The scientists investigated the Yellow River and its reservoirs to understand where nutrients come from, helping plan better ways to manage water quality. By studying different regions in the river, they found that certain nutrients like phosphorus mainly come from the soil washing into the river, especially in spring, while nitrogen pollution is a mix of industrial and natural sources, more noticeable in autumn. They also figured out specific indicators to track different pollution sources: potassium, magnesium, and bicarbonate point to non-factory pollution, while sodium, chloride, and sulfate point to industrial pollution. These findings help design strategies to keep the Yellow River's water clean.