Modelling phosphorus loading to the largest shallow lake in northern China in different shared socioeconomic pathways

Abstract

Excessive nutrients inputs cause anthropogenic lake eutrophication worldwide. It is thus crucial to provide information on future trends of nutrient loading and its implications for the lake’s trophic state. Here we quantified total phosphorus (TP) loading to the Lake Baiyangdian (BYD), the largest shallow lake in northern China, and assessed their future trend and the trophic state of the lake. The TP loading to the Lake BYD by rivers in 2015 was 276 ton, which was in a relatively low level in lakes from China. Based on the five shared socioeconomic pathways (SSPs), the TP loading to the Lake BYD in 2050 will increase only at the fragmentation scenario (SSP3) by an increment of 34.4%, in which the directly discharged animal manure become the main source. The lowest TP loading in 2050 is observed at the sustainability scenario (SSP1), in which sewage system will be the dominant contributor. At the sub-basin scale, compositions of river exported TP in rural areas will be more influenced by future socioeconomic developments than those in urban areas. The twenty years nutrient dynamics from clear or turbid state in the Lake BYD were simulated by the PCLake model to calculate the critical P loading (CPL). The results indicated that the CPL in the Lake BYD was 2.06 mg P m−2 d−1 for eutrophication and 0.84 mg P m−2 d−1 for oligotrophication. The only scenario in which Lake BYD will become eutrophic is SSP3, which should be avoided in the future development. To restore the lake water to the oligotrophic state, more efforts are necessary to reduce direct discharge of animal manure and increase the TP removal rates, especially in rural areas.