Publications by year
In Press
Karwan DL, Siegert CM, Levia DF, Pizzuto J, Marquard J, Aalto RE, Aufdenkampe AK (In Press). Beryllium-7 wet deposition variation with storm height, synoptic classification, and tree canopy state in the mid-Atlantic USA.
Hydrological ProcessesAbstract:
Beryllium-7 wet deposition variation with storm height, synoptic classification, and tree canopy state in the mid-Atlantic USA
Short-lived fallout isotopes, such as beryllium-7 (7Be), are increasingly used as erosion and sediment tracers in watersheds. Beryllium-7 is produced in the atmosphere and delivered to Earth's surface primarily in precipitation. However, relatively little has been published about the variation in 7Be wet deposition caused by storm type and vegetation cover. Our analysis of precipitation, throughfall, and sediments in two forested, headwater catchments in the mid-Atlantic USA indicates significant variation in isotope deposition with storm type and storm height. Individual summer convective thunderstorms were associated with 7Be activity concentrations up to 5.0 Bq L−1 in precipitation and 4.7 Bq L−1 in throughfall while single-event wet depositional fluxes reached 168 Bq m−2 in precipitation and 103 Bq m−2 in throughfall. Storms originating from the continental USA were associated with lower 7Be activity concentrations and single-event wet depositional fluxes for precipitation (0.7 – 1.2 Bq L−1 and 15.8 – 65.0 Bq m−2) and throughfall (0.1 – 0.3 Bq L−1 and 13.5 – 98.9 Bq m−2). Tropical systems had relatively low activity concentrations, 0.2 – 0.5 Bq L−1 in precipitation and 0.2 – 1.0 Bq L−1 in throughfall, but relatively high single-event depositional fluxes due to large rainfall volumes, 32.8 – 67.6 Bq m−2 in precipitation and 25.7 – 134 Bq m−2 in throughfall. The largest sources of 7Be depositional variation were attributed to storm characteristics including precipitation amount and maximum storm height. 7Be activity associated with fluvial suspended sediments also exhibited the highest concentration and variability in summer (175 – 1450 Bq kg−1). We conclude the dominant source of variation on event-level 7Be deposition is storm type. Our results illustrate the complex relationships between 7Be deposition in precipitation and throughfall and demonstrate event-scale relationships between the 7Be in precipitation and on suspended sediment.
Abstract.
Singer, M, Aalto RE, James, L, Kilham, N, Higson, J, Ghoshal, S (In Press). Enduring legacy of a toxic fan via episodic redistribution of california gold mine debris. Proceedings of the National Academy of Sciences of USA
Schwendel A, Nicholas AP, Aalto R, Sambrook Smith GH, Buckley S (In Press). Interaction between meander dynamics and floodplain heterogeneity in a large tropical sand-bed river: the Rio Beni, Bolivian Amazon. Earth Surface Processes and Landforms
Schwendel A, Nicholas AP, Aalto R, Sambrook Smith G, Buckley S (In Press). Interaction between meander dynamics and floodplain heterogeneity in a large tropical sand-bed river: the Rio Beni, Bolivian Amazon. Earth Surface Processes and Landforms
Hackney C, Darby S, Parsons D, Leyland J, Best J, Aalto R, Nicholas A, Houseago R (In Press). River bank instability from unsustainable sand mining in the lower Mekong River. Nature Sustainability
2019
Grenfell MC, Aalto R, Grenfell SE, Ellery WN (2019). Ecosystem engineering by hummock-building earthworms in seasonal wetlands of eastern South Africa: Insights into the mechanics of biomorphodynamic feedbacks in wetland ecosystems.
Abstract:
Ecosystem engineering by hummock-building earthworms in seasonal wetlands of eastern South Africa: Insights into the mechanics of biomorphodynamic feedbacks in wetland ecosystems
Abstract.
Marquard J, Aalto RE, Barrows TT, Fisher BA, Aufdenkampe AK, Stone JO (2019). Topographic variation in soil erosion and accumulation determined with meteoric <sup>10</sup> Be.
Earth Surface Processes and Landforms,
44(1), 98-111.
Abstract:
Topographic variation in soil erosion and accumulation determined with meteoric 10 Be
Understanding natural soil redistribution processes is essential for measuring the anthropogenic impact on landscapes. Although meteoric beryllium-10 ( 10 Be) has been used to determine erosion processes within the Pleistocene and Holocene, fewer studies have used the isotope to investigate the transport and accumulation of the resulting sediment. Here we use meteoric 10 be in hilltop and valley site soil profiles to determine sediment erosion and deposition processes in the Christina River Basin (Pennsylvania, USA). The data indicate natural erosion rates of 14 to 21 mm 10 −3 yr and soil ages of 26 000 to 57 000 years in hilltop sites. Furthermore, valley sites indicate an alteration in sediment supply due to climate change (from the Pleistocene to the Holocene) within the last 60 000 years and sediment deposition of at least 0.5–2 m during the Wisconsinan glaciation. The change in soil erosion rate was most likely induced by changes in geomorphic processes; probably solifluction and slope wash during the cold period, when ice advanced into the mid latitudes of North America. This study shows the value of using meteoric 10 be to determine sediment accumulation within the Quaternary and quantifies major soil redistribution occurred under natural conditions in this region. © 2018 John Wiley & Sons, Ltd.
Abstract.
2018
Karwan DL, Pizzuto JE, Aalto R, Marquard J, Harpold A, Skalak K, Benthem A, Levia DF, Siegert CM, Aufdenkampe AK, et al (2018). Direct Channel Precipitation and Storm Characteristics Influence Short-Term Fallout Radionuclide Assessment of Sediment Source.
Water Resources Research,
54(7), 4579-4594.
Abstract:
Direct Channel Precipitation and Storm Characteristics Influence Short-Term Fallout Radionuclide Assessment of Sediment Source
Fallout radionuclides (FRNs) and their ratios, such as Beryllium-7 (7Be) and excess Lead-210 (210Pbxs), have been used to determine suspended sediment source and age in catchments. These models are based on numerous assumptions, for example, that channel deposition of FRNs from precipitation is negligible in comparison to their delivery to the channel from land surface erosion during individual storm events. We test this assumption using a mass balance approach during eight storms from summer 2011 to fall 2012 in a mid-Atlantic United States piedmont region watershed with mixed land use. Event peak discharge and storm type corresponded to the importance of direct channel FRN deposition from precipitation. During relatively low discharge summer thunderstorms, with minimal overland flow, less than 1% of 7Be and 210Pbxs flux deposited on the watershed exits the watershed associated with suspended sediment. The majority but not all deposited on the stream channel exits the watershed associated with suspended sediment (60% of 7Be and 80% of 210Pbxs). Here precipitation and throughfall onto the wetted channel area can be responsible for any FRN newly associated with suspended sediment, as opposed to landscape surface erosion. Furthermore, FRNs can be stored with sediments in the channel between events. Events with higher discharges, including hurricanes, show the opposite pattern—FRN flux associated with suspended sediment exported from the reach is greater than channel FRN wet deposition, suggesting net erosion from the watershed landscape and/or stored material during these types of storms.
Abstract.
Nicholas AP, Aalto RE, Sambrook Smith GH, Schwendel AC (2018). Hydrodynamic controls on alluvial ridge construction and avulsion likelihood in meandering river floodplains. Geology, 46(7), 639-642.
Fisher BA, Aufdenkampe AK, Yoo K, Aalto RE, Marquard J (2018). Soil carbon redistribution and organo-mineral associations after lateral soil movement and mixing in a first-order forest watershed.
Geoderma,
319, 142-155.
Abstract:
Soil carbon redistribution and organo-mineral associations after lateral soil movement and mixing in a first-order forest watershed
We test the hypothesis that erosion driven soil movement on hillslopes results in an increase in new organomineral associations and overall organic matter storage in colluvial deposits within a forested hillslope. We measured mineral specific surface area (SSA), organic carbon (OC), meteoric radioisotopes (210Pb, 137Cs, 10Be), soil physical properties, C/N, δ15N, δ13C, and ∆14C in bulk soil and density fractions in a hillslope transect of soil pits. The quantity of OC per unit of mineral surface area (OC/SA) and OC inventories increased by a factor of 2–3 in depositional sites as result of soil mixing due to erosional movement as confirmed by 210Pb, 137Cs, and 10Be profiles and inventories. Soil mixing systematically decreased C/N and enriched stable isotopes of δ13C and δ15N, revealing that formation of organomineral associations instead of microbial processing was responsible for depth trends in organic matter composition. Our findings indicate that the processes that associate organic matter and minerals are fundamentally linked with organic matter composition, and OC/SA, C/N, δ13C, and δ15N provide proxies for organic matter stabilization by soil minerals.
Abstract.
2017
Brown AG, Tooth S, Bullard JE, Thomas DSG, Chiverrell RC, Plater AJ, Murton J, Thorndycraft VR, Tarolli P, Rose J, et al (2017). The geomorphology of the Anthropocene: emergence, status and implications.
Earth Surface Processes and Landforms,
42(1), 71-90.
Abstract:
The geomorphology of the Anthropocene: emergence, status and implications
The Anthropocene is proposed as a new interval of geological time in which human influence on Earth and its geological record dominates over natural processes. A major challenge in demarcating the Anthropocene is that the balance between human-influenced and natural processes varies over spatial and temporal scales owing to the inherent variability of both human activities (as associated with culture and modes of development) and natural drivers (e.g. tectonic activity and sea level variation). Against this backdrop, we consider how geomorphology might contribute towards the Anthropocene debate by focusing on human impact on aeolian, fluvial, cryospheric and coastal process domains, and how evidence of this impact is preserved in landforms and sedimentary records. We also consider the evidence for an explicitly anthropogenic geomorphology that includes artificial slopes and other human-created landforms. This provides the basis for discussing the theoretical and practical contributions that geomorphology can make to defining an Anthropocene stratigraphy. It is clear that the relevance of the Anthropocene concept varies considerably amongst different branches of geomorphology, depending on the history of human actions in different process domains. For example, evidence of human dominance is more widespread in fluvial and coastal records than in aeolian and cryospheric records, so geomorphologically the Anthropocene would inevitably comprise a highly diachronous lower boundary. Even to identify this lower boundary, research would need to focus on the disambiguation of human effects on geomorphological and sedimentological signatures. This would require robust data, derived from a combination of modelling and new empirical work rather than an arbitrary ‘war of possible boundaries' associated with convenient, but disputed, ‘golden’ spikes. Rather than being drawn into stratigraphical debates, the primary concern of geomorphology should be with the investigation of processes and landform development, so providing the underpinning science for the study of this time of critical geological transition. Copyright © 2016 John Wiley & Sons, Ltd.
Abstract.
Hackney CR, Darby SE, Parsons DR, Leyland J, Aalto R, Nicholas AP, Best JL (2017). The influence of flow discharge variations on the morphodynamics of a diffluence-confluence unit on a large river. Earth Surface Processes and Landforms, 43(2), 349-362.
2016
Karwan DL, Siegert CM, Levia DF, Pizzuto J, Marquard J, Aalto R, Aufdenkampe AK (2016). Beryllium-7 wet deposition variation with storm height, synoptic classification, and tree canopy state in the mid-Atlantic USA.
Hydrological Processes,
30(1), 75-89.
Abstract:
Beryllium-7 wet deposition variation with storm height, synoptic classification, and tree canopy state in the mid-Atlantic USA
Short-lived fallout isotopes, such as beryllium-7 (7Be), are increasingly used as erosion and sediment tracers in watersheds. 7Be is produced in the atmosphere and delivered to the Earth's surface primarily in precipitation. However, relatively little has been published about the variation in 7Be wet deposition caused by storm type and vegetation cover. Our analysis of precipitation, throughfall, and sediments in two forested, headwater catchments in the mid-Atlantic USA indicates significant variation in isotope deposition with storm type and storm height. Individual summer convective thunderstorms were associated with 7Be activity concentrations up to 5.0Bql-1 in precipitation and 4.7Bql-1 in throughfall, while single-event wet depositional fluxes reached 168Bqm-2 in precipitation and 103Bqm-2 in throughfall. Storms originating from the continental USA were associated with lower 7Be activity concentrations and single-event wet depositional fluxes for precipitation (0.7-1.2Bql-1 and 15.8-65.0Bqm-2) and throughfall (0.1-0.3Bql-1 and 13.5-98.9Bqm-2). Tropical systems had relatively low activity concentrations, 0.2-0.5Bql-1 in precipitation and 0.2-1.0Bql-1 in throughfall, but relatively high single-event depositional fluxes due to large rainfall volumes, 32.8-67.6Bqm-2 in precipitation and 25.7-134Bqm-2 in throughfall. The largest sources of 7Be depositional variation were attributed to storm characteristics including precipitation amount and maximum storm height. 7Be activity associated with fluvial suspended sediments also exhibited the highest concentration and variability in summer (175-1450Bqkg-1). We conclude the dominant source of variation on event-level 7Be deposition is storm type. Our results illustrate the complex relationships between 7Be deposition in precipitation and throughfall and demonstrate event-scale relationships between the 7Be in precipitation and on suspended sediment.
Abstract.
Perreault LM, Yager EM, Aalto R (2016). Effects of gradient, distance, curvature and aspect on steep burned and unburned hillslope soil erosion and deposition. Earth Surface Processes and Landforms, 42(7), 1033-1048.
Leyland J, Hackney C, Darby S, Parsons D, Best J, Nicholas AP, Aalto R, Lague D (2016). Extreme flood-driven bank erosion and sediment transport on a mega-river: Direct process measurements using integrated Mobile Laser Scanning (MLS) and hydro-acoustic techniques. Earth Surface Processes and Landforms
Darby SE, Hackney CR, Leyland J, Kummu M, Lauri H, Parsons DR, Best JL, Nicholas AP, Aalto R (2016). Fluvial sediment supply to a mega-delta reduced by shifting tropical-cyclone activity.
Nature,
539(7628), 276-279.
Abstract:
Fluvial sediment supply to a mega-delta reduced by shifting tropical-cyclone activity.
The world's rivers deliver 19 billion tonnes of sediment to the coastal zone annually, with a considerable fraction being sequestered in large deltas, home to over 500 million people. Most (more than 70 per cent) large deltas are under threat from a combination of rising sea levels, ground surface subsidence and anthropogenic sediment trapping, and a sustainable supply of fluvial sediment is therefore critical to prevent deltas being 'drowned' by rising relative sea levels. Here we combine suspended sediment load data from the Mekong River with hydrological model simulations to isolate the role of tropical cyclones in transmitting suspended sediment to one of the world's great deltas. We demonstrate that spatial variations in the Mekong's suspended sediment load are correlated (r = 0.765, P
Abstract.
Author URL.
Vermeulen B, Hoitink AJF, Zolezzi G, Abad JD, Aalto R (2016). Multiscale structure of meanders.
Geophysical Research Letters,
43(7), 3288-3297.
Abstract:
Multiscale structure of meanders
© 2016. The Authors. River meander planforms can be described based on wavelet analysis, but an objective method to identify the main characteristics of a meander planform over all spatial scales is yet to be found. Here we show how a set of simple metrics representing meander shape can be retrieved from a continuous wavelet transform of a planform geometry. We construct a synoptic multiple looping tree to establish the meander structure, revealing the embedding of dominant meander scales in larger-scale loops. The method can be applied beyond the case of rivers to unravel the meandering structure of lava flows, turbidity currents, tidal channels, rivulets, supraglacial streams, and extraterrestrial flows.
Abstract.
2015
Hackney C, Best J, Leyland J, Darby SE, Parsons D, Aalto R, Nicholas A (2015). Modulation of outer bank erosion by slump blocks: Disentangling the protective and destructive role of failed material on the three-dimensional flow structure.
Geophysical Research LettersAbstract:
Modulation of outer bank erosion by slump blocks: Disentangling the protective and destructive role of failed material on the three-dimensional flow structure
© 2015. American Geophysical Union. All Rights Reserved. The three-dimensional flow field near the banks of alluvial channels is the primary factor controlling rates of bank erosion. Although submerged slump blocks and associated large-scale bank roughness elements have both previously been proposed to divert flow away from the bank, direct observations of the interaction between eroded bank material and the 3-D flow field are lacking. Here we use observations from multibeam echo sounding, terrestrial laser scanning, and acoustic Doppler current profiling to quantify, for the first time, the influence of submerged slump blocks on the near-bank flow field. In contrast to previous research emphasizing their influence on flow diversion away from the bank, we show that slump blocks may also deflect flow onto the bank, thereby increasing local shear stresses and rates of erosion. We use our measurements to propose a conceptual model for how submerged slump blocks interact with the flow field to modulate bank erosion.
Abstract.
Walsh JP, Wiberg PL, Aalto R, Nittrouer CA, Kuehl SA (2015). Source-to-sink research: Economy of the Earth's surface and its strata. Earth-Science Reviews
2014
Pizzuto J, Schenk ER, Hupp CR, Gellis A, Noe G, Williamson E, Karwan DL, O'Neal M, Marquard J, Aalto R, et al (2014). Characteristic length scales and time-averaged transport velocities of suspended sediment in the mid-Atlantic Region, USA.
Water Resources Research,
50(2), 790-805.
Abstract:
Characteristic length scales and time-averaged transport velocities of suspended sediment in the mid-Atlantic Region, USA
Watershed Best Management Practices (BMPs) are often designed to reduce loading from particle-borne contaminants, but the temporal lag between BMP implementation and improvement in receiving water quality is difficult to assess because particles are only moved downstream episodically, resting for long periods in storage between transport events. A theory is developed that describes the downstream movement of suspended sediment particles accounting for the time particles spend in storage given sediment budget data (by grain size fraction) and information on particle transit times through storage reservoirs. The theory is used to define a suspended sediment transport length scale that describes how far particles are carried during transport events, and to estimate a downstream particle velocity that includes time spent in storage. At 5 upland watersheds of the mid-Atlantic region, transport length scales for silt-clay range from 4 to 60 km, while those for sand range from 0.4 to 113 km. Mean sediment velocities for silt-clay range from 0.0072 km/yr to 0.12 km/yr, while those for sand range from 0.0008 km/yr to 0.20 km/yr, 4-6 orders of magnitude slower than the velocity of water in the channel. These results suggest lag times of 100-1000 years between BMP implementation and effectiveness in receiving waters such as the Chesapeake Bay (where BMPs are located upstream of the characteristic transport length scale). Many particles likely travel much faster than these average values, so further research is needed to determine the complete distribution of suspended sediment velocities in real watersheds. ©2014. American Geophysical Union. All Rights Reserved.
Abstract.
Warrick JA, Milliman JD, Walling DE, Wasson RJ, Syvitski JPM, Aalto RE (2014). Earth is (mostly) flat: Apportionment of the flux of continental sediment over millennial time scales. Geology, 42(2).
Warrick JA, Milliman JD, Walling DE, Wasson RJ, Syvitski JPM, Aalto RE (2014). Earth is (mostly) flat: Apportionment of the flux of continental sediment over millennial time scales: Comment. Geology, 42(1).
Grenfell MC, Nicholas AP, Aalto R (2014). Mediative adjustment of river dynamics: the role of chute channels in tropical sand-bed meandering rivers.
Sedimentary Geology,
301, 93-106.
Abstract:
Mediative adjustment of river dynamics: the role of chute channels in tropical sand-bed meandering rivers
This paper examines processes of chute channel formation in four tropical sand-bed meandering rivers; the Strickland and Ok Tedi in Papua New Guinea, the Beni in Bolivia, and the lower Paraguay on the Paraguay/Argentina border. Empirical planform analyses highlight an association between meander bend widening and chute initiation that is consistent with recent physics-based modelling work. GIS analyses indicate that bend widening may be driven by a variety of mechanisms, including scour and cutbank bench formation at sharply-curving bends, point bar erosion due to cutbank impingement against cohesive terrace material, rapid cutbank erosion at rapidly extending bends, and spontaneous mid-channel bar formation. Chute channel initiation is observed to be predominantly associated with two of these widening mechanisms; i) an imbalance between cutbank erosion and point bar deposition associated with rapid bend extension, and ii) bank erosion forced by spontaneous mid-channel bar development. The work extends previous empirical analyses, which highlighted the role of bend extension (elongation) in driving chute initiation, with the observation that the frequency of chute initiation increases once bend extension rates and/or widening ratios exceed a reach-scale threshold. A temporal pattern of increased chute initiation frequency on the Ok Tedi, in response to channel steepening and mid-channel bar development following the addition of mine tailings, mirrors the inter- and intra-reach spatial patterns of chute initiation frequency on the Paraguay, Strickland and Beni Rivers, where increased stream power and sediment load are associated with increased bend extension and chute initiation rates. The process of chute formation is shown to be rate-dependent, and the threshold values of bend extension and widening ratio for chute initiation are shown to scale with measures of river energy, reminiscent of slope-ratio thresholds in river avulsion. Furthermore, Delft3D simulations suggest that chute formation can exert negative feedback on shear stress and bank erosion in the adjacent mainstem bifurcate, such that the process of chute formation may also be rate-limiting. Chute formation is activated iteratively in space and time in response to changes in river energy (and sediment load), predominantly affecting sites of rapid channel elongation, and thereby mediating the river response. © 2013.
Abstract.
2013
Perreault LM, Yager EM, Aalto R (2013). Application of <sup>210</sup>Pb<inf>ex</inf> inventories to measure net hillslope erosion at burned sites.
Earth Surface Processes and Landforms,
38(2), 133-145.
Abstract:
Application of 210Pbex inventories to measure net hillslope erosion at burned sites
Fallout radionuclides, including lead-210 excess (210Pbex), have been broadly and successfully used to quantify net hillslope sediment transport in agricultural, pastoral and forested landscapes but have only recently been applied in burned terrain. Quantifying post-fire erosion is important because fires can amplify hillslope erosion, impacting terrestrial and aquatic habitat and water quality. However, we lack a basic understanding of the fate of 210Pbex in fires. To address this knowledge gap, we collected over 400 soil samples from unburned, moderately and severely burned forested sites in central Idaho. We measured soil 210Pbex content at stable reference and eroding sites and in mineral and organic soil components. At all sites, organic matter had the highest concentration of 210Pbex, representing 30% to 73% of the total activity. At the severely and moderately burned sites, 210Pbex reference inventories were lower by 58% and 41%, with about 40% less organic mass, relative to the unburned site. These results indicate that most 210Pbex in our semi-arid, forested sites was bound to organic matter, and that a substantial portion of this lead was lost due to forest fires. These losses likely occurred through volatilization and wind transport of smoke and ash. In the moderately burned site, 210Pbex losses were more spatially variable, potentially due to spatially uneven fire intensity and effects. Despite equal percent losses of 210Pbex, lower inventories at the burned sites produced lower calculated net erosion rates relative to the unburned site. Thus, given methodological uncertainties, 210Pbex losses due to fire, and the subsequent sensitivity of calculated net erosion rates to these lower 210Pbex inventories, we suggest this method should not be used in burned terrain to calculate absolute net erosion and deposition rates. However, within a given burned site, 210Pbex inventories still provide useful information describing relative soil losses and storage across the landscape. © 2012 John Wiley & Sons, Ltd.
Abstract.
Dunne T, Aalto RE (2013). Large River Floodplains. In (Ed)
Treatise on Geomorphology, 645-678.
Abstract:
Large River Floodplains
Abstract.
Grenfell MC, Nicholas AP, Aalto R (2013). Mediative adjustment of river dynamics: the role of chute channels in tropical sand-bed meandering rivers. Sedimentary Geology
Hoffmann T, Mudd SM, van Oost K, Verstraeten G, Erkens G, Lang A, Middelkoop H, Boyle J, Kaplan JO, Willenbring J, et al (2013). Short Communication: Humans and the missing C-sink: erosion and burial of soil carbon through time.
EARTH SURFACE DYNAMICS,
1(1), 45-52.
Author URL.
Brown AG, Tooth S, Chiverrell RC, Rose J, Thomas DSG, Wainwright J, Bullard JE, Thorndycraft VR, Aalto R, Downs P, et al (2013). The Anthropocene: is there a geomorphological case?. Earth Surface Processes and Landforms
Brown AG, Tooth S, Chiverrell RC, Rose J, Thomas DSG, Wainwright J, Bullard JE, Thorndycraft VR, Aalto R, Downs P, et al (2013). The Anthropocene: is there a geomorphological case?.
Earth Surface Processes and Landforms,
38(4), 431-434.
Abstract:
The Anthropocene: is there a geomorphological case?
The 'Anthropocene', as used to describe the interval of recent Earth history during which humans have had an 'overwhelming' effect on the Earth system, is now being formally considered as a possible new geological Epoch. Such a new geological time interval (possibly equivalent to the Pleistocene Epoch) requires both theoretical justification as well as empirical evidence preserved within the geological record. Since the geological record is driven by geomorphological processes that produce terrestrial and near-shore stratigraphy, geomorphology has to be an integral part of this consideration. For this reason, the British Society for Geomorphology (BSG) has inaugurated a Fixed Term Working Group to consider this issue and advise the Society on how geomorphologists can engage with debates over the Anthropocene. This ESEX Commentary sets out the initial case for the formalisation of the Anthropocene and a priori considerations in the hope that it will stimulate debate amongst, and involvement by, the geomorphological community in what is a crucial issue for the discipline. The Working Group is now considering the practical aspects of such a formalization including the relative magnitude problem, the boundary problem and the spatial diachrony of 'anthropogenic geomorphology'. © 2013 John Wiley & Sons, Ltd.
Abstract.
2012
Aalto RE, Nittrouer CN (2012). 210-Pb Geochronology of Flood Events in Large Tropical River Systems.
Philosophical Transactions of the Royal Society AAbstract:
210-Pb Geochronology of Flood Events in Large Tropical River Systems
Floodplain sedimentation removes sediment from fluvial transport, and constructs
stratigraphic records of flooding, biogeochemical sequestration and other aspects of the
environmental history of river basins – insight which is enhanced by accurate geochronology.
The natural radionuclide 210Pb, often employed to date lacustrine and marine sediments, has
previously been used to determine floodplain accumulation rates over decadal-to-century
timescales on the assumption that both input concentration and sedimentation rates are
constant. We test this model in ~110 cores from pristine floodplains along ~2000 km of the
Rios Beni and Mamore in northern Bolivia; over 95% of the 210Pb profiles depict individual
episodic deposition events, not steady-state accumulation, requiring a revised
geochronological methodology. Discrete measurements of down-core, Clay-Normalized
Adsorbed XS 210Pb activity (CNAX) are coupled with a new conceptual model of 210Pb input
during floods: Constant Initial Reach Clay Activity, Unknown Sedimentation (CIRCAUS).
This enhanced methodology yields 210Pb dates which correspond well with 1) dates
determined from meteoric caps, 2) known dates of deposition, 3) known flood dates, and 4)
dates from nearby cores along the same transect. Similar results have been found for other
large rivers. The CIRCAUS method for geochronology therefore offers a flexible and precise
method for dating both episodic (decadal recurrence frequency) and constant (annual
recurrence) sediment accumulation on floodplains.
Abstract.
Perreault LM, Yager EM, Aalto R (2012). Application of 210Pb ex inventories to measure net hillslope erosion at burned sites. Earth Surface Processes and Landforms
2011
Karwan DL, Aalto R, Aufdenkampe AK, Denis Newbold J, Pizzuto JE (2011). Characterization and source determination of stream suspended particulate material in White Clay Creek, USA.
Applied Geochemistry,
26(SUPPL.).
Abstract:
Characterization and source determination of stream suspended particulate material in White Clay Creek, USA
The material exported from a watershed reflects its origin and the processes it undergoes during downhill and downstream transport. Due to its nature as a complex mixture of material, the composition of suspended particulate material (SPM) integrates the physical, biological and chemical processes effecting watershed material. This study will use a sediment fingerprinting approach to quantify the composition and sources of SPM in the White Clay Creek Watershed in SE Pennsylvania and Delaware, USA, examine longitudinal trends in SPM composition and source in first to fourth reaches of the White Clay Creek, quantify the differences in composition and source with hydrologic variations produced by storms and seasonality. © 2011 Elsevier Ltd.
Abstract.
Grenfell MC, Aalto RE, Nicholas AP (2011). Chute channel dynamics in large, sand-bed meandering rivers.
Earth Surface Processes and LandformsAbstract:
Chute channel dynamics in large, sand-bed meandering rivers
Meander bends of many large, sand-bed meandering rivers are partitioned by chute channels that convey permanent flow, and co-exist with the mainstem for decades. As a first step toward understanding the dynamics and morphodynamic implications of these ‘bifurcate meander bends’, this study applied binary logistic regression analysis to determine whether it is possible to predict chute initiation based on attributes of meander bend character and dynamics. Regression models developed for the Strickland River, Papua New Guinea, the lower Paraguay River, Paraguay/Argentina, and the Beni River, Bolivia, revealed that the probability of chute initiation at a meander bend is a function of the bend extension rate (the rate at which a bend elongates in a direction perpendicular to the valley axis trend). Image analyses of all rivers and field observations from the Strickland suggest that the majority of chute channels form during scroll–slough development. Rapid extension is shown to favour chute initiation by breaking the continuity of point bar deposition and vegetation encroachment at the inner bank, resulting in widely-spaced scrolls with intervening sloughs that are positively aligned with primary over-bar flow. The rivers plot in order of increasing chute activity on an empirical meandering-braided pattern continuum defined by potential specific stream power (ωpv) and bedload calibre (D50). Increasing stream power is considered to result in higher bend extension rates, with implications for chute initiation. In addition, chute stability is shown to depend on river sediment load relative to flow discharge (Qs/Q), such that while the Beni may plot in the region of highly braided rivers by virtue of a high potential specific stream power, the formation of stable chute channels is suppressed by the high sediment load. This tendency is consistent with previous experimental studies, and results in a planform that is transitional between single-thread meandering and braided.
Abstract.
Knudsen SE, Riggan H, Aufdenkampe A, Aalto R, Dickens AF (2011). Isotopic study of the cycling and distribution of plant-wax lipids in an Andean watershed. In (Ed)
.
Author URL.
Aufdenkampe AK, Mayorgo E, Raymond PA, Melack JM, Aalto RE, Alin SR, Yoo K (2011). Rivers key to coupling biogeochemical cycles between land, oceans and atmosphere.
Frontiers in Ecology and the Environment,
1(9), 53-60.
Abstract:
Rivers key to coupling biogeochemical cycles between land, oceans and atmosphere
Streams, rivers, lakes, and other inland waters are important agents in the coupling of biogeochemical cycles
between continents, atmosphere, and oceans. The depiction of these roles in global-scale assessments of
carbon (C) and other bioactive elements remains limited, yet recent findings suggest that C discharged to the
oceans is only a fraction of that entering rivers from terrestrial ecosystems via soil respiration, leaching, chemical
weathering, and physical erosion. Most of this C influx is returned to the atmosphere from inland waters as
carbon dioxide (CO2) or buried in sedimentary deposits within impoundments, lakes, floodplains, and other
wetlands. Carbon and mineral cycles are coupled by both erosion–deposition processes and chemical weathering,
with the latter producing dissolved inorganic C and carbonate buffering capacity that strongly modulate
downstream pH, biological production of calcium-carbonate shells, and CO2 outgassing in rivers, estuaries, and coastal zones. Human activities substantially affect all of these processes.
Abstract.
2010
Ghoshal S, James LA, Singer MB, Aalto RE (2010). Channel and Floodplain Change Analysis over a 100-Year Period: Lower Yuba River, California. Remote Sensing, 7(2), 1797-1825.
Ghoshal S, James LA, Singer MB, Aalto R (2010). Channel and floodplain change analysis over a 100-year period: Lower Yuba river, California.
Remote Sensing,
2(7), 1797-1825.
Abstract:
Channel and floodplain change analysis over a 100-year period: Lower Yuba river, California
Hydraulic gold mining in the Sierra Nevada, California (1853-1884) displaced ~1.1 billion m 3 of sediment from upland placer gravels that were deposited along piedmont rivers below dams where floods can remobilize them. This study uses topographic and planimetric data from detailed 1906 topographic maps, 1999 photogrammetric data, and pre- and post-flood aerial photographs to document historic sediment erosion and deposition along the lower Yuba River due to individual floods at the reach scale. Differencing of 3 × 3-m topographic data indicates substantial changes in channel morphology and documents 12.6 × 10 6 m 3 of erosion and 5.8 × 10 6 m 3 of deposition in these reaches since 1906. Planimetric and volumetric measurements document spatial and temporal variations of channel enlargement and lateral migration. Over the last century, channels incised up to ~13 m into mining sediments, which dramatically decreased local flood frequencies and increased flood conveyance. These adjustments were punctuated by event-scale geomorphic changes that redistributed sediment and associated contaminants to downstream lowlands. © 2010 by the authors.
Abstract.
2009
Singer MB, Aalto RE (2009). Floodplain development in an engineered setting.
Earth Surface Processes and Landforms,
34(2), 291-304.
Abstract:
Floodplain development in an engineered setting
Engineered flood bypasses, or simplified conveyance floodplains, are natural laboratories in which to observe
floodplain development and therefore present an opportunity to assess delivery to and sedimentation within a specific class of
floodplain. The effects of floods in the Sacramento River basin were investigated by analyzing hydrograph characteristics,
estimating event-based sediment discharges and reach erosion/deposition through its bypass system and observing sedimentation
patterns with field data. Sediment routing for a large, iconic flood suggests high rates of sedimentation in major bypasses, which
is corroborated by data for one bypass area from sedimentation pads, floodplain cores and sediment removal reporting from a
government agency. These indicate a consistent spatial pattern of high sediment accumulation both upstream and downstream of
lateral flow diversions and negligible sedimentation in a ‘hydraulic shadow’ directly downstream of a diversion weir. The pads
located downstream of the shadow recorded several centimeters of deposition during a moderate flood in 2006, increasing
downstream to a peak of ~10 cm thick and thinning rapidly thereafter. Flood deposits in the sediment cores agree with this spatial
pattern, containing discrete sedimentation layers (from preceding floods) that increase in thickness with distance downstream of
the bypass entrance to several decimeters thick at the peak and then thin downstream. These patterns suggest that a quasi-natural
physical process of levee construction by advective overbank transport and deposition of sediment is operating. The results
improve understanding of the evolution of bypass flood control structures, the transport and deposition of sediment within these
environments and the evolution of one class of natural levee systems.
Abstract.
2008
Alin S, Aalto RE, Richey J, Dietrich WE (2008). Biogeochemical evidence for high carbon loading in the Strickland and Fly Rivers, Papua New Guinea.
JGR Earth Surface,
113(F1).
Abstract:
Biogeochemical evidence for high carbon loading in the Strickland and Fly Rivers, Papua New Guinea
The highstanding islands of Oceania are recognized as a source of significant
particulate organic carbon delivered to nearshore marine environments. The existing data
on carbon export in Oceania are largely derived from small mountainous watersheds
(
Abstract.
Hagedorn B, Aalto RE, Sletten RS, Hallet B (2008). Frost boil dynamics using 210Pb as a tracer for soil movement. In Kane DL, Hinkel KM (Eds.)
Ninth International Conference on Permafrost, University of Alaska, Fairbanks, USA, 613-618.
Abstract:
Frost boil dynamics using 210Pb as a tracer for soil movement
Abstract.
Author URL.
Swanson KM, Watson E, Aalto R, Lauer JW, Bera MT, Marshall A, Taylor MP, Apte SC, Dietrich WE (2008). Sediment load and floodplain deposition rates: Comparison of the Fly and Strickland rivers, Papua New Guinea.
Journal of Geophysical Research: Earth Surface,
113(1).
Abstract:
Sediment load and floodplain deposition rates: Comparison of the Fly and Strickland rivers, Papua New Guinea
Rates of aggradation and infilling of accommodation space along lowland channels in response to postglacial sea level rise should depend on sediment supply. The Strickland and Fly rivers join at just 6 m above sea level and have experienced the same Holocene sea level rise. Historically, the Strickland has carried about 7 times the sediment load and 1.4 times the water discharge as the Fly. Therefore we hypothesize that the lowland Strickland floodplain should be more developed and consequently should presently be capturing proportionately less sediment than the floodplain of the lowland Fly River. We use mine-derived elevated Pb and Ag concentrations in 111 shallow (
Abstract.
Swanson KM, Watson E, Aalto RE, Lauer JW, Dietrich WE, Apte S, Bera M, Marshall A, Taylor M (2008). Sediment load and floodplain deposition rates: Comparison of the fly and Strickland rivers, Papua New Guinea.
JGR Earth Surface,
113(F1).
Abstract:
Sediment load and floodplain deposition rates: Comparison of the fly and Strickland rivers, Papua New Guinea
Rates of aggradation and infilling of accommodation space along lowland channels in response to postglacial sea level rise should depend on sediment supply. The Strickland and Fly rivers join at just 6 m above sea level and have experienced the same Holocene sea level rise. Historically, the Strickland has carried about 7 times the sediment load and 1.4 times the water discharge as the Fly. Therefore we hypothesize that the lowland Strickland floodplain should be more developed and consequently should presently be capturing proportionately less sediment than the floodplain of the lowland Fly River. We use mine-derived elevated Pb and Ag concentrations in 111 shallow (< 1 m) floodplain cores collected in 2003 to determine deposition rates across the lower Strickland floodplain. Sediment deposition rates decrease across the floodplain with distance from the channel bank, and the average rate of deposition is 1.4 cm/a over the first 1 km. Overbank deposition along the lowland sandbedded Strickland results in similar to 13% loss of the total load, similar to 0.05%/km of channel length of the main stem. Deposition rates over the first 1 km from the channel bank on the Strickland are about 10 times those on the Fly (for estimated natural sediment loads); however, the proportional loss per channel length on the Strickland is less than that on the Fly (0.09%/km of main stem channel length) because of an extensive network of tributary and tie channels that convey sediment to the floodplain on the Fly. Furthermore, the lateral migration of the Strickland channel is similar to 5 times that on the Fly, such that most overbank deposits on the Strickland are returned to the channel, causing the net loss of sediment to the floodplain to be small. We conclude that the Strickland River, which has a much higher overbank deposition rate than the Fly River as a function of distance from channel bank, nonetheless has significantly less net accumulation than the Fly because (1) a large proportion of the sediment load is conveyed up tributaries and tie channels on the Fly, and (2) lateral migration (which presumably results from the higher load) on the Strickland sweeps sediment back into the channel. Hence our field observations support our initial hypothesis, though the primary reason for this is because of active lateral migration rather than low overbank deposition rates.
Abstract.
Aalto RE, Lauer JW, Dietrich WE (2008). Spatial and temporal dynamics of Strickland River floodplains during the past century.
JGR Earth Surface,
113(F1).
Abstract:
Spatial and temporal dynamics of Strickland River floodplains during the past century
We investigated the processes of sediment exchange between the Strickland River
and its lowland floodplain, documenting (1) the rates, textures, and distributions of
sediment accumulation, (2) temporal variations in these rates, (3) the remobilization of
sediment by erosive processes, and (4) whether net storage is significant over century
timescales. We used 210Pb geochronology of floodplain cores from 11 transects to measure
deposition rates over the past. 65 years, finding a decline from 5.5 cm/a (0–10 m
distance from the channel) to 0.9 cm/a ( 400 m) to. 0.1 cm/a (>1 km). Rates are elevated
along curved sections of channel and are stable over time, and episodic accumulation
is prevalent and may be correlated to floods. Integrated temporally and spatially, the
average rate is 1.6 cm/a. Integrating along both sides of. 318 river km we studied for
the lowland Strickland, we calculate 12–19 Mt of annual sediment accumulation
( 0.05 Mt/km or 0.07% of the annual load per km of river length), representing 17–27%
of the total annual sediment flux. We used georeferenced Landsat images (1972–2001) to
quantify channel migration and the resulting return of sediment to the channel. Mean
lateral migration was 5.1 ± 0.8 m/a. Given the floodplain width of. 10 km, this implies a
waiting time of. 1 ka between floodplain formation and subsequent reentrainment
of the bank as the channel migrates laterally. This raises the possibility that the net return
of material from the floodplain due to channel migration could balance the overbank
deposition we observed. The exchange flux between cut bank erosion and point bar
deposition is 20–40 Mt, highlighting the significance of sediment recycling ( 50% of the
total load). Such sediment trapping and recycling affects the transport, storage, and
evolution of biogeochemically reactive particles, the evolution of the floodplain, and
the morphodynamics of basin infilling.
Abstract.
Singer MB, Aalto RE, James LA (2008). Status of the Lower Sacramento Valley Flood-Control System within the Context of its Natural
Geomorphic Setting.
Natural Hazards Review,
9(3), 104-115.
Abstract:
Status of the Lower Sacramento Valley Flood-Control System within the Context of its Natural
Geomorphic Setting
The Sacramento River’s flood-control system was conceived as a series of weirs and bypasses that routes floods out of the
leveed main channel into natural floodways engineered to drain directly into the bay delta. The system, superimposed on a natural
geomorphic setting consisting of geologic, sedimentary, and tectonic controls, still relies on weirs and bypasses to keep low-lying
communities dry during floods. However, the Sacramento Valley bypass system exhibits widespread evidence of impairment by sedimentation,
especially at prehistoric loci of alluvial splays. Episodic flooding in the basin delivers large volumes of sediment that accumulate
throughout the flood bypasses, especially from legacy tailings fans that originated in the hydraulic mining era. In addition to decreasing
flow capacity, these deposits promote colonization of vegetation, which, in turn, increases roughness and decreases flood conveyance. We
document three bypass regions that are affected by natural geomorphic controls, where consistent sedimentation occurred prior to and
since bypass construction. Deposits forming at the entrance to Colusa and Yolo Bypasses increase stage thresholds for flows entering the
floodway, exacerbating flood risk in the main channel downstream of the entrance. Deposits forming in downstream reaches of bypasses
such as Colusa Bypass affect flood conveyance, potentially causing backwater effects that could limit diversion of flood discharge into the
bypass system. Systematic bypass deposition tends to occur in locations where local backwater effects are imposed by river confluences.
One particularly acute choke point for sediment occurs at the confluence of Sutter Bypass, Feather River, and Sacramento Rivers, where
the ancestral Cache Creek fan compresses valley drainage. These factors and concerns generated by the Katrina disaster have motivated
sediment removal from the inlets to bypasses and levee repair along main channels, but it is unclear how effective these measures will be
in the coming decades, especially within the context of flood conveyance throughout the entire system and regional climate change.
Abstract.
Goni MA, Monacci N, Gisewhite R, Crockett J, Nittrouer CA, Ogston A, Alin SR, Aalto RE (2008). Terrigenous Organic Matter in Sediments from the Fly River Delta (Papua New Guinea).
JGR Earth Surface,
113(F1).
Abstract:
Terrigenous Organic Matter in Sediments from the Fly River Delta (Papua New Guinea)
Although an inordinate fraction of the global sediment flux to the ocean occurs in
tropical mountainous river margins, little is known regarding the sources and fate of
organic matter in these systems. To address these knowledge gaps, the distribution and
composition of organic matter in sediments from the Fly River delta-clinoform were
examined in the context of the source-to-sink study of the Papuan Continuum. The
significant contrasts in the texture of seabed sediments measured across the study area
coincided with stark contrasts in concentration and composition of the sedimentary
organic matter. Coarser sediments displayed significantly lower organic carbon and
nitrogen contents, more enriched stable carbon and nitrogen compositions, lower lignin
product yields, and distinctly different lignin and nonlignin product compositions than
their fine-textured counterparts. Compositional differences were also measured between
high- and low-density fractions of selected sediment samples. Subsurface sediments
showed marked compositional variations that were predominantly associated with changes
in the texture of the deposits. Most sediments were characterized by moderate carbon
loadings (0.5–1.0 mg C m 2), although several samples from the outer topset region, an
area of sediment bypass, were characterized by lower carbon loadings indicative of
enhanced carbon losses. Overall, the organic matter in both surface and subsurface
sediments appeared to have predominantly a terrigenous origin, with no evidence for
dilution and/or replacement by marine carbon. The measured compositions were
consistent with contributions from modern vascular plant detritus, aged soil organic
matter, and very old or fossil organic matter devoid of recognizable biochemicals.
Abstract.
Goni MA, Monacci N, Gisewhite R, Crockett J, Nittrouer C, Ogston A, Alin SR, Aalto R (2008). Terrigenous organic matter in sediments from the Fly River delta-clinoform system (Papua New Guinea).
Journal of Geophysical Research: Earth Surface,
113(1).
Abstract:
Terrigenous organic matter in sediments from the Fly River delta-clinoform system (Papua New Guinea)
Although an inordinate fraction of the global sediment flux to the ocean occurs in tropical mountainous river margins, little is known regarding the sources and fate of organic matter in these systems. To address these knowledge gaps, the distribution and composition of organic matter in sediments from the Fly River delta-clinoform were examined in the context of the source-to-sink study of the Papuan Continuum. The significant contrasts in the texture of seabed sediments measured across the study area coincided with stark contrasts in concentration and composition of the sedimentary organic matter. Coarser sediments displayed significantly lower organic carbon and nitrogen contents, more enriched stable carbon and nitrogen compositions, lower lignin product yields, and distinctly different lignin and nonlignin product compositions than their fine-textured counterparts. Compositional differences were also measured between high- and low-density fractions of selected sediment samples. Subsurface sediments showed marked compositional variations that were predominantly associated with changes in the texture of the deposits. Most sediments were characterized by moderate carbon loadings (0.5-1.0 mg C m-2), although several samples from the outer topset region, an area of sediment bypass, were characterized by lower carbon loadings indicative of enhanced carbon losses. Overall, the organic matter in both surface and subsurface sediments appeared to have predominantly a terrigenous origin, with no evidence for dilution and/or replacement by marine carbon. The measured compositions were consistent with contributions from modern vascular plant detritus, aged soil organic matter, and very old or fossil organic matter devoid of recognizable biochemicals. Copyright 2008 by the American Geophysical Union.
Abstract.
2007
RAalto, Alin S, Dietrich WE, Goni M (2007). Biogeochemical characterization of carbon sources in the Strickland and Fly rivers, Papua New Guinea.
Goni MA, Monacci NM, Gisewhite R, Crockett J, Ogston A, Nittrouer C, Alin SR, Aalto RE (2007). GEOC 27-Terrigenous organic matter in sediments from the Fly River delta-clinoform system (Papua New Guinea). In (Ed) , USA: AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA.
RAalto, Dietrich WE, Lauer W (2007). Spatial and temporal dynamics of sediment accumulation and exchange along Strickland River floodplains (PNG), over decadal-to-centennial time scales.
2006
Aalto RE, Dunne T, Guyot JL (2006). Geomorphic controls on Andean denudation rates.
Journal of Geology,
114, 85-99.
Abstract:
Geomorphic controls on Andean denudation rates
To predict erosion rates throughout the Andes, we conducted a multiple regression analysis of the sediment discharge
from 47 drainage basins in the Bolivian Andes and various topographic, climatologic, and geologic parameters. These
mountainous basins are typically large (17–81,000 km2; meanp11,000 km2), often have decades of measurement
data on daily water and sediment discharge, and display an extraordinary range of denudation (0.01–6.9 mm/yr), runoff
(16–2700 mm/yr), and local topographic relief (700–4300 m), yet the underlying lithology (granitic plutons, metasediments,
and Quaternary deposits) can be classified into a small number of homogeneous types, and anthropogenic
disturbance is limited. The steep nature of the channels precludes sediment storage, and unlike previous global studies
of fluvial denudation rates, based on data compilations from very large river basins (1100,000 km2), this analysis
distinguishes the sediment production in mountains from sediment entrapment within adjacent sedimentary basins.
Lithology and average catchment slope account for 90% of the variance in sediment yield, and yield is not significantly
correlated with runoff. However, because runoff over geologic timescales orchestrates the processes of channel network
incision and sediment evacuation, climate could ultimately govern basin hillslope conditions and thereby the rates
of hillslope erosion. Several theoretical geomorphic models for mass wasting are tested to assess hillslope-scale
sediment yield models for the study basins. When applied throughout the Amazonian Andes, such empirical models
predict an annual Andean sediment flux to the lowland Amazon Basin of 2.3–3.1 Gt. Because ∼1.3 Gt/yr of sediment
reach the gauged tributaries of the mainstem Amazon River, the intervening foreland basins appear to intercept about
half of the total Andean sediment discharge.
Abstract.
Aalto R, Dunne T, Guyot JL (2006). Geomorphic controls on Andean denudation rates.
JOURNAL OF GEOLOGY,
114(1), 85-99.
Author URL.
Hoorn C, Aalto RE, Kaandorp RJG, Lovejoy NR (2006). Miocene semidiurnal tidal rhythmites in Madre de Dios, Peru.
GeologyAbstract:
Miocene semidiurnal tidal rhythmites in Madre de Dios, Peru
Hovikoski et al. (2005) acknowledge that their results contradict
Campbell et al. (2000) who described the Madre de Dios Formation in
SW Amazonia as the last major cycle of Cenozoic continental deposition.
Yet they propose that their rhythmite statistics settle the debate (also with
Hoorn, 1996) that the sediments are of marine origin. However, Hoorn
et al. believe Hovikoski et al. have not provided suffi cient proof for the
existence of a long-lived marine connection between Amazonia and the
sea during the Late Miocene.
Abstract.
Author URL.
2005
Safran EB, Bierman PR, Aalto RE, Dunne T, Whipple KX, Caffee M (2005). Erosion rates driven by channel network incision in the Bolivian Andes.
Earth Surface Processes and Landforms,
30(8), 1007-1024.
Abstract:
Erosion rates driven by channel network incision in the Bolivian Andes
The Bolivian Andes flank one of Earth’s major topographic features and dominate sediment
input into the Amazon Basin. Millennial-scale erosion rates and dominant controls on erosion
patterns in this range are poorly known. To define these patterns, we present 48 erosion
rate estimates, derived from analysis of in situ 10Be in quartz-bearing alluvium collected
from the Upper Beni River basin.
Erosion rates, corrected for the non-uniform distribution of quartz in the sample basins,
range from 0·04 mm a−1 to 1·35 mm a−1 and thus integrate over 102–104 years. Mean and modal
values are 0·42 (standard deviation: 0·29) and 0·2–0·4 mm a−1 respectively, within the range of
long-term average erosion rates in this area derived from apatite fission track thermochronology
(0·1–0·6 mm a−1). Hence, our data do not record any significant variation in erosion rate
over the last several million years. Mean and modal short-term erosion rates for the Andes
are an order of magnitude lower than rates in the Ganges River headwaters in the High
Himalaya and an order of magnitude greater than rates typical of the European Alps.
In the Upper Beni River region of the Bolivian Andes, short-term, basin-averaged erosion
rates correlate with normalized channel steepness index, a metric of relative channel gradient
corrected for drainage area. Neither normalized channel steepness index nor basin-averaged
erosion rate shows strong correlation with mean basin hillslope gradient or mean basin local
relief because many hillslopes in the Upper Beni River region are at threshold values of slope
and local relief. Patterns of normalized channel steepness index appear primarily to reflect
tectonic patterns and transient adjustment to those patterns by channel networks. Climate
and lithology do not appear to exert first-order controls on patterns of basin-averaged erosion
rates in the Bolivian Andes.
Abstract.
Safran EB, Bierman PR, Aalto R, Dunne T, Whipple KX, Caffee M (2005). Erosion rates driven by channel network incision in the Bolivian Andes.
EARTH SURFACE PROCESSES AND LANDFORMS,
30(8), 1007-1024.
Author URL.
Aalto RE, Dietrich W (2005). Sediment accumulation determined with Pb-210 geochronology for Strickland River flood plains, Papua New Guinea. In Walling, E D, Horowitz, J A (Eds.)
Sediment Budgets I, 303-309.
Abstract:
Sediment accumulation determined with Pb-210 geochronology for Strickland River flood plains, Papua New Guinea
Abstract.
2003
Aalto R, Maurice-Bourgoin L, Dunne T, Montgomery DR, Nittrouer CA, Guyot J-L (2003). Episodic sediment accumulation on Amazonian flood plains influenced by El Niño/Southern Oscillation.
Nature,
425(6957), 493-497.
Abstract:
Episodic sediment accumulation on Amazonian flood plains influenced by El Niño/Southern Oscillation.
Continental-scale rivers with a sandy bed sequester a significant proportion of their sediment load in flood plains. The spatial extent and depths of such deposits have been described, and flood-plain accumulation has been determined at decadal timescales, but it has not been possible to identify discrete events or to resolve deposition on near-annual timescales. Here we analyse (210)Pb activity profiles from sediment cores taken in the pristine Beni and Mamore river basins, which together comprise 720,000 km2 of the Amazon basin, to investigate sediment accumulation patterns in the Andean-Amazonian foreland. We find that in most locations, sediment stratigraphy is dominated by discrete packages of sediments of uniform age, which are typically 20-80 cm thick, with system-wide recurrence intervals of about 8 yr, indicating relatively rare episodic deposition events. Ocean temperature and stream flow records link these episodic events to rapidly rising floods associated with La Niña events, which debouch extraordinary volumes of sediments from the Andes. We conclude that transient processes driven by the El Niño/Southern Oscillation cycle control the formation of the Bolivian flood plains and modulate downstream delivery of sediments as well as associated carbon, nutrients and pollutants to the Amazon main stem.
Abstract.
Author URL.
Aalto RE, Maurice-Bourgoin L, Dunne T, Montgomery DR, Nittrouer CA, Guyot JL (2003). Episodic sediment accumulation on Amazonian floodplains influenced by ENSO.
Nature,
425, 493-497.
Abstract:
Episodic sediment accumulation on Amazonian floodplains influenced by ENSO
Continental-scale rivers with a sandy bed sequester a significant
proportion of their sediment load in flood plains. The spatial
extent and depths of such deposits have been described1,2, and
flood-plain accumulation has been determined at decadal timescales3–
5, but it has not been possible to identify discrete events or
to resolve deposition on near-annual timescales. Here we analyse
210Pb activity profiles from sediment cores taken in the pristine
Beni and Mamore river basins, which together comprise
720,000 km2 of the Amazon basin, to investigate sediment
accumulation patterns in the Andean–Amazonian foreland. We
find that in most locations, sediment stratigraphy is dominated
by discrete packages of sediments of uniform age, which are
typically 20–80 cm thick, with system-wide recurrence intervals
of about 8 yr, indicating relatively rare episodic deposition
events. Ocean temperature and stream flow records link these
episodic events to rapidly rising floods associated with La Nin˜a
events, which debouch extraordinary volumes of sediments from
the Andes. We conclude that transient processes driven by the El Nin˜o/Southern Oscillation cycle control the formation of the
Bolivian flood plains and modulate downstream delivery of
sediments as well as associated carbon, nutrients and pollutants
to the Amazon main stem.
Abstract.
2002
Aalto R, Dunne T, Nittrouer CA, Maurice-Bourgoin L, Montgomery DR (2002). Fluvial transport of sediment across a pristine tropical foreland basin: Channel-flood plain interaction and episodic flood plain deposition. In (Ed)
, 339-344.
Abstract:
Fluvial transport of sediment across a pristine tropical foreland basin: Channel-flood plain interaction and episodic flood plain deposition
Abstract.
Aalto RE, Dunne T, Nittrouer CA, Maurice-Bourgoin L, Montgomery DR (2002). Fluvial transport of sediment across a pristine tropical foreland basin: channel-flood plain interaction and episodic flood plain deposition. In Dyer FJ, Thoms MC, Olley JM (Eds.)
The Structure, Function and Management Implications of Fluvial Sedimentary Systems, Wallingford, UK: IAHS Press, 339-344.
Abstract:
Fluvial transport of sediment across a pristine tropical foreland basin: channel-flood plain interaction and episodic flood plain deposition
Abstract.
Maurice L, Aalto RE, Guyot JL (2002). Sediment-associated mercury distribution within a major Amazonian tributary: century-scale contamination history and importance of flood plain accumulation. In Dyer, J F, Thoms, C M, Olley, M J (Eds.)
The Structure, Function and Management Implications of Fluvial Sedimentary Systems: Wallingford, Wallingford, UK: , 161-168.
Abstract:
Sediment-associated mercury distribution within a major Amazonian tributary: century-scale contamination history and importance of flood plain accumulation
Abstract.
1999
Aalto RE, Aalto KR, Garrison-Laney CE, Abramson HF (1999). Tsunami (?) sculpturing of the Pebble Beach Wave-cut Platform, Crescent City area, California. Journal of Geology, 107, 607-622.
1997
Aalto RE, Montgomery DR, Hallet B, Abbe TB, Buffington JM, Cuffey KM, Schmidt KM (1997). A Hill of Beans. Science, 277(5334), 1909-1914.
Aalto R, Montgomery DR, Hallet B, Abbe TB, Buffington JM, Cuffey KM, Schmidt KM, Densmore AL, Anderson RS, Ellis MA, et al (1997). A hill of beans [3] (multiple letters). Science, 277(5334), 1911-1913.
