In its natural state, peatland is one of the largest carbon stores in nature. This is because the soil is so waterlogged and low in oxygen that dead plant material breaks down very slowly. The plants do not fully decompose but instead accumulate over thousands of years, forming thick layers of peat. When a peatland is drained for agricultural use, the water level drops and oxygen enters the peat layer. Microorganisms can then break down the old plant material much faster, releasing carbon that has been stored for many years as the greenhouse gas carbon dioxide (CO₂).