The abstract is usually in the past tense due to it showing what has already been studied. Example: “This study was conducted at the Iyarina Field School, and within the indigenous Waorani community ...

The past tense is used for things that have already happened. He was sticky. The present tense is used when something is happening now or when something happens regularly. He is sticky.

The usual practice is to have the present tense express a current event while the past tense indicates the past. But there is a dramatic situation the present tense can state a past occurrence too.