The researchers studied nitrate levels in the Ganjiang River to understand where it comes from and how it affects Lake Poyang. They looked at nitrate concentrations and nitrogen isotopes in different parts of the river during dry and wet seasons. They found that nitrate levels were higher in areas with more agriculture and residential land, and lower in forested areas. Agriculture, especially paddy fields, was the main source of nitrate in the river. The researchers also discovered that less nitrate in the Ganjiang River comes from sewage compared to other areas in the Yangtze River Basin.