Complex sentence: The Port of South Louisiana, also based in the New Orleans area, is the world's busiest in terms of bulk tonnage and, when combined with the Port of New Orleans, it forms the 4th-largest port system in volume handled.
Split into simpler sentences: The Port of South Louisiana, also based in the New Orleans area, is the world's busiest in terms of bulk tonnage. When combined with the Port of New Orleans, it forms the 4th-largest port system in volume handled.