A novel framework for turbidity source apportionment of the urban lakeside river network

Turbidity source apportionment is essential but complex for precise environmental rehabilitation of worldwide urban lakeside river networks impaired by turbidity. A new turbidity source analysis framework including in-situ sampling, vessel monitoring, remote sensing, and hydrodynamic modelling was proposed, where the critical processes of flow reversal from the turbid lake, navigation, and urban non-point source in urban lakeside river networks were explicitly considered. The case study results showed that the turbidity problem (mean value was 211.3 nephelometric turbidity units (NTU)) was primarily led by suspended inorganic matter (58%), followed by suspended organic matter (19%) and other matter. The Tiaoxi River and busy shipping contributed most to the annual total suspended solids load of the target river, with the same percentage of 34%. The turbid Lake Taihu provided 64,663 tonnes and 31% of the total suspended solids load, focusing on the autumn and winter months. Tiaoxi River load was highly concentrated on the storm events, which accounted for 71.4% of the annual Tiaoxi River source (209846 tonnes). The large water volume of reverse flow and the high TSS concentration of Lake Taihu in the autumn and winter months accounted for the seasonal change in Lake Taihu's TSS load. The coronavirus disease lockdown reduced the mean monthly total suspended solids concentration of 152.4 mg/L in November and December 2019 to 49.2 mg/L in January and February 2020, by limiting the waterway transportation and the market demand for building materials. The river estuary's vegetation interception belt, shipping restriction and rerouting, and integrated catchment management were advised to mitigate the urban river network turbidity.