A modelling framework to track phosphorus sources of the drinking water intakes in a large eutrophic lake

Abstract

Excess phosphorus (P) in freshwater lakes is a global challenge due to its potential cause of harmful algal blooms threating drinking water safety. However, quantifying the P sources for a specific site in a large lake is extremely challenging due to the complex interaction between internal and external P loading to surface water. To address this challenge, this study developed a modelling framework to track P sources of two drinking water intakes in a large shallow lake (Lake Taihu) in China. The framework proposed a new-developed index (PSCI, P source contribution index) to quantify the contributions of various P sources for the drinking water intakes. PSCI was derived by a three-dimensional hydrodynamic and water quality model that describes the complex processes of P sources, sinks and transportation in both horizontal and vertical directions within the lake. Application of the framework to these two drinking water intakes (Jinshu and Shangshan) achieved a surprising finding that internal P loading from sediment was a significant P source with a contribution as high as 47.1% and 30.4%, respectively. Central Lake Taihu had a large contribution of 49.5% and 68.3% for Jinshu and Shangshan, and inflow river (Wangyu River) had a contribution of < 5%. The high contribution of internal P loading was mainly due to the sediment P accumulation for years and large external P loading. Our study highlighted the important role of internal P loading affecting the P concentration of drinking water intake in a large eutrophic lake, and demonstrated the high value of the modelling framework in quantifying the P sources for a specific site (e.g., drinking water intake) in a lake.