Contrasting Transit Times and Water-rock Interaction in Australian Upland Catchments Draining Peatland and Eucalypt Forest

Catchments draining upland peat in the Victorian Alps, Australia contain water that has ³H activities closely similar to modern rainfall implying very short transit times (<2 years). By contrast the water that drains adjacent eucalypt forest has mean transit times of several years to decades. The differences in transit times most likely reflect the higher evapotranspiration rates in the eucalypt forests that results in lower infiltration rates and slower rates of flow. Major ion concentrations reflect a combination of evapotranspiration and water-rock interaction and may be used to provide first-order estimates of transit times. The short transit times in the peat imply that it does not represent a long-term store of water for the river systems during drought. The peat is also highly susceptible to drying during low rainfall periods, which renders it vulnerable to the periodic bushfires that impact the region.