Holocene Climate Change and Ecohydrological Responses Preserved in Subalpine Fens in Colorado

Stratigraphy and peat humification analysis of subalpine fens from a variety of sites in Colorado indicate that these peatlands preserve a unique Holocene record of climate change and ecohydrological feedback. Much of the research investigating the record of environmental change in peat archives focuses on high latitude or tropical bogs. Relatively little research has focused on midlatitude minerotrophic fens. However, a large number of fens occupy favorable sites in mountain environments. The conditions that favor peat development in the mountain west include the presence of springs fed by snowpack melting that extends into mid or late summer. This project has yielded a sensitive paleoenvironmental record extending through the Holocene. We were interested in determining how increases in summer temperatures early in the Holocene influenced precipitation, particularly summer monsoons, and thus, groundwater. A further question concerned the extent to which the fens preserve evidence of lower magnitude changes, including those associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Due to the relatively marginal conditions that allow fens to persist in the region, fens are very sensitive to fluctuations in climate and consequent hydrological responses. Our results indicate that warmer conditions earlier in the Holocene led to earlier snowmelt, particularly at lower elevations. We have found that fens located near the lower margins of the subalpine zone (<3100 m elevation) ceased to accumulate peat and reverted to alluvial depositional environments during periods of warming earlier in the Holocene, and then returned to peat accumulation when cooling occurred. These results are similar to results of other researchers working in the Sierra Nevada, California. Colorado fens at higher elevation persisted as peatlands throughout the Holocene, but warmer periods produced changes in the rates of peat accumulation and the degree of humification during these intervals. The changes in temperature associated with the MCA and LIA are reflected as changes in organic matter as determined by loss on ignition, and ecohydrological changes are evidenced in the results of peat humification. Based on this research we argue that potentially warmer summers over the next century will likely result in earlier snowmelt and the subsequent loss of lower elevation fens, and changes in the carbon sequestration of higher elevation fens in the subalpine zone. These changes will have significant impacts on water quality and hydrology in Colorado.