James S. Aber
The upper Cucharas Creek drainage basin has been investigated for the past several years by ESU faculty, students,1 and visiting scholars.2 Studies have focused on Pleistocene (ice age) and Holocene (recent/modern) environmental conditions, including the extent of glaciation, periglacial (frozen ground) phenomena, dendroclimatology, lichenometry (Vopata et al. 2006), and wetland conditions. The region in question includes a substantial complex of end and lateral moraines at Bear and Blue Lakes and extends upward to Trinchera Peak, spanning an elevation range from about 3000 m to over 4100 m.
|Map of the upper Cucharas Creek and Culebra Range vicinity, south-central Colorado. Extent of Pinedale Glaciation is indicated by green shading. Bogs are located in kettleholes of an end moraine between Blue and Bear lakes: 1 - Cottongrass bog, 2 - Beaver bog. Adapted from Aber (2008, fig. 2). |
|View from Cordova Pass westward to the Culebra Range. Typical spring snow cover depicted in May 2004. Glaciers in three valleys (1,2,3) descended and joined to build a massive moraine complex where Blue and Bear lakes are located.|
|View from crest of Culebra Range down to the east. Bogs are situated in kettleholes of the moraine complex at Blue and Bear lakes. 1 - Cottongrass bog, 2 - Beaver bog. Photo date Sept. 2005.|
|Panoramic view of Cottongrass bog looking southward; east to left, west to right. Picture is assembled from three images that were taken from a tall tree (~8 m high) on north side of bog. E. Volkova stands in water to left side. Images taken in late Aug. 2005.|
|Panoramic view of Beaver bog looking toward northwest; east to right, west to left. Picture is assembled from three images that were taken from a tall tree (~8 m high) on southeast side of bog. Images taken in late Aug. 2005.|
|View looking southward over central and western margin of Cottongrass bog. Small trees and woody vegetation can be seen on the near margin. Image date late Aug. 2005.|
|Left: western margin of the bog with cottongrass in the foreground. Right: closeup view of cottongrass. Image date late Aug. 2005.|
|Closeup view of bog center showing higher stand of emergent aquatic vegetion. Image date late Aug. 2005.|
|Closeup view of moss growing beneath various grass and herbaceous plants. Moss along with roots of other plants is the primary constituent of the underlying peat. Image date late Aug. 2005.|
|Panoramic view of the Beaver bog. Notice numerous channels cutting through the bog surface. Peat is exposed in walls and floors of these channels. Dead spruce trees to right stand on an old beaver dam.|
|View from northern margin of the bog toward the southwest. Notice brushy vegetation, which indicates a relatively low water table beneath the surface. Image date late Aug. 2005.|
|Soil pit in the brushy zone, near center of bog. A temperature data logger is buried ~½ m deep. Notice peat piled behind the hole and lack of water at bottom of hole, indicating low water table. Image date early Aug. 2006.|
A long-term soil temperature record was collected from early September 2005 until early August 2006. The temperature logger was buried ~½ m deep in peat near the center of the bog. Beginning in late summer just below 10°C (50°F), temperature declined steady reaching a stable level just above freezing in January 2006. This stable temperature continued until May, after which temperature gradually increased, finally reaching ~10°C again in late July 2006.
This region currently is included in plant hardiness zone 5, meaning that minimum winter air temperature is typically in the -10 to -20°F range (-23 to -29°C)--see hardiness zone map. However, the insulating effect of peat and snow cover prevented freezing at shallow depth in the bog throughout the long, cold winter. This temperature regime is characteristic of many bogs in cold climates and has important implications for year-round biologic activity and organic conditions in the shallow peat.
Blue and Bear lakes, upper Cucharas Creek valley.
A peat core was collected from near the center of Beaver bog to determine peat thickness and date the age of the basal peat. The core was 2½ m long, and the basal peat yielded a conventional radiocarbon age of 3420±40 years before present (BP) with a corrected calendar date of 3700 to 3630 years BP (Beta 2007). This suggests that peat accumulation begin nearly four millennia ago during the Neoglacial period of cooler, wetter climate in the late Holocene. Given a thickness of 2½ m and maximum age of 3700 years, the average rate of peat accumulation is about two-thirds mm per year, which is typical for bogs in cold climates.
|Peat core extracted from near the center of Beaver bog by students in field geology. Left: coring tool extended to 2½ m length. Right: core laid out on plastic. Below: closeup view of the basal end of the core. Photos taken June 2007.|