TLDR; snippets from the article:
A shocking amount of disinformation (“fake news”) is also created by and spread from smaller, fringe Web communities that have relatively outsized influence on the greater Web.
We set out to measure just how this influence flows in a systematic and methodological manner, analyzing how URLs from 45 mainstream and 54 alternative news sources are shared across 8 months of Reddit, 4chan, and Twitter posts. Highlights:
1. Reddit and 4chan post mainstream news URLs at over twice the rate than Twitter does
2. Alternative news URLs spread much faster than mainstream URLs, perhaps an artifact of automated bots
3. 4chan was also the most successful at “reviving” old stories
We found that Twitter does have heavy influence on the spread of fake news. The_Donald and /pol/ are responsible for around 6% of mainstream news URLs over 4.5% of alternative news URLs on Twitter.
Whole story in the arxiv paper: https://arxiv.org/abs/1705.06947