Thanks for all your answers
@Theo & @StephanM: My website is not international, it's a dutch website (http://goo.gl/9nwq9) so i think it cannot be the panda update because i heard they did not launch it in Europe yet or did they? However, 24 february is almost the exact date the drop in traffic initiated.
As for the website that uses our RSS feed, we blocked the feed for that particular website. Not only because our suspicions but also because they loaded the feed on every single page request. We know it is not a popular website because over a course of 1,5 years we only received 40 visitors from that domain while the links to our website were clearly visible on each page.
Still i think it's weird that our old articles are doing just fine and only the new articles are affected. Also, the rest of the website is ranking as usual.
@Dave: Good point, it could be that the refering site got a penalty that devalued the links to our website thus causing a drop in ranking and traffic. I'm not sure if they had a penalty before we noticed the drop in traffic, im quite sure they have one now. But looking at the amount of traffic we received from them over a period of 1.5 years i suspect they always had a penalty but again i'm not sure.
