Ecological Modelling 222 (2011) 3701–3717 Contents lists available at SciVerse ScienceDirect Ecological Modelling jo ur n al homep ag e: www.elsevier.com/locate/ecolmodel Coupling Xinanjiang model and SWAT to simulate agricultural non-point source pollution in Songtao watershed of Hainan, China Shengtian Yang a,b,∗ , Guotao Dong a,b , Donghai Zheng a,b , Honglin Xiao c , Yunfei Gao a,b , Yang Lang a,b a State key laboratory of Remote Sensing Science, Jointly Sponsored by Beijing Normal University and the Institute of Remote Sensing Applications of Chinese Academy of Sciences, Beijing 100875, PR China b Research Center for Remote Sensing and GIS, Beijing Key Laboratory for Remote Sensing of Environment and Digital Cities, School of Geography, Beijing Normal University, Beijing 100875, PR China c The Department of History and Geography, Elon University, Elon, NC 27244, USA a r t i c l e i n f o Article history: Received 14 April 2011 Received in revised form 1 September 2011 Accepted 8 September 2011 Keywords: Coupled non-point source pollution model Modified Xinanjiang model SWAT model EcoHAT Tropical Zone Remote sensing a b s t r a c t Agriculture has been identified as the major contributor of non-point source pollution of Hainan water resources. In this study, we coupled the Xinanjiang model and SWAT to a new model, EcoHAT, to assess the non-point source pollution in Hainan. The study site is located around the Songtao reservoir, Hainan Island, China, which is regarding as the most important water source system for Hainan. EcoHAT, includ- ing algorithms for the hydrological cycle, nutrient cycle, and plant growth cycle, simulated the non-point source pollution for the watershed in calculated grid cell units based on remote sensing data. Remote sensing data were used to interpret the spatial land surface information and derive the model param- eters. Besides the remote sensing data, other essential databases such as the meteorological databases, soil chemical and physical databases, and plant nutrients databases were also used in this study. The EcoHAT model was calibrated and validated with 5 years of monitored water quantity and quality data in the Songtao reservoir watershed. The study results indicated that the EcoHAT model has simulated the hydrologic pollutant adequately. After the calibration and validation, the parameters were applied to simulate the nutrient and sediment transport in the Songtao watershed during 2003–2007. In the end, the effects of several specific scenarios of changes in the land covers or management practices on the local watershed nutrients transport were also simulated. The results revealed that: (1) the model has pre- dicted the runoff volume within a range of acceptable accuracy which was reflected by a large coefficient of determination; (2) regression analysis between the observed and simulated values resulted in high values of coefficient of determination (R 2 ) during the calibration and validation period. The high values of Nash–Sutcliffe simulation efficiency were achieved with a close agreement between the observed and simulated pollutants concentrations in the runoff. It also indicated that the model simulated the NO 3 –N, NH 4 + –N, and P concentrations in the runoff for the Songtao watershed with considerable accuracy; (3) the sediment loads, TN, and TP, experienced temporal and spatial variations, with strong correlations existing between the parameters and the land use as well as the precipitation; (4) the scenario analysis showed that with 40% fertilization reduction, 7.51% and 7.76% reduction on TN and TP loads respectively could be reached. Besides, the conservation measures are more effective in the study area to reduce the sediment loads than in other areas. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Non-point source (NPS) pollutants are recognized as the sin- gle largest threat to the surface and subsurface sources of drinking water throughout the world (Corwin et al., 1997). NPS pollution is a major contributor to the degradation of the surface water qual- ity. NPS pollution is caused by water movement over and through ∗ Corresponding author. E-mail address: yangshengtian@bnu.edu.cn (S. Yang). the surface of the land. The water runoff picks up and transports natural and man-made pollutants, which are then transported into rivers, lakes, wetlands, coastal waters, and ground water. The study of NPS pollution started in the 1960s in Europe and North Amer- ica. In the United States, the Clean Water Act was amended in 1987 (Section 319) to include specific provisions for NPS manage- ment. In 1989, the European Union (EU) commission discussed the problem of nitrogen fertilizer pollution discharged by agricultural production, and then promulgated the correlated environmental protection policies. Nevertheless, agricultural NPS continues to be a major concern for water quality in the United States (U.S.-EPA, 0304-3800/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2011.09.004