Is Water Age a Reliable Indicator for Evaluating Water Quality Effectiveness of Water Diversion Projects in Eutrophic Lakes?

Zhang XL(#), Zou R(#), Wang YL, Liu Y(*), Zhao L, Zhu X, Guo HC

ABSTRACT: Water diversion has been increasingly applied to promote the lake water exchange and lake eutrophication control. Water has been transfered to Lake Dianchi, China for eutrophication restoration since December, 2013. The accelerated water exchange and mass transport by water diversion can be usually represented by water age. But the responses of receiving water quality to water diversion is still hotly disputed. The reliability of water age used for evaluating effectiveness of water diversion projects in the eutrophiclake thereby should be further explored. A three-dimensional hydrodynamic and water quality model and eight scenarios were developed in this study to quantity the influence of water diversion project on water quality in Lake Dianchi. The model results showed that (a) Water quality (TP, TN and Chla) could be improved by 13.5%-32.2%, much lower than the approximate 50% reduction percentage of water age; (c) Water exchange had a strong positive relationship with mean TP, and mean Chla had exactly the same response to water diversion as mean TN; (d) Water-level was more beneficial to improve hydrodynamic and nutrients than variation condition of the diverted inflowing water volume; (e) Scenerio B4 was the best water diversion mode for mean hydrodynamics and TP, but Scenerio B2 was the optimum one for mean TN and Chl a; (f) Water age was an reliable indicator for evaluating the effectiveness of water diversion on the improvement of TP, while not for TN and Chla.

KEYWORDS: Lake eutrophication; Hydrodynamics; Water quality; Water Age; Three-dimensional Model