Resistivity imaging across native vegetation and irrigated Vertosols of the Condamine catchment—a snapshot of changing regolith water storage

摘要

Over use of one of Queensland's most productive groundwater systems, the Condamine River alluvium, has led to substantial depletion in groundwater levels. Most use is for irrigation (mainly furrow), which is known to increase deep drainage below the root zone. Thus irrigation should create greater groundwater recharge, but this is not generally detected in groundwater levels. The enhanced deep drainage may be filling a moisture deficit in the unsaturated zone and is therefore not yet causing greaterrecharge. Geophysical 2D resistivity imaging and soil coring was used to look at changes in stored regolith water in the alluvium. Transects were imaged across naturally vegetated landscapes (as a reference) into irrigated paddocks. All soils under native vegetation were found to be very dry (low conductivity) even when only sparsely populated by trees. In contrast, significant long-term migration of water has occurred to deep within the regolith (up to 15 m) in most irrigated paddocks. A wet (close tosaturated) zone was found in the upper 6 m of soil in the irrigated paddocks. Deeper regolith (20-60 m) was resistive, both above and below the water Table, due to low salinities in the groundwater and coarser textures.