The company that wants to build one of the world’s largest indoor salmon farms in Belfast has taken steps to preserve an undeveloped 80-acre tract that contains nearly 3 miles of the popular Little River Trail. According to a preliminary plan hashed out between Nordic Aquafarms Inc. and the Belfast Water District, the quasi-municipal utility that owns the land, the parcel around the Little River’s upper reservoir would eventually be transferred to a land trust, the company said in a statement. But first, the Norwegian-based salmon company plans to donate funds to Belfast so the city can purchase the parcel from the Belfast Water District at a reduced cost.