Abstract
Intensive agricultural activities in the Hetao irrigation district have severely degraded local aquatic ecosystems and water quality, and Ulansuhai Lake is now the most rapidly degrading eutrophic lake in China. A better understanding of the hydro-agronomic and pollutant transport processes in the area is thus urgently needed. This study simulated monthly streamflow, total nitrogen (TN) and total phosphorus (TP) for the Hetao irrigation district using the Soil and Water Assessment Tool (SWAT) to evaluate the nutrient load, source areas, and hydrological pathways. The Nash-Sutcliffe efficiency (NSE) values obtained for the streamflow simulations were 0.75 and 0.78 for the calibration and evaluation periods, respectively. The SWAT model captured the temporal variation in streamflow (R2 > 0.8) for two periods; the NSE values for the TN and TP loads were 0.63 and 0.64 for the calibration period and 0.48 and 0.42 for the evaluation period, respectively. The predicted monthly TN load was correlated with irrigation (r = 0.61) and the monthly TP load with precipitation (r = 0.89), indicating that nitrogen transport is primarily associated with soil leaching and groundwater flow, and phosphorus is primarily transported by sediments caused by rainfall erosion. A case study of split nitrogen fertilizer applications demonstrated reduced annual TN load by as much as 13% in one year. Fertilization timing also affects the load in different pathways especially in lateral subsurface flow and shallow groundwater. Better agricultural management could thus reduce nitrogen losses, and buffer strips could minimize phosphorus transport.
Highlights
Agriculture is a basic economic factor for every country and this is especially the case for China, which is a developing agricultural country
The predicted monthly total nitrogen (TN) load was correlated with irrigation (r = 0.61) and the monthly total phosphorus (TP) load with precipitation (r = 0.89), indicating that nitrogen transport is primarily associated with soil leaching and groundwater flow, and phosphorus is primarily transported by sediments caused by rainfall erosion
The catchment was divided into 55 subbasins, representing 364 hydrologic response units (HRUs) in the ArcSWAT 2009
Summary
Agriculture is a basic economic factor for every country and this is especially the case for China, which is a developing agricultural country. Irrigation districts provide the foundation for much of the country’s food crop production, which is largely conducted in six very large irrigation districts with areas greater than 335,000 ha each. Excessive fertilization has been common, and there has been serious deterioration of water quality in these areas due to agricultural non-point source (ANPS) pollution. The intensification of agricultural activities in recent years has been clearly identified as the major contributor to ANPS pollution of water resources [1]. Many studies on water balance and ANPS management in agricultural areas have been carried out worldwide [2]. The impacts of climate change, uncertainties in agricultural land management
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