Tim

SEO primarily increases visits where as the content of your website is responsible for the behaviour once they are there (such as bounce rate).

2.5% is an extremely low BR. so if visits were relatively low in the first place then an increase in vistors will likely shoot this figure up. Blogs such as yours should expect a high bounce rate as people read the article they are interested in and move on to somewhere else.

All your articles seem to be on the same page so i’d suggest you look into ‘paginating’ them. So have them across multiple pages. This means when someone is actually engaged by an article they will trigger as a non bounce. As it stands someone could land on one of your articles, read the majority of it and still count as a bounce.

Looking into the increase in visits and the landing pages is the best place to start.