Leaching from restored peatlands: Is there a connection between porewater and runoff quality?

Ecological restoration has emerged as a conservation approach for peatlands, which often experience increased leaching of dissolved organic carbon (DOC) and soluble nitrogen (N tot ) and phosphorus (P tot ) following drainage. Restoration, however, introduces new disturbances that temporarily elevate leaching, while monitoring peatland runoff remains challenging, highlighting the need for new methods to assess restoration success. We studied changes and connections of porewater and runoff quality across three pristine and five drained and restored boreal peatland sites, quantified runoff loads, and developed regression models to estimate loads using porewater data. After restoration, median runoff DOC, N tot , and porewater and runoff P tot concentrations showed respective increases of 35, 34, 67, and 224% compared to the drained state, peaking within 1–4 years before declining. Porewater DOC and N tot levels started decreasing immediately. Porewater concentrations approached near-pristine levels within roughly 4–10 years depending on the parameter and site, whereas runoff levels stayed elevated through tenth year with only site-specific exceptions. Porewater and runoff DOC and N tot were strongly correlated, while P tot correlations varied among drained, restored, and pristine states. DOC, N tot , and P tot loads initially rose after restoration but declined over the following >3 years post-restoration to 61.3, 1.52, and 0.038 kg/ha/yr, typically falling below drained state levels. Regression models overestimated produced annual runoff loads from porewater concentrations by an average of 50.9%. Models predicted DOC most accurately, while performance for N tot and P tot was weaker and varied across sites. • Porewater quality reached natural levels roughly 4–10 years after restoration. • In the 10th year runoff quality remained elevated but lower than in the drained state. • Runoff load increased immediately after restoration but decreased for the later years. • Porewater quality correlated well with runoff quality. • We estimated runoff load from porewater concentrations with varying accuracy.