Power laws governing hydrology and carbon dynamics in northern peatlands

Environmental and biological variables fluctuate over different time scales. On the basis of power spectral analysis of 14 time series at four sites from northern peatlands (fens and raised bogs), the temporal variability of physical environment (temperatures, water tables) and biological variables (CO2 flux) shows power-law behaviour, with a scaling exponent ranging from about 0.5 to 1.5. The scaling exponents of air temperatures change from 1.5 at high frequency to 0.5 at low frequency, with a break point at diurnal period. Comparison with similar analysis of temperature data from climate stations suggests that the atmosphere above peatlands has more active heat exchange with waterlogged peatlands than with upland terrestrial ecosystems. Water tables from different peatlands show almost identical power spectra, with a scaling exponent of 1.0 over all time scales. CO2 exchange has more complex spectral structure, with two break points at daily and monthly periods. This spectral structure suggests scale-dependent influence of climatic and hydrological fluctuations on CO2 fluxes. CO2 flux responds to air temperature with a distinct diurnal spectral peak. These results indicate that time scales are important in discussing hydrology and carbon dynamics in peatlands, and that scaling up of short-term experimental results may be inadvisable. Further statistical analysis on drained and harvested peatlands would provide insights into understanding shift in peatland dynamics due to human disturbance.