|Title:||Modelling water quality to improve agricultural practices and land management in a Tunisian catchment using SWAT |
|Authors:||Aouissi, J., B. Sihem, L.C. Zohra and C. Christophe |
|Journal:||Journal of Environmental Quality |
|Article ID:|| |
|URL (non-DOI journals):|| |
|Broad Application Category:||hydrologic & pollutant |
|Primary Application Category:||BMP assessment |
|Secondary Application Category:||nutrient cycling/loss and transport |
|Watershed Description:||418 km^2 Joumine in northern Tunisia |
|Calibration Summary:|| |
|Validation Summary:|| |
|General Comments:||This article is part of a JEQ special SWAT section. |
|Abstract:||Agriculture intensification impaired water quality. In this study, the risk of pollution by nitrates was assessed by experimental monitoring; spatial integration of farm census and modelling of water quality using the Soil and Water Assessment Tool (SWAT), version 2009, over the period of 1990 to 2006 for a catchment located northern Tunisia. Under semiarid climate the water quality is influenced by the predominating agriculture activities.
The hydrological results are compared to the observed flows derived from measurements at the outlet of Joumine watershed. Model performance showed good statistical agreements with a Nash-Sutcliffe efficiency of 0.9 and r2 value of 0.92 after monthly calibration. The model predicted the timing of monthly peak flow values reasonably well. During the validation period, SWAT simulations were nearly as accurate with E and r2 values of 0.89 and 0.92 respectively.
The model was used to simulate nitrate concentrations. The predicted nitrates concentrations values were compared to in situ measured concentration. The simulated and measured NO3-N concentrations varied in the same range of 0 to 5 mg L-1 at E3 and E5 locations. The calibrated model was then used for simulating the impact of the BMPs scenarios in order to reduce nitrates loads to the river. The first set-up consisted of reducing the nitrogen fertilizer application by 20% and by 100% from the current state. These two scenarios induced a reduction in nitrate loads by 22% and 72% respectively. The second set-up consisted of using vegetation filter strips. The last scenario combined filter strips and a reduction of 20% in N fertilizer application. Results showed nitrate reduction rates of 20% and 36% respectively. The SWAT model allowed managers to have several options to improve the water quality in the Joumine watershed. |
|Keywords:||Water quality, Intensive agriculture, Nitrate loads, SWAT model, BMPs |