A case study of water retention and ecosystem functioning restoration in Wenying Lake (China)

Abstract

Wenying Lake in Datong, China, has been drying for the last several years. Analysis of standard penetration test data revealed that a missing waterproof layer of silt soil and silty clay in the south part of the lake, resulting from frequent flood flushing, was responsible for the water loss from the lake. Accordingly, 6.7 · 10 5 m 2 of geosynthetic clay liner (GCL) was used in May 2010 to repair the area of sediment exhibiting the water leakage, equivalent to 15.6% of the total lake bottom area. Approximately 4.1 · 10 6 m 3 of floodwater was then diverted from upstream rivers to the lake. Eight months later, about 0.9 · 10 6 m 3 of the water was retained, with the water loss being reduced from 4.0 to 1.1 m 3 m )2 year )1 . Ecologically safe and cost-effective clay materials also can be used to furthermore improve the water retention characteristics. Modelling results indicated that capping the whole lake with a 2 cm layer of bentonite with a permeability coefficient of 5.0 · 10 )9 cm s )1 could reduce the sediment water leakage to 0.04 m 3 m )2 year )1 . The quality of the retained water after GCL treatment project was poor, with a total nitrogen concentration of 11.0 mg L )1 and sulphate 307.0 mg L )1 , which were 5 and 300 times higher, respectively, than the Chinese class V surface water standard. Restoration of aquatic vegetation in the lake and constructed wetlands near the lake inlets could be helpful to improve the lake’s water quality over the long term.