The effects of long term drainage and restoration on soil properties of southern Rocky Mountain sedge fens

Abstract

Mountain sedge fens are unique ecosystems which require thousands of years to form, provide refuge for rare plant species, and are easily disturbed by human activity. Peatland soils are significant players in the global carbon cycle, storing 1/3 of the terrestrial carbon stock. Drained peat is a persistent source of atmospheric CO2, restoring the carbon storage function to disturbed peatlands is an increasingly important justification for peatland restoration. I measured water table dynamics and CO2 flux at three small fens (< 10 ha) in SW Colorado for one year before and one year after restoration. The fens were hydrologically restored with the installation of small check dams in ditches that had drained the sites for a century. Water tables in restored areas increased during the driest periods of the summer from -45 cm below the surface to -15 cm. We measured CO2 flux (net ecosystem exchange (NEE), ecosystem respiration (ER), and gross ecosystem photosynthesis (GEP)) bi-weekly during the two growing seasons using an infrared gas analyzer attached to a 60 x 60 x 60 cm closed chamber. Mean NEE over the two year study was lowest in the disturbed areas (-1.28 g CO2 m-2 hr-1). Mean NEE in the reference area was -1.74 g CO2 m-2 hr-1 and in the restored areas was -2.19. Mean ER was similar across treatments, ranging from 0.77 and 0.92 g CO2 m-2 hr-1. Soil samples were extracted from three fens restored during this study and 1 restored in 1990 to test the effects of long term drainage and restoration on the physical properties of peat soil including; bulk density, porosity, % organic matter (OM), residual water content, and saturated hydraulic conductivity. Disturbance has caused significant changes in the peat soil including; 25% reduction in soil OM, increased bulk density, decreased porosity, and reduced saturated hydraulic conductivity. These effects persist in peat soil 20 years after restoration. Calculated OM losses of 1.4 to 3.6 kg m-2 have resulted in an estimated loss of 14.7 to 91 tons OM from each of these fens. The hydrologic regime and CO2 storage has been successfully restored in these fens, while the peat soil bears a legacy of disturbance two decades after restoration.