How to get URL argument

Hi,
when a user registers on our site (not through 3rd party), I am setting a value in the user profile based on a URL argument. This is done in a rule and works fine. However when a user registers through Facebook it does not recognise the argument. This is what I am using

User/register?type=xx xx

How and where can I read the value for type so I can update the user profile accordingly?

Thanks