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Comparative study of two watershed scale models to calculate diffuse phosphorus pollution.
1Department of Sanitary and Environmental Engineering, Budapest University of Technology and Economics, Muegyetem rakpart 3, H-1111 Budapest, Hungary. kovax@vkkt.bme.hu
Summary
Comparing phosphorus emission models, this study found the MONERIS empirical model and SWAT physically-based model yielded different results. SWAT requires adjustments for sediment-bound phosphorus in transport-limited watersheds for accurate river load calculations.
Area of Science:
- Environmental Science
- Hydrology
- Water Quality Management
Background:
- Accurate assessment of diffuse phosphorus emissions is crucial for watershed management and water quality protection.
- Different modeling approaches, such as empirical and physically-based models, exist for estimating phosphorus loads.
- Comparative studies are needed to understand the strengths and limitations of these models in specific watershed contexts.
Purpose of the Study:
- To compare and assess the performance of the MONERIS empirical model and the SWAT physically-based model in calculating diffuse phosphorus emissions.
- To evaluate the accuracy of these models against measured river loads in a selected watershed.
- To identify the suitability of each model for different applications, such as long-term planning versus detailed scenario development.
Main Methods:
- Application of the MONERIS and SWAT models to a sub-basin of the Hungarian Zala River watershed over a five-year period.
- Validation of model-calculated river phosphorus loads against measured data at the catchment outlet.
- Analysis of discrepancies in water balance, erosion calculations, and phosphorus emission computations between the two models.
Main Results:
- Significant differences in computed phosphorus emissions were observed between the MONERIS and SWAT models, attributed to variations in water balance and erosion calculations.
- The SWAT model showed inaccuracies in phosphorus river load calculations for transport-limited watersheds due to its omission of inorganic phosphorus-sediment interactions during channel transport.
- The MONERIS model provided acceptable river loads by assuming substantial in-stream retention, while incorporating channel processes improved SWAT's accuracy.
Conclusions:
- For transport-limited watersheds, the SWAT model requires enhancement to account for phosphorus-sediment dynamics during channel transport to improve accuracy.
- The MONERIS model offers a viable empirical approach for long-term phosphorus emission estimations and preliminary design support.
- Physically-based models like SWAT are more appropriate for detailed emission assessments and the development of specific management scenarios.