Abstract
Nonโpoint source (NPS) pollution from agricultural land is increasing exponentially in many countries of the world, including India. A modified approach based on the conservation of mass and reaction kinetics has been derived to estimate the inflow of nonโpoint source pollutants from a river reach. Two water quality variables, namely, nitrate (NO~3~) and orthoโphosphate (oโPO~4~), which are main contributors as nonโpoint source pollution, were monitored at four locations of River Kali, western Uttar Pradesh, India, and used for calibration and validation of the model. Extensive water quality sampling was done with a total of 576 field data sets collected during the period from March 1999 to February 2000. Remote sensing and geographical information system (GIS) techniques were used to obtain land use/land cover of the region, digital elevation model (DEM), delineation of basin area contributing to nonโpoint source pollution at each sampling location and drainage map.
The results obtained from a modified approach were compared with the existing massโbalance equations and distributed modelling, and the performances of different equations were evaluated using error estimation viz. standard error, normal mean error, mean multiplicative error and correlation statistics. The developed model for the River Kali minimizes error estimates and improves correlation between observed and computed NPS loads. Copyright ยฉ 2007 John Wiley & Sons, Ltd.