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Modelling phosphorus transport in soil and groundwater with two consecutive reactions

Notodarmojo, S. (1992) Modelling phosphorus transport in soil and groundwater with two consecutive reactions. PhD thesis, Murdoch University.

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A one-dimensional model of phosphorus transport in soils and groundwater applicable for steady state or transient unsaturated waterflow conditions has been developed. Convective transport, hydrodynamic dispersion and time-dependent phosphorus sorption are accounted for in the model formulation. Time-dependent sorption of phosphorus is considered to follow the empirical model of Barrow and Shaw (1979), which can be described by S = k.Cntm. The assumed sorption model allows model parameters to be obtained by independent batch and column experiments.

Numerical techniques were used to solve the solute transport equations. For the steady state model, a correction to the numerical dispersion to improve the numerical solution is presented. Analytical solutions for a simplified case are also presented and used to test the numerical solution. For the transient model, numerical solutions of water and solute transport are tested against published data. Parameter sensitivity analysis conducted for the steady state model shows that influent concentration and the parameter k strongly effect the initial breakthrough time for the solute.

The above solute transport equations which assume that the contact time between the entire soil in the column and solute starts when the solute is introduced into the column are also corrected for, by initiating the contact time for every segment in the column when the soil solution is greater than zero. Numerical solutions of the solute transport equations with corrected and non-corrected contact time are also compared. For the range of laboratory soil column experiments, it was found that the difference is small.

Batch experiments and miscible displacement experiments using soil column techniques and sectioned columns were conducted to verify the applicability of the model. For steady state condition, P transport under saturated and unsaturated waterflow conditions were examined. Miscible displacement experiments using soils which had been previously waterlogged for 30 days to see the effect of waterlogging were also conducted. For transient waterflow condition, solute and water transport during infiltration was investigated. Gavin and Joel sandy soils from Bassendean soil system (Western Australia) and 3 different volcanic soils from Bandung (Indonesia) were used.

Experimental results show that Barrow and Shaw's sorption model can be used to describe phosphorus sorption in batch experiments. The transport model formulated in Australian sandy soils, and one of the Indonesian soils. The steady state model, however, fails to simulate the phosphorus movement in other Indonesian soils. In most cases, experimental breakthrough lags behind theoretical curve. The failure of the model is due to different conditions between continuous miscible displacement experiment in the soil columns and batch baking experiments. It is recommended that a procedure to carry out batch experiments which minimizes the effect of the presence of antecedent anions and soil-to-solution ration be developed.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: A digital copy of this thesis is not available. Your library can request a copy from Murdoch University Library via Document Delivery. A fee applies to this service.
Supervisor: Ho, Goen, Scott, W.D. and Newman, Peter
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