Investigation Of Nitrate Pollution Source Based On Land Use And Nitrogen Stable Isotope In The Ganjiang River

The Ganjiang River, as the largest tributary of the Poyang Lake Basin.the nitrate form the Ganjiang River is the main pollution source of nitrogen input the Poyang Lake. Based on the land use and nitrogen stable isotope Indentifying the source of nitrate in the Ganjiang River has great signification for Poyang Lake, characteristics of nitrate nitrogen and ammonia nitrogen and nitrite nitrogen in the mainstream and major tributaries of the Ganjiang river in January and June of 2013, used stable isotope and correlation analysis to find out the main source of inorganic nitrogen though land use structure classification and comparison on the basis of space scale in Ganjiang river.On the basis of field investigation designed sampling points rationally and used GIS and RS technology as a platform to analysis land use of the Ganjing river basin. Identifying the main source of nitrate pollution in Ganjiang river basin and the Poyang lake water protection provides an important basis, fixed-point investigation and sampling in Ganjiang river basin of January and June of 2013, analysis of inorganic nitrogen and chlorine ion in Ganjiang water features by using water chemistry research means and combined with basin types of land use structure and nitrogen stable isotope. The results of the study mainly included several aspects:(1) Analyzed different sampling of inorganic nitrogen of Ganjiang river basin in January and June of 2013, and research shows that N03--N is the main insisted way for inorganic nitrogen output in Ganjiang river, average of NO3--N is 1.80 mg/L, which accounts for about 78% of the total inorganic nitrogen; Followed by NH4+-N, with a mean of 0.52 mg/L, which accounts for about 20% of the total inorganic nitrogen; NO2--N content is very small, most of the sample point below the monitoring value of 0.02 mg/L.(2) Analyzed the characteristics of inorganic nitrogen distribution in Ganjiang river, and research shows that the content of NO3--N and NH4+-N in dry season more than wet season. the ranges of NO3--N contention in dry season change bigger than wet season, the ranges of NH4+-N contention has the similar manifestation in dry season and wet season, the change of NO3--N and NH4+-N contention in dry season clearly than wet season, compared with the national surface water quality standard, sampling points in different season most of the inorganic nitrogen content higher than II categories of water standards.(3) Analyzed the structure of land use in the Ganjiang River basin, and the results showed that forest land area ratio reached 62.5%, paddy field area ratio was 18%, the dry land and residential construction land was 16%, the paddy field and water area was a source of nitrate nitrogen, while forest and grass land was a sink.(4) Combine with different spatial scales in the Ganjiang River, sub-basin division method than buffer method is more suitable for nitrate source analysis of Ganjiang River basin, selecting a smaller spatial scale of sub-basin division can better highlight the effect between land use and inorganic nitrogen, under the second land use classification, among the paddy field, hill paddy field was the main source of NO3--N, followed by plain paddy and mountain paddy field, rural land was the main source of NO3--N in the Ganjiang River, while the urban land and industrial and mining land among the residential construction land were the main source of NH4+-N.(5) The delta of δ1SN-NO3- value in small variations between 0.79～5.93‰ in the mainstream of the Ganjiang River, and the delta of δ15 N～NO3-value in wide variations between-1.31‰o～8.6‰ in the tributaries of the Ganjiang River, the average of value in dry season less than wet season, the change of nitrate pollution sources in the tributaries of the Ganjiang River were different due to difference of regional land use type.(6) Compared with inorganic nitrogen and δ15N-NO3-value in the Ganjiang River, The δ15N-NO3- value falls within the scope of inorganic fertilizers and soil nitrogen, illustrate the pollution of nitrate mainly comes from agricultural fertilizer and soil nitrogen.