The study looked at nitrogen and phosphorus pollution in Beijing's surface water. They found that most water bodies were polluted by high levels of total nitrogen, exceeding national standards. Ammonia and phosphorus levels were also high in certain water systems. Nitrate levels were generally low and met water quality requirements. Overall, Daqinghe, Jiyunhe, and Beiyunhe river systems, as well as parts of Yongdinghe and Chaobaihe, were heavily contaminated. The researchers used statistical methods to show that nitrogen, ammonia, and phosphorus were linked to pollution from human activities.