Postglacial Stream Research Articles

Substrate, sediment, and slope controls on bedrock channel geometry in postglacial streams

AbstractThe geometry of channels controls the erosion rate of rivers and the evolution of topography following environmental change. We examine how sediment, slope, and substrate interact to constrain the development of channels following deglaciation and test whether theoretical relationships derived from streams reacting to tectonic uplift apply in these settings. Using an extensive data set of channel geometry measurements from postglacial streams in the Scottish Highlands, we find that a power law width‐drainage area scaling model accounts for 81% of the spatial variation in channel width. Substrate influences channel form at the reach scale, with bedrock channels found to be narrower and deeper than alluvial channels. Bedrock channel width does not covary with slope, which may be due to downstream variations in sediment flux. Bedrock channel width‐to‐depth ratios increase with discharge (or area) and sediment flux, consistent with increasing bed cover promoting lateral widening. We find steep, wide, and shallow bedrock channels immediately below lakes, which we interpret as the result of limited erosion due to a lack of sediment “tools.” Where sediment supply is sufficient to exceed transport capacity, alluvial channels develop wider, shallower geometries constrained primarily by flow hydraulics. Our results indicate that simple scaling models of channel width with drainage area are applicable at regional scale, but locally, channel width varies with substrate, and in the case of bedrock channels, with sediment flux.

Long‐term ecological patterns of alpine streams: An imprint of glacial legacies

AbstractWe examined for a glacial fingerprint on the ecology of two postglacial streams within the Swiss National Park over a 14 yr period (1999‐2013). One stream (Aqua) emerges from a small rock glacier (0.2% of the catchment area), whereas the other stream (Fuorn) flows from a remnant ice field (0.02% of the catchment area). In general, abiotic and biotic properties of each stream showed a typical glacial‐nival seasonality and strong between‐year synchrony. Benthic organic matter and periphyton biomass peaked during so‐called “windows of opportunity” in early spring and late autumn as in other glacial streams. Importantly, the streams contrasted regarding the glacial signature in which Fuorn had highest average turbidity, total inorganic carbon (TIC), particulate organic carbon and phosphorus levels, whereas Aqua had highest average nitrogen levels and lowest temperature and electrical conductivity. The difference in glacial signature also was evident in macroinvertebrate density (fourfold higher in Aqua) and diversity (lower in Aqua) differences between streams. In contrast to most proglacial streams, macroinvertebrate assemblages were relatively diverse and dominated by typical alpine stream species, stoneflies in particular. Both streams experienced increases in phosphorus and TIC following 2006 in response to external climate drivers with concomitant increases in simuliids and Leuctra stoneflies and decreases in heptageniid mayflies in Fuorn and Protonemura stoneflies in Aqua. Our results suggest that a glacial legacy is an inherent feature of most postglacial alpine streams, this being especially important as glacial streams transform to postglacial status in response to ongoing transformation of alpine glacial landscapes globally.

Salmon carcasses as a marine-derived resource for benthic macroinvertebrates in a developing postglacial stream, Alaska

Streams formed in Glacier Bay, southeast Alaska, following glacial recession rapidly support populations of spawning salmon. Using both observational and experimental approaches, we examined the importance of pink salmon ( Oncorhynchus gorbuscha ) carcasses for benthic macroinvertebrate communities, approximately 10 years after salmon first colonized Wolf Point Creek, a first-order, lake-fed stream. Macroinvertebrate abundance on carcasses naturally accumulating in the stream channel was low, dominated by chironomids ( Eukiefferiella spp.). Macroinvertebrate drift was significantly lower from artificial experimental channels containing salmon flesh (P < 0.001) compared with channels without. However, the density and community structure of macroinvertebrates colonizing rock baskets in channels was not significantly different between treatments. In a separate experiment, colonization of substrate trays with salmon and control (inert) fillets were associated with differences in community structure; simuliids dominated control fillets, and chironomids dominated fish fillets, while underlying stone substrate was colonized by a more diverse community including Ephemeroptera, Plecoptera, and Trichoptera taxa (EPT). Excluding simuliids, abundance was significantly higher on fish compared with control fillets (P < 0.001). These data suggest that scales and mucus prevent the direct consumption of flesh from whole carcasses, highlighting the role predators–scavengers in facilitating flesh consumption by benthic macroinvertebrates.

Macroinvertebrate community succession in Wolf Point Creek, Glacier Bay National Park, Alaska

Summary 1 Macroinvertebrate community development in Wolf Point Creek in Glacier Bay National Park, Alaska formed by ice recession was investigated from 1991 to 1994 as part of a long-term study of colonization now exceeding 20 years. Chironomidae, the first taxon to colonize the stream, still dominated the community comprising 75–95% by number, but species succession was apparent. 2 Species richness in August increased from five species in 1978 to 11 in 1991 and 16 in 1994. 3 Diamesa species, abundant in 1978 at densities exceeding 2 750 m-2, were not collected in 1994, while Pagastia partica dominated the community with densities exceeding 10 000 m-2. 4 Sixteen taxa, never previously collected, colonized the stream between 1991 and 1994 including representatives of Coleoptera, Muscidae, Trichoptera, and the first noninsect taxon, Oligochaeta. Colonization by new taxa was associated with an increase in summer water temperature and the development of riparian vegetation. 5 Inter-specific competition is suggested as a possible factor in species succession and is incorporated into a taxa richness model of community development in postglacial streams incorporating stable and unstable channels.

Origin of placer gold nuggets and history of formation of glacial gold placers, Gold Creek, Granite County, Montana

Placer gold along the upper portions of Gold Creek, near Deer Lodge, Montana, occurs in Pliocene(?) fossil alluvial placers, Pleistocene till, and alluvium. The upper Gold Creek placers yielded an estimated 175 to 200 kg gold during 1890 to 1990. The gold probably originated in veins, skarn, or replacement deposits in Paleozoic and Mesozoic sedimentary units near the contact with Late Cretaceous granodiorite of the Royal stock. Gold was initially concentrated in alluvial placers along the ancestral Gold Creek valley during late Tertiary (Pliocene) time. Pleistocene glaciers scoured the Pliocene placers from most parts of the valley, although the fossil placers were locally buried beneath till and gold was also incorporated into till that was deposited farther down valley. Gold from Pliocene and Pleistocene placers has locally been reconcentrated into alluvium as a result of postglacial stream incision.The placer gold occurs as coarse-sized, oval to elongate grains characterized by rounded protuberances and inclusions of quartz and sulfide minerals. In polished section the grains have alternating convex and concave borders interrupted by pits and embayments. Grain borders and interiors of embayments display supergene gold rims averaging 98.8 percent Au. Microprobe analysis of cores indicate average compositions of 83.6 percent Au and 16.5 percent Ag and spectrographic data indicate a trace element signature enriched in Cu, Pb, and Sb, which is compatible with derivation from mesothermal plutonic lode deposits associated with the Royal stock.

Stream Development in Glacier Bay National Park, Alaska, U.S.A.

The effects of hydraulics, sediment supply, channel condition, and riparian vegetation on stream development were examined in a chronosequence of five streams in Glacier Bay National Park where rapid retreat of glacial ice has exposed landscapes of different ages within a confined region. The youngest stream, Wolf Point Creek (deglaciated around 1955), is fed by a remnant glacier and had the highest suspended sediment concentrations of all streams (103-111 mg L-1 at baseflows). The main channel of Wolf Point Creek was relatively wide and stable because of the peak flow buffering effects of the remnant glacier and associated lake. However, the floodplain was periodically inundated and only sparsely vegetated and highly braided. The study reach at Nunatak Creek (deglaciated around 1950) was actively downcutting through fine glacial outwash deposits creating a deeper thalweg and redepositing some material near channel margins. About 100 yr after deglaciation (Ice Valley stream), woody riparian vegetation begins to stabilize streambanks and becomes established on gravel bars where it provides potential sites for incipient woody debris dams. The Ice Valley channel shows only minimal degradation. The increased accumulation of woody material and the subsequent colonization of gravel bars by alder and willow have begun to increase channel and bank stability and pool formation in Berg Bay South (deglaciated around 1830). Berg Bay South appears to be near equilibrium with respect to sediment supply and transport. Berg Bay North, a stream of similar age to Berg Bay South, stabilized more rapidly because of the buffered peak flows and greater sediment trapping efficiency attributed to the lakes and bogs in the north stream system. Fish habitat improves as postglacial streams develop: pools begin to form, riparian cover increases, and sediment transport decreases.

Studies On Crescentic Fractures and Crescentic Gouges with the Help of Close-range Photogrammetry

AbstractStudies on cresceatic fractures and crescentic gouges were carried out in the central part of the Alpine piedmont glaciation and the Quaternary Alpine mountain ice sheet. The test sites were situated in the pro-glacial area of the Hornkees south Berliner Hütte (Oberer Zemmgrund, Zillertal, Tyrol, Austria). This is also the area of the former confluence with another glacier which flowed at about 90° to Hornkees during the late-glacial period. It was therefore possible to make a comparison between different older glacier systems, different flow directions, and different ice thicknesses. About 12 000 minor features were measured by close-range photogrammetry; the result was 240 pairs of stereophotographs which were interpreted on first-order equipment. The single forms were registered point by point by coordinates. It was therefore possible to obtain three-dimensionally registered forms. One important result was that the late-glacial and the post-glacial glaciers of the Zemmgrund produced minor features with a large variation in size. A further result was the definition of possible glacier-flow directions by interpretation of the different directions of crescentic fractures and crescentic gouges. By this means it was possible to obtain several working reconstructions of the late- and post-glacial stream lines of the merged glaciers.

Studies On Crescentic Fractures and Crescentic Gouges with the Help of Close-range Photogrammetry

Abstract Studies on cresceatic fractures and crescentic gouges were carried out in the central part of the Alpine piedmont glaciation and the Quaternary Alpine mountain ice sheet. The test sites were situated in the pro-glacial area of the Hornkees south Berliner Hütte (Oberer Zemmgrund, Zillertal, Tyrol, Austria). This is also the area of the former confluence with another glacier which flowed at about 90° to Hornkees during the late-glacial period. It was therefore possible to make a comparison between different older glacier systems, different flow directions, and different ice thicknesses. About 12 000 minor features were measured by close-range photogrammetry; the result was 240 pairs of stereophotographs which were interpreted on first-order equipment. The single forms were registered point by point by coordinates. It was therefore possible to obtain three-dimensionally registered forms. One important result was that the late-glacial and the post-glacial glaciers of the Zemmgrund produced minor features with a large variation in size. A further result was the definition of possible glacier-flow directions by interpretation of the different directions of crescentic fractures and crescentic gouges. By this means it was possible to obtain several working reconstructions of the late- and post-glacial stream lines of the merged glaciers.

DRAINAGE INTENSITY IN WESTERN NEW YORK∗

Three drainage intensity regions of the Allegheny Plateau formed on renewed surfaces in response to conditions imposed by glacial and periglacial processes. Because of the severe transformation of an antecedent surface into streamlined form, postglacial stream concentrations are highest in the north and decrease southward as the degree of glacial modification diminishes, permitting the survival of relict landforms better adapted to normal erosional processes. Southward differences in surface mantle characteristics consonantly affect the generation of drainage lines.

Morphometric Analysis of Glaciofluvial Terraces in the Esk Basin, Midlothian

This paper describes the wastage of the last ice-sheet of the Esk basin, Midlothian, with particular reference to the dissected glaciofluvial valley-train along the course of the River North Esk. Following the formation of an icedivide to the south of the basin, glaciofluvial material was carried into the basin from the south-west and deposited in contact with a northward-retreating ice front in the central and northern parts of the basin. From mapping and measuring the heights of the fragments of the dissected valley-train, twelve stages of downcutting have been recognized, the first eleven related to northward glacial retreat and the last to post-glacial sea-level changes. Each glacial retreat stage is marked by a stream profile terminated by an ice-contact front; the heights of the terminal features correspond to the intake heights of a set of glacial meltwater channels on the eastern edge of the basin. The northward glacial retreat was interrupted by a minor readvance of ice from the north. This is indicated by the Roslin Till, a thin deposit of limited areal extent. The paper includes a detailed description of the field measurements undertaken and the height-distance method of representing glacial and post-glacial stream profiles; the errors inherent in the methods are discussed. IT HAS long been realized that east-central Scotland is a critical area for the study of glacial ice movements, as it has been affected by ice sheets emanating from both the Highlands and the Southern Uplands. This paper has developed out of a study of ice movements and of the landforms associated with glacial and deglacial phases of ice-sheet coverage. In Midlothian along the River North Esk, there is a belt of glaciofluvial sands and gravels about I6 km long, extending from south of Penicuik to near the coast north of Dalkeith. The dissected glaciofluvial surfaces are partly overlain by the most recent till of this district, the Roslin Till, but are nevertheless so well preserved that the writer was induced to attempt to measure the surfaces and relate them to the general glacial stratigraphy. The height-distance method of representing the glacial and post-glacial stream profiles is described in detail, as the errors inherent in this method are seldom explicitly stated. The account also offers an explanation for the presence of the Roslin Till that is contrary to earlier explanations. Description of the Esk Basin The Esk basin occupies about 300 km2 on the south side of the Firth of Forth (Fig. I). The western edge is marked by the Pentland Hills which extend north-east to south-west for about 30 km. The maximum elevation of these hills is just over 575 m, but there are more than I5o km2 over 300 m in height, the sandstones, tuffs, and lavas having been eroded to form domes and broad-shouldered spurs. On the eastern side, the Roman Camp ridge separates the basin from the upper Tyne valley. This ridge is a small anticline of Carboniferous rocks extending for about 13 km north-north-east to south-south-west and dropping in height from about 250 m at the southern end to about 80 m near the coast at Prestonpans. The synclinal Esk basin itself has a gently undulating surface with a steady gradient

The Physiography and Glacial Geology of the Valley Region, Park County, Wyoming

This article presents: (1) A brief description of the rocks together with the early geologic history of this region; (2) a consideration of the two plateau levels which may represent old erosion surfaces; (3) a discussion of the valley forms and their relation to the glacial history; (4) two hypotheses to explain the depth of erosion by glacial agencies and the amount of postglacial stream erosion. The first hypothesis postulates a small amount of ice erosion and a large amount (500 ft.) of postglacial stream erosion in the lower South Fork Valley together with narrow gorge cutting (600 ft.) in the tributary streams. The second hypothesis, which is favored, requires deepening of the lower South Fork Valley to its present depth by glaciation. This overdeepening left the tributaries as hanging valleys and postglacial erosion was responsible for cutting gorges 600 feet deep in the tributaries and also for cutting the box canyon 500 feet deep in the upper South Fork.

THE PRESENT STATUS OF SCOLOPENDRIUM IN NEW YORK STATE

The purpose of this paper is to offer data concerning the occurrence and abundance of Scolopendrium vulgare Sm. in the central New York area. Its former distribution is also considered and comparisons are made in an effort to throw some light upon its probable future. The work was begun in the autumn of I9I6, and was completed in January, I92I. Data concerning several of the colonies have been obtained from field notes and other information kindly placed at my disposal by Dr. Loren C. Petry of Syracuse University, Dr. M. S. Markle of Earlham College, and Dr. John B. Todd, a physician of Syracuse. While certain topographic conditions due to glacial action are coincident with the occurrence of Scolopendrium in this region, it is not deemed necessary to give details of this topography' beyond a brief mention of the three well-defined situations under which Scolopendrium occurs. These situations are: (a) on the south slopes of glacial channels, which usually extend almost due east and west; (b) on the south and west slopes of deep plunge basins which head such channels; (c) on the west slopes of steep gorges cut by post-glacial streams flowing in a northerly direction. The latter situation occurs only at the Chittenango and Perryville Falls stations. These three situations are all similar in certain respects. The slopes are usually bordered by an overhanging cliff, and in all instances where this is the case Scolopendrium occurs well below the cliff, about midway of the slope. A further characteristic of its occurrence is that of growing in distinct groups or colonies, with no scattered plants between. In this paper the term station is applied to the widely separated regions; distinct areas within the stations are termed substations, and these may in turn be divided into colonies. The first comprehensive account of the occurrence of Scolopendrium in the New York area was published by Maxon (2) in I900. In this paper he gives an account of the discovery of the various stations of Scolopendrium in America, along with facts concerning its condition at various stations at that time. Since I9I6 the stations in central New York cited by Maxon have been relocated, the surrounding areas examined, and all discoveries 1 For a discussion of the physiography of this area the reader is referred to the series of papers on this subject by Dr. H. L. Fairchild, and especially to his Glacial Waters in Central New York, N. Y. State Museum Bull. 127. Albany, I909.