Temporal-Spatial Distribution of Nitrogen in the Dongjiang River and Its Tributaries

To examine the temporal-spatial distribution of nitrogen in the Dongjiang River basin,we sampled river water regularly and repeatedly in 47 sampling points dispersed in the mainstream and major tributaries of three times(July2009 and 2010 for flood season,and December of 2009 for dry season).We found that the average concentration of total nitrogen(TN)in the river water were(1.45～1.93)mg/L,and up to 42% of the water samples from the mainstream and tributaries were polluted grades IV to V according to the national water quality standards.The average nitrogen concentration in the forms of TN、DIN、NH 4-N and NO 3-N changed seasonally,being lower in flood season than that in dry season.According to the average nitrogen concentration in river water,the mainstream of Dongjiang River could be divided into five different reach sectors:the low value sector upstream of river source;the high value sector upstream of Fengshuba Reservoir;the medium value sector upstream of Xinfengjiang Reservoir;the medium value sector upstream of Huizhou City area;and the high value sector downstream from Huizhou City area.The pollution sources of nitrogen for the two most heavily-polluted sectors were different.Upstream of Fengshuba Reservoir,the sources were primarily non-point pollution origins from agriculture,whereas downstream from Huizhou City area the sources came mainly from point pollutants from industrial wastewater and domestic sewage,particularly from tributaries of the Qiuxiangjiang River,Xizhijiang River,Danshuihe River,Shimahe River and Shahe River.