Complex sentence: This use is known to date back to before 1600, and an estimated ten million tons of sediment was removed from the estuary between 1836 and 1989, mostly for agricultural purposes and mostly from the Doom Bar.
Split into simpler sentences: This use is known to date back to before 1600. An estimated ten million tons of sediment was removed from the estuary between 1836 and 1989, mostly for agricultural purposes and mostly from the Doom Bar.