anglais vers français Autre Environnement et écologie hydrologic and hydraulic study

This extract is part of a chapter called 'conclusions and recommendations' following a hydrologic and hydraulic study.

The phrase is part of the following sentence :

Increased inundation and presence of stagnant water (...) is believed to be the principal cause of observed tree death due to water over saturation of soil and roots.

I am a bit confused as to whether tree death is caused by increased inundation and presence of stagnant water AND due to water ...

And I am not sure how to translate OVER in that phrase.

Many thanks for your help