Complex sentence: In the 1970s a bird reserve was established on the marshes and it's currently run by the RSPB.on part of the Elmley national national nature reserve which is owned and managed by Elmley Conservation Trust.
Split into simpler sentences: In the 1970s a bird reserve was established on the marshes. It is currently run by the RSPB and forms part of the Elmley National Nature Reserve, which is owned and managed by the Elmley Conservation Trust.