MODELING GEOMORPHIC AND GEOCHEMICAL CHARACTERISTICS OF ALPINE FEN SYSTEMS IN THE SAN JUAN MOUNTAINS, COLORADO

Fens are dynamic landform systems that are influenced by various components ranging from geomorphology, hydrology, geochemistry, climatology to ecology. Fens occur throughout the San Juan Mountains of Colorado, which contain thousands of fens. Five fens were studied in the San Juan Mountains, each extending ~ 0.4 km² and 0.7 km² in area and situated higher than 3,000 m in elevation. Although numerous studies have focused on the ecological aspects of fens, only a couple of studies have investigated the geomorphological, hydrological, and geochemical aspects of these forms. Determining the role that these components play in fen development and activity is fundamental to understanding the geological role fens play in alpine environments. Geomorphological, hydrological, and geochemical data were collected and used as inputs to a dynamic model. Detailed geomorphological mapping provided data for the physical characteristics; isotopic analysis of Pb suggested fens serve as sinks as historical recorders of lead (Pb), and analysis of cores containing ¹³⁷Cs suggests rates of recent accumulation of sediment in the fens. A model using STELLA^® software simulated inputs, outputs, pathways, storages, and thresholds of the fen system. Atmospheric, hydrological, geomorphological, and geochemical subsystems were linked to simulate flows of energy and mass through an alpine fen system. By separately altering subsytems of the STELLA model, the role of alpine fens can be better understood. The results from the simulation highlight fen development in an alpine environment.