This study examines the impacts of a young blue gum tree plantation on the groundwater and surface water resources at a paired catchment study site in southwest Victoria. The site is on a Devonian granite in the broad Victoria Valley within the Grampians, where one catchment is a farm used for sheep grazing, and the other is almost entirely covered in a Eucalyptus Globulus plantation, planted in July 2008.
Twenty three bores across both catchments were sampled for standard cations and anions, stable isotopes, 14C and tritium. Most of the groundwater was 1000 years or older, meaning that it was not possible to determine the effect of the young plantation on the hydrochemistry. However, analysis of the chemistry data showed a strong depletion in all the major chemical species with respect to rainfall input. The results indicate that the past native vegetation removed these chemical species from the groundwater or soil water when transpiring, overwriting almost all evidence water-rock interactions.
The groundwater levels and streamflow at the study catchments were measured using loggers and v-notch weirs respectively. The main control on groundwater recharge at the site was found to be topography, with more recharge occurring in the lowland areas through focused recharge than upland areas. The tree plantation was found to have reduced groundwater recharge and stream flow, and a water balance carried out for both catchments emphasises this.
Transpiration was measured at the plantation using the heat pulse sap flow technique, with measurements indicating 901.7 mm of evapotranspiration occurring during 2012, while the water balance suggested evapotranspiration should be closer to 671 mm. The salt balance indicates that the trees are too young to be having an effect on salinity export from the catchment.
Principal NCGRT researcher: Joshua Dean
Other researchers/collaborators/co-authors: John Webb, Evan Dresel (DEPI Victoria), Edoardo Daly (Monash), Geraldine Jacobsen and Robert Chisari (both ANSTO).