Conservation, Nature Reserves Mangrove Swamp … Mud 8 May 2019 Ian Alexander The handsome mottled colours are called gleying. The reds and browns indicate oxidised (oxygen-rich) Iron and Manganese compounds; the greys or greenish tinges indicate reduced (oxygen-deprived) states of these minerals. Reduction occurs when the soil is waterlogged and bacteria living there extract oxygen from minerals, in the absence of free oxygen from the air.