Search

River red gum (Eucalyptus camaldulensis Denhn.) trees along the lower River Murray, Australia, have suffered severe dieback as a result of river regulation and drought. As an environmental flow initiative, the height of the lower River Murray in South Australia was raised during a period of increased flow in the spring and summer of 2005–2006. This was performed by increasing the level of the rivers in channel weirs. This increased the level of anabranch creeks on the Chowilla floodplain and through horizontal recharge freshened the adjacent groundwater, providing water to riparian river red gums. Groundwater depth rose concurrently with the rise in creek level, likely recharging the saline floodplain water table with fresh creek water. Multistate Markov modelling showed that along four creeks, most healthy trees responded positively to the rise in water level and remained healthy 1 year after the surcharge. Healthy trees were three times more likely to respond than stressed trees and thirty times more likely to respond than defoliated trees. Stressed trees were ten times more likely to respond than defoliated trees. Forty eight percent of trees that had no leaves at the start of the study responded to the surcharge by producing new growth. This study demonstrates how existing regulatory infrastructure can be used to manipulate water levels and that the hydrological connection between surface water and groundwater can be used to provide water to riparian trees. Copyright © 2013 John Wiley & Sons, Ltd.

Lowland rivers impounded by weirs are often operated to provide stable water levels. In the lower River Murray, stable water levels promote algal biofilms dominated by stalked diatoms, filamentous green algae and Cyanobacteria. In summer 2005–2006, the Lock 5 weir pool was surcharged for environmental benefit. Algal biofilms grown on artificial substrates were compared to the following year when the water level remained stable. On both occasions, substrates were fixed at 300-mm depth in the river channel and a connected wetland. During the surcharge, additional floating substrates were deployed to control for the change in water level. The algal communities that developed during both years were dominated by diatoms. A greater diversity in the biofilm community was evident during the 4-month surcharge when compared with the following year. This was due to a much greater change in algal biofilm community composition over the 4 months of the surcharge, compared with biofilms grown during a period of stable water level, when the community changed little after 1 month. The lack of difference between fixed and floating substrates suggests that the change in water level was not responsible for the difference between the surcharge and stable level biofilms. Possible reasons for the difference between years include light, nutrients and water temperature. Although the effect of the surcharge could not be definitively defined, these results provide some evidence that weir pool surcharge may be used to improve algal biofilm diversity when compared with the current stable water level regime. Copyright © 2011 John Wiley & Sons, Ltd.

Summary For decades the floodplain forests of the River Murray have endured the effects of prolonged water stress. This has resulted in significant crown dieback and loss of condition. The Living Murray (TLM) initiative aims to restore the ecological health of six Icon Sites along the River. The two eucalypts River Red Gum (Eucalyptus camaldulensis) and Black Box (Eucalyptus largiflorens) that dominate the forests at five of the six Icon Sites are undergoing widespread decline. To enable effective management and restoration of these forests, we developed a standardised tree condition assessment method. Named the TLM tree condition assessment method, it utilises visual assessment of a range of tree crown variables (extent and density of the foliage in the crown, epicormic growth, new tip growth, reproductive activity, leaf die-off, mistletoe infestation) and measurements of bark condition, diameter at breast height and dominance class. This article describes the TLM tree condition assessment method and assesses it for consistency between multiple observer teams after limited training. The level of observer agreement between six teams each comprised of two observers was assessed for seven of the ten variables. Intra-class correlation was used to compare scores of 30 River Red Gum trees assessed on Gunbower Island on the River Murray. The level of agreement for all variables was statistically significant with six of seven variables having correlation coefficients over R = 0.5. The TLM tree condition assessment method was found to provide accurate estimates of a range of tree variables that can be used to determine tree condition. The TLM tree condition assessment method provides a valuable monitoring tool that can be used to assess management interventions, such as management flooding and silvicultural thinning.

The delivery of environmental flows to riverine floodplains is often constrained by water scarcity and infrastructure. This means that areas of floodplain are unable to receive environmental water through mechanisms like dam release, weir pool surcharge and artificial flooding of low lying areas. This study trials aquifer injection as a method of providing environmental flows to areas of stressed river red gum (Eucalyptus camaldulensis) on the floodplain of the lower River Murray. The objective was to inject fresh river water at the top of the saline alluvial aquifer to reduce root zone salinity and improve the condition of E. camaldulensis. Localized radial freshening of ∼10 m was observed at each of the five injection wells when 4·9 Ml (megalitres) of river water was injected into the aquifer over 45 days. Injection was abandoned after 45 days due to aquifer and well clogging, and increases in groundwater head, which caused four of the five wells to breach the confining clay layer. The trial resulted in localized and short-lived freshening of the groundwater, which reduced salinity in the associated capillary fringe. This did not result in an improvement in the tree condition as they lay beyond the lateral extent of the freshening and were unable to access the water. Solutions to technical issues such as aquifer clogging and well breaching, as well as a need to increase the lateral extent of freshening, are required before shallow aquifer injection can be recommended as a method of delivering environmental flows. Copyright © 2009 John Wiley & Sons, Ltd.

Many of South Australia's remnant temperate native grasslands are degraded by introduced livestock grazing. As a conservation measure, grazing was excluded from three 50 × 50 m exclosures in grazed native grassland. After 4 years, grazing removal had a noticeable effect on the grassland structure, increasing basal vegetation cover. Grazing removal had no significant effect on either native or exotic species richness, rather differences in richness changed as a result of interannual differences, such as the amount of rainfall that fell in the growing season. The percent cover of the native tussock grass Austrostipa spp. and the introduced annual grass Avena barbata, whilst fluctuating from year to year, both increased following the removal of grazing. Multivariate analyses showed that whilst only interannual differences affected community taxon richness, changes in structure were affected by the interaction between grazing treatment and year. Excluding livestock from a degraded grassland resulted in limited recovery and restoration of these endangered plant associations will require active rehabilitation efforts.