Modelling of pH changes in alkaline lakes with water transfer from a neutral river

While water transfer from rivers to alkaline lakes has been proposed to solve lake water level drawdown and ecological degradation problems, its effectiveness for achieving ecological goals is often questionable. A sudden pH decline in alkaline lakes due to water transfer is considered likely to harm the lake ecology. However, it remains unclear to what extent water transfer affects alkaline lake pH. Thus, a three-dimensional numerical model coupling a pH calculation method considering the carbonate balance with the MIKE3 hydrodynamic model was developed to predict pH changes in an alkaline lake. Laboratory and field measurements verified the model reliability. The model accurately simulated the mixed-water pH during water transfer, with a root mean square error of 0.03-0.07 and a coefficient of determination of 0.894-0.998. The model was then applied to predict the pH response to water transfer in Lake Chenghai. The results showed that the pH response to water transfer demonstrated spatial and temporal variability, and a low-pH diffusion zone (pH <= 9) formed in the northern parts of the lake during annual water transfer; the effects of water transfer on the pH in the lake were cumulative over time, and the average pH in Lake Chenghai after five years decreased by 0.2 units; strong wind and low inflow could effectively reduce the low-pH diffusion area; and daily thermal stratification of the plateau region threatened the low-pH diffusion area control in Lake Chenghai. Our results provide a new reference for formulating ecological water transfer strategies for alkaline lakes and similar water bodies.

Automated summary

Water transfer from rivers to alkaline lakes has been proposed as a solution for lake water level drawdown and ecological degradation, but its effectiveness is often questioned due to the potential harm to lake ecology caused by a sudden pH decline in alkaline lakes. To understand the extent of this pH change, researchers developed a numerical model that couples a carbonate balance-based pH calculation method with a hydrodynamic model. The model accurately simulated the pH changes during water transfer and was applied to predict pH responses in Lake Chenghai. The results showed spatial and temporal variability in pH response, cumulative effects over time, and the impact of wind and inflow on the diffusion area of low-pH water. This study provides valuable insights for developing ecological water transfer strategies for alkaline lakes and similar water bodies.