Latitudinal Trends in Organic Carbon Accumulation in Temperate Freshwater Peatlands

The 30-year rate of organic carbon (C) accumulation, based on cesium- 137 (137Cs), was measured in 15 freshwater peatlands across a latitudinal gradient from southern Florida (26°N) to northern Minnesota (47°N) to identify relationships between climate (temperature) and C accumulation. Organic C accumulation was inversely related to mean annual air temperature (MAAT, °C) in acidic peatlands (pH < 5) (C, g m

–2

year

–1

= 199 – 7.94 × MAAT;

r

2

= 0.64,

p

≤0.01), with greatest accumulation in the coldest climate. There was a weak but nonsignificant relationship between C accumulation and MAAT in circumneutral peatlands (pH > 5) (

r

2

= 0.41,

p

≤ 0.17). A regression model that incorporated both temperature and precipitation (rain factor,

f

= mean annual precipitation in cm/MAAT) was no more effective in predicting organic C accumulation than one with temperature alone (

r

2

= 0.57 for acidic peatlands,

r

2

= 0.36 for circumneutral peatlands). Across all sites, circumneutral peatlands sequestered less C (49 ± 11 g m

–2

year

–1

) than acidic peatlands (88 ± 20 g m

–2

year

–1

) regardless of temperature. Our findings suggest that, like terrestrial ecosystems, organic C accumulation in freshwater peatlands is linked to climate through the effects of temperature. Local factors such as pH, hydroperiod and nutrient enrichment also should be considered when assessing the potential of freshwater wetlands to sequester C.