GEOMORPHIC SETTING, CLASSIFICATION, AND PEAT-ACCUMULATION RATES OF SELECTED WETLANDS IN THE UINTA MOUNTAINS, UTAH

The glaciated valleys of the Uinta Mountains of northeastern Utah contain a variety of wetland types, including patterned peatlands of the Reader Lakes area (3300 m) and wet meadows (mostly non-peat-forming) of the Christmas Meadows area (2700 m). We conducted a variety of geomorphic, stratigraphic, hydrologic, and geochemical studies to collect baseline data related to wetland formation and classification, including radiocarbon dating of basal peats and the monitoring of water levels and chemistry in piezometers, springs, and streams.

The wetlands of the Reader Lakes area are classic patterned fens with string-and-flark morhpology and peat accumulations ranging from about 1 m in slope settings to more than 2 m on the valley floor. This may be one of the southernmost occurrences of this type of wetland in the Rocky Mountains. Four (4) distinct phytogeomorhpic subenvironments were delineated within the fen: (1) sedge (Carex spp.) expanses ("flarks"); (2) peaty ridges with small (<1 m) scarps ("strings"); (3) hummocky side slopes; and (4) riverine floodplains and levees. The wetlands of the Christmas Meadows area are wet meadows, developed on mineral soils, and marginal peatlands (peat <1 m). Both areas have slope wetlands that grade into riverine wetlands on the local floodplain.

Geochemically, both wetland areas have slightly acidic to circum-neutral surface water, indicating moderate-rich to extreme-rich fen condtions. However, both areas exhibit very low total dissolved solids (TDS), typical of poor-fen or even bog conditions. Similar wetland geochemistry has been observed in montane peatlands of Wyoming, and has been designated transitional rich fen conditions (Cooper & Andrus, 1994).

Radiocarbon dating of basal peat from the Reader Lakes area reveals that the fens began forming on the valley floor during the middle Holocene (ca. 5600 yr BP). The sloping patterned fen began to form approximately 3400 yr BP. The average rate of peat accumulation in the older floodplain sedge expanses (Reader Lakes area) has been 470 ± 70 mm per 1000 yr. The rate in the younger sloping patterned fen has been 270 ± 30 mm per 1000 yr. These rates are comparable to Holocene rates of peat accumulation reported by other workers globally.