DES MOINES, Iowa—The Iowa Utilities Board has approved a settlement agreement granting Interstate Power and Light Company a portion of a requested natural gas service rate increase in Iowa.  The settlement allows the utility’s permanent annual revenue from natural gas to increase by 4.8%.  Actual changes won’t be seen for three years because IPL will use tax credits to reduce the impact on residents.  The rate will increase about $3 per month once the tax credits expire.  IPL has already had a temporary rate increase in place since last June and has collected $8.6 million.  The rate increase is directed toward the cost of improvements within the distribution system and is not a part of the cost of natural gas which is passed on to the customer dollar for dollar.