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The Caribou-Poker Creeks Research Watershed (CPCRW) is a 104 km2 basin north of Fairbanks, Alaska. The watershed is reserved for ecological, hydrological, and climatic research. It is owned jointly by the State of Alaska and the University of Alaska Fairbanks. Much of the research is done by the Bonanza Creek Long Term Ecological Research Program.
The entrance to the Research Watershed is located on the Steese Highway about 31 miles from Fairbanks. Access is restricted, and permission for access or to conduct research can be obtained by contacting the Site Coordinator, Jamie Hollingsworth.
Miscellaneous maps and diagrams
Description and Location
The Caribou-Poker Creeks Research Watershed (CPCRW) is located in the Yukon-Tanana Uplands of the Northern Plateaus Physiographic Province (Wahrhaftig 1965), near the town of Chatanika in interior Alaska. It is centered on 65o10' N latitude and 147o30' W longitude, and can be found on the Livengood A-1 and A-2 USGS 1:63,360 topographic map quadrangles. The Yukon-Tanana Uplands are a region of northeast-trending, round-topped ridges with gentle slopes. The elevations of these ridges range from 450 to 900 meters with rises of 150 to 500 meters above the adjacent valley bottoms. The alluvial-covered valley floors are generally flat.
The CPCRW basin is a northeast-southwest trending oval about 16 kilometers and eight kilometers wide. The total area of the watershed is about 104 km2, with the Caribou Creek drainage comprising about 40 percent of the area. Elevations within CPCRW range from 210 meters at Poker Creek near the Chatanika River to 826 meters at the northern part of the watershed.
The Caribou-Poker Creeks Research Watershed (CPCRW) is a relatively pristine, 104 km2, basin reserved for meteorologic, hydrologic, and ecologic research, with no current human influence (other than scientific research). The Boreal Ecology Cooperative Research Unit and Water and Environmental Research Center have been collecting climate and hydrology data since 1969, as well as ecological studies on a more sporadic schedule. The data collection infrastructure has recently been upgraded from analog (e.g. paper charts) to digital (e.g. solid-state dataloggers) instrumentation. In addition, access to the watershed has been upgraded by the construction of a bridge across the Chatanika River, completed on 5 August 1995. There is a rustic field camp with accommodations for sleeping and eating, and field laboratory with a generator for line power.
The CPCRW is unique among such research areas in the United States in that it is the only one in the zone of discontinuous permafrost, which comprises a large portion of the state of Alaska, including most of interior Alaska. It is fairly representative of upland headwater stream basins in subarctic Alaska. The hydrology of CPCRW is a major driver of the aquatic ecology and biogeochemistry of the basin, while events in the terrestrial portions of the watersheds set the stage. Hydro-biological research in CPCRW has several major thrusts: to assess the role of disturbance in the terrestrial landscape (e.g. wildfire, herbivory, logging) on subarctic stream ecosystems, to assess the influence of discontinuous permafrost on fresh water ecology, and to assess the validity of the River Continuum concept in a subarctic context.
The mosaic of plant communities found in the subarctic biome is structured by a number of ecological processes. Wildfire is common in the subarctic uplands, and is the primary reset mechanism for forest succession in terrestrial upland ecosystems. In the lowland floodplains, the meandering of large rivers exposes silt bars which are then colonized by shrubs and trees, initiating primary forest succession. Local conditions such as hydrology, topography and microclimate determine the path and rate of forest succession in both floodplains and uplands. Superimposed on this forest mosaic are insect and mammalian herbivores that can influence ecosystem properties such as palatability and decomposability of leaves and leaf litter, and indeed can restructure forest succession (e.g. massive tree mortality caused by spruce bark beetles). CPCRW does not contain the full range of these forest types and ages: stand-initiating fires, and perhaps some logging by early settlers, since the turn of the century have resulted in young (i.e. 60-90 year old) stands of birch and aspen on south facing slopes, while older uneven aged (e.g. up to 200 year) black spruce stands dominate on north facing slopes. White spruce may be under-represented. Stream valley bottoms are generally treeless. Moose and beaver are common in CPCRW, so it is likely that there are patches of herbivore-impacted vegetation. The tops of the peaks and ridges provide near-alpine habitat.
Permafrost is discontinuously distributed within CPCRW, determined by low sun angle at high latitude, local topography, and successional status. The permafrost mosaic of the surrounding taiga forest uplands exerts a powerful influence over hydrological patterns within the watershed. Stream flow is a mixture of highly variable shallow subsurface storm runoff events from permafrost dominated areas and consistent groundwater base flows from permafrost free areas. In addition to physical effects on stream ecology, these two distinct flow regimes have divergent influences on stream biogeochemistry with important ramifications for food webs. Permafrost here may be sensitive to global climate change because of its position close to the southern limit of permafrost in Alaska. In CPCRW, there are first order streams with a range of 4% to 55% of their catchments underlain by permafrost, allowing tests of a number of hypotheses of permafrost effects on stream ecosystems, including patterns of concentrations and export of carbon, nutrients and sediment.
The Caribou-Poker Creeks Research Watershed is entirely underlain by the Yukon-Tanana metamorphic complex (formerly the Birch Creek Formation). This basement complex of meta-sedimentary rocks covers approximately 75 percent of the Yukon-Tanana Uplands. Chapman et al. (1971) described the complex in the watershed as a greenschist facies, dominated by chlorotic and quartz-mica schists, with some micaceous quartzites, garnet-mica schists, phyllites, and possible greenstone or impure marbles. Immediately south of the watershed in the Chatanika terrain (Metz 1981) of the Fairbanks mining district, the rocks consist of quartzite, quartz-mica schist, mica schist, marble, amphibolite, and calc-magnesium schist (Swainbank and Forbes 1975).
Mertie (1937) assigned the formation to the Precambrian era based on its unfossilized, highly recrystallized rocks and its relation to fossiliferous limestone deposits. However, more recent work by a number of investigators as cited by Hawkins et al. (1982) concluded that the sedimentary protoliths were deposited from late Precambrian through late Paleozoic. Areas east and south of the watershed are intruded by granitic batholiths of Cretaceous age while to the north and northeast unmetamorphosed Paleozoic sediments are found.
Radiometric dates in the Fairbanks mining district range from 102.5 plus or minus 3 million years to 478.5 plus or minus 35 million years (Forbes 1982), with differences explained by thermal resetting of the mica dates (Hall 1985). This, however, corresponds to the date of recrystallization and not the age of deposition.
Hall (1985) identified four distinct fold and fabric generating events in the Fairbanks mining district. The study compiled by Hall indicated a dominant northeast trend in the regional structure. Koutz and Slaughter (1972) reported similar findings in CPCRW. The research watershed underwent metamorphism during the emplacement of the Pedro Dome intrusion, which is composed of a phorphyritic granite that forms a northeast trending antiform.
Outcrops in the watershed are rare, usually confined to the upper slopes and ridges, with the largest near the summit of Haystack Mountain.
Glaciation occurred in central Alaska during the Illinoian and Wisconsin (Pewe 1965). The watershed was not glaciated, as the snowline for the two events were 1,220 meters and 1,370 meters respectively. With the snowline at such a high elevation for interior Alaska, only 3-5% of the Yukon-Tanana Uplands was glaciated (Pewe et al. 1967). The watershed was, however, affected by periglacial action as indicated by the presence of small solifluction lobes, subdued block fields, and tors (Koutz and Slaughter 1972). (Taken from from Ray 1988 [below]).
Permafrost is ground that is continuously frozen through at least two successive cold seasons and the intervening summer. Globally, permafrost is found in higher latitudes and elevations, where mean annual soil temperature is below freezing (Brown and Andrews 1982; Young 1989). Nearly one-fourth of the earth's surface is influenced by permafrost (Brown and Andrews 1982). Ice-rich permafrost is commonly impervious to infiltration of water (Young 1989), providing the basis for the "paradox of the arctic," i.e. the abundance of saturated soils and impressive biological productivity of vegetation despite very low annual precipitation. In colder regions such as the North Slope of Alaska, permafrost is "continuous," underlying virtually the entire landscape except beneath large water bodies. In the somewhat warmer subarctic regions such as the taiga of central Alaska, permafrost is discontinuous and is found in locally cold settings (e.g. north-facing slopes and low-lying, poorly drained locales). In interior Alaska, where permafrost is present, temperatures of the upper layers of the permafrost are in the range of -0.5C to -2.0C.
Permafrost presence and the depth of summer thaw (the "active layer") are major controls on vegetation distribution and productivity. In central Alaska, discontinuous permafrost, topographic variations and varying surficial geology result in a mosaic of plant communities, typified by white spruce (Picea glauca), birch (Betula papyrifera) and aspen (Populus tremuloides) stands on south-facing slopes with dry mineral soils with a thin organic horizon (2-10 cm organic layer), and black spruce (Picea mariana) stands on north-facing slopes and in low-lying areas with thick (50-100 cm) organic soils (Viereck et al. 1986). Soil carbon density is high in boreal ecosystems compared to other, warmer systems (Schlesinger 1977; Post et al. 1982). Soil carbon densities reflect the balance between input (organic matter production) and decomposition. In the cold and often water-saturated soils common at high latitudes, decomposition is much reduced and, while primary production is low, soil carbon still accumulates over very long time periods. Thus, there is a positive relationship between the amount of soil organic matter and the amount of permafrost in a watershed.
Permafrost also affects the hydrological regimes of subarctic streams: streams dominated by permafrost are more "flashy," i.e. more extreme, than those relatively permafrost-free (Carlson 1974; Dingman 1973). Snowmelt runoff is later and higher in a permafrost-dominated basin than snowmelt runoff from a permafrost-free basin. Likewise, peak stormflow discharge from a permafrost-dominated basin is much higher than in a non-permafrost stream (Figure 1), but during rain-free periods and in winter, flow is much lower (Haugen et al, 1982). This pattern is a result of the flow-paths of precipitation as it travels to the stream. On permafrost dominated north-facing slopes, precipitation enters the thick organic layer and flows above the permafrost to the stream. On permafrost-free south-facing slopes, precipitation enters the bedrock groundwater, and is released much more slowly to the stream. Differences in discharge result in different patterns of carbon and sediment flux from basins with differing amounts of permafrost, and likely result in different patterns of channel geomorphology and nutrient flux (see below). Thus, the synergistic effects of altered flowpath and organic carbon accumulation combine to make permafrost soils true wetland soils.
As mentioned above, central Alaska is the region of discontinuous permafrost. General circulation models all predict that global warming from increased concentrations of radiatively active gasses will occur earlier and to a larger extent at high latitudes. Because the temperature of permafrost in this area is so close to the melting point, we are at what might be called the "thermal ecotone," that is, the region in which small changes in temperature will have large consequences to ecosystems. Colder regions (i.e. colder than interior Alaska) must experience larger warming increments before permafrost melting occurs. Thus, we believe that interior Alaska is an ideal area to investigate and monitor the potential effects of climate change.
The Caribou-Poker Creeks Research Watershed (CPCRW) is about 50 km northeast of Fairbanks and slightly higher in elevation (210 m at the lowest point) than the Fairbanks International Airport, where Fairbanks weather data are collected (about 140 m). Hence, temperature and precipitation are also slightly different. The figure below shows daily minimum and maximum air temperatures at the Fairbanks airport, in the Caribou Creek valley bottom, and at the top of Haystack Mountain, at 775 m (check this!) on the western boundary of CPCRW. Note that the daily range is less on Haystack Mountian, but greater at Caribou Main, than at Fairbanks. Although summer temperatures are colder on Haystack than at Caribou Main, winter temperatures are warmer, and the mean annual temperature (1975-1979) was -3.3oC on Haystack and -4.9oC at Caribou Main. The long-term mean annual temperature at Fairbanks is -3.5oC (Haugen et al. 1982).
Physical and hydrologic characteristics of the Caribou-Poker Creeks Research Watershed.
Tributaries of Poker Creek are designated with a P, and tributaries
for Caribou Creek are designated with a C. Links are provided to
the site description database for those basins that have ongoing
studies. If there is no link, then the basin is not currently being
Soils of Caribou-Poker Creeks Research Watershed
During the Illinoian and Wisconsin glaciations, large amounts of glacial silt were deposited in the braided river channels of the Yukon and Tanana Rivers to the north and south of the Yukon-Tanana Uplands. Southerly winds transported this silt and deposited it in the uplands as loess. The thickest loess deposits in the area are on south-facing slopes and in valley bottoms immediately adjacent to the Tanana River. In CPCRW, there is a but a thin cap of loess on most sites.
Rieger et al. (1972) identified seven soils series in the reasearch watershed
(Table 1, Figure 1). These seven series can be grouped into two general
categories: permafrost-dominated soils that are poorly drained and have
high moisture and ice contents, and well-drained, permafrost-free soils
(Figure 2). See permafrost page for more information.
Figure 1. Soil type distribution in Caribou-Poker Creeks Research Watershed (after Rieger et al. 1972).
Following the 1967 Fairbanks flood, it was realized that very little was known about the precipitation and hydrology of upland headwater streams in interior Alaska, and that all the USGS gages were on major rivers and did not predict the 1967 flood. The Inter-Agency Technical Committee for Alaska (IATCA), which had been set up under the president's Water Research Council, had a mandate to "develop a comprehensive plan for use as a general guide by all agencies in establishing hydrologic stations required in connection with developing the water resources of Alaska" (Slaughter and Lotspeich 1977). A research coordination committee was created to, among other things, identify an upland taiga watershed for designation as a research watershed for "long term studies of complete catchments in permafrost-dominated uplands" (Slaughter and Lotspeich 1977). The Caribou and Poker Creek watersheds were identified as the most likely, because they would provide ease of access, were of manageable size, had a lack of human influence, and were owned by state and federal agencies. In 1969, a Cooperative Agreement between the IATCA and the Alaska Department of Natural Resources (DNR) was written and signed, designating the basin as the CARIBOU-POKER CREEKS WATERSHED for a period of 50 years, and outlining the responsibilities of the signing parties. This document says that DNR will "recognize research into water and land/water related resources... ...as being the presently known highest and best use of these lands, and to permit only compatible uses." The agreement was amended to delegate to the Institute of Northern Forestry (INF), USDA Forest Service, "authority and responsibilities" set forth in the original agreement. INF has been managing the site since the early 1970s under the assumption that the agreement of 1970 essentially constituted a lease, much like that between DNR and INF for the Bonanza Creek Experimental Forest.
Much effort has gone into improving the infrastructure of CPCRW over the years. In the initial years of the early 1970s, access was by foot or by helicopter. Various structures and instruments were donated by cooperating agencies, including a laboratory trailer that was airlifted onto site by a Chinook helicopter and another laboratory trailer donated by the Geophysical Institute and airlifted in with a Sikorsky skycrane helicopter. Trails were cut during the early 1970s for snow machine and off-road vehicles, and the primary access was over Haystack Mountain from the Elliott Highway. Several miles (perhaps 10) of gravel roads, including four bridges, passable by four-wheel drive pickup truck were constructed in the late 1970s. These roads and one bridge are in need of repair. Since the construction of the road "system," the main access to CPCRW has been by fording the Chatanika River at about mile 31 Steese Highway. As one might imagine, access was limited or impossible during spring breakup and summer storm events. A steel cable and a basket on pulleys provided limited access in times of high water. In 1995, with cooperation from the US Army and CRREL and funding support from the US Forest Service, a Bailey bridge was constructed across the Chatanika River, immensely improving access to CPCRW.
Since it's inception, research at CPCRW has focused on hydrology and climate. Initially, streams were gauged by manual methods on a circum-weekly schedule by personnel that hiked into the watershed. In the mid- to late 1970s, fiberglass Partial flumes with water level recorders were installed at five sites, and water level recorders were installed at several other sites with streams too large for flumes. Many of the large capacity rain gauges were installed by helicopter. Hydrology and climate data have been collected continuously since 1970, although individual sites may not have a complete record. Also, due to logistical difficulties, discharge data for snowmelt runoff are often missing.
In December of 1993, the leadership of the Bonanza Creek Long Term Ecological Research (BNZ) program requested of the National Science Foundation that CPCRW be added to the Bonanza Creek Experimental Forest (the main site for BNZ), and that the name and acronym be changed to BNZ-CPW to reflect the additional site. The addition was approved, but the name change was not, so now the BNZ LTER actually includes both the original site at the Bonanza Creek Experimental Forest (BCEF) and the CPCRW site even though the name does not reflect that. Thus far, most of the LTER-related research in CPCRW has been aquatic, but there are plans to expand terrestrial research to CPCRW, especially research on the effects of large-scale disturbance such as wildfire and timber harvest.
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The Bonanza Creek LTER, including this website, is supported by the National Science Foundation through awards DEB-1026415, DEB-0620579, DEB-0423442, DEB-0080609, DEB-9810217, DEB-9211769, DEB-8702629 and by the USDA Forest Service, Pacific Northwest Research Station through agreement number RJVA-PNW-01-JV-11261952-231. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the supporting agencies or the program as a whole.
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