Delayed Response and Quantified Lake Health Indexes

The water resources development has changed the water and sediment situation in the waterway and ruined the balance between the lake system and the eco-environment. It is important to realize the new environment after the change of the water and sediment situation, and to explore the effective environmental improvement measures for the sustainable development and the lake health. Healthy lake is a lake whose social functions and natural functions can be balanced or compromised in corresponding periods. The indexes reflecting a healthy lake should be favorable lake bed, acceptable water quality and favorable lake ecosystem, and the social functions and natural functions of a lake perform in a balanced way. The lake health indexes should reflect the lake´s natural function status which includes the lake bed, water quality, lake ecosystem and the relative runoff. The variety and quantity would be different for different lakes because of different natural features and social background. The indexes should be decided according to the requirement of maintaining lake´s normal natural functions and the extent whether the social functions and the natural functions could perform in the balanced way, and also the indexes should be adjusted according to the change of the natural features and social background. The key to describe the lake health situation is to find out the relatively balanced lake situation based on several critical quantified indexes such as the runoff discharge into the lake, water quality etc., which are influenced by the delayed response of the lake to the changing upstream water and sediment conditions. This paper proposed a method to identify the relatively balanced lake condition and lake health indexes.