Trees for Special Purposes: Wastewaters and Saline Land
Evolution of the Research
Hugh Stewart (bio)
In the 1970s in Victoria about 60% of Municipal Sewerage Authorities used secondary treated wastewater to irrigate pastures, sometimes grazed by livestock. At the start of the decade, extensive trials were carried out in south-east Melbourne testing the suitability of treated wastewater for irrigating agricultural and horticultural crops. In 1973 the Forests Commission Victoria started trials to test the irrigation of planted trees with wastewater. This work followed studies in the USA, pioneered by the Pennsylvania State University in the early 1960s, that indicated the benefits of using natural forests for the renovation of wastewater. The trials in Victoria were ramped up in 1977 with support from the Reclaimed Water Committee of the Ministry of Water Resources and Water Supply. (A member of the committee, John Mann, Director of Water Resources, told the Senate Committee on Natural Resources in 1977 that Victoria hoped to have the technical expertise to re-use almost all of the State’s wastewater by the end of the century.) Other field trials were conducted by the Melbourne Metropolitan Board of Works (MMBW, at Carrum and at Werribee), and by the CSIRO.
Screening for Species
As a precursor, the Forests Commission Research Branch had carried out trials in 1972 and 1973 in cooperation with the Department of Agriculture, at the Animal and Irrigated Pastures Research Institute at Kyabram, to test the feasibility of growing short rotation tree plantations under irrigation (agricultural water), to produce wood fibre. This work was triggered, in part, by the 1973 oil crisis that saw the international oil price skyrocket, leading countries to think about sources of fibre for production of biofuel. Forty-one species were evaluated with preference for species that could provide wood products for local and regional markets. Species such as Flooded Gum ( Eucalyptus grandis) and Sydney Blue Gum ( E. saligna) showed early promise.
In 1972, consultants to the Swan Hill Sewerage Authority sought advice from the Forests Commission on the potential for irrigating tree plantations with municipal wastewater. Other enquiries followed. Subsequently, trials were established at municipal wastewater treatment sites by the Forests Commission at Swan Hill (1973, 1974), Cobram (1975), and Mildura (1976). Early results from these trials were used to select species for further testing at Mildura (1977, 2.4 ha), Horsham (1977, 1.2 ha), Dutson Downs (1978, 2.0 ha), and Robinvale (1979, 1.6 ha). 1973 was one of the wettest years on record and travel and establishment was made difficult by widespread flooding across the Goulburn Valley. A team of Aboriginal workers assisted with the planting at Robinvale.
A new trial followed in 1980 at Wodonga (1.1 ha) in collaboration with the Albury Wodonga Development Corporation – this was the most sophisticated and intensively monitored of all the trials, with six tree species plus bare earth and pasture controls in a fully randomized, replicated layout. Measurements at age 14 years at the Wodonga trial showed mean annual increments (MAI) of 41 and 31 cubic metres per hectare per annum for Flooded Gum and Sydney Blue Gum, respectively. One Flooded Gum was measured at 15.5 metres tall at age 3.5 years.
The largest research project irrigated with wastewater was established at Werribee in 1990, supported by the National Afforestation Program ($70,000 research grant) and done in cooperation with the MMBW. At the time the Werribee farm of 11,000 hectares treated about 500 million litres of sewage daily (approx. 55% of Melbourne’s output). After passing through lagoons, grass filtration (in winter) or pasture irrigation (in summer), the treated sewage was discharged into Port Phillip Bay. The MMBW had set up species screening trials at Werribee in 1973. Forward nearly two decades, their thinking was that trees could be a viable option to use more sewage than the irrigated pastures or, alternatively, trees could be planted at the lower end of the flood irrigation bays to absorb excess runoff rather than re-treating the excess by pumping it to lagoons. The idea was promoted by the National Party’s spokesman on Conservation, Forests and Lands, Mr Evans, in a newspaper report (“The Age”, 29 August 1988), that referenced results from the Wodonga trial and observed that livestock sales from the Werribee farm (one of the biggest livestock enterprises in Victoria) had been suspended following the detection of excessive levels of toxic polychlorinated biphenyls (PCBs) in seven bulls. In July 1990, 16 hectares of Eucalypts were established as a commercial demonstration of hardwood production from plantations irrigated with raw sewage and primary treated sewage. Planted were Flooded Gum, Sydney Blue Gum, Blue Gum ( E. globulus), and Red Gum ( E. camaldulensis), at densities ranging from 1,333 to 4,444 stems per hectare, on an alluvial soil site and a basalt soil site. A 20-year management agreement was struck between the MMBW and the Department of Conservation and Environment. Things started well with good establishment. However, a change in management and strategy at MMBW together with upheavals in departmental research arrangements sealed the fate of the trial – the agreement lapsed, and the alluvial site was converted to other uses. The Werribee complex has evolved into a modern tertiary treatment facility producing recycled water for industrial and agricultural use. Nevertheless, the basalt site survives, and a block of trees (9 ha) can be seen today from the Princes Highway, about 2 km south along Point Wilson Road. (Current management has reassured - July 2021 - that there are no plans to convert the plantation.)
In 1993, the Centre for Forest Tree Technology (1993-1998) set up a short rotation coppice trial irrigated with wastewater at the Shepparton Wastewater Treatment Complex. At age four years, growth rates in the trial were amongst the highest reported in Australia, with the MAI of Blue Gum up to 36 cubic metres per hectare per annum (Duncan et al. 1998).
Another trial was planted at Merbein (1977, 1.6 ha) in cooperation with Mildara Wines and irrigated with winery wastewater. The Kyabram trials using agricultural irrigation water were extended in 1976 with a planting density experiment and a test of 31 provenances of four Eucalypt species – Flooded Gum, Sydney Blue Gum, Blue Gum, and Red Gum. This trial proved again the superior performance of the Lake Albacutya provenance of Red Gum.
Site preparation at most sites included cultivation and formation of mounds, and pre-planting weed control. Most trials were setup as replicated, randomized designs, and planted at a density of 2,222 trees per hectare. Irrigation was either applied by flooding, via sprinklers or via micro-sprays. More than 60 species were tested from a wide range of genera – the best performers were Eucalypts, Casuarinas, and Poplars.
CSIRO (Robin Cromer) started trials in the mid-1970s irrigating Radiata Pine with wastewater at Dutson Downs, south Gippsland. The Dutson Downs farm of 10,000 hectares had about 1,000 hectares of irrigated pastures for disposal of the wastewater. In 1977, the Latrobe Valley Water and Sewerage Board, CSIRO, APM Forests and the Forests Commission started a three-year study in which 15-year-old Radiata Pine was fertilised and irrigated with wastewater. Irrigation doubled plantation growth over the treatment period. (Stewart 1985)
Baker, T., Duncan, M. and Stackpole, D. (2005). Growth and silvicultural management of irrigated plantations. In Nambiar, S. and Ferguson, I. (Eds), New Forests: Wood Production and Environmental Services. CSIRO Publishing, pp. 113-134.
Baldwin, P.J. and Stewart, H.T.L. (1987). Distribution, length and weight of roots in young plantations of Eucalyptus grandis W. Hill ex Maiden irrigated with recycled water. Plant Soil 97: 243-252.
Duncan, M., Baker, T. and Wall, G. 1998. Wastewater irrigated tree plantations: productivity and sustainability. Pap. pres. at 61st Annual Water Industry Engineers and Operators’ Conference, held 2-3 September, 1988, Shepparton, Victoria.
Edgar, J.G. and Stewart, H.T.L. (1978). Trees for effluent disposal in northern Victoria. Wat. Talk 41: 11-15.
Flinn, D.W., Stewart, H.T.L. and O'Shaughnessy P.J. (1979). Screening of weedicides for overspraying Eucalyptus, Pinus and Casuarina on clay soils irrigated with treated effluent. Aust. For. 42: 215-225.
Heuperman, A.F., Stewart, H.T.L. and Wildes, R.A. (1984). The effect of eucalypts on water tables in an irrigation area of northern Victoria. Wat. Talk 52: 4-8.
Hopmans, P., Stewart, H.T.L., Flinn, D.W. and Hillman, T.J. (1990). Growth, biomass production and nutrient accumulation by seven tree species irrigated with municipal effluent at Wodonga, Australia. For. Ecol. Manage. 30: 203-211.
McKimm, R.J. (1984). Fence posts from young trees irrigated with sewage effluent. Aust. For. 47: 172-78.
Stewart, H.T.L., Flinn, D.W., Baldwin, P.J. and James, J.M. (1981). Diagnosis and correction of iron deficiency in planted eucalypts in north-west Victoria. Aust. For. Res. 11: 185-190.
Stewart, H.T.L. and Flinn, D.W. (1984). Establishment and early growth of trees irrigated with wastewater at four sites in Victoria, Australia. For. Ecol. Manage. 8: 243-256.
Stewart, H.T.L. (1985). The effects of fertilisation and wastewater irrigation on the biomass and nutrient content of Pinus radiata D. Don. MSc thesis. The University of Melbourne: Melbourne, Victoria, 169 pp.
Stewart, H.T.L. and Salmon, G.R. (1986). Irrigation of tree plantations with recycled water. 2. Some economic analyses. Aust. For. 49: 89-96.
Stewart, H.T.L., Hopmans, P., Flinn, D.W. and Hillman, T.J. (1990). Nutrient accumulation in trees and soil following irrigation with municipal effluent in Australia. Environ. Pollution 63: 155-177.
Benyon, R., Hutchinson, D., Stewart, H.T.L. and O'Shaughnessy, P.J. (1991). Establishment of eucalypt plantations irrigated with sewage at Werribee, Victoria. In 'Productivity in Perspective' (ed. P.J. Ryan), pp. 107-108. Proc. Third Aust. For. Soils and Nutrition Conf., Melbourne, 7–11 October 1991. Forests Commission: Sydney, New South Wales.
Hopmans, P., Stewart, H.T.L., Flinn, D.W. and Hillman, T.J. (1987). Growth, biomass production and nutrient uptake by seven tree species irrigated with municipal effluent at Wodonga, Australia. Pap. pres. at IUFRO meeting 'Management of Water and Nutrient Relations to Increase Forest Growth', held 19–22 October, 1987, Canberra, ACT.
Morris, J., Mann, L. and Collopy, J. (1998). Transpiration and canopy conductance in a eucalypt plantation using shallow saline groundwater. Tree Physiology 18: 547-555.
Stewart, H.T.L., Craig, F.G. and Dexter, B.D. (1979). Effluent treatment and reclamation in Victoria using tree plantations. Proc. Symposium on Wastewater Renovation Using Trees, April 1979, Albury, New South Wales. Murray Valley League: Albury, New South Wales, pp. 14-18.
Stewart, H.T.L. and Boardman, R. (1991). The potential for irrigated plantation development in Australia. In 'Integrating Forestry and Farming', Appendix B, pp. 95-140, a report of the National Plantations Advisory Committee. Department of Primary Industries and Energy: Canberra, Australia.
Stewart, H.T.L., Flinn, D.W. and Baldwin, P.J. (1982). Irrigation of tree plantations with wastewater in Victoria. 1. Site characteristics, establishment and maintenance procedures, and tree survival and growth between 1977 and 1981. Res. Branch Rep. No. 207. Forests Commission: Melbourne, Victoria, 59 pp.
Stewart, H.T.L. (1984). Field trials of trees irrigated with wastewater in Victoria. Proc. Seminar on Off-river Disposal of Treated Sewage Effluent, 11 November 1984, Wodonga, Victoria. River Murray Commission: Canberra, ACT, pp. 44-45.
Stewart, H.T.L., Allender, E., Sandell, P. and Kube, P. (1986). Irrigation of tree plantations with recycled water. 1. Research developments and case studies. Aust. For. 49: 81-88.
Stewart, H.T.L., Hopmans, P., Flinn, D.W., Hillman, T.J. and Collopy, J. (1988). Evaluation of irrigated tree crops for land disposal of municipal effluent at Wodonga. Tech. Rep. No. 7. Albury-Wodonga Development Corporation: Wodonga, Victoria, 28 pp.
Stewart, H.T.L. (1988). A review of irrigated forestry with Australian native species. Proc. The International Forestry Conference for the Australian Bi-centenary, 25 April to 1 May 1988, Albury, New South Wales. Australian Forest Development Institute: Canberra, ACT, Vol. II of V, 18 pp.
Stewart, H.T.L. (1990). Guidelines for establishment of eucalypt woodlots on irrigated land. Proc. Woodlots Workshop, 10-11 April 1990, Mildura, Victoria. Dept. Agriculture and Rural Affairs: Mildura, Victoria, pp 38-42.