| In this case, the Taige canal was studied. Water samples and main N sources were collected in the spring (April), summer (July) and autumn (November) of2013. Based on the concentration of nutrients in water body, the eutrophic condition was evaluated. The isotopic characteristic values of different N sources were also analyzed. Combined with the mass conservation principle, a mixing model was developed to quantitatively estimate the contribution of different important sources.The concentration of total nitrogen, nitrate, ammonia nitrogen, total phosphorus and phosphate in Taige canal were2.0～5.5mg/L,1.0～4.8mg/L,0～1.6mg/L,0～0.7mg/L respectively, showed a eutrophic state in this river. TN/TP reflected algae growth was limited by phosphorus(P) in April and October, while it was suitable for algal growth in July. Thus, the algae bloom risk was higher in summer.In spring (April), summer (July) and autumn (November), the average of N isotope values were+16.20±5.47%‰,+10.79±3.83‰,+8.57±2.59‰, respectively. The average of O isotope values were-3.21±5.24‰、-0.74±2.49%o.-0.42±1.74‰, respectively. By using the mixing model, the contribution of sewage was calculated in the range of39～100%, while the range of industrial and fertilizer were0～65%. The rain water contribute least N pollution, with a range of0～13%.In general, the main N pollution source was still sewage, followed by chemical fertilizers and industrial waste water. The contribution rate of rainwater was relatively small, showed it was a less important N source. The contribution rate of domestic sewage decreased from spring to autumn, while the contribution rate of fertilizers and industrial waste water increased in this period. The contribution rate change of the rainwater was relatively stable. All of these reflected that the contribution of different N source also existed obvious spatial and temporal variation in this area. |
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