Figure 3.
Nitrogen (N) and phosphorus (P) inputs to rivers in China (Tg/year) by form: dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), and by source. Point sources include human waste from wastewater treatment plants (WWTPs) and direct discharges of animal manure to rivers. Diffuse sources include synthetic fertilizer use, manure applied on land, biological N2 fixation by agricultural crops and by natural vegetation, atmospheric N deposition, leaching of organic matter, and weathering of P-containing minerals from agricultural and non-agricultural soils, and human waste from populations that are unconnected to sewage systems that stay on the land. Others refer to the human waste from urban and rural populations that are unconnected to sewage systems but discharged directly to rivers.