Variations in stream water uptake by Eucalyptus camaldulensis with differing access to stream water

Abstract

The stable isotopes H andO were used to determine the water sources of Eucalyptus camaldulensis at three sites with varying exposure to stream water, all underlain by moderately saline groundwater. Water uptake patterns were a function of the long-term availability of surface water. Trees with permanent access to a stream used some stream water at all times. However, water from soils or the water table commonly made up 50% of these trees' water. Trees beside an ephemeral stream had access to the stream 40-50% of the time (depending on the level of the stream). No more than 30% of the water they used was stream water when it was available. However, stream water use did not vary greatly whether the trees had access to the stream for 2 weeks or 10 months prior to sampling. Trees at the third site only had access to surface water during a flood. These trees did not change their uptake patterns during 2 months inundation compared with dry times, so were not utilising the low-salinity flood water. Pre-dawn leaf water potentials and leaf C measurements showed that the trees with permanent access to the stream experienced lower water stress and had lower water use efficiencies than trees at the least frequently flooded site. The trees beside the ephemeral stream appeared to change their water use efficiency in response to the availability of surface water; it was similar to the perennial-stream trees when stream water was available and higher at other times. Despite causing water stress, uptake of soil water and groundwater would be advantageous to E. camaldulensis in this semi-arid area, as it would provide the trees with a supply of nutrients and a reliable source of water. E. camaldulensis at the study site may not be as vulnerable to changes in stream flow and water quality as previously thought.

Influence of groundwater depth on the seasonal sources of water accessed by Banksia tree species on a shallow, sandy coastal aquifer

“…Precision of the analysis is estimated to be ±1‰ for δ 2 H. Water source mixing model A time course of the mean monthly δ 2 H composition of xylem sap water in Banksia and H. hypericoides was plotted along with δ 2 H composition of groundwater and soil water to illustrate the seasonal changes in source water utilisation and highlight difference between sites and species. A three component water-source mixing model (see Appendix for formula and example) was then applied to the data to determine the relative contributions of the potential water sources to the xylem water of the study species (White et al 1985;Mazor 1991;Thorburn and Walker 1994). The δ 2 H of water in the xylem sap of twigs was used as an index of the water source or mixture of sources being used by a plant at the time of sampling.…”

Ground Water Chlorinated Ethenes in Tree Trunks: Case Studies, Influence of Recharge, and Potential Degradation Mechanism

“…Moreover, plant utilization of water is influenced by species (Smith et al 1991;Busch et al 1992;Thorburn and Walker 1994;Kolb et al 1997). Therefore, it is useful to examine areal TCE concentration differences within individual species.…”

“…For example, in areas where rainfall is unreliable, riparian trees may develop roots primarily in the capillary fringe and phreatic zone rather than throughout the soil profile (Ehleringer and Dawson 1992) western Arizona used ground water throughout the growing season regardless of the depth to ground water (Busch et al 1992). Plants with roots distributed in multiple soil zones may use various combinations of ground water, rainfall infiltrate, and stream water, sometimes responding opportunistically to rainfall events (Mensforth et al 1994;Thorburn and Walker 1994;Dawson and Pate 1996;Jolly and Walker 1996). Trees near a perennial stream in California used shallow soil water early in the growing season and then primarily used ground water in the latter part of the season when the soil dried (Smith et al 1991).…”

Water resource partitioning, stem xylem hydraulic properties, and plant water use strategies in a seasonally dry riparian tropical rainforest

“…The occurrence of varied rooting strategies in a plant community has been thought of as a form of niche differentiation, although this remains to be shown across a substantial range of habitats (Caldwell 1987;Lamont and Bergl 1991). Rooting strategies may also be a product of water reliability rather than water distribution per se (Dawson and Ehleringer 1991;Ehleringer et al 1991;Flanagan et al 1992; Thorburn and Walker 1994;Goldstein et al 1998).…”