*2.1.2 Contradiction*

The contradiction reflects the two sides of the impact of dam demolition, that is, while it is beneficial to one element, it is harmful to the other. For example, the removal of dams to restore the connected state of rivers is conducive to the breeding of migratory fish but also easy to cause species invasion.

### *2.1.3 Space-time continuity*

The impact caused by reservoir removal can be spatially from the upstream to the downstream of the dam site, from the river where the dam site is located to the river, and even from the river basin. The time span can be days, months, or even decades. Short-term effects have been generated in the process of dam removal, such as sediment release from the reservoir area, pollution caused by sediment output, water oversaturation, etc. Long-term effects include natural water recovery, the reservoir area becoming a flowing river again, the change of river temperature, the gradual recovery of sediment movement, and so on.
