Effect of groundwater freshening on riparian vegetation water balance

Abstract

Abstract:In the floodplains of the lower River Murray (Australia), riparian open forests and woodlands dominated by River Red Gum (Eucalyptus camaldulensis Dehn.), Black Box (E. largiflorens F. Muell.) and River Cooba (Acacia stenophylla A. Cunn. Ex Benth.) have been severely impacted by salinization and drought. The 'Bookpurnong Experiment' was developed to test the hypothesis that watertable lowering combined with groundwater freshening would reduce tree water stress and improve floodplain vegetation health. Tree water use and water stress following groundwater freshening were examined using measurements of sapflow, pre-dawn leaf water potentials and stable isotope composition of xylem water. Water use and water stress varied markedly across the floodplain. The open mixed forest lining the bank of the River Murray, with access to fresh groundwater, used five times more groundwater over the measurement period and maintained greater canopy vigour than the open mixed woodland at inland sites. The River Cooba trees approximately 80 m from the river responded to watertable lowering of 0Ð65 m and to groundwater freshening by increasing transpiration. Black Box trees at the same site experienced reduced plant water stress, with no increase in transpiration. However, at a third site, approximately 170 m from the river, where the saline watertable (total dissolved solids D 36 300 mg l 1 ) was lowered by 1 m, no change in plant water stress or pattern of plant water use was observed. These results indicate that groundwater lowering combined with groundwater freshening can provide an accessible water source for water-stressed floodplain vegetation.

Quantifying water savings from willow removal in Australian streams

“…Willow transpiration rates in all measurement years were assumed to be similar to low rates measured in August 2005 during the dormancy period, however future research will measure willow transpiration for a 12 month period to refine the current estimate. Red Gum transpiration rates for the unmeasured period in 2005/06 were estimated using transpiration rates at the beginning and the end of the measurement period for that year and estimates of Red Gum transpiration in similar semi-arid environments (Benyon et al, 2006;Doody et al, 2008).…”

Drip irrigation enhances shallow groundwater contribution to crop water consumption in an arid area

“…In the San Joaquin Valley of America, large‐scale irrigation occurs, which lacks drainage‐water disposal facilities, and results in severe salinity and land retirement (Hanson, May, Šim̊unek, Hopmans, & Hutmacher, ). In Australia, soil salinization impacts the natural vegetation creating poor health and death in relation to changes of the surface water regime of the River Murray, which alters groundwater–surface water interactions (Doody, Holland, Benyon, & Jolly, ; Jolly, Walker, & Thorburn, ). Faced with reductions in stream water availability, introduced vegetation is often removed from within riparian areas in Australia and the United States, in order to return water to streams (Doody et al, ; Doody, Benyon, Theiveyanathan, Koul, & Stewart, ).…”

Water use strategies of two co‐occurring tree species in a semi‐arid karst environment

“…Water balance techniques have been successfully applied over a wide range of habitats and tree species throughout Australia (e.g. Cook et al ., ; Benyon and Doody, ; Benyon et al ., ; Mitchell et al ., ; Doody et al ., ; Feikema et al ., ; Holland and Benyon, ; Doody and Benyon, ). Investigating the source of tree water in shallow groundwater regions using environmental tracers can support water balance assessments.…”