Site descriptions: Rivers and Streams

  The current stream research emphasizes long-term monitoring of two tundra rivers, whole-river nutrient enrichment experiments, intensive studies (¹⁵N tracer studies) and extensive surveys of selected stream reaches of contrasting size and landscape setting.

Long-term Monitoring and Nutrient Enrichment Studies

The Kuparuk River has been our primary site for long-term monitoring and whole-stream fertilization study. The Kuparuk River is a fourth order stream where it crosses the Dalton Highway about 10-km northeast of the Toolik Lake Research Station.

Phosphorus (as H₂PO₄) has been continuously added to the Kuparuk River every summer since 1983.  Within the first four years a dramatic response to fertilization was observed at all trophic levels with increases in epilithic chlorophyll accumulation and insect and fish (Thymallus arcticus) growth rates.  

The long-term fertilization of the Kuparuk River has led to major shifts in primary producer species and in production.  After ten years of P-fertilization, the epilithic diatom dominated system has been replaced by moss, primarily Hygrohypnum spp.  There has been a large impact of the increase in moss cover on the macroinvertebrate community structure.  While fertilization has stimulated growth in both young-of-the-year and adult Arctic Grayling in most years, so far the moss-driven changes in the lower trophic levels have had no apparent effect on fish.  Photo (right):  Aerial view of the Kuparuk R., downstream of the Dalton Highway and the pipeline.

Oksrukuyik Creek

A second stream, Oksrukuyik Creek is located approximately 20-km northeast of the Toolik Station. Like the Kuparuk River, this stream is a clear-water tundra river, but with discharge averageing about half that of the Kuparuk River. Oksrukuyik Creek was a whole-stream fertilization study site for 6 years and continues to be a long-term monitoring site.  The addition of phosphorus plus nitrogen, every summer from 1991 through 1996, stimulated production at all trophic levels.  The recovery from fertilization was monitored until 1999.  We are currently conducting maintenance level monitoring of an unfertilized reach (previous reference reach) of Oksrukuyik Creek.  Photo (left): Oksrukuyik Creek.

Kuparuk River (1983 - 1998) estimates of epilithic algal chlorophyll, percent bryophyte cover in riffles, chironomid and Brachycentrus densities, young-of-the-year and adult grayling growth from the reference (above the phosphorus dripper) and the phosphorus fertilized reaches

Intensive Stream Reach Studies

The objective of these investigations is to increase our understanding of nutrient processing by the stream ecosystem.  Using 15-N  labeled ammonium tracers, we have intensively studied biogeochemical processing in several different arctic stream types, including: lake outlet streams, beaded and non-beaded tundra streams, ranging in low summer flows from 0.02 to 30 m³/sec.  The first tracer addition studies took place in the Kuparuk River in 1991 (reference) and 1995 (P-fertilized reach).  These whole-stream 15-N enrichments have continued every year since, in order to study the ecology of arctic streams of different geomorphology and size.  In 1994, Blueberry Creek, the outlet stream of Lake I-8 in the Toolik Lake drainage, was the site of the 15-N tracer study. 

Intensive study reaches from 1996 through 2000 include the following: Lower Kuparuk R. (coastal plain braided river), E-1 (1st order lake outlet stream in the Toolik Lake drainage), Trevor Creek (glacier-fed stream), Hershey Creek (second order lake outlet stream and tributary to the Kuparuk River), and Toolik River (second order tundra stream).  Photo (left): third order lake outlet stream.

These studies have shown that tundra streams retain and recycle inorganic nitrogen very rapidly.  Uptake for NH₄ occurs within a few tens to hundreds of meters in the smallest streams and within a few kilometers in the largest streams in the basin (Wollheim et al. 2001).  All components of the food web become labeled with the tracer within a few weeks of addition.  The pattern of tracer movements allows us to determine the trophic connection in the food web.  Finally, tracer retention in the experimental reach has been measured for up to two years after the tracer addition was stopped.  The tracer data has made possible the development and testing of models of nitrogen flow in tundra stream ecosystems.

Toolik Regional Stream Surveys

We have surveyed several different streams across the eastern North Slope of Alaska, including tundra, glacier-fed, spring and mountain streams. The goal of these surveys is to characterize the biogeochemical variability among the major arctic stream types.  The biogeochemical characteristics of each stream type are mainly a function of landscape geomorphology (e.g., glaciers and springs).  The water sources for all of these stream types are very different and are dictated by their landscape position.  By studying these different stream types we will increase our understanding of the diversity of stream biota and the impact of regional change upon the stream networks. Photo (left): Ivishak Hot Spring, 1999.

Spring streams derive water from underground sources.  As a result, springs are rich in cations and nutrients, flow year-round and have stable water temperatures.  This provides a stable, enriched habitat for primary and secondary producers leading to high biomass and diversity of algae, moss and insects.  Photo (left): A spring stream tributary of the Echooka River, 1997.

Glacier streams are fed from glacier melt water.  While, glacier-fed streams have moderate nutrient levels, supplied by subsurface runoff of the melt water, they also have very high sediment loads.  The sediment is made up of fine rock particulates called glacial "flour".  This suspended sediment blocks light and scours the stream bottom. These streams also have highly variable discharge and water temperature on a diurnal cycle.  They are high gradient streams with unstable substrate.  All of these factors inhibit the colonization of substantial amounts of algae and insects, leading to the low biodiversity found in glacier-fed streams.  Photo (top left):  Glacier located approximately 40 miles south of the Toolik Lake Field Station, 2000 and a glacial tributary to the Ribdon River (top right), a glacier-fed river, 1998.

Mountain Streams are common along the North Slope of the Brooks Range.  They originate on the slopes of mountains and they are derived from rainwater and spring snowmelt.  Mountain streams also have a moderate amount of nutrients mainly supplied by subsurface runoff of rain and melting snow on the mountain slopes.  Unlike glacial streams, the mountain stream water is clear, with no glacial flour.  

The unstable flow regimes and substrate lead to low levels of primary and especially secondary production. Photo (right): tributary of the Atigun R., a mountain stream.

Tundra Streams drain the foothills and coastal plains of the North Slope, which is underlain by permafrost.  Tundra streams have clear water that is often stained light brown with organic matter from the tundra. Much of nutrients are locked within the permafrost, although there may be pulses of high nutrient levels during the spring runoff.  In contrast to the mountain and glacier-fed streams, the low gradient and more stable flows of most tundra streams allow for the colonization of benthic algae and insects. However, a short growing season and the lack of phosphorus limit substantial algal accumulation.  Where lateral inputs of surface and subsurface runoff  (seeps and springs) occur, bryophytes usually become established and local productivity may be as high as in some arctic spring streams.  Arctic Grayling densities are relatively high in tundra streams, mainly due to the stable flow regimes and high macroinvertebrate abundance. Photo:  (left) Toolik River, a beaded stream.

The Kuparuk River and Oksrukuyik Creek are both examples of meandering tundra streams.  They have rocky bottoms with alternating stretches of riffles and pools.  There is little or no overhanging vegetation and the dominant primary producers in these streams is epilithic diatoms, filamentous algae and some moss. Photo: (bottom left) Kuparuk River.

The beaded streams ("beaded" refers to the pools connected by short, stream segments) are formed by thermal erosion.  Typically these low order streams are shaded by overhanging vegetation (Salex spp.) and have peaty bottoms and channels, resulting in large amounts of allochthonous inputs (leaves and peat). Photo: (bottom right) Hershey Creek, and beaded reach.

 References

Wollheim, W.M., B.J. Peterson, L.A. Deegan, M.Bahr, J.E. Hobbie, D.Jones, W.B. Bowden, A.E. Hershey, G.W. Kling, and  M.C. Miller.  1999. A coupled field and modeling approach for the analysis of nitrogen cycling in streams. Journal of the North American Benthological Society 18(2):199-221.

Wollheim, W.M., B.J. Peterson, L.A. Deegan, B. Hooker, W.B. Bowden, K.J. Edwardson, and D.B. Arscott. 2001.  Influence of stream size on ammonium and suspended particulate nitrogen processing.  Limnology and Oceanography 46(1):1-13.

The Kuparuk River arises in the foothills of the Brooks Range and flows north draining a large area of the North Slope (Peterson et al. 1986). Our study site is from its headwaters to 5 km below its intersection with the Haul Road. The river down to this point has a main channel length of 25 km, drains an area of 143 km², and has an average channel slope of 3.13%. It is a clear-water stream, frozen solid from late September until late May. The Kuparuk River has a spring flood resulting from melting snow followed by lower flows in the summer. Summer water temperatures may reach 20^oC and average 8-10^oC. Stream discharge has ranged from 0.3 to 28.3 m3 sec-1 and the total suspended sediment load ranged from 0.4 to 35 mg ^-1. Flow nearly ceases by late September and the riffles become dry. The pools freeze solid in October and there is no flow until mid to late May.

The watershed of the Kuparuk River has terrestrial vegetation typical of this region. The vegetation of the upper basin consists of alpine communities at the higher elevations and moist tundra communities, predominantly the cotton grass Eriophorum vaginatum, in the foothills. Along the stream banks there are patches of dwarf willows and birches, some reaching 1 m in height. The upper layers of the soils consist of 30 to 70 cm of peat underlain by alluvial and glacial deposits of coarse sand and gravel. Permafrost is present throughout the area to a depth of up to 800 m; the mean thawed depth of the active layer is about 40 cm during August.

Nutrients are low in the Kuparuk. Typical mean annual values are > 0.5 µM NH₄-N, 1.5 µM NO₃-N, 18 µM DON-N, 0.3 µM total dissolved PO₄-P, and 0.2 µM fine particulate P. Nitrate concentrations are inversely correlated with flow whereas particulate phosphorus concentrations increase during high flows.

About 92% of the total organic carbon export is dissolved organic carbon (Peterson et al. 1986). The remaining 8% is particulate carbon (fine is 7% and large is 0.7%). The lateral input of carbon from the tundra is mostly in the form of peat because there is little movement of litter from the tundra surface; estimated input from bank erosion ranged from 17 to 25 mol C m^-2 y^-1. The detritus (particulate organic carbon) on the river bottom equals 2.3 mol C m-² while epilithic algal biomass is 0.02 mol C m^-2 and net primary production averages about 1 mol C m^-2 yr-¹.

The insect community in the river is dominated by four species. Black flies, predominantly Prosimulium martini, account for the major portion of secondary production in the river. Baetis lapponicus, the most abundant mayfly, contributes about 10 to 20% as much production as the black flies. The dominant chironomid is Orthocladius rivulorum. The next most important insect is Brachycentrus americanus, a caddisfly that contributes about 1% of the secondary production in the river.

The fish community has only one species, the arctic grayling (Thymallus arcticus), which feeds mainly on drifting insects and particulate matter although they also forage on pool bottoms. We commonly observe from two to five adult grayling (30-40 cm) in each pool. During the late summer, grayling move upstream to a headwater lake where they overwinter. Young-of-the-year (YOY) grayling exhibit high annual variations in abundance. In a good year, such as 1990, there may be as many as several hundred per pool. They are drift feeders almost from hatching, but also take food off the bottom.

The Kuparuk River is similar to many temperate streams in that allochthonous carbon inputs dominate the carbon cycle in the river in spite of the absence of shading vegetation. Much of this carbon is more refractory than the leaf and litter input to temperate streams. The standing stocks of chlorophyll on the rocks and the levels of gross and net primary productivity are low in comparison with temperate streams; apparently this occurs because of phosphorus limitation and the short growing season. The export of organic carbon from the watershed is about average for rivers but because the Kuparuk watershed has low terrestrial net primary productivity, the percentage of the total watershed organic carbon production exported via the river is relatively high (2-6%). Dissolved organic carbon is over 90% of the total export. The Kuparuk thus has a combination of characteristics that make it similar in some respects, but quite different in others, to boreal and temperate streams.

Key Streams references (reviews, overviews, summaries)