If you wish to disable notifications from the board, this is how you do it:
Go to your Profile > Modify Profile section of the menu, then click Notifications & Email... untick the two boxes alongside
Receive reply notification only for the first unread reply.
Turn notification on when you post or reply to a topic.
and select Nothing at all from the drop down menu below that, then click Save Settings.
Even if you turn off notifications in Profile you can still ask for them on a post by post basis or a thread by thread or board by board basis to suit. Turning them off in Profile stops you getting them by default (i.e. globally) but still allows you to decide what you do want locally.
To turn off existing notifications go to the same page but scroll to the second section and tick the boxes alongside each of the notifications to turn them off for anything you're getting them for already and then click the Unsubscribe button.
To turn them back on just resubscribe using the Notify link at the top left of each topic you want to watch.