Variations in the water storage capacity of a mountain peatland with complex stratigraphy

Abstract

Peatlands in mountain regions commonly occur in valley bottoms and tend to have a complex soil profile due to the geomorphically dynamic environment. Characterization of the specific yield for mountain peatlands is rare despite that it is a parameter that is critical for modelling water table position, determining the water release rate and simulating carbon storage dynamics. The specific yield of a fen peatland in the Canadian Rocky Mountains, Alberta, Canada, was studied along with the factors affecting it. Specific yield was estimated using the water table fluctuation method for 82 rainfall events at a series of shallow well sites, totaling 225 event-well combinations. Specific yield showed strong depth dependency declining logarithmically with depth, but only within the upper 50 cm. Below 50 cm depth, the variability of specific yield increased. Specific yield at depth was controlled by spatial variations in peat-sediment stratigraphy. The bootstrapped, depth-integrated median specific yield [lower, upper 95 % confidence intervals] was 0.21 [0.17, 0.25] for the peat-mineral-gravel soil profile, 0.11 [0.07, 0.16] for the peat-mineral-peat soil profile, and 0.16 [0.12, 0.22] for the Carex-Sphagnum peat soil profile. The analysis also shows a strong effect of year, with lower specific yield occurring in drier years. The study has implications for the modelling of hydrologic and carbon dynamics of mountain fens, and for supporting low flows under climate change.