. 2015 compared to 2014 net income increased $ 17.9 million primarily due to the write-off in 2014 of the regulatory assets associated with new nuclear generation development costs as a result of a joint stipulation entered into with the mississippi public utilities staff , subsequently approved by the mpsc , partially offset by higher depreciation and amortization expenses , higher taxes other than income taxes , higher other operation and maintenance expenses , and lower net revenue