Predicting nitrate and Phosphate Load from Paddy field Using WASP Model and Remote sensing (Case study: Pasikhan river)

Discharges of urban, hospital, industrial and agricultural drainage wastes into rivers not only reduce the quality of river, but also it has irreversible effect on ecosystems. Estimation of pollution loads from various contaminants is important in quality and quantity planning of water resources. Pasikhan River is one of the major rivers of Guilan that is at risk of pollution due to adjoining to residential areas, fish ponds and paddy fields and their discharge of drains. In this research a new approach include of simultaneous application of water quality model and satellite images were studied to estimate the loading of pollution from agricultural activities in Pasikhan River. For this purpose, the WASP model was used to simulate spatial and temporal trend of nitrate and phosphate in Pasikhan River. For model calibration and validation, the quality of the river including of nitrate and phosphate was analyzed in 1390. The model simulated nitrate and phosphate with a determination coefficient 0.84 and 0.89 respectively. After determining the cultivation area of paddy fields in the study area and using the DEM map, nitrate and phosphate pollution loads into the river was estimated by calibrated model. Comparing observed pollution load (16.0 and 1.68 kg/ha) and model estimation (14.18 and 1.40 kg/ha) in terms of nitrate and phosphate, show appropriate accuracy of method for estimating pollution in agricultural land.