Catchment Erosion Research Articles

General soil-landscape distribution patterns in buffer zones of different order streams

Understanding landscape and soil distribution patterns in buffer zones along a stream network in a watershed can improve riparian zone management and the representation of soil-landscape parameters in watershed modeling. We analyzed landscape features and soil properties within a 300-m buffer zone of different order streams in a large agricultural watershed (the East Mahantango Creek Watershed) located in the Ridge and Valley Physiographic Province in Pennsylvania, USA. The mean elevation displays an obvious decreasing trend downstream, and increases gradually with the distance away from the streams. Within the buffer distance of approximately 75 m, buffer zone's mean slope shows a rapid increase regardless of stream order; however, it starts to decrease after 75 m in the 1st to 3rd order stream buffers, but continues to increase in a more gradual manner in the 4th and 5th order stream buffers. Agricultural land area percentage increases by 10–25% from near stream area to about 100 m buffer, and becomes nearly the same in 100–300 m buffer zone. The opposite trend holds for forested land area in all stream buffer zones. The 1st to 2nd order stream buffers have 12–28% greater agricultural land area percentage and 0.45–1 m shallower soil depth than the 3rd to 5th order stream buffers, suggesting that the headwater areas in the study watershed are important in preventing nonpoint source pollution due to the more intensive agricultural land use and potential erosion in headwater catchments. The distributions of soil properties in the buffer zones are consistent with the observed landscape patterns. The top two soil layers (approximately A and B horizons) in the 0–100 m buffer zones of the 1st and 2nd order streams generally display a greater clay content and a higher bulk density, but a lesser organic matter content and a lower available water capacity, than those in the similar buffer zones of the 3rd to 5th order streams. Beyond the 100 m buffer distance and in the third layer of the soil profiles (approximately C horizons), the soil properties examined in all stream buffer zones become less distinguishable. With a few exceptions, soil clay content and bulk density increase with increasing buffer distance (particularly within 0–100 m range), while organic matter content and available water capacity decrease with buffer distance. Such patterns reflect the impacts from the landscape features, fluvial processes, and land use in the Ridge and Valley Physiographic region. The results of this study, though maybe specific to the watershed studied, suggest that soil and landscape distribution patterns along stream networks are helpful to guide riparian zone management and nonpoint source pollution prevention in agricultural watersheds.

A Lateglacial and Holocene lake record from the Nianbaoyeze Mountains and inferences of lake, glacier and climate evolution on the eastern Tibetan Plateau

Our 12.81m long record from Lake Ximencuo provides insight into the Lateglacial and Holocene evolution of the lake and the Nianbaoyeze glacier in its catchment, and the regional climate history since ∼19kyr. Lake Ximencuo was a permanent deep lake throughout its history. In contrast to numerous lakes on the Tibetan Plateau which experienced shallow lake levels or even desiccation during the Lateglacial, Lake Ximencuo was fed by large quantities of meltwater in the Lateglacial. The existence of glaciated upper catchment areas is apparently a prerequisite for lakes on the Tibetan Plateau which maintained relatively high water levels during the generally cold and dry periods following the global LGM (∼21kyr). A minor re-advance of the Nianbaoyeze glacier was recorded coeval with the Greenland Stadial 2a (∼16.4 and 14.5kyr), followed by rapid warming apparently synchronous with the Greenland Interstadial 1. Warmest conditions were recorded at Lake Ximencuo during the early Holocene which was punctured by a remarkable pulse of climate deterioration around 8.3kyr. This spell represents probably the 8.2kyr event of the North Atlantic region, suggesting that it had a significant impact on the Tibetan Plateau. Colder conditions of longer duration occurred from 4.7 to 3.7kyr, apparently in phase with numerous records signalling colder and drier conditions on the Tibetan Plateau. Two minor spells of colder conditions and probably catchment erosion were recorded in the late Holocene between 2.0 and 1.4kyr and between 0.5 and 0.1kyr with the latter representing the Little Ice Age. It is unclear, whether human activities may have accelerated or even solely triggered the late Holocene erosion events.

Rock-type control on erosion-induced uplift, eastern Swiss Alps

There is growing evidence that Quaternary rock uplift in parts of the European Alps is a consequence of climate- and erosion-driven isostatic rebound. Contemporary rates of rock uplift U in the Swiss Alps show two distinctive dome-like peak regions that attain ~ 1.6 mm yr − 1 . We focus on the Alpenrhein catchment and its surroundings, where one of these peak regions spatially coincides with widely exposed Cretaceous Bündner schist and lower Tertiary flysch. Field assessments and analyses of hillslope gradient distributions quantitatively demonstrate the low rock-mass strength and high erodibility of these rocks. This is reflected in mean postglacial catchment erosion rates D ~ 4 mm yr − 1 , as opposed to 0.7 mm yr − 1 in more resistant crystalline rocks. Though largely inferred from landslide- and debris-flow prone tributary catchments < 20 km 2, the localised erosion rates in Bündner schist and flysch are among the highest documented for the Alps, and corroborated by historic suspended sediment yields, and thus export, from the region. We further find that the steepness of bedrock rivers, the density of large landslides, and D correlate with the highest values of U. Our observations highlight the possibility that erosion of mechanically weak Bündner schist and flysch enhanced by large landslides may have contributed to regional crustal unloading, and concomitant rock uplift. Irrespective of whether this is betraying a coupling between long-term uplift and erosion modulated by rock type, our findings indicate that long-term (10 3 to 10 4 yr) geomorphic signals contained in bedrock-river steepness, spatial density of large landslides, and postglacial erosion rates strikingly correlate with regional gradients of historic (10 1 yr) rock uplift rates.

Theoretical cosmogenic nuclide concentration in river bed load clasts: Does it depend on clast size?

Terrestrial Cosmogenic Nuclides (TCNs) have been widely used to date the exposure of alluvial surfaces and to estimate catchment-scale erosion rates. However, TCN concentration differences in samples of different grain sizes remain to be fully understood. In order to explore the possibility that river processes generate such differences, we develop a numerical model to calculate along-stream clast-scale TCN concentrations. Using the hillslope model, there is a progressive detachment of successive clasts of specific sizes followed by their instantaneous fall into the river. In the river, transport velocity and TCN concentration evolution in a clast depend 1) on the probability of being trapped in the sediment mixing layer of the river or within an adjacent terrace; 2) on its size which decreases downstream by attrition. The size-dependent transport law corresponds to the partial transport state in a river. We model the distribution of TCN concentrations in different clast size fractions in the 0–5 cm radius range for catchments in steady-state erosion, and for catchments experiencing sedimentation. We propose that clast attrition tends to increase the variance of TCN concentrations of the small clast size fractions because these fractions incorporate initially big clasts that travelled a long distance in addition to small clasts contributed near the outlet. We obtained numerous clast size–TCN concentration correlations, positive or negative, the significance of which depends on the initial clast size distribution, hillslope erosion rate, river length and lithology. For an equilibrium catchment, even large, we found that the addition of TCN concentration acquired during river transport is negligible compared to TCN concentration acquired on a hillslope, although a clast size–TCN concentration relationship can result from or be modified by clast attrition. On the contrary, aggrading catchments may show a significant clast size-dependent TCN concentration increase during river transport. This may introduce a small bias in the TCN-derived catchment erosion rate, but it could be used positively to quantify the mean transport velocity of clasts of different sizes over thousands of years. In addition, the lack of correlation between TCN concentration and clast size does not imply that the mean transport velocity is the same for all clast size fractions. Overall, our study provides an alternative explanation for observed clast size-dependent TCN concentrations and brings to the fore the need for measuring TCN concentration in larger clast size fractions than is usually done. To see if the byproducts of abrasion dilute or increase the TCN concentration of sand, all products should be included in a future study.

Bank erosion and channel width change in a tropical catchment

AbstractCatchment sediment budget models are used to predict the location and rates of bank erosion in tropical catchments draining to the Great Barrier Reef lagoon, yet the reliability of these predictions has not been tested due to a lack of measured bank erosion data. This paper presents the results of a 3 year field study examining bank erosion and channel change on the Daintree River, Australia. Three different methods were employed: (1) erosion pins were used to assess the influence of riparian vegetation on bank erosion, (2) bench‐marked cross‐sections were used to evaluate annual changes in channel width and (3) historical aerial photos were used to place the short term data into a longer temporal perspective of channel change (1972–2000). The erosion pin data suggest that the mean erosion rate of banks with riparian vegetation is 6·5 times (or 85%) lower than that of banks without riparian vegetation. The changes measured from cross‐section surveys suggest that channel width has increased by an average of 0·74 (±0·47) m a−1 over the study period (or ∼0·8% yr−1). The aerial photo results suggest that over the last 30 years the Daintree River has undergone channel contraction of the order of 0·25 m a−1. The cross‐section data were compared against modelled SedNet bank erosion rates, and it was found that the model underestimated bank erosion and was unable to represent the variable erosion and accretion processes that were observed in the field data. The reach averaged bank erosion rates were improved by the inclusion of locally derived bed slope and discharge estimates; however, the results suggest that it will be difficult for catchment scale sediment budget models to ever accurately predict the location and rate of bank erosion due to the variation in bank erosion rates in both space and time. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Microfossils and geochemistry of some modern, Holocene and Pleistocene travertines from North Yorkshire and Derbyshire

Summary The geochemistry of some modern, Holocene (4–4.5 ka) and Pleistocene (&gt;100 ka) travertines from the UK is described. Four facies were recognized: one bryophyte, two algal and one clastic. In the Holocene travertine, from Gordale, Yorkshire, concentrations of Fe, Mn, Sr, Zn and the travertine porosity showed significant differences between facies that were related to the content of acid-insoluble residues and differences in meteoric diagenesis. The modern, active travertines, also from Gordale, similarly showed significant geochemical differences between facies types. All geochemical determinands in the modern travertines were higher by a factor of about two compared with the Holocene travertine. This is believed to be due to increased catchment erosion over the past few centuries and travertine deposits may therefore provide information on rates of soil erosion. The stable isotopic compositions of the travertine averaged −5.9‰ for δ 18 O and −9.6‰ for δ 13 C, but there were no significant differences between the facies. Seventeen diatom taxa were found in the Holocene deposits but numbers were low when compared with the modern deposits, which were higher by a factor of about 1000. Dissolution of diatoms after burial would be sufficient to account for all of the authigenic quartz observed in these deposits. Four classes of organic matter were identified in the Holocene and Pleistocene samples: filaments, perforated plates, spores and amorphous forms. Their abundance differed little between facies. Some of the filamentous structures were probably post-depositional fungal hyphae utilizing carbon resources within the deposits.

A multiproxy palaeolimnological investigation of Holocene environmental change, between c. 10 700 and 7200 years BP, at Holebudalen, southern Norway

Geochemical analyses (x-ray fluorescence, δ13C and C/N ratios) were used to reconstruct early Holocene environments (between 10685 and 7260 cal. yr BP) at a small lake near Holebudalen, southern Norway. Results show a period of increasing stability, with reduced catchment inwash (shown by titanium and potassium minerals), vegetation stabilization and increasing aquatic productivity (C/N ratios). However, periods of instability (loss on ignition (LOI) decrease) are also seen (most notably at c. 9060 cal. yr BP). Chironomid-inferred July temperature (CI-T) reconstructions show a cooling of c. 2°C (RMSEP = 1.0°C) between c. 8400 and 8000 cal. yr BP and so high-resolution (5 mm; c. 20 yr) diatom analyses were conducted between 8675 and 7830 cal. yr BP in order to further investigate this change. Between c. 8270 and 8000 cal. yr BP there were large reductions (&gt; 50%) in the abundance of tychoplanktonic diatoms (eg, Aulacoseira species) and absolute increases in periphytic diatom communities (eg, Navicula pupula, Pinnularia mesolepta). The multiproxy analyses suggest a period of increased lake ice cover with associated reductions in turbulence during this time. Diatom flora changes are concomitant with a fall in percent LOI and increased catchment erosion at the site and other evidence of regional climatic perturbations in the early Holocene. Therefore, superimposed upon an early Holocene warming trend at Holebudalen, there are climatic perturbations, for example reflected between c. 8200 and 8000 cal. yr BP by diatom communities.

Integrated varve and pollen-based temperature reconstruction from Finland: evidence for Holocene seasonal temperature patterns at high latitudes

A detailed understanding of decadal to millennial-scale climate changes requires seasonal-scale (summer-winter) reconstructions of past precipitation and temperature fluctuations. Comparing seasonally resolved varve records with pollen-based sum of growing degree-days (GDD) reconstructions from Lake Nautajärvi, we examined the intra-annual nature of climate variability in central southern Finland during the Holocene. The organic varve record and the GDD reconstruction show roughly comparable trends supporting the interpretation that both proxies predominantly reflect summer temperatures in the study area. The records suggest low but rising early-Holocene (9500 to 8500 cal. yr BP) summer temperatures. The Holocene Thermal Maximum (HTM) in the GDD record dates to about 7500 to 4500 cal. yr BP, but the organic varve record along with reconstructed changes in vegetation composition, notably a peak of Tilia pollen percentages, indicate that during the HTM there was a trend towards a more continental climate with maximum mid-summer temperatures reached at 6500 to 4500 cal. yr BP. Both records reflect the start of the post-HTM cooling at about 4500 cal. yr BP, simultaneously with an increase of the amount of catchment erosion and mineral matter influx into the lake, suggesting gradually colder and/or longer winters with high net accumulation of snow. The organic varve record and the GDD record start to diverge at 2000 cal. yr BP, possibly owing to the human influence on catchment processes. The reconstructed mid-Holocene summer temperature peak deviates from the regional climate model outputs, which suggest highest summer temperatures during the early Holocene.

The history of soil erosion and fluvial deposits in small catchments of central Europe: Deciphering the long-term interaction between humans and the environment — A review

During the last few decades, many case studies focused on the dynamics of fluvial systems in response to hillslope erosion, land-use impact, and climate changes. This paper will review the current state of knowledge of the dynamics of past soil erosion and gullying in small catchments (< 1 km 2), the effects to adjacent fluvial systems and possible feedback mechanisms to land-use changes for the last 7000 years in central Europe. The discussed studies were made on hillslopes and gully systems in low mountain range areas. They are characterised by coupled slope–channel systems as well as uncoupled systems like closed depressions in Pleistocene lowlands, maars, lakes, and sunken areas. The studies show that sediment fluxes in small catchments are highly sensitive to local land-use changes while river sediments show regional trends in land-use and climate changes. Peaks of soil erosion and gullying took place during phases of rapid climate change. Particularly, extreme precipitation events caused intensive runoff on slopes used for agriculture. The most remarkable phases occurred in the first half of 14th and in the mid-18th to the early 19th century. Most of the gully systems in Europe today are a result of these catastrophic occurrences. These punctuated events triggered land abandonment and influenced the ecosystem and the socio-economic situation. The results imply that a future increase in land-use intensity and extreme precipitation events during climatic change might have severe consequences regarding soil erosion, flood risk, and ecological aspects.

Controls on sediment evacuation from glacially modified and unmodified catchments in the eastern Sierra Nevada, California

AbstractThe degree of glacial modification in small catchments along the eastern Sierra Nevada, California, controls the timing and pattern of sediment flux to the adjacent fans. There is a close relationship between the depth of fan‐head incision and the pattern and degree of Late Pleistocene catchment erosion by valley glaciers; catchments with significant glacial activity are associated with deeply incised fan heads, whereas fans emerging from glacially unmodified catchments are unincised. We suggest that the depth of fan‐head incision is controlled by the potential for sediment storage during relatively dry ice‐free periods, which in turn is related to the downstream length of the glacially modified valley and creation of accommodation through valley floor slope lowering and glacial valley overdeepening and widening. Significant storage in glacially modified basins during ice‐free periods leads to sediment supply‐limited conditions at the fan head and causes deep incision. In contrast, a lack of sediment trapping allows quasi‐continuous sediment supply to the fan and prevents incision of the fan head. Sediment evacuation rates should thus show large variations in glacially modified basins, with major peaks during glacial and lows during interglacial or ice‐free periods, respectively. In contrast, sediment removal from glacially unmodified catchments in this type of setting should be free of this effect, and will be dominated instead by short‐term variations, modulated for example by changes in vegetation cover or storm frequency. This distinction may help improve our understanding of long‐term sediment yields as a measure of erosional efficiency. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Impacts of land‐use/cover changes on the hydrology of the transboundary Mara River, Kenya/Tanzania

AbstractThe Mara River is the lifeline of the transboundary Mara basin across Kenya and Tanzania. The basin is considered one of the more serene subcatchments of the Lake Victoria Basin and ultimately the Nile Basin, and traverses the famous Maasai Mara and Serengeti National Parks. The basin also contains forests, large‐scale farms, smallholder farms, pastoral grazing lands, as well as hunter gatherers and fishers. There is growing concern, however, regarding land degradation in the basin, particularly deforestation in the headwaters, that is affecting the natural resource base and the river flows. Accurate scientific data are required to advise policy, and to plan appropriate mitigation measures. This study utilizes remote sensing and geographical information system (GIS) tools, and hydrological and ground‐truth studies to determine the magnitude of the land‐use/cover changes in the Mara River Basin, and the effects of these changes on the river flows over the last 30 years. The study results indicate that land‐use/cover changes have occurred. In 1973, for example, rangelands (savannah, grasslands and shrublands) covered 10 989 km2 (79%) of the total basin area. The rangelands had been reduced to 7245 km2 (52%) by 2000, however, while the forest areas were reduced by 32% over the same period. These changes have been attributed to the encroachment of agriculture, which has more than doubled (203%) its land area over the same period. The hydrology of the Mara River also has changed, with sharp increases in flood peak flows by 7%, and an earlier occurrence of these peaks by 4 days between 1973 and 2000. There is evidence of increased soil erosion in the upper catchments, with silt build‐up in the downstream floodplains. This has caused the Mara wetland to expand by 387%, adversely affecting riparian agriculture. There is need for urgent action to stem the land degradation of the Mara River Basin, including planning and implementing appropriate mitigation measures.

Characterizing changes in the sedimentary environment of a varved lake sediment record in southern central Finland around 8000 cal. yr BP

AbstractThe varved lake sediment record of Lake Nautajärvi in southern central Finland indicates fluctuations in the annual sedimentation pattern and lake environment around 8000 cal. yr BP. Annual accumulation of catchment‐derived mineral matter peaks a number of times and there are changes in the deposition rate of organic matter. Based on evidence from the Lake Nautajärvi sediment record, the climate was characterised by a millennial‐scale colder period that terminated at one or several cooling events around 8000 cal. yr BP. During one of these events, diatom composition undergoes a change from planktonic species dominance to more littoral species dominance at 8160 cal. yr BP, and a recovery around 8010 cal. yr BP. The timing of this 150‐year‐long diatom anomaly is convergent with increased catchment erosion and decreased organic matter accumulation. We interpret that during such a period, the environment was characterised by colder winter temperatures, prolonged duration of ice cover, higher than normal spring discharge and rapid development of thermal stratification in the spring, coupled with reduced water circulation and shorter growing seasons. Copyright © 2008 John Wiley &amp; Sons, Ltd.

A transport‐distance approach to scaling erosion rates: 1. Background and model development

AbstractThe process basis of existing soil‐erosion models is shown to be ill‐founded. The existing literature builds directly or indirectly on Bennett's (1974) paper, which provided a blueprint for integrated catchment‐scale erosion modelling. Whereas Bennett recognized the inherent assumptions of the approach suggested, subsequent readings of the paper have led to a less critical approach. Most notably, the assumption that sediment movement could be approximated by a continuity equation that related to transport in suspension has produced a series of submodels that assume that all movement occurs in suspension. For commonly occurring conditions on hillslopes, this case is demonstrably untrue both on theoretical grounds and from empirical observations. Elsewhere in the catchment system, it is only partially true, and the extent to which the assumption is reasonable varies both spatially and temporally. A second ground‐breaking paper – that of Foster and Meyer (1972) – was responsible for subsequent uncritical application of a first‐order approximation to deposition based on steady‐state analysis and again a weak empirical basis. We describe in this paper an alternative model (Mahleran – Model for Assessing Hillslope‐Landscape Erosion, Runoff And Nutrients) based upon particle‐travel distance that overcomes existing limitations by incorporating parameterizations of the different detachment and transport mechanisms that occur in water erosion in hillslopes and small catchments. In the second paper in the series, we consider the sensitivity and general behaviour of Mahleran, and test it in relation to data from a large rainfall‐simulation experiment. The third paper of the sequence evaluates the model using data from plots of different sizes in monitored rainfall events. From this evaluation, we consider the scaling characteristics of the current form of Mahleran and suggest that integrated modelling, laboratory and field approaches are required in order to advance the state of the art in soil‐erosion modelling. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Eleanora Bliss Knopf and Unequal Erosion

Eleanora Bliss Knopf (1883-1974) was one of several American women geologists working in the Appalachians during the first two decades of the twentieth century. Though primarily a petrologist, she made astute observations concerning inequalities in erosion in catchments and hence the survival of palaeoforms in the landscape.

Rapid ecosystem response to abrupt climate changes during the last glacial period in western Europe, 40–16 ka

We present a high-resolution and independently dated multiproxy lake sediment record from the paleolake at Les Echets in southeastern France that displays synchronous changes in independent limnic and terrestrial ecosystem proxies, in concert with millennial-scale climate oscillations during the last glacial period. Distinct lake-level fluctuations, low lake organic productivity, and open, treeless vegetation indicate cold and dry conditions in response to Heinrich events. Alternating phases of higher and low lake organic productivity, stratified surface waters and long-lasting lake ice cover, decreased or increased catchment erosion, and tree-dominated or herb-dominated vegetation resemble Dansgaard-Oeschger interstadialstadial variability. Transitions between different ecological states occurred in as little as 40–230 yr and seem to have been controlled by the position of the Polar Front. Ecosystem response after 30 ka suggests that local climate conditions became more important. Our results demonstrate that all parts of the terrestrial system responded to the abrupt and dramatic climatic changes associated with Dansgaard-Oeschger and Heinrich events, and that regional factors modulated ecosystem response.

Geomorphology of upland peat: erosion, form and landscape change

Series Editors' Preface. Acknowledgements. 1. Introduction. 1.1 The aims of this volume. 1.1.1 Thematic coverage. 1.1.2 Geographical context. 1.2 Terminology, definitions and peatland geomorphology. 1.2.1 Definitions of Peat. 1.2.2 The Physical and geotechnical properties of peat. 1.2.3 Peatland classification. 1.3 The geography of blanket mire complexes. 1.4 Patterns of peat erosion in space and time. 1.4.1 The onset of peat erosion. 1.4.2 Direct observation of the onset of erosion. 1.5 Causes of peat erosion. 1.6 A brief history of the evolution of peatland geomorphology. 1.6.1 Accounts of erosion in the natural science tradition. 1.6.2 Descriptive accounts of widespread peat erosion. 1.6.3 Quantitative observations of blanket peatlands. 1.7 Structure of this volume and the peat land system model. 2. The Hydrology of Upland Peatlands. 2.1 Introduction. 2.2. Controls on water movement in peatland systems. 2.2.1 Hydraulic conductivity of upland peat soils. 2.2.2 The diplotelmic mire hypothesis. 2.2.3 Groundwater flow in upland peatlands. 2.2.4 Evaporation. 2.2.5 Runoff generation. 2.2.6 The Water balance of ombrotrophic mires. 2.3 Geomorphology and the hydrology of upland peatlands. 3. Sediment Production. 3.1 Introduction. 3.1.1 Monitoring sediment production using erosion pins. 3.1.2 Sediment trap data. 3.2 Sediment production as a control on catchment sediment flux. 3.3 Evidence from field observation. 3.3.1 Climate correlations with trap data. 3.3.2 Direct observations of surface change. 3.4 Evidence from controlled experiments. 3.5 Timescales of sediment supply. 3.6 Conclusion. 4. Fluvial Processes and Peat Erosion. 4.1 Introduction. 4.2 Gully erosion of blanket peat. 4.2.1 Gully morphology and topology. 4.2.2 Processes of Gully erosion. 4.3 Erosion and transport of peat in perennial stream channels. 4.3.1 Production of peat blocks by fluvial erosion. 4.3.2 Transport of peat blocks in stream channels. 4.3.3 The fate of fine peat sediment in channel. 4.4 Sediment yield. 4.4.1 A conceptual model of sediment dynamics in eroding blanket peatlands. 4.4.2 Sediment yield, sediment supply and assessing catchment erosion status. 4.5 Conclusions. 5. Slope Processes and Mass Movements. 5.1 Introduction. 5.2 Peat covered hillslopes. 5.2.1 Limits to the stability of peat on slopes. 5.2.2 Creep on peat hillslopes. 5.3 Morphology of rapid peat mass movements. 5.3.1 Source zone. 5.3.2 Rafted peat debris. 5.3.3 Runout track. 5.3.4 Secondary tension and compression features. 5.3.5 Bog burst and peat slides - are they different?. 5.4 Mechanism of peat failure. 5.4.1 Speed of failure and movement. 5.5 Significance of surface hydrology in peat failures. 5.5.1 Water content and pore pressures. 5.5.2 Rainfall. 5.5.3 Slope drainage. 5.6 Stability analysis and modelling of peat mass movements. 5.7 The changing frequency of peat mass movements over time. 5.8 Summary and overall framework. 6. Wind Erosion Processes. 6.1 Introduction. 6.2 Wind erosion in the uplands and the significance in peatland environments. 6.3 Mechanisms of wind erosion. 6.4 The significance of wet or dry wind erosion processes. 6.5 Direct measurements of wind erosion of peat. 6.6 Aeolian landforms. 6.7 The significance of wind erosion for landscape development in upland peatlands. 6.8 Conclusions. 6.8.1 Further research - an agenda for pluvio-aeolian studies of upland peat. 7. Peat Erosion Forms - from Landscape to Micro-relief. 7.1 Rationale and introduction. 7.2 Macroscale - Region / Catchment Scale. 7.3 Mesoscale - Slope-Catena Scale. 7.4 Microscale - material structure scale. 7.5 Linking the geomorphological and the ecohydrological. 7.6 Conclusions. 8. Sediment Dynamics, Vegetation, and Landscape Change. 8.1 Introduction. 8.2 The effect of peatland dynamics on long term sediment budgets. 8.3 Mass balance evidence of patterns of long term erosion. 8.4 Re-vegetation of eroding peatlands. 8.4.1 Artificial re-vegetation of bare peat surfaces. 8.4.2 Natural revegetation of eroded landscapes. 8.5 Controls and mechanisms of natural re-vegetation. 8.5.1 Extrinsic controls on re-vegetation. 8.5.2 Intrinsic controls on re-vegetation. 8.5.3 Eriophorum spp. as Keystone Species for Re-vegetation of Eroded Peatlands. 8.5.4 Geomorphology, ecology, and 'erosion-regeneration complexes'. 8.5.5 Re-vegetation dynamics and long term patterns of erosion. 8.6 Stratigraphic evidence of erosion and re-vegetation. 8.7 The future of blanket peat sediment systems. 8.8 Changes in pollution climate. 8.9 Climate change impacts. 8.9.1 Increased summer drought. 8.9.2 Increased summer and winter storminess. 8.9.3 Changes in the growing season and vegetation. 8.9.4 Overall response of the peat land system. 8.10 Relative importance of peat erosion in wider upland sediment budgets. 8.11 Conclusions. 9. Implications and Conclusions. 9.1 Implications of widespread peat erosion. 9.2 Upland peatland erosion and carbon budgets. 9.2.1 Case Study Example: the Rough Sike sediment-carbon budget. 9.3 Release of stored contaminants from eroding peatlands. 9.4 Restoration of eroded upland peatlands. 9.4.1 Frameworks for restoration. 9.4.2 Approaches to restoration. 9.4.3 Implications of the landsystems model and sediment budget work for restoration. 9.5 Conclusions. 9.5.1 The nature of upland peatlands. 9.5.2 Geomorphological processes in upland peatlands. 9.5.3 The future of upland peatlands. 9.5.4 Representativeness of the peat land system model. Index.

New constraints on sediment-flux–dependent river incision: Implications for extracting tectonic signals from river profiles

We present new field data from rivers draining across active normal faults that incise across the same lithology at the fault, have been subjected to similar climatic regimes and tectonic settings, and were perturbed by a well-documented increase in fault slip rate ca. 1 Ma. In spite of these similarities, the rivers exhibit markedly different long profiles and patterns of catchment incision. We use channel slope and hydraulic geometry data for each river to calculate bed shear stresses (τb), and show that there is no simple relationship between peak τb and the relative uplift rates across the faults, U , which differ by a factor of four. The long-term average sediment supply to each channel ( Q s), estimated from time-averaged catchment erosion rates, can explain the τb versus U data if bedload modulates bedrock incision rate, E , in a strongly nonlinear way. Together these field data allow us, for the first time, to evaluate theoretical predictions of the role of sediment on river profile evolution and to quantify the magnitude of the effect in natural systems.

Wildfire thermochronology and the fate and transport of apatite in hillslope and fluvial environments

Wildfire heating of the outer few centimeters of exposed rock or soil generates short‐duration, high‐temperature thermal events that produce characteristic thermochronologic signatures in minerals. Contrasting activation energies of fission track annealing and He diffusion in apatite lead to a kinetic crossover whereby wildfire heating resets fission track (FT) ages much faster than (U‐Th)/He ages, resulting in “inverted” FT‐He ages in single grains. This can be used to trace wildfire‐affected detritus at the Earth's surface. We show that in exposed bedrock, inverted apatite FT‐He ages vary systematically with depth to ∼3 cm, and detrital clasts on hillslopes also show strong but heterogeneous wildfire‐resetting signatures. In soils, colluvium, and low‐order channel sediments, strongly wildfire‐reset apatite grains are abundant, and in some cases dominate the population of detrital apatite, to depths at least as great as 10 cm. Wildfire‐reset apatite is rare, however, in fluvial sediments sampled from larger basins, indicating a strong fractionation of apatite populations from hillslopes to rivers. Characteristic dissolution features in hillslope apatite and slower relative dissolution rates of other common minerals suggest that wildfire‐reset apatite grains are rare or absent in rivers because they dissolve relatively rapidly in soil profiles. Apatite that does contribute to fluvial sediments is likely to be dominantly derived from bedrock landslides in steep regions or from large clasts containing grains protected from both wildfire heating and dissolution. This means that apatite in fluvial sediment is spatially fractionated with respect to its sources in the catchment, even if catchment erosion rates are spatially uniform.

A sedimentary record of the rise and fall of the metal industry in Bergslagen, south central Sweden

Detailed stratigraphic analyses of sediments deposited in Lake Botjarnen, a small boreal forest lake in the shield terrain of central Sweden, clearly reflect progressively increasing human impact on terrestrial and aquatic ecosystems following settlement and establishment of an iron industry in the 17th century. Rising frequencies of pollen and spores from light-demanding plants provide evidence of extensive forest clearance for charcoal and timber production, which peaked in the early 20th century. An associated increase in catchment erosion is reflected by changing carbon and nitrogen elemental content and carbon–isotope composition of sediment organic matter and by increased magnetic susceptibility of the sediments. Records of air-borne pollutants (lead, zinc and sulphur) can be correlated to the development of local and regional mining and metal industry as inferred from historical accounts. Rapid recession of the iron industry led to re-forestation and recovery of the aquatic nutrient status to pre-industrial conditions over the past 100 years. The chronology of the sediment succession, which is based on 210Pb and 137Cs radionuclide data in combination with radiocarbon dating, is confirmed by historical lead pollution trends established for the region.

Hydrologic response of upland catchments to wildfires

To which extent do wildfires affect runoff production, soil erosion and sediment transport in upland catchments? This transient effect is investigated here by combining data of long term precipitation, sediment yield and wildfire records with a fine resolution spatially distributed modeling approach to flow generation and surface erosion. The model accounts for changes in the structure and properties of soil and vegetation cover by combining the tube-flux approach to topographic watershed partition with a parsimonious parametrization of hydrologic processes. This model is used to predict hydrologic and sediment fluxes for nine small catchments in Saint Gabriel mountains of southern California under control (pre-fire) and altered (post-fire) conditions. Simulation runs using a 45 years record of hourly precipitation show the passage of fire to significantly modify catchment response to storms with a major effect on erosion and flood flows. The probability of occurrence of major floods in the post-fire season is shown to increase up to an order of magnitude under same precipitation conditions. Also, the expected anomaly of sediment yield can increase dramatically the desertification hazard in upland wildfire prone areas. One should further consider the role of firefloods produced by the combined occurrence of wildfires and storms as a fundamental source of non-stationarity in the assessment of hydrologic hazard.