Subsurface Complexity of Rocky Mountain Peatlands Regulates Carbon and Nitrogen Dynamics

Abstract:

Mountain wetlands, most commonly fens in the Rocky Mountains of North America, provide many important hydrologic, biogeochemical, and biological functions. Since these functions are often governed by subsurface structure, understanding the complexities of fen stratigraphy is critical. We used a 200 MHz ground penetrating radar (GPR) and soil core analysis to study the stratigraphy of nine fens in the southern Canadian Rocky Mountains. We discovered that wetlands that appear as fens at the land surface had a stratigraphy that ranged from pure peat to heavily stratified with silt, sand or marl mineral layers. We then evaluated, in one of these peatlands, how the presence of buried mineral horizons regulated peat carbon (C) and nitrogen (N) distributions and mineralization rates. Revealed was that cumulative C mineralization rates (after a 63 d lab incubation) in peat soils with silt and marl horizons were significantly lower than in those without mineral horizons, owing to variations in water content and TOC concentrations. Differences in TOC concentrations among varying stratigraphic configurations were most apparent deeper in the peat column implying that transport via groundwater may be important. Peat underlain by marl had the lowest net ammonification rates, likely due to the high pH. Our results suggest the development history of mountain fens is complex and highly spatially variable, dependent on the effects of local and regional geomorphic and environmental factors, and has important implications for peatland biogeochemical functioning.