Improved semi-distributed model for phosphorus losses from Irish catchments

Abstract

Phosphorus (P) is one of the important limiting elements governing the quality of natural waters in Ireland. Good models that simulate the loss of P from catchments to water bodies are needed to understand the mechanism and transport of P and to assist in formulating appropriate policies and practices to control or manage the problem. In the present study, a new combined model (NCM) is developed as a hybrid between soil and water assessment tool (SWAT) and Hydrological Simulation Program FORTRAN (HSPF) packages. The developed NCM model was tested, with the data from the Oona catchment in Ireland, and evaluated to insure it is capable of predicting flow and total P loads at the same level or better than SWAT and HSPF packages when used alone. The NCM produced better flow simulation in terms of Nash–Sutcliffe efficiency (R²) than SWAT when used alone for both calibration and validation periods when hourly time steps are used for rainfall and evapotranspiration. In addition, calibration for the total phosphorus load gave better R² values than previously reported result for either HSPF or SWAT and showed better performance for most of the validation period. Using multi-objective optimization methods for optimizing both flow and total P loads gave better simulated results than using sequential optimization of flow followed by total phosphorus. Hence, the NCM model developed here can be used to improve the prediction of phosphorus loss to water bodies in Ireland.

Keywords:

• hybrid model
• phosphorus modelling
• SWAT
• HSPF
• optimization

Acknowledgements

The first author is extremely grateful to Teagasc and CWRR for their financial and other support during the course of study. The authors gratefully acknowledge the use of data collected by Professors Kiely, Jordan and Moles as part of the EPA funded LS2 project.

Funding

This work was supported by a Teagasc Walsh Fellowship and UCD's Centre for Water Resources Research (CWRR) and formed part of PhD research project of the first author.