfall. The pulse's advance may have also been delayed by the upward movement of soil water indicated by the distribution of hydraulic potential under different hydrological conditions. The result was an increase in soil water transit time particularly below 1.0 m. There was also evidence in the tracer profiles for rapid by-pass flow but the volumes concerned could not be quantified in this experiment.

Hydrologic pathways and stormflow hydrochemistry at South Creek, northeast Queensland

“…The decrease in these quantities is minor, and the subsequent recovery exceeds the initial levels significantly, as well as the corresponding levels in South Creek. Most obvious, however, is the discrepancy between the respective levels in gully A and in gully C. In accordance with the discussion of event 1, this constitutes prima-facie evidence that, in this event, preceded only 5 days earlier by a 177.7 mm rainfall, the runoff in gully A consists to a considerable extent of subsurface stormflow, derived from upper soil horizons, above the 'hydrologic throttle' (Bonell and Balek, 1993, p. 215) (Bonell et al, 1984). These layers are more likely to contribute as the dry periods between events decrease.…”

Water transport and tracer mixing in volcanic ash soils at a tropical hillslope: A wet layered sloping sponge

“…These findings are in line with those reported for organic rich soils in the Scottish highlands (Tetzlaff et al, ). The formation of this layer likely results from the abrupt vertical K sat reduction in this soil layer compared to the overlying rooted layer (Table ), caused by the lower density of fine roots (Bonell, Cassells, & Gilmour, ). Moreover, the high moisture (soil water storage) likely results from the high organic matter and clay content of the andic horizon (Table ), to which water molecules can be easily bound (Yang et al, ).…”

Regional application of PnET‐N‐DNDC for estimating the N2O source strength of tropical rainforests in the Wet Tropics of Australia

“…To account for this phenomenon, we adjusted soil porosity, calculated as a function of bulk density and increased the saturated hydraulic conductivity for all texture classes by a factor of approximately 2. This figure is based on our own measurements and on investigations by Bonell et al (1983), who showed for a catchment in the center of the study area that values for the saturated hydraulic conductivity were up to 20 m day À1 .…”