Runoff and Flowrate

There are many features, in addition to their morphologies, that make these streams unique. Because these streams occur in permafrost regions, the active layer (the layer of soil that thaws in the summer months) only reaches depths of 20-60 cm (Kane et al. 1989). Because of the shallow active layer, very little water can be stored in the ground; this means that the flow rate of beaded streams is strongly influenced by precipitation events. During periods of low precipitation, the flow rates of beaded streams are relatively low, but following major rainfall, the flow rate dramatically increases due to the limited groundwater storage. Flow rate is typically at its highest following snow melting in late May/ early June, as snow melting creates a large amount of runoff. This variability in flow throughout the summer months can be seen in the figure below which is sourced from Hydrology of Imnavait Creek, an Arctic Watershed. Note that this graph only displays the summer months; starting in September-October these streams begin to freeze over and do not begin to flow again until melting in May-June.

Stratification

Beaded streams often stratify during the summer months. Stratification occurs in beads during periods of low flow. During stratification, the beads the water in the beads divides into different layers. The surface water has higher temperatures, with the lower section being cooler and more nutrient-rich; the nutrient composition in the bottom layer is similar to the soil in the ground surrounding the pool. Merck et al. explain the reasons behind and impacts of stratification in Variability of In-Stream and Riparian Storage in a Beaded Arctic Stream. The diagram below depicts stratification; water that is transported through the active layer is cooled by the permafrost and plunges to the bottom of the bead. Due to the low flows, the water does not mix between the upper and lower layers of the stream, resulting in an upper layer that is active and flowing between beads, and a lower layer that acts as in-pool storage.

Although layers will have differences in metrics such as DOC, CDOM, conductivity, the most simple way to see stratification is by looking at temperature. Below is a graph showing the temperature, at three different depths, of a bead in Imnavait Creek in August 1985. This bead has distinct temperatures at different levels until late August, meaning it is stratified. Following periods of high flow, the layers mix and stratification collapses; this can be seen on August 15th when the temperatures for the different depths go from being distinct to all being the same temperature (Kane et al. 1989). It is important to note that there are many factors contributing to stratification, and stratification is not a constant feature in beaded streams. Throughout the summer months, beads may become stratified and unstratified; in one stream there may be one bead that is stratified, and one bead that is unstratified lying right next to each other. For a more comprehensive understanding of stratification, we recommend reading Variability of In-Stream and Riparian Storage in a Beaded Arctic Stream and Modelling In-Pool Temperature Variability in a Beaded Arctic Stream.

Formation and Expansion

There is no proven explanation for why and how these beaded streams form; however, the widely accepted theory was presented by Troy L. Péwé at the 1966 Permafrost International Conference. The theory is that beads form on the intersections of ice wedges; ice wedges form over hundreds of years in permafrost landscapes, as cracks in the permafrost are filled with water which expands when the soil freezes. Following thawing, the wedge is wider and the next year more water is able to fill and expand the crack, making the wedge wider and wider over hundreds of years. Troughs are formed in between these wedges and this is where the beaded streams are theorized to form. These troughs can be seen well at https://media.arcus.org/album/wildreach-graphics/3401.

Because ice wedges are continually eroding, some papers such as Distribution and biophysical processes of beaded streams in Arctic permafrost landscapes, hypothesize that beads will expand over time. They found that beads expand, but channels in between the beads remain constant. Formation of beaded streams and changes over time are both topics that are not well studied and the current literature and is something that future research could address.

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Our Research Goals

Our team is interested in identifying landscape controls on beaded stream transitions. Many beaded streams evolve from the beaded morphology to alluvial channels, which are channels made up of loose sediments that do not have beads. Currently, there exist uncertainties as to how easily and quickly beaded streams are eroded and transition into alluvial channels, as well as the permanence of these features. In order to investigate these transitions, we will measure slope, channel and bead dimensions, suspended sediment, discharge, and temperature in stream reaches before and after these transition zones. A large number of transitions will be studied and the conditions leading up to the transitions will be compared between streams. The beaded stream seen below is beginning to transition from beaded to alluvial. On the left side of the image, there are distinct beads in the river, but as the stream transitions, the beaded morphology begins to collapse; on the right-hand side of this image, it is very difficult to identify distinct beads. What landscape conditions prior to this reach of the stream influence the shift from the beaded pattern to an alluvial state?

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In addition to our goals to identify landscape controls on beaded streams, we are also hoping to collect data on a large number of streams in the Arctic foothills. Many of the current studies on beaded streams in the Arctic foothills do not focus on many streams, and most of them exclusively study Imnavait Creek because of its proximity to Toolik Field Station. Distribution and Biophysical Processes of Beaded Streams in Arctic Permafrost Landscapes is a paper that studies a large number of beaded streams, but much of the focus is on the Fish Creek watershed, which lies in the Arctic Coastal Plain. There is not a broad study of streams outside of this study, and collecting data on 10-20 streams in the Arctic foothills will be valuable in possibly understanding geographical differences in these geological features, as well as adding to the current lack of extensive data on beaded streams.

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Current Research

Beaded streams are not very well studied; we have currently found in the range of 15 peer-reviewed papers that study these geological features. Listed below are some of the published papers that are most relevant to our team’s current science goals. Many of the existing studies only focus on one stream, and most of them focus on the Imnavait Creek, which is a creek very close to Toolik.

Distribution and Biophysical Processes of Beaded Streams in Arctic Permafrost Landscapes is a paper that compares a larger number of streams. This study mapped 400+ beaded streams in Alaska, Canada, and Russia and compared the distribution and density of streams throughout the different regions. Then focusing on the Fish Creek watershed (a watershed to the north of Toolik and outside of the area we will study), they survey individual beaded streams. Importantly, they compare two streams in their transitions to alluvial channels, examining the slopes and drainage areas of the rivers leading up to the transition zones. This is the most similar study to our research goals, as they conduct a broad survey of streams as well as looking at transitions to alluvial. This study was largely conducted on the Arctic Coastal Plain; we will study the Alaskan foothills, and focus more heavily on transitional zones than this paper. Two transitional zones of streams were compared and as expected decreasing channel slope and increasing drainage area lead to these transitions, but sediment transport also likely plays a role.

It remains unclear if beaded streams are impermanent features. In Beaded Channels of Small Rivers in Permafrost Zones, Tarbeeva and Surkov conclude that beaded streams are not permanent hydrological features, and the beads are easily eroded and filled with sediment, morphing into alluvial channels. However, Arp et al. agree that sediments play a role in beaded streams transitioning to alluvial channels; however, they suggest this is done later in the watershed, and beaded morphology may be permanent in lower-order streams.

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Other Studies on Beaded Streams

Arp, C. D., M. S. Whitman, B. M. Jones, G. Grosse, B. V. Gaglioti, and K. C. Heim. “Distribution and Biophysical Processes of Beaded Streams in Arctic Permafrost Landscapes.” Biogeosciences 12, no. 1 (January 6, 2015): 29–47. https://doi.org/10.5194/bg-12-29-2015.

Kane, D. L., L. D. Hinzman, C. S. Benson, and K. R. Everett. “Hydrology of Imnavait Creek, an Arctic Watershed.” Holarctic Ecology 12, no. 3 (1989): 262–69.

Merck, M. F., and B. T. Neilson. “Modelling In-Pool Temperature Variability in a Beaded Arctic Stream.” Hydrological Processes 26, no. 25 (2012): 3921–33. https://doi.org/10.1002/hyp.8419.

Merck, M. F., B. T. Neilson, R. M. Cory, and G. W. Kling. “Variability of In-Stream and Riparian Storage in a Beaded Arctic Stream.” Hydrological Processes 26, no. 19 (September 15, 2012): 2938–50. https://doi.org/10.1002/hyp.8323.

Oswood, Mark W., K. R. Everett, and Donald M. Schell. “Some Physical and Chemical Characteristics of an Arctic Beaded Stream.” Holarctic Ecology 12, no. 3 (1989): 290–95.

Tarbeeva, A. M. and Surkov, V. V. “Beaded channels of small rivers in permafrost zones”, Geography and Natural Resources, 34, 27– 32, doi:10.1134/S1875372813030049, 2013.

Whitman, M S, C D Arp, B Jones, W Morris, G Grosse, and R Kemnitz. “Developing a Long-Term Aquatic Monitoring Network in a Complex Watershed of the Alaskan Arctic Coastal Plain,” 2011, 7.