|Due to its ability to thrive under water logged and flooded conditions,
vetiver is currently being used in 2 wetland research projects in Queensland:
1- Pesticide Run-off Control Using Artificial Wetlands
Background and importance
A study into the use of wetland plants as bio-filters for pesticide
contaminated run-off water is to be conducted as part of the BRIA (Burdekin River
Irrigation Area) Wetlands Project. Pesticides applied to farmlands are essential to
control weeds in crops, unfortunately the externalities that are involved in such
practices dictates that the effects are wider reaching. For example, atrazine is
recommended to be applied at a rate of 4-6L/ha as a pre-emergence weedicide to control
broadleaf weeds. Consequently, the expected atrazine concentration rate in run-off water
is 200 ug/L (Rice et al., 1997). This is considerable high as atrazine inhibits algal
growth and photosynthesis at concentrations less than 1.0 ug/L (Spawn and Siefried, 1997).
Pesticide residues from weed control will primarily accumulate in
sediments but other examples of adversely affected accumulators are algae, zooplankton and
fish. The need for wetlands to control the amount of pesticides in run-off is essential
for all aquatic life. Wetlands have demonstrated to be effective in reducing BOD,
suspended solids, coliforms, nitrogen and sometimes phosphorus in controlled flow events
(Raisin and Mitchell, 1996). Therefore it is not unreasonable to expect that a wetlands
system will reduce pesticide concentrations in run-off from farmlands as well. The
concentration of pesticides found in water bodies that enter wetlands depends on the
amount of removal by volatilisation, photo-decomposition, microbial degradation and uptake
by aquatic organisms. The ability to reduce the amount of pesticide in waterways by plant
removal is of particular importance in this study.
The two pesticides under investigation are atrazine and diuron (both active
ingredients) due to their use in sugar cane crops in not only the BRIA but also throughout
Queensland and NSW. In particular, atrazine has been detected in the water and sediments
of the BRIA Wetlands Project site at Clare Agricultural College, where artificial wetlands
have been established since 1995.
Diuron and atrazine are formulated to control grasses and broadleaf
weeds in pre-emergent plant and ratoon cane crops. Diuron is noted as being more
persistent than atrazine in field situations (Hamilton, 1996) creating concerns for more
than one run-off event containing detectable levels of diuron. Atrazine has a higher
leaching potential than diuron therefore mobility within the soil profile is at a slower
rate. This leads to surface layers containing unevenly larger amounts of diuron
susceptible to run-off movement.
Objectives and Methods
The purpose for this study is to investigate the effects of pesticide addition
to the growth of 4 emerged macrophytes: Phragmites australis (common reed), Typha
domingensis (cumbungi), Vetiveria zizanioides L. (Nash) and Schoenopliectus
validus (river clubrush). This study centres on plant growth parameters, for example
leaf area index and water usage, as indicators to the viability of certain plant species
in tropical wetlands. Further study into the quantification of pesticide uptake into the
shoots and roots of Vetiver will also be undertaken.
The factorial pot trial will simulate wetland conditions, as plants will be growing in
pots surrounded by a constant free water level (1.5cm). Each pot will be subjected to a
single dose of atrazine or diuron at a zero, low (20 ug/L), medium (200 ug/L) or a high
(2000 ug/L) rate. The pesticide will be applied to each of the four species, once adequate
establishment of plants has occurred (approximately 6 weeks). Comparison within each
species to pesticide rate responses is made possible using 3 repetitions.
During the course of the experiment it is hoped that plant growth will respond
sufficiently under various rates of pesticide This will allow for future research into
strategically placing these plant species into wetlands to reduce the effects of pesticide
contaminated run-off. Vetiver may not only be suitable for bank stabilisation but also
acting as a pesticide filter in the deeper margins of the wetlands.
Result to date
In a preliminary trial conducted to select suitable species for this trial, it was
found that vetiver grew at least 4 times faster than other species in terms of leaf area
and dry mater. The same growth rate is being recorded for the current trial where all
species are planted in pots where the water level is kept constantly at 20mm above ground
level. This is a very impressive growth and if found resistant to weedicide in runoff
water as well vetiver would be an ideal plant for wetland application.
2- Atrazine Degradation in Wetland Systems.
In conjunction with the above study an additional experiment is being conducted
into atrazine degradation in wetland systems. This will centre on the use of 3 wetland
plants: Iris, Shoenoplectus and Vetiver, to determine the rate of atrazine degradation by
these species as apposed to a non-plant system. Many studies have shown the ability of the
wetlands to remove herbicides such as atrazine (Kadlec, 1994), but very little research
has been done to investigate the specific role of wetland species in the degradation
process. Redox potential will also be a factor in this experiment as under anaerobic
conditions, found in wetland soil environment, the rate of atrazine degradation will be
slowed compared to an aerobic system.
- Hamilton, D. and Haydon G. (1996). Pesticides and Fertilisers in the Queensland Sugar
Industry Estimates of Usage and Likely Environmental Fate. Department of
Primary Industries, Brisbane.
- Kadlec, R.H. and Hey, D.L. (1994). Constructed Wetlands for River Water Quality
Improvement. Water Science and Technology, 29(4): 159-168.
- Kruger, E.L., Anhalt, J.C., Anderson, T.A. and Coats, J.R. (1997). Phytoremediation of
Herbicide-Contaminated Surface Water with Aquatic Plants. In: Phytoremediation of Soil
and Water Contaminants Symposium. American Chemical Society, Washington, DC.
- Raisin, G.W. and Mitchell, D.S. (1996). Diffuse Pollution and the Use of Wetlands for
Ameliorating Water Quality in the Australian Context. In: Downstream Effects of Land
Use. (Eds. Hunter, H.M., Eyles, A.F., Rayment, G. E.). Department of Natural
- Spawn, R.L. and Siefried, B.D. (1997). Effects of Alachlor on an algal community from a
midwestern agricultural stream. Environmental Toxicology and Chemistry, 16:
- Sluggett, R. (1997). Chemical Weed Control in Sugarcane. Bureau of Sugar
Experiment Stations, Brisbane.