Subsidence rates and carbon loss in peat soils following conversion to pasture in the Waikato Region, New Zealand

Drainage of peat soils for agriculture can lead to large carbon losses due to oxidation of peat. We estimated peat subsidence rates and total carbon losses, due to 40 years of dairy farming on a former peat bog, by measuring the thickness of peat and total carbon of farmland and of an adjacent unmodified peat bog above a marker tephra layer that was deposited about 200 AD. Subsidence rates averaged 3.4 cm yr –1 (95% confidence interval of 3.2 to 3.5 cm yr –1 ) and carbon loss averaged 3.7 t ha –1 yr –1 (95% confidence interval of 2.5 to 5.0 t ha –1 yr –1 ). On average, 63% of the subsidence was due to consolidation, with the remainder (37%) attributed to losses of organic matter due to peat mineralization.