A comparison of porewater chemistry between intact, afforested and restored raised and blanket bogs

Afforestation is a significant cause of global peatland degradation. In some regions, afforested bogs are now undergoing clear-felling and restoration, often known as forest-to-bog restoration. We studied differences in water-table depth (WTD) and porewater chemistry between intact, afforested, and restored bogs at a raised bog and blanket bog location. Solute concentrations and principal component analysis suggested that water-table drawdown and higher electrical conductivity (EC) and ammonium (NH₄-N) concentrations were associated with afforestation. In contrast, higher dissolved organic carbon (DOC) and phosphate (PO₄-P) concentrations were associated with deforestation. Drying-rewetting cycles influenced seasonal variability in solute concentrations, particularly in shallower porewater at the raised bog location. WTD was significantly deeper in the oldest raised bog restoration site (~9 years post-restoration) than the intact bog (mean difference = 6.2 cm). However, WTD in the oldest blanket bog restoration site (~17 years post-restoration), where furrows had been blocked, was comparable to the intact bog (mean difference = 1.2 cm). When averaged for all porewater depths, NH₄-N concentrations were significantly higher in the afforested than the intact sites (mean difference = 0.77 mg L^-1) whereas significant differences between the oldest restoration sites and the intact sites included higher PO₄-P (mean difference = 70 μg L^-1) in the raised bog and higher DOC (mean difference = 5.6 mg L^-1), EC (mean difference = 19 μS cm^-1) and lower SUVA₂₅₄ (mean difference = 0.13 L mg^-1 m^-1) in the blanket bog. Results indicate felled waste (brash) may be a significant source of soluble C and PO₄-P. Mean porewater PO₄-P concentrations were between two and five times higher in furrows and drains in which brash had accumulated compared to other locations in the same sites where brash had not accumulated. Creating and maintaining brash-free buffer zones may therefore minimise freshwater impacts.