INFLUENCE OF LAND USE CHANGE ON TOTAL NITROGEN EXPORT IN NAOLI RIVER WATERSHED FROM 1954 TO 2010

Evaluation of the influence of land use change on total nitrogen (TN) export to the stream water can give us useful knowledge on both land and water resource planning and management of the watershed. The present study was conducted in Naoli River watershed, northeast China, where there experienced vast area of wetland reclamation in the past few decades, using the export coefficient approach to evaluate impact of land use change on TN export in the watershed from 1954 to 2010. The results showed that in an annual average scale, the highest rate of TN export is from the residential area, followed by the upland, water body and forest. The paddy field in Naoli River watershed has a relatively low TN export coefficient, acting more like a type of treatment wetland rather than the crop land regarding the TN pollution. Land use change in Naoli River watershed in the past few decades has dramatically altered the nitrogen discharge into river water. TN export experienced an increase from 2627 t to 3821 t over the period of 1954-1995 as a result of the wetland reclamation into upland and then decreased to 3666 t in 2010 due to the `upland conversion into paddy field' in 1995-2010. The uncertainty analysis and the results of the export efficient model estimation suggested that reduction of the upland area in Naoli River watershed would be an effective way to reduce TN pollution.