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 ... untick the box alongside Turn notification on when you post or reply to a topic and select Nothing at all from the drop down menu alongside For topics and boards I've requested notification on, notify me of, then click Save Settings.
If you want to receive some notifications then tick the box alongside Turn notification on when you post or reply to a topic and then select your preferences from the drop down menus alongside each of the following two lines...
For topics and boards I've requested notification on, notify me:
For topics and boards I've requested notification on, notify me of
Even if you turn off notifications in Profile you can still ask for them on a post by post, or a thread by thread, or board by board basis to suit you. 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.