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Papers by Thabo Thayalakumaran

Environmental Modelling & Software, 2016

Hydrological Processes, 2015

ACS Symposium Series, 2005

Plant and Soil, 2003

EDTA-enhanced phytoremediation of copper contaminated soil was evaluated. Up to 740 µg g −1 of Na... more EDTA-enhanced phytoremediation of copper contaminated soil was evaluated. Up to 740 µg g −1 of Na 2 H 2 EDTA in solution was added to repacked soil columns, and intact cores of a sandy loam of volcanic origin, that was growing Agrostis tenuis. The soil contained up to 400 µg g −1 of copper due to a history of fungicide spraying. EDTA application increased the herbage copper concentration of the grass growing in repacked soil from 30 to 300 µg g −1 , but the same application to an intact core only brought about an increase from 10 to 60 µg g −1 . More copper accumulated in the herbage when the EDTA was applied in numerous small doses than in just one or two larger amounts. Calculation of the concentration of copper in the water taken up by the grass revealed this to be two orders of magnitude lower than that in the soil solution. As a result of the EDTA applications, about 100 times more copper was leached than was taken up by the herbage. This means that a strategy for managing leaching losses needs to be part of any plan for EDTA-enhanced phytoremediation.

Developments in Soil Science, 2008

Groundwater, 2014

Elevated dissolved organic carbon (DOC) has been detected in groundwater beneath irrigated sugarc... more Elevated dissolved organic carbon (DOC) has been detected in groundwater beneath irrigated sugarcane on the Burdekin coastal plain of tropical northeast Australia. The maximum value of 82 mg/L is to our knowledge the highest DOC reported for groundwater beneath irrigated cropping systems. More than half of the groundwater sampled in January 2004 (n = 46) exhibited DOC concentrations greater than 30 mg/L. DOC was progressively lower in October 2004 and January 2005, with a total decrease greater than 90% indicating varying load(s) to the aquifer. It was hypothesized that the elevated DOC found in this groundwater system is sourced at or near the soil surface and supplied to the aquifer via vertical recharge following above average rainfall. Possible sources of DOC include organic-rich sugar mill by-products applied as fertilizer and/or sugarcane sap released during harvest. CFC-12 vertical flow rates supported the hypothesis that elevated DOC (>40 mg/L) in the groundwater results from recharge events in which annual precipitation exceeds 1500 mm/year (average = 960 mm/year). Occurrence of elevated DOC concentrations, absence of electron acceptors (O2 and NO3 (-) ) and both Fe(2+) and Mn(2+) greater than 1 mg/L in shallow groundwater suggest that the DOC compounds are chemically labile. The consequence of high concentrations of labile DOC may be positive (e.g., denitrification) or negative (e.g., enhanced metal mobility and biofouling), and highlights the need to account for a wider range of water quality parameters when considering the impacts of land use on the ecology of receiving waters and/or suitability of groundwater for irrigated agriculture.

Australian Journal of Soil Research, 2003

Plants pump large amounts of water, solutes, and organic matter as part of their normal physiolog... more Plants pump large amounts of water, solutes, and organic matter as part of their normal physiological processes. This pumping action can be exploited to improve degraded environments by stabilising, removing, or breaking-down contaminants in the substrates. In addition, soil amendments such as fertilisers and microbes may also be added to enhance the efficacy of the operation. Basic plant physiology sets limits on the capacity of phytoremediation. However, combining this technology with the production of saleable products may render the extra time needed for clean-up relatively unimportant. Phytoremediation is still poorly developed, particularly the phytoextraction of heavy metals. Continual innovation will greatly expand the scope and efficacy of phytoremediation. The greatest potential use for this technology may be in developing countries that have the highest levels of environmental degradation, and scant funds for remediation. Phytoremediation could provide a low-cost and sustainable way to improve local economies. Here a case study is reported on the phytoremediation of a 3.6 ha sawdust pile that was leaching unacceptable amounts of boron (B) into local waterways. High water-use poplars were used to control leaching and potentially remove B from the site via phytoextraction. Selected trees that are coppiced before leaf-fall could be mulched and used to provide 'organic' B on nearby orchards that are deficient in this element. S R 0 2 1 3 1 P h y t o r e m e d i a t i o n B R o b i n s o n e t a l .

Geoderma, 2011

Deep percolation under irrigation is often indirectly estimated from Richards' equation models. A... more Deep percolation under irrigation is often indirectly estimated from Richards' equation models. A Richards' equation model requires soil hydraulic and crop specific parameters that may be estimated from soil moisture data at different soil depths. This paper examined whether parameters of a Richards' equation model estimated from soil moisture data can be used to adequately predict deep percolation under surface irrigation. For this purpose, we used data from a lysimeter experiment on a loam soil under surface irrigation. Monte Carlo simulations of a 1-D Richards' equation model were generated using a set of model parameters sampled from a feasible range of parameter values. For each Monte Carlo simulation (a set of model parameters), adequacy of model predictions was evaluated against lysimeter data on soil moisture and independently measured deep percolation. Adequacy was assessed by fitting a linear regression of observed data on simulated values and testing for the null hypotheses of unit slope and zero intercept. Using this approach, we did not succeed in predicting simultaneously soil moisture and deep percolation. This lack of simultaneous fit likely indicates an inadequate model structure as data uncertainty was of secondary importance in our lysimeter study. For surface irrigation, preferential infiltration can probably not be avoided even when soil cracking is not apparent. Under such conditions, the use of a simple Richards' equation model appears inadequate. A conceptual model that was published earlier is considered to be more appropriate as it adequately predicted deep percolation, effectively accounts for preferential infiltration during surface irrigation and required less data than the Richards' equation model.

Agricultural Water Management, 2007

ABSTRACT The long-term sustainability of irrigated agriculture depends on protecting land and wat... more ABSTRACT The long-term sustainability of irrigated agriculture depends on protecting land and water resources from salinity. Generally, a favourable salt balance (mass out ≥ mass in) is considered necessary for sustainable irrigated agriculture. This concept has been used in irrigated agricultural systems to satisfy varying objectives. In this paper we discuss the application of the salt balance concept at various spatial scales including root-zone, farm, irrigation-region and catchment scales. The relationship between the spatial scales, the governing processes and the time to reach salt equilibrium is discussed. Recognised management options for achieving a favourable salt balance are questioned with regard to (a) the uncertainties in salt balance estimation caused by a mismatch of surface and sub-surface hydrological boundaries, (b) the large subsoil salt store, (c) impacts on downstream water quality and (d) the implications of achieving a favourable salt balance. It is argued that aiming for a favourable salt balance is critical and achievable at a root-zone scale for maintaining production. For scales larger than the root-zone, managing for a favourable salt balance is often not practical nor necessarily beneficial. Management of the water balance is more important at the larger scale to prevent the formation of a shallow watertable and the remobilising of salt stored in the subsoil. The management of the water balance is likely to be more effective in managing productivity and the off-site impacts of irrigation than managing a farm or regional salt balance.

Agricultural Water Management, 2008

... PDF (1930 K); Export citation; E-mail article; Highlight keywords on: ... These concentration... more ... PDF (1930 K); Export citation; E-mail article; Highlight keywords on: ... These concentrations are compared with atmospheric CFC concentrations curves to obtain an apparent CFC-age ([Cook and Solomon, 1997] and [Busenberg and Plummer, 1992]). 4. Results and discussion. 4.1 ...

Australian Journal of Soil Research, 2003

The EDTA-enhanced remediation of copper contaminated sandy-loam soil of volcanic origin was inves... more The EDTA-enhanced remediation of copper contaminated sandy-loam soil of volcanic origin was investigated. The soil, from an orchard, was contaminated with about 250 mg/kg of copper due to the extensive use of copper sprays. Copper-contaminated soil was packed into 100-mm-long columns, and solutions of Na 2 H 2 EDTA with CaCl 2 , raised to a pH of 6.2, were applied at a flow rate of 24 mm/h. Application of an excess of 0.01 M EDTA leached about half the acid-extractable copper from the soil; most of it coming out in the first 3 liquid-filled pore volumes (PV). Also a 0.5 PV pulse of 0.001 M EDTA was applied to similar soil columns and then either leached immediately with 0.005 M CaCl 2 , or left for periods of up to 1 month before leaching. With immediate leaching, 70% of the EDTA applied was complexed with copper in the leachate, but after a month's delay only 24% was complexed with copper in the leachate, the rest being complexed with iron. There was no evidence of EDTA retardation or adsorption.

Environmental Modelling & Software, 2016

Hydrological Processes, 2015

ACS Symposium Series, 2005

Plant and Soil, 2003

EDTA-enhanced phytoremediation of copper contaminated soil was evaluated. Up to 740 µg g −1 of Na... more EDTA-enhanced phytoremediation of copper contaminated soil was evaluated. Up to 740 µg g −1 of Na 2 H 2 EDTA in solution was added to repacked soil columns, and intact cores of a sandy loam of volcanic origin, that was growing Agrostis tenuis. The soil contained up to 400 µg g −1 of copper due to a history of fungicide spraying. EDTA application increased the herbage copper concentration of the grass growing in repacked soil from 30 to 300 µg g −1 , but the same application to an intact core only brought about an increase from 10 to 60 µg g −1 . More copper accumulated in the herbage when the EDTA was applied in numerous small doses than in just one or two larger amounts. Calculation of the concentration of copper in the water taken up by the grass revealed this to be two orders of magnitude lower than that in the soil solution. As a result of the EDTA applications, about 100 times more copper was leached than was taken up by the herbage. This means that a strategy for managing leaching losses needs to be part of any plan for EDTA-enhanced phytoremediation.

Developments in Soil Science, 2008

Groundwater, 2014

Elevated dissolved organic carbon (DOC) has been detected in groundwater beneath irrigated sugarc... more Elevated dissolved organic carbon (DOC) has been detected in groundwater beneath irrigated sugarcane on the Burdekin coastal plain of tropical northeast Australia. The maximum value of 82 mg/L is to our knowledge the highest DOC reported for groundwater beneath irrigated cropping systems. More than half of the groundwater sampled in January 2004 (n = 46) exhibited DOC concentrations greater than 30 mg/L. DOC was progressively lower in October 2004 and January 2005, with a total decrease greater than 90% indicating varying load(s) to the aquifer. It was hypothesized that the elevated DOC found in this groundwater system is sourced at or near the soil surface and supplied to the aquifer via vertical recharge following above average rainfall. Possible sources of DOC include organic-rich sugar mill by-products applied as fertilizer and/or sugarcane sap released during harvest. CFC-12 vertical flow rates supported the hypothesis that elevated DOC (>40 mg/L) in the groundwater results from recharge events in which annual precipitation exceeds 1500 mm/year (average = 960 mm/year). Occurrence of elevated DOC concentrations, absence of electron acceptors (O2 and NO3 (-) ) and both Fe(2+) and Mn(2+) greater than 1 mg/L in shallow groundwater suggest that the DOC compounds are chemically labile. The consequence of high concentrations of labile DOC may be positive (e.g., denitrification) or negative (e.g., enhanced metal mobility and biofouling), and highlights the need to account for a wider range of water quality parameters when considering the impacts of land use on the ecology of receiving waters and/or suitability of groundwater for irrigated agriculture.

Australian Journal of Soil Research, 2003

Plants pump large amounts of water, solutes, and organic matter as part of their normal physiolog... more Plants pump large amounts of water, solutes, and organic matter as part of their normal physiological processes. This pumping action can be exploited to improve degraded environments by stabilising, removing, or breaking-down contaminants in the substrates. In addition, soil amendments such as fertilisers and microbes may also be added to enhance the efficacy of the operation. Basic plant physiology sets limits on the capacity of phytoremediation. However, combining this technology with the production of saleable products may render the extra time needed for clean-up relatively unimportant. Phytoremediation is still poorly developed, particularly the phytoextraction of heavy metals. Continual innovation will greatly expand the scope and efficacy of phytoremediation. The greatest potential use for this technology may be in developing countries that have the highest levels of environmental degradation, and scant funds for remediation. Phytoremediation could provide a low-cost and sustainable way to improve local economies. Here a case study is reported on the phytoremediation of a 3.6 ha sawdust pile that was leaching unacceptable amounts of boron (B) into local waterways. High water-use poplars were used to control leaching and potentially remove B from the site via phytoextraction. Selected trees that are coppiced before leaf-fall could be mulched and used to provide 'organic' B on nearby orchards that are deficient in this element. S R 0 2 1 3 1 P h y t o r e m e d i a t i o n B R o b i n s o n e t a l .

Geoderma, 2011

Deep percolation under irrigation is often indirectly estimated from Richards' equation models. A... more Deep percolation under irrigation is often indirectly estimated from Richards' equation models. A Richards' equation model requires soil hydraulic and crop specific parameters that may be estimated from soil moisture data at different soil depths. This paper examined whether parameters of a Richards' equation model estimated from soil moisture data can be used to adequately predict deep percolation under surface irrigation. For this purpose, we used data from a lysimeter experiment on a loam soil under surface irrigation. Monte Carlo simulations of a 1-D Richards' equation model were generated using a set of model parameters sampled from a feasible range of parameter values. For each Monte Carlo simulation (a set of model parameters), adequacy of model predictions was evaluated against lysimeter data on soil moisture and independently measured deep percolation. Adequacy was assessed by fitting a linear regression of observed data on simulated values and testing for the null hypotheses of unit slope and zero intercept. Using this approach, we did not succeed in predicting simultaneously soil moisture and deep percolation. This lack of simultaneous fit likely indicates an inadequate model structure as data uncertainty was of secondary importance in our lysimeter study. For surface irrigation, preferential infiltration can probably not be avoided even when soil cracking is not apparent. Under such conditions, the use of a simple Richards' equation model appears inadequate. A conceptual model that was published earlier is considered to be more appropriate as it adequately predicted deep percolation, effectively accounts for preferential infiltration during surface irrigation and required less data than the Richards' equation model.

Agricultural Water Management, 2007

ABSTRACT The long-term sustainability of irrigated agriculture depends on protecting land and wat... more ABSTRACT The long-term sustainability of irrigated agriculture depends on protecting land and water resources from salinity. Generally, a favourable salt balance (mass out ≥ mass in) is considered necessary for sustainable irrigated agriculture. This concept has been used in irrigated agricultural systems to satisfy varying objectives. In this paper we discuss the application of the salt balance concept at various spatial scales including root-zone, farm, irrigation-region and catchment scales. The relationship between the spatial scales, the governing processes and the time to reach salt equilibrium is discussed. Recognised management options for achieving a favourable salt balance are questioned with regard to (a) the uncertainties in salt balance estimation caused by a mismatch of surface and sub-surface hydrological boundaries, (b) the large subsoil salt store, (c) impacts on downstream water quality and (d) the implications of achieving a favourable salt balance. It is argued that aiming for a favourable salt balance is critical and achievable at a root-zone scale for maintaining production. For scales larger than the root-zone, managing for a favourable salt balance is often not practical nor necessarily beneficial. Management of the water balance is more important at the larger scale to prevent the formation of a shallow watertable and the remobilising of salt stored in the subsoil. The management of the water balance is likely to be more effective in managing productivity and the off-site impacts of irrigation than managing a farm or regional salt balance.

Agricultural Water Management, 2008

... PDF (1930 K); Export citation; E-mail article; Highlight keywords on: ... These concentration... more ... PDF (1930 K); Export citation; E-mail article; Highlight keywords on: ... These concentrations are compared with atmospheric CFC concentrations curves to obtain an apparent CFC-age ([Cook and Solomon, 1997] and [Busenberg and Plummer, 1992]). 4. Results and discussion. 4.1 ...

Australian Journal of Soil Research, 2003

The EDTA-enhanced remediation of copper contaminated sandy-loam soil of volcanic origin was inves... more The EDTA-enhanced remediation of copper contaminated sandy-loam soil of volcanic origin was investigated. The soil, from an orchard, was contaminated with about 250 mg/kg of copper due to the extensive use of copper sprays. Copper-contaminated soil was packed into 100-mm-long columns, and solutions of Na 2 H 2 EDTA with CaCl 2 , raised to a pH of 6.2, were applied at a flow rate of 24 mm/h. Application of an excess of 0.01 M EDTA leached about half the acid-extractable copper from the soil; most of it coming out in the first 3 liquid-filled pore volumes (PV). Also a 0.5 PV pulse of 0.001 M EDTA was applied to similar soil columns and then either leached immediately with 0.005 M CaCl 2 , or left for periods of up to 1 month before leaching. With immediate leaching, 70% of the EDTA applied was complexed with copper in the leachate, but after a month's delay only 24% was complexed with copper in the leachate, the rest being complexed with iron. There was no evidence of EDTA retardation or adsorption.