Elsevier

CATENA

Volume 145, October 2016, Pages 68-82
CATENA

Estimates of late Holocene soil production and erosion in the Snowy Mountains, Australia

https://doi.org/10.1016/j.catena.2016.05.013Get rights and content

Highlights

  • Soil development rates comparable to previous alpine measurements (20–220 t/km2/yr)

  • Erosion rates were low (60 t/km2/yr) compared to non-alpine Australian hillslopes.

  • Soil development on balance exceeded erosion over mid-late Holocene.

  • Contemporary erosion rates > order of magnitude lower than grazing era

  • High soil development and low erosion rates attributed to alpine vegetation

Abstract

Soil production in actively uplifting or high precipitation alpine landscapes is potentially rapid. However, these same landscapes are also susceptible to erosion and can be sensitive to changes in climate and anthropogenic activity which can upset the balance between soil production and erosion. The Snowy Mountains, southeastern Australia, are a tectonically stable, low relief, moderate precipitation mountain environment. The alpine area is extensively blanketed by soil that has been subjected to more intensive episodes of erosion during past periods of anthropogenic disturbance and under cold climate conditions of the late Quaternary. In this study, rates of soil development and hillslope erosion were investigated using radiocarbon dating, fallout radionuclides and sediment cores collected from lakes and reservoirs. Estimated Holocene soil development rates were 20–220 t/km2/y. Erosion rates determined from the radionuclides 137Cs and 210Pb were equivocal, due to the inherent spatial variability of radionuclide inventories relative to apparent erosion rates. Estimated average erosion rates over the past 100 years, determined from 210Pbex inventories, were 60 t/km2/y (95% CI: 10, 90). Inventories of 137Cs observed at the same site implied that more recent erosion rates (over the past 60 years) was below the detection limits of the sampling method applied here (i.e. < 70 t/km2/y). The upper estimate of 90 t/km2/y is comparable to the mean erosion rate estimated using the radionuclide method for uncultivated sites in Australia and is significantly lower than that measured at sites were vegetation cover was disturbed by livestock grazing prior to its exclusion from the alpine area in the 1940s CE. Low erosion and high soil production rates relative to the lowland soils are likely related to extensive vegetation cover, which, in this context, protects soils against erosion and contributes to the formation of organic alpine soils, that rapidly accumulate organic matter by comparison to other soil types.

Introduction

On a global scale, alpine landscapes are recognised as regions of relatively high geomorphic activity (Dedkov and Moszherin, 1992, Milliman and Syvitski, 1992). This has been ascribed to their climate, which is typically cold and wet, tectonic activity and corresponding high elevations and steep slopes (high potential energy), which in combination promote rapid physical weathering, erosion and sediment transport (Milliman and Syvitski, 1992, Syvitski and Milliman, 2007, Vanmaercke et al., 2011, Walling and Webb, 1996). For example, rivers draining mountain basins transport a disproportionately large proportion of the global sediment yield, that is, 870 t/km2/y compared to 115 t/km2/y for the rest of the World's rivers (Milliman and Farnsworth, 2011). Especially in tectonically active mountain ranges, erosion can be so rapid as to equal or exceed the rate of uplift (Brozović et al., 1997, Koppes and Montgomery, 2009, Mitchell and Montgomery, 2006).

Despite high rates of geomorphic activity, the historical perception was that in cold mountain environments, rates of chemical weathering and, therefore, soil formation were low (e.g. Peltier, 1950). Contrary to this assumption, rapid rates of soil production have been measured in alpine environments, especially in regions experiencing rapid uplift and high precipitation. For example, in the Southern Alps New Zealand, where rainfall may exceed 10 m/y and uplift approximates 10 mm/y, soil production rates may reach 2.5 mm/y (Larsen et al., 2014), an order of magnitude higher than soil production rates measured elsewhere (Larsen et al., 2014). The potential significance of chemical weathering in mountain environments is further evidenced by the existence of extensive soil mantles in a variety of alpine settings worldwide (Dixon and Thorn, 2005, Egli et al., 2014, Norton and von Blanckenburg, 2010, Riebe et al., 2004).

Soils in high mountain environments have been shown to be sensitive to changes in climate and human activity, which alter soil production processes and may accelerate the erosion rates by multiple orders of magnitude (Barsch and Caine, 1984). Episodic changes in climate, vegetation cover, fire frequency and human disturbance are therefore likely to be important controls on the balance between soil production and erosion in some mountain environments (Hewawasam et al., 2003, Kirchner et al., 2001, Koppes and Montgomery, 2009, Schmidt et al., 2002).

In tectonically stable, non-glaciated, high to moderate rainfall, i.e. less than 2 m/y, alpine areas, such as the Snowy Mountains in south-eastern Australia, rates of soil production and erosion have received less attention. The Snowy Mountains have traditionally been viewed as distinct from other alpine regions (Costin, 1989, Kirkpatrick, 1994). This is due to their intra-plate setting and resulting tectonic stability and moderate relief (slopes) (Bishop and Goldrick, 2000). In addition, they experienced relatively limited Pleistocene glaciation (Barrows et al., 2001). These characteristics have facilitated the development of a relatively thick soil mantle (0.6 to < 1 m) over almost the entire alpine area (Costin, 1989). Nevertheless, the Snowy Mountains are considered to have experienced pulses of intensified sediment transport in response to changing climate during the late Quaternary (Costin, 1972, Kemp and Rhodes, 2010, Ogden et al., 2001, Page et al., 2009) and as a result of livestock grazing between the mid-1800s and 1940s CE (Costin et al., 1960).

The quantification of inherently spatially and temporally variable soil production and erosion rates remains a major challenge within geomorphology. Measurement of hillslope erosion has been undertaken by a variety of methods that can be broadly categorised into: plot and survey approaches (e.g. Costin et al., 1960); measurement of sediment yields by either stream gauging, or by measurement of the mass of sediment accumulated in geomorphic sinks, such as lakes (e.g. Neil, 1991, Tomkins et al., 2007); erosion tracer methods using fallout radionuclides (e.g. 137Cs and 210Pb) (Blake et al., 2009, Loughran et al., 1988, Porto et al., 2009, Ritchie and McHenry, 1990, Walling et al., 2003) and; the application of cosmogenic nuclides (e.g. Dixon and Riebe, 2014, Heimsath et al., 2002). These methods are each limited by the challenges of upscaling point measurements in time and space in relation to the representativeness of reference sites, the spatial heterogeneity of tracer fallout and transport and the issues of sediment storage and delivery (Chappell et al., 2011b, de Vente et al., 2007, Zhang et al., 2015). In addition, these methods provide data over different time periods, e.g. stream gauging typically provides short term data (event to decadal scale), radionuclides provide decadal to centennial scale data, and commonly used cosmogenic nuclides integrate over millennial scales. As a result, different approaches will commonly yield very different results (e.g. Tomkins et al., 2007, Wasson et al., 1996) that are then subject to various interpretations.

The objective of this study is to quantify soil development and erosion rates in a tectonically stable, currently non-glaciated mountain environment and to advance the understanding of the relative controls that changing climate and anthropogenic activities place on landscape stability and sediment budgets. In doing so the likely age of these soils is discussed, which in this setting is likely to be constrained by glaciation and/or periglacial processes to at least < 11–16 ka (Barrows et al., 2001, Costin, 1972). This study employs multiple methods to attempt to quantify rates of soil development, hillslope erosion and sediment transport. Hillslope erosion rates are investigated using fallout radionuclides (137Cs and 210Pbex) and by calculating sediment mass accumulation rates in alpine lakes and reservoirs. Soil development rates are examined using geomorphic and paleoclimate evidence combined with radiocarbon analysis. These approaches overlap in time, allowing the balance between soil development and erosion rates to be investigated. Results are placed within the context of past climate variability and athropogenic impact in the Snowy Mountains.

Section snippets

Regional setting

The Snowy Mountains are a high' elevation plateau of moderate (undulating) relief. Despite being the highest region of Australia, they reach an elevation of only 2228 m at their highest point (Mt Kosciusko) and local relief of the alpine area is usually < 200 m. The Snowy Mountains are the erosional remnants of uplift associated with the Cretacous breakup of Gondawana, beginning at 100 ma with most intense tectonic activity centered around 55 ma (Bishop and Goldrick, 2000). Their intraplate setting

Study locations

Estimates of rates of soil development, hillslope erosion and sediment yield were undertaken within the catchment of Guthega Reservoir, located in the headwaters of the Snowy River (Fig. 1). Guthega catchment includes the highest peaks of the Main Divide. Sixty-five percent of the catchment lies within the alpine zone, which is characterised by both high relative precipitation and high runoff coefficients (Reinfelds et al., 2014). Much of this area is comprised of high elevation plateaux

Radiocarbon ages

For the Guthega soil catena, returned 14C AMS ages for the A/BC horizon transition show good agreement between the three profiles with ages for the ridge-crest ranging from 2330–2430 y cal. BP; 2520–2750 y cal. BP for the mid-slope and, 2150–2310 y cal. BP in the toe-slope profile (Fig. 2 and Table 2). Minimum age differences are as small as 30 years between the ridge-crest and toe-slope and do not display a consistent downslope relationship. The maximum radiocarbon age of the organic A horizon is,

The age of alpine and subalpine soils in the Snowy Mountains and its implications for sediment production

It is generally accepted that late Pleistocene sediment erosion and transport rates in the highlands of Australia were greater than present (Kemp and Rhodes, 2010, Page and Nanson, 1996, Page et al., 1991). This is demonstrated in the major rivers which drain the Snowy Mountains (the Murray and Murrumbidgee Rivers), which are known to have experienced markedly different channel forms and sediment characteristics, i.e. braided, low sinuosity channels transporting bedload by comparison to the

Soil development, erosion and sedimentation – summary and implications

The results of this study imply that the Snowy Mountains experience both rapid soil development rates and slow erosion rates by comparison to lowland sites. Maximum and minimum net soil development rates estimated by this study (20–220 t/km2/y) exceed the maximum and minimum estimates of the net soil loss which has occurred over the past 100 years (10–90 t/km2/y) (Fig. 5). This is consistent with the occurrence of widespread shallow alpine soils in the Snowy Mountains.

The 210Pbex erosion rates

Acknowledgments

This research was funded by Snowy Hydro Ltd. and by an Australian Institute of Nuclear Science and Engineering (AINSE) Post Graduate Research Award (PGRA No. 10085). We thank the staff of the Environmental Radioactivity Measurement Centre (ANSTO), in particular, Daniela Fierro for performing the radionuclide measurements and the many people at Snowy Hydro Ltd. who provided field work and logistics support. We also thank Bob Wasson and Ken Ferrier whose thoughtful comments improved this

References (139)

  • D.A. Hodell et al.

    Abrupt cooling of Antarctic surface waters and sea ice expansion in the South Atlantic sector of the Southern Ocean at 5000 cal yr B.P

    Quat. Res.

    (2001)
  • J. Kemp et al.

    Episodic fluvial activity of inland rivers in southeastern Australia: palaeochannel systems and terraces of the Lachlan River

    Quat. Sci. Rev.

    (2010)
  • R. Kilian et al.

    A review of Glacial and Holocene paleoclimate records from southernmost Patagonia (49–55°S)

    Quat. Sci. Rev.

    (2012)
  • G. Kirchner

    Establishing reference inventories of 137Cs for soil erosion studies: methodological aspects

    Geoderma

    (2013)
  • F. Lamy et al.

    Holocene rainfall variability in southern Chile: a marine record of latitudinal shifts of the Southern Westerlies

    Earth Planet. Sci. Lett.

    (2001)
  • S.W. Leavitt et al.

    Radiocarbon and δ13C depth profiles of soil organic carbon in the U.S. Great Plains: a possible spatial record of paleoenvironment and paleovegetation

    Quat. Int.

    (2007)
  • N.A. Lifton et al.

    Fractals in geomorphology tectonic, climatic and lithologic influences on landscape fractal dimension and hypsometry: implications for landscape evolution in the San Gabriel Mountains, California

    Geomorphology

    (1992)
  • L. Mabit et al.

    Comparative advantages and limitations of the fallout radionuclides 137Cs, 210Pbex and 7Be for assessing soil erosion and sedimentation

    J. Environ. Radioact.

    (2008)
  • L. Mabit et al.

    Assessment of erosion and deposition rates within an Austrian agricultural watershed by combining 137Cs, 210Pbex and conventional measurements

    Geoderma

    (2009)
  • A.R.H. Martin

    Late glacial and holocene alpine pollen diagrams from the Kosciusko National Park, New South Wales, Australia

    Rev. Palaeobot. Palynol.

    (1986)
  • C. Martinez et al.

    Comparison of fallout radionuclide (caesium-137) and modelling approaches for the assessment of soil erosion rates for an uncultivated site in south-eastern Australia

    Geoderma

    (2009)
  • S.K. Marx et al.

    Estimates of Australian dust flux into New Zealand: quantifying the eastern Australian dust plume pathway using trace element calibrated 210Pb as a monitor

    Earth Planet. Sci. Lett.

    (2005)
  • S.K. Marx et al.

    Holocene dust deposition rates in Australia's Murray-Darling Basin record the interplay between aridity and the position of the mid-latitude westerlies

    Quat. Sci. Rev.

    (2011)
  • S.K. Marx et al.

    Long-range dust transport from eastern Australia: a proxy for Holocene aridity and ENSO-induced climate variability

    Earth Planet. Sci. Lett.

    (2009)
  • S.G. Mitchell et al.

    Influence of a glacial buzzsaw on the height and morphology of the Cascade Range in central Washington State, USA

    Quat. Res.

    (2006)
  • M. Moros et al.

    Holocene climate variability in the Southern Ocean recorded in a deep-sea sediment core off South Australia

    Quat. Sci. Rev.

    (2009)
  • K.P. Norton et al.

    Silicate weathering of soil-mantled slopes in an active Alpine landscape

    Geochim. Cosmochim. Acta

    (2010)
  • R. Ogden et al.

    Sediment dates with implications for the age of the conversion from palaeochannel to modern fluvial activity on the Murray River and tributaries

    Quat. Int.

    (2001)
  • P.N. Owens et al.

    Spatial variability of caesium-137 inventories at reference sites: an example from two contrasting sites in England and Zimbabwe

    Appl. Radiat. Isot.

    (1996)
  • L. Petherick et al.

    Climatic records over the past 30 ka from temperate Australia – a synthesis from the Oz-INTIMATE workgroup

    Quat. Sci. Rev.

    (2013)
  • J. Pfitzner et al.

    137Cs and excess 210Pb deposition patterns in estuarine and marine sediment in the central region of the Great Barrier Reef Lagoon, north-eastern Australia

    J. Environ. Radioact.

    (2004)
  • D. Barsch et al.

    The nature of mountain geomorphology

    Mt. Res. Dev.

    (1984)
  • P. Bishop et al.

    Geomorphological evolution of the east Australian continental margin

  • BOM

    Climate Statistics Charlotte Pass

  • J.M. Bowler et al.

    Late Quaternary stratigraphy and radiocarbon chronology of water level fluctuations in Lake Keilambete, Victoria

    Nature

    (1971)
  • R. Brewer et al.

    Some aspects of the genesis of an alpine humus soil

    Aust. J. Soil Res.

    (1972)
  • R. Brewer et al.

    Proposal for soil stratigraphic units in the Australian Stratigraphic Code

    J. Geol. Soc. Aust.

    (1970)
  • C. Bronk-Ramsey

    Bayesian analysis of radiocarbon dates

    Radiocarbon

    (2009)
  • J. Brown et al.

    Aspects of the meteorology and hydrology of the Australian Alps

  • N. Brozović et al.

    Climatic limits on landscape development in the northwestern Himalaya

    Science

    (1997)
  • G.M. Brune

    Trap efficiency of reservoirs

    EOS Trans. Am. Geophys. Union

    (1953)
  • Bryant

    Deterioration of vegetation and erosion in the Guthega catchment area, Snowy Mountains

    N.S.W. Soil Conserv. J.

    (1971)
  • A. Chappell et al.

    Spatial uncertainty of the 137Cs reference inventory for Australian soil

    J. Geophys. Res. Earth Surf.

    (2011)
  • A. Chappell et al.

    Spatial uncertainty of 137Cs-derived net (1950s–1990) soil redistribution for Australia

    J. Geophys. Res. Earth Surf.

    (2011)
  • T.J. Cohen et al.

    Mind the gap: an absence of valley-fill deposits identifying the Holocene hypsithermal period of enhanced flow regime in southeastern Australia

    The Holocene

    (2007)
  • A.B. Costin

    A Study of the Ecosystems of the Monaro Region of New South Wales With Special Reference to Soil Erosion

    (1954)
  • A.B. Costin

    The Alps in a global perspective

  • A.B. Costin et al.

    Studies in pedogenesis in New South Wales III. The alpine humus soils

    J. Soil Sci.

    (1952)
  • A.B. Costin et al.

    Studies in catchment hydrology in the Australian Alps. II. Surface run-off and soil loss

  • J. de Vente et al.

    The sediment delivery problem revisited

    Prog. Phys. Geogr.

    (2007)
  • Cited by (0)

    View full text