UN-PATTERNING PATTERNED PEATLANDS: AN ECOHYDROLOGICAL FEEDBACK TO CLIMATE CHANGE

Many peatlands are characterized by surface microforms consisting of hummocks and hollows and in some peatlands this microtopography is arranged into larger ridge and pool patterns. These ridge and pool patterns are oriented perpendicular to the slope of the peatland and are believed to form due to differences in water table controlled peat accumulation rates. Indeed a unimodal relationship between water table position and peat accumulation has been observed in both contemporary gas exchange and paleo-ecological studies with pools and ridges generally representing a source of CO2 and lawns being net carbon sinks. We suggest that the ecohydrological processes controlling peatland carbon cycling represent an important feedback to climate change and that patterned peatlands will un-pattern in a drier climate. We test this hypothesis by applying contemporary carbon storage-water table relationships from a subarctic peatland to a simple peatland hydrological model and compare these results with a field-based water table drawdown experiment. Model results demonstrate that a climate change from wet to dry conditions can cause the microtopography of pools and ridges to disappear. Long-term peat accumulation rates were enhanced by a fluctuating water supply: dry periods prevented microtopography from becoming too strong, allowing high rates of peat accumulation during subsequent wet periods; and the microtopography maintained by wet periods helped to retard runoff and thereby enhance peat accumulation in dry periods. These model results are confirmed by the field experiment where hummocks lost more CO2 following water table drawdown while hollows remained unchanged and in some cases became a larger sink for atmospheric CO2.