Bonds that are more a source of savings than an investment

After the 2008 recession, the amount of reserves in the us banking system increased. because of federal reserve actions, required reserves increased from $44 billion to $60 billion. however, banks started holding more reserves than required. by january 2009, banks were holding $900 billion in excess reserves. the federal reserve started paying interest on the excess reserves that the banks held. what possible impact will these unused reserves have on the economy?