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Modelling subsurface movement of manurial nitrogen in a shallow unconfined aquifer

University of British Columbia

Increasing pressures towards efficient decision-making in agricultural waste management and groundwater pollution control, are creating the need for improved pollutant routing methods. To optimize the land application of organic wastes, the estimation of the leaching loss of nitrate-nitrogen from the root zone, and the prediction of resulting long-term increases of nitrate concentrations in the receiving groundwater system, are required. Two mathematical models are developed, to simulate, (1), the seasonal vertical movement of nitrates beneath a disposal field, and (2), their long-term areal redistribution in the regional unconfined aquifer. The solute transport formulation accounts for simultaneous convection and hydrodynamic dispersion in the unsaturated and saturated zones. The models are applied to a shallow glacial outwash aquifer in the Lower Fraser Valley of B.C., to illustrate the methodology for their use as a waste management guide. Data was collected at a swine farm located on the upper reaches of the aquifer system, for a pasture site receiving heavy manure applications. Nitrate loss from the field is estimated over one leaching season. Assuming the continuation of current practices on the farm, assessment of the long term impact on regional groundwater quality is attempted. To estimate the precision obtained on the above determinations, the sensitivity of the model outputs to the calibration inputs and to the transport parameters, is tested. This sensitivity analysis also allows for establishing the importance of the transport parameters in controlling the system behaviour. Validity and applicability of the models are discussed. Current data limitations precluded their complete verification. Some weaknesses are identified and modifications are recommended. Recommendations are also made for data acquisition procedures, to further validate the models and to apply the proposed methodology to other similar sites.

Text

2010-02-24

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http://hdl.handle.net/2429/20881

Chemical and Biological Engineering

University of British Columbia

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