Gustav Mahler’s First Symphony makes for a breathtaking calling card – completed when the composer was just 27 and rich in allusions to the natural world, it absolutely fizzes with ideas and imagination. It’s the focal point of New Zealander Gemma New’s first Bridgewater Hall concert with the orchestra – which also includes Alissa Firsova’s potent evocation of the stormy affair between composer Alma Mahler and painter Oskar Kokoschka, and Elgar’s luscious song cycle, sung tonight by rising-star contralto Jess Dandy.