By Devika Krishna Kumar NEW YORK (Reuters) - Citadel's commodities investments are up at least $1 billion for the year, according to three sources familiar with the matter, helping to drive strong overall performance at one of the world's largest hedge funds. Citadel, which manages more than $30 billion in assets, has profited from a strong performance in European natural gas and power trading, two of the sources said. Its flagship Wellington fund has gained more than 15% this year through October, one source close to the fund said.