Watershed-scale phosphorus balance evaluation using a mass balance method

Abstract

It is crucial for assessing the eutrophication risk of lake by analyzing the phosphorus (P) balance of lake watershed quantitively. A mass balance method was used to calculate P balance of both Yangzonghai lake watershed and the lake itself in one year. The imported P load was 725.1 t in 2010, while the exported P load was 317.3 t, which indicated that 56.2 % (407.8 t yr−1) of P was retained in the lake watershed. Such a high retention load implied that the lake, which was mesotrophic, was under great pressure of further eutrophication. Among all the input pathways, the largest P input contributor was fertilizer, contributing 679.0 t P and accounting for 93.6 % of input P, followed by atmospheric deposition (44.7 t P, 6.2 %). Plant product (264.6 t, 83.4 %) was the largest P output contributor, followed by animal products (50.2 t, 15.8 %).