<b>Pathways for Agricultural Phosphorus in Rivers Toward Clean-Water Thresholds: Adapting to Legacy Effects and Climate Change</b>

We assessed agricultural DIP inputs to rivers (defined as DIP entering surface water from synthetic fertilizer and animal manure application in the agricultural areas) for 2000-2019 and 2020-2099 under different scenarios using three storylines for agricultural P management, i.e. an assumed constant P surplus levels as observed in 2019 throughout the projection period (S1) a linear decrease in P surplus from 2019 levels to no surplus by 2050 until 2099 (S2) and no P surplus across the entire projection period (2020-2099), in combination with two climate scenarios, i.e. the lowest and highest Representative Concentration Pathway, i,e. RCP 2.6 and RCP 8.5. We also proposed spatially explicit thresholds of agricultural DIP inputs to rivers to assess their environmental risk under different climate change and P management scenarios. These thresholds represent the maximum allowable agricultural DIP inputs to rivers that comply with clean surface waters, using Grade Ⅰ-III standards (GB3838-2002), for water that is suitable for swimming and potable use following conventional treatment.