FTIR spectral data and derivative indices produced across peatland forestation gradient and depth profiles for 30 peatlands in the midwest United States

Peatlands contain enormous carbon stocks, but the stability of this carbon is variable. Peatlands can vary in tree cover from completely open to forested with associated differences in peat quality. Peat quality, or potential for mineralization, is a contributing factor affecting how the carbon balance of peatland ecosystems could change with climate or land use changes. We compared the peat quality of open peatlands dominated by Sphagnum mosses to forested, or silvic, peatlands dominated by black spruce and tamarack or northern white cedar to quantify the effects of different carbon sources on peat quality. We used Fourier-transform infrared spectrometry (FTIR) to analyze peat properties throughout the depth profile of 30 peat cores across the hemi-boreal Upper Great Lakes region. We found that tree cover was associated with differences in both surficial and deep peat quality. Silvic peat had lower peat quality than Sphagnum peat as shown by FTIR indices. Sphagnum peat also had significantly higher peat quality at the surface compared to at depth. However, silvic peat showed no significant difference with depth in any indices. Our results indicate that the dominant plant functional type is a strong driver of peat quality as we identified key differences between silvic and Sphagnum peatlands. These relatively local differences are similar in magnitude to those found across biomes comparing tropical swamps to boreal Sphagnum peatlands. This implies that the dominant plant functional type (e.g. tree, shrub, graminoid, or moss) may be more important to peat quality than species identity - or even latitude - in peatlands.