Bridging the gap between models and measurements of peat hydraulic conductivity

Peat saturated hydraulic conductivity, Ksat, declines strongly with increasing degree of decomposition, providing a potentially important negative ecohydrological feedback that may buffer peatlands from climate-induced drying. However, the quantitative nature of this relationship is poorly understood. We measured downcore changes in Ksat and carbon-to-nitrogen concentration quotients (C/N) in fourteen shallow (~0.5 m deep, 0.1 m diameter) peat cores from a Swedish raised

bog. We used the C/N measurements to approximate the fraction of original peat mass remaining. A linear mixed effects (LME) model predicts log10(Ksat) from i) our C/N-derived estimate of fractional

remaining mass; ii) depth; iii) microhabitat (hummock, hollow); and iv) location (treeless bog center, treed bog margin). The LME model indicated no significant random effects or interactions between predictors, so we derived a non-linear multiple regression (NLMR) model to predict Ksat on its original scale. Both LME and NLMR models predict that Ksat decreases exponentially with depth and that Ksat is lower beneath hollows than beneath hummocks for equivalent depths below the

surface. Fractional remaining mass was an important predictor in the LME model, but not in the NLMR model. The distinction between central and marginal areas of the bog was not an important predictor. We demonstrate for the first time that the relationship between fractional remaining mass and Ksat is log-linear, and suggest revisions that should be made to peatland development models. In particular, depth – usually ignored in modeling studies – exerted a strong control over Ksat ndependently of decomposition and should be included explicitly in model algorithms.