Changes In Erosion Rates Research Articles

Short-lived increase in erosion during the African Humid Period: Evidence from the northern Kenya Rift

The African Humid Period (AHP) between ∼15 and 5.5 cal. kyr BP caused major environmental change in East Africa, including filling of the Suguta Valley in the northern Kenya Rift with an extensive (∼2150 km2), deep (∼300 m) lake. Interfingering fluvio-lacustrine deposits of the Baragoi paleo-delta provide insights into the lake-level history and how erosion rates changed during this time, as revealed by delta-volume estimates and the concentration of cosmogenic 10Be in fluvial sand. Erosion rates derived from delta-volume estimates range from 0.019 to 0.03 mm yr−1. 10Be-derived paleo-erosion rates at ∼11.8 cal. kyr BP ranged from 0.035 to 0.086 mm yr−1, and were 2.7 to 6.6 times faster than at present. In contrast, at ∼8.7 cal. kyr BP, erosion rates were only 1.8 times faster than at present. Because 10Be-derived erosion rates integrate over several millennia, we modeled the erosion-rate history that best explains the 10Be data using established non-linear equations that describe in situ cosmogenic isotope production and decay. Two models with different temporal constraints (15–6.7 and 12–6.7 kyr) suggest erosion rates that were ∼25 to ∼300 times higher than the initial erosion rate (pre-delta formation). That pulse of high erosion rates was short (∼4 kyr or less) and must have been followed by a rapid decrease in rates while climate remained humid to reach the modern 10Be-based erosion rate of ∼0.013 mm yr−1. Our simulations also flag the two highest 10Be-derived erosion rates at ∼11.8 kyr BP related to non-uniform catchment erosion. These changes in erosion rates and processes during the AHP may reflect a strong increase in precipitation, runoff, and erosivity at the arid-to-humid transition either at ∼15 or ∼12 cal. kyr BP, before the landscape stabilized again, possibly due to increased soil production and denser vegetation.

Abrupt Change in Forest Height along a Tropical Elevation Gradient Detected Using Airborne Lidar

Most research on vegetation in mountain ranges focuses on elevation gradients as climate gradients, but elevation gradients are also the result of geological processes that build and deconstruct mountains. Recent findings from the Luquillo Mountains, Puerto Rico, have raised questions about whether erosion rates that vary due to past tectonic events and are spatially patterned in relation to elevation may drive vegetation patterns along elevation gradients. Here we use airborne light detection and ranging (LiDAR) technology to observe forest height over the Luquillo Mountain Range. We show that models with different functional forms for the two prominent bedrock types best describe the forest height-elevation patterns. On one bedrock type there are abrupt decreases in forest height with elevation approximated by a sigmoidal function, with the inflection point near the elevation of where other studies have shown there to be a sharp change in erosion rates triggered by a tectonic uplift event that began approximately 4.2 My ago. Our findings are consistent with broad geologically mediated vegetation patterns along the elevation gradient, consistent with a role for mountain building and deconstructing processes.

137Cs tracing dynamics of soil erosion, organic carbon, and total nitrogen in terraced fields and forestland in the Middle Mountains of Nepal

The Middle Mountains is one of the regions of Nepal most vulnerable to water erosion, where fragile geology, steep topography, anomalous climatic conditions, and intensive human activity have resulted in serious soil erosion and enhanced land degradation. Based on the Cs-137 tracing method, spatial variations in soil erosion, organic carbon, and total nitrogen (TN) in terraced fields lacking field banks and forestland were determined. Soil samples were collected at approximately 5 m and 20 m intervals along terraced field series and forestland transects respectively. Mean 137Cs inventories of the four soil cores from the reference site was estimated at 574.33 +/- 126.22 Bq m(-2) (1 Bq (i.e., one Becquerel) is equal to 1 disintegration per second (1 dps)). For each terrace, the Cs-137 inventory generally increased from upper to lower slope positions, accompanied by a decrease in the soil erosion rate. Along the entire terraced toposequence, Cs-137 data showed that abrupt changes in soil erosion rates could occur between the lower part of the upper terrace and the upper part of the immediate terrace within a small distance. This result indicated that tillage erosion is also a dominant erosion type in the sloping farmland of this area. At the same time, we observed a fluctuant decrease in soil erosion rates for the whole terraced toposequence as well as a net deposition at the toe terrace. Although steep terraces (lacking banks and hedgerows) to some extent could act to limit soil sediment accumulation in catchments, soil erosion in the terraced field was determined to be serious. For forestland, with the exception of serious soil erosion that had taken place at the top of slopes due to concentrated flows from a country road situated above the forestland site, spatial variation in soil erosion was similar to the "standard" water erosion model. Soil organic carbon (SOC) and TN inventories showed similar spatial patterns to the Cs-137 inventory for both toposequences investigated. However, due to the different dominant erosion processes between the two, we found similar patterns between the < 0.002 mm soil particle size fraction (clay sized) and Cs-137 inventories in terraced fields, while different patterns could be found between Cs-137 inventories and the < 0.002 mm soil particle size fraction in the forestland site. Such results confirm that Cs-137 can successfully trace soil erosion, SOC and soil nitrogen dynamics in steep terraced fields and forestland in the Middle Mountains of Nepal.

Observations and modeling of fjord sedimentation during the 30 year retreat of Columbia Glacier, AK

ABSTRACTTo explore links between glacier dynamics, sediment yields and the accumulation of glacial sediments in a temperate setting, we use extensive glaciological observations for Columbia Glacier, Alaska, and new oceanographic data from the fjord exposed during its retreat. High-resolution seismic data indicate that 3.2 × 108m3of sediment has accumulated in Columbia Fjord over the past three decades, which corresponds to ~5 mm a−1of erosion averaged over the glaciated area. We develop a general model to infer the sediment-flux history from the glacier that is compatible with the observed retreat history, and the thickness and architecture of the fjord sediment deposits. Results reveal a fivefold increase in sediment flux from 1997 to 2000, which is not correlated with concurrent changes in ice flux or retreat rate. We suggest the flux increase resulted from an increase in the sediment transport capacity of the subglacial hydraulic system due to the retreat-related steepening of the glacier surface over a known subglacial deep basin. Because variations in subglacial sediment storage can impact glacial sediment flux, in addition to changes in climate, erosion rate and glacier dynamics, the interpretation of climatic changes based on the sediment record is more complex than generally assumed.

The Influence of Benthic Macrofauna on the Erodibility of Intertidal Sediments with Varying mud Content in Three New Zealand Estuaries

Fine sediment inputs can alter estuarine ecosystem structure and function. However, natural variations in the processes that regulate sediment transport make it difficult to predict their fate. In this study, sediments were sampled at different times (2011–2012) from 45 points across intertidal sandflat transects in three New Zealand estuaries (Whitford, Whangamata, and Kawhia) encompassing a wide range in mud (≤63 μm) content (0–56 %) and macrofaunal community structure. Using a core-based erosion measurement device (EROMES), we calculated three distinct measures of sediment erosion potential: erosion threshold (Ʈ c ; N m−2), erosion rate (ER; g m−2 s−1), and change in erosion rate with increasing bed shear stress (m e ; g N−1 s−1). Collectively, these measures characterized surface (Ʈ c and ER) and sub-surface (m e ) erosion. Benthic macrofauna were grouped by functional traits (size and motility) and data pooled across estuaries to determine relationships between abiotic (mud content, mean grain size) and biotic (benthic macrofauna, microbial biomass) variables and erosion measures. Results indicated that small bioturbating macrofauna (predominantly freely motile species <5 mm in size) destabilized surface sediments, explaining 23 % of the variation in Ʈ c (p ≤ 0.01) and 59 % of the variation in ER (p ≤ 0.01). Alternatively, mud content and mean grain size cumulatively explained 61 % of the variation in m e (p ≤ 0.01), where increasing mud and grain size stabilized sub-surface sediments. These results highlight that the importance of biotic and abiotic predictors vary with erosion stage and that functional group classifications are a useful way to determine the impact of benthic macrofauna on sediment erodibility across communities with different species composition.

Effect of antecedent soil moisture content on soil critical shear stress in agricultural watersheds

Agricultural fields act as major sources of sediment pollution for surface waters. Grassed waterways are often used as a best management practice to prevent gully erosion and control the amount of sediment delivered from the edge of agricultural fields to receiving water bodies. A widely accepted method for estimating erosion of cohesive soils (excess shear stress equation) involves determining the critical shear stress of the soil and comparing it to the shear stress exerted by the flow. Antecedent soil moisture is an important factor influencing runoff and erosion and understanding the relationship between antecedent moisture and critical shear stress for key features within an agricultural watershed (e.g. field and grassed waterway) can improve soil erosion prediction. Critical shear stress was measured in situ using a Cohesive Strength Meter for varying soil moisture conditions in a 3×3m grid in: (1) a field and (2) a grassed waterway, in an agricultural watershed located in Southwestern Wisconsin. Soil properties including bulk density, organic matter content, plastic limit, liquid limit and plasticity index were also measured. Results showed that critical shear stress in the grassed waterway and in the agricultural field increased as soil moisture increased until the soil moisture content reached a breakpoint that was approximately equal to the plastic limit. Above this breakpoint, critical shear stress of the soil decreased making the soil more susceptible to erosion. Exponential relationships between critical shear stress and soil moisture content below the breakpoint indicate that soil moisture explained more of the variability in critical shear stress for the grassed waterway (68%) compared to the agricultural field (27%). These relationships were used in conjunction with the excess shear stress equation and continuous soil moisture measurements to demonstrate changes in soil erosion rate with changes in soil moisture.

Investigation of slurry concentration effects on solid particle erosion rate for an impinging jet

The slurry particle concentration effect on the erosion rate of tool components is a critical factor in the design and maintenance of industrial equipment. The relationship between slurry particle concentration and erosion rate was tested and evaluated at a jet impingement test facility using glass spheres impacting acrylonitrile butadiene styrene (ABS) coupons. Particle concentration ranged from 4.6% to 22.4% by weight, and three different nozzle standoff heights were used (H/D=3.0, 5.2, and 7.4). The results show the erosion rate is dependent on the slurry concentration and the test duration. Two distinct erosion profiles correlated with changes in erosion rate over the test duration. The transition between the erosion profiles and the change in erosion rate were dependent on the initial test geometry and slurry concentration.

Interactions among millennial-scale geomorphic processes in different parts of a drainage basin, arid China

The geomorphic evolution of different parts of the Shiyang River catchment was analyzed in this study, using Quaternary chronologies, sedimentary facies, grain size, geochemical proxies, and pollen proxies of sedimentary sections and study sites to examine millennial-scale geomorphic processes. Results indicate that during the early and middle Holocene, most sections and study sites were eroded in the upper reaches, with an average erosion rate around 0.042 cm/yr, while sediment deposition appeared in the middle reaches, at a rate of 0.091 cm/yr. At the same time, the average deposition rate was 0.062 cm/yr in the lower reaches. During the late Holocene, erosion in the upper reaches was more severe, with the rate of 0.169 cm/yr, due to the development of steep river banks. The middle reaches showed an average late-Holocene erosion rate of 0.089 cm/yr, and sediments in the lower reaches were deposited at a rate of 0.011 cm/yr. Characteristics of all proxies are well related to the changes of erosion and deposition rates; therefore, climate change is assumed to be the primary factor for geomorphic evolution at the millennia scale, and geomorphic responses of different parts of the river are understood to be connected but distinct.

Impact of change in erosion rate and landscape steepness on hillslope and fluvial sediments grain size in the Feather River basin (Sierra Nevada, California)

Abstract. The characteristics of the sediment transported by rivers (e.g. sediment flux, grain size distribution – GSD) dictate whether rivers aggrade or erode their substrate. They also condition the architecture and properties of sedimentary successions in basins. In this study, we investigate the relationship between landscape steepness and the grain size of hillslope and fluvial sediments. The study area is located within the Feather River basin in northern California, and studied basins are underlain exclusively by tonalite lithology. Erosion rates in the study area vary over an order of magnitude, from &gt;250 mm ka−1 in the Feather River canyon to &lt;15 mm ka−1 on an adjacent low-relief plateau. We find that the coarseness of hillslope sediment increases with increasing hillslope steepness and erosion rates. We hypothesise that, in our soil samples, the measured 10-fold increase in D50 and doubling of the amount of fragments larger than 1 mm when slope increases from 0.38 to 0.83 m m−1 is due to a decrease in the residence time of rock fragments, causing particles to be exposed for shorter periods of time to processes that can reduce grain size. For slopes in excess of 0.7 m m−1, landslides and scree cones supply much coarser sediment to rivers, with D50 and D84 more than one order of magnitude larger than in soils. In the tributary basins of the Feather River, a prominent break in slope developed in response to the rapid incision of the Feather River. Downstream of the break in slope, fluvial sediment grain size increases, due to an increase in flow competence (mostly driven by channel steepening) as well as a change in sediment source and in sediment dynamics: on the plateau upstream of the break in slope, rivers transport easily mobilised fine-grained sediment derived exclusively from soils. Downstream of the break in slope, mass wasting processes supply a wide range of grain sizes that rivers entrain selectively, depending on the competence of their flow. Our results also suggest that, in this study site, hillslopes respond rapidly to an increase in the rate of base-level lowering compared to rivers.

Biotic interactions influence sediment erodibility on wave-exposed sandflats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 523:15-30 (2015) - DOI: https://doi.org/10.3354/meps11164 Biotic interactions influence sediment erodibility on wave-exposed sandflats Rachel J. Harris1,*, Conrad A. Pilditch1, Judi E. Hewitt2, Andrew M. Lohrer2, Carl Van Colen4, Michael Townsend2, Simon F. Thrush3 1School of Science, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand 2National Institute of Water and Atmospheric Research Ltd. (NIWA), PO Box 11115, Hamilton 3240, New Zealand 3Institute of Marine Science, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand 4Research Group of Marine Biology, Ghent University, Krijgslaan 281/S8, 9000 Ghent, Belgium *Corresponding author: harris.rachelj@gmail.com ABSTRACT: Biological activities in marine soft-sediments can modify the sedimentary environment through processes that change erosion rates. In low-energy environments, bioturbating macrofauna destabilizes sediments while microbes bind sediments and stabilize them. The degree to which these counter-acting processes influence sediment movement in a physically dynamic environment has not been well quantified. In a field experiment, we established 56 (1 m2) plots on an exposed intertidal sandflat. We used shade cloth and manipulated grazing pressure exerted by the deposit-feeding bivalve Macomona liliana (0-200 ind. m-2) to alter the microphytobenthic community. Three months post-manipulation, initiation of sediment transport (Ʈc) and change in sediment erosion rate with increasing bed shear stress (me) were measured. Mean grain size, density of the spionid polychaete Aonides trifida, density of adult M. liliana, and bulk carbohydrate concentration could account for 54% of the variation in Ʈc (0.3-1.1 N m-2 s-1). Mean grain size was the only significant predictor (p ≤ 0.01) of me explaining 22% of the variability (6-20 g N-1 s-1). Ʈc was negatively correlated with density of several abundant shallow-dwelling bioturbators (indicating sediment destabilization), but we did not observe the expected increase in Ʈc with microbial biomass. Furthermore, there was a positive correlation between adult M. liliana and Ʈc as well as evidence for several positive feedbacks between abundant shallow-dwelling macrofauna and microbial biomass. These study results demonstrate that despite frequent reworking by tidal currents and waves, bioturbating macrofauna are important to initiating sediment transport regardless of their effects on microbial biomass. KEY WORDS: Deposit-feeding · Microphytobenthos · Benthic macrofauna · Sediment stability · Infauna · Positive feedbacks · Macomona liliana · Habitat modifiers Full text in pdf format PreviousNextCite this article as: Harris RJ, Pilditch CA, Hewitt JE, Lohrer AM, Van Colen C, Townsend M, Thrush SF (2015) Biotic interactions influence sediment erodibility on wave-exposed sandflats. Mar Ecol Prog Ser 523:15-30. https://doi.org/10.3354/meps11164 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 523. Online publication date: March 16, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Coupled Effects between Solid Particles and Gas Velocities on Erosion of Elbows in Natural Gas Pipelines

The damage of materials caused by erosion of solid particles occurs on a large scale in different fields, including machinery, aviation, and pipeline transportation, resulting in considerable economic losses in the world. Therefore, the erosion of elbows has been extensively researched, with emphasis on single factors such as properties of solid particles, gas velocities, incidence angles, and temperatures. Erosion is generally affected by two or more coupled factors, however very few studies have been conducted on this subject. Thus, this study investigates the coupled effect between solid particles and gas velocities on the erosion of elbows in natural gas pipelines. A simulation was performed by combining the theoretical model of erosion and the Lagrange discrete phase model. The simulation result was then compared with the results of the working conditions and test platform based on a similar principle. Moreover, the properties of solid particles and the speed of natural gas in pipelines were coupled to analyze the change of erosion rate at different velocities and properties of solid particles (i.e., sizes, shapes, quantities, and incidence angles). Results showed that the erosion rate increases with the increase in size and quantity of solid particles. The small shape coefficient of solid particles causes severe erosion, and their incidence angle influences the rate and position of erosion of the elbows. A complicated coupling effect between solid particles and gas velocities on the erosion of elbows in natural gas pipelines occurs.

Combined hillslope diffusion and sediment transport simulation applied to landscape dynamics modelling

AbstractWe present a new numerical approach for simulating geomorphic and stratigraphic processes that combines open‐channel flow with non‐uniform sediment transport law and semi‐empirical diffusive mass wasting. It is designed to facilitate modelling of surface processes across multiple space‐ and time‐scales, and under a variety of environmental and tectonic conditions. The physics of open‐channel flow is primarily based on an adapted Lagrangian formulation of shallow‐water equations. The interaction between flow and surface geology is performed by a non‐uniform total‐load sediment transport law. Additional hillslope processes are simulated using a semi‐empirical method based on a diffusion approach. In the implementation, the resolution of flow dynamics is made on a triangulated grid automatically mapped and adaptively remeshed over a regular orthogonal stratigraphic mesh. These new methods reduce computational time while preserving stability and accuracy of the physical solutions. In order to illustrate the potential of this method for landscape and sedimentary system modelling, we present a set of three generic experiments focusing on assessing the influence of contrasting erodibilities on the evolution of an active bedrock landscape. The modelled ridges morphometrics satisfy established relationships for drainage network geometry and slope distribution, and provide quantitative information on the relative impact of hillslope and channel processes, sediment discharge and alluviation. Our results suggest that contrasting erodibility can stimulate autogenic changes in erosion rate and influence the landscape morphology and preservation. This approach offers new opportunities to investigate joint landscape and sedimentary systems response to external perturbations. The possibility to define and track a large number of materials makes the implementation highly suited to model source‐to‐sink problems where material dispersion is the key question that needs to be addressed, such as natural resources exploration and basin analysis. Copyright © 2014 John Wiley &amp; Sons, Ltd.

The RUSLE erosion index as a proxy indicator for debris flow susceptibility

Debris flows represent dangerous occurrences in many parts of the world. Several disasters are documented due to this type of fast-moving landslides; therefore, natural-hazard assessment of debris flows is crucial for safety of life and property. To this aim, much current work is being directed toward developing geotechnical-hydraulic models for the evaluation of debris flow susceptibility. A common base for such current models is parameterization of background predisposing and triggering factors such as inherent characteristics of geo-materials, topography, landscape and vegetation cover, rainfall regime, human activities, etc. which influence the occurrence of these processes on slopes. The same factors are also taken into account in soil erosion prediction models. Consequently, it seems worth investigating the effectiveness of the soil erosion index as debris flows susceptibility indicator. To this aim, a logistic regression analysis was carried out between the erosion index assessed by means of the Revised Universal Soil Loss Equation (RUSLE) model and the inventory of debris flows that have occurred in an area in Sicily (Southern Italy). Model assumptions were verified and validated by means of a series of statistical tools. Different possible scenarios were also evaluated by considering hypothetical changes in soil erosion rate under different rain erosivity conditions. Notwithstanding the rough approximations in model data collection, the outcomes appear encouraging.

Experimental Study of Rill Evolution Processes and Relationships between Runoff and Erosion on Clay Loam and Loess

Rill erosion accounts for approximately 70% of the total erosion of upland areas in China's Loess Plateau. A laboratory rainfall experiment with deionized water was conducted to examine the process of rill evolution and the relationship between runoff, rill evolution, and erosion rates for clay loam and loess soils given a fixed slope gradient (10°) and two rainfall intensities (1.5 and 2.0 mm min−1). The results show that rills evolved from a series of parallel drop‐pit chains along the down‐slope direction. Clay loam soil produced rills under a rainfall intensity of 1.5 mm min−1, and loess soil produced rills only under higher rainfall intensity. The temporal change in sediment concentration and erosion rate shows good consistency with the emergence of drop pits and rills. An increase in rainfall intensity had little effect on the sediment concentration and erosion rate for clay loam soil, whereas for loess soil, both increased rapidly and exceeded those of clay loam soil, with the emergence of a rill when the rainfall intensity was higher. Rills have a much greater effect on sediment concentration and erosion rate for loess soil than for clay loam soil. This study indicates that soil texture has a major impact on rill formation; clay loam soil is more subject to rill formation, but the rills formed are generally small and do not substantially increase soil loss. In contrast, the well‐developed rills in silt loam soil can result in intensive soil loss, though rills occur infrequently. Basic understanding of these results, causes, and quantification are essential for the prediction and evaluation of soil loss.

GIS Based Estimation of Sediment Discharge and Areas of Soil Erosion and Deposition for the Torrential Lukovska River Catchment in Serbia

In the present study the SHETRAN river basin modelling system was used in conjunction with Geographic Information System (GIS) to estimate potential erosion and deposition rates within the catchment and the concentrations of sediment in a flow at the catchment outlet on the example of the 114.31 km2 mountainous torrential Lukovska River catchment in Serbia. The streams in the Lukovska River catchment are short, steep and often produce hazardous torrential floods as a consequence of strong rainfall of short duration. The soil erosion and sediment discharge were analysed in view of the catchment response to physical characteristics of the catchment. Considering that the most of total annual sediment discharge in watersheds of torrential character is achieved during storm events, the SHETRAN modelling system was calibrated on the example of a storm event in 1986 and validated for three other storm events in 1974, 1976 and 1979. The simulated results of discharges and sediment concentrations at the catchment outlet for both calibration and validation events were compared with the observed data and found to be reasonable. The changes of erosion and deposition rates within the catchment and in the course of time were estimated for the calibration event in 1986. The simulated erosion rates were within the range of 1 to 10.5 t/ha and corresponded to the observed rates of erosion in Europe during extreme rain events. The presented methodology is useful in identifying the erosion vulnerable regions in a catchment where erosion control measures should be implemented.

Impact of climate change on soil erosion — A high-resolution projection on catchment scale until 2100 in Saxony/Germany

This study investigates changes in erosion rates at high temporal and spatial resolution for three example catchments in West, North and East Saxony/Germany under climate change. The study is based on the A1B IPCC-scenario and model outputs of four models: ECHAM5-OPYC3 (general circulation model), WETTREG2010 (statistical downscaling climate model), METVER (agricultural model for calculation of daily initial soil moisture) and EROSION 3D as a process-based soil erosion model. Simulations were run for measured and projected single rainstorm events at a temporal resolution of 5min. Soil loss was simulated for two future periods from 2041 to 2050 and 2091 to 2100, respectively. Results were compared to simulated soil loss based on 10years of measured climate data from 1989 to 2007. Expected changes in land use, soil management due to changed crop rotation and shifted harvest date are taken into account as scenario studies.Outputs of the regional climate model show that the total number of rainstorms with intensities≥0.1mm/min is decreasing in future while rainfall intensities are increasing. Periods of heavy rainstorms will mostly shift from summer to autumn. While the total amount of annual rainfall is decreasing and the duration of sunshine is strongly increasing, soils become drier. Dry periods will appear more often in late autumn.Results of the simulations with EROSION 3D quantify the impacts of climate change on erosion rates. Climate change will lead to a significant increase of soil loss by 2050 and a partial decrease by 2100. Not adapting soil management and land use will aggravate erosion rates.The impacts of land use, soil management and soil properties on soil erosion by water are higher than the effects of changed precipitation patterns. Current soil protection measures are suitable for soil conservation under conditions of a changed climate.

Rock uplift and erosion rate history of the Bergell intrusion from the inversion of low temperature thermochronometric data

The Bergell intrusion (European Alps) was one of the first locations where thermochronometry was used to resolve changes in erosion rate, yet, relating these changes to variations in climate or in local tectonics remains challenging. One approach that enables changes in erosion rate to be related to changes in climate or rock uplift rate is to utilize landscape evolution models, as topographic response to these forcing parameters is unique. Furthermore, low temperature thermochronometric systems have the potential to resolve topography through time and thus topographic response. We present new (U-Th)/He data for samples collected across 2 km of relief from the Bergell. The ages range from ∼2 to ∼16 Ma and define an age elevation with an apparent exhumation rate of 0.1 km/Myr. In order to infer erosion rates, we use a thermokinematic model to solve the heat equation in the crust, track material points through time and predict thermochronometric data. Paleo-topography and erosion rate are parameterized using the stream power model. We find that rock uplift rates were 0.4 km/Myr from ∼25 to ∼20 Ma and subsequently decreased to 0.05 km/Myr. This results in a gradual decrease in erosion rate from rates of 0.4 to 0.1 km/Myr. A recent increase in rock uplift rate at ∼4 Ma to ∼0.6 km/Myr is required to explain the youngest ages and high topographic relief.

Conifer epicuticular wax as a biomarker of air pollution: an overview

Epicuticular wax covering the conifer tree species surface has been used, mainly in conifers, as a biomarker of air pollution damage. Using Scanning Electron Microscopy (SEM) various alterations in wax structure and chemistry caused by natural and anthropogenic factors have been noticed. SEM enables to evaluate wax deterioration at a very early stage, before visible symptoms occur. Symptoms of wax injury are, in general, not specific to the air pollutant type. Most common alterations in wax were the following: an undeveloped structure, various type of wax tubes fusion or erosion (deformed and disfunctioned stomatal complexes, a decrease in wax tube distribution, increased enrichment of completely amorphous stage), shifted annual wax erosion rate, chemical and needle wettability changes. To use SEM as an accurate tool for evaluating wax alteration, it is essential to distinguish air pollution and natural factors from artefacts caused by inappropriate usage of technique.

Late-Cenozoic relief evolution under evolving climate: A review

Abstract The present review paper is an attempt to summarize quantitative evidence of Late Cenozoic changes in topographic relief. Different meanings of the word “relief”, as it is commonly used, and detail the metrics used to quantify it. We then specify methodological tools used to quantify relief change (primarily low-temperature thermochronometry and terrestrial cosmogenic nuclides), and analyze published evidence for different regions. Our review first shows that relief changes and rates of changes are more important at mid-, than high- or low-latitudes, and appear to be insensitive to mean precipitation rates. It also show that relief change is positive (relief increases) in most of the reported cases (~ 80%). We subsequently define two functional relationships between relief and erosion, depending on the chosen definition of relief, and propose a conceptual model of landscape memory. We conclude, following others, that erosion rates depend non-linearly on relief evolution, itself being a function of the spatial distribution and rates of erosion. The relief increases documented in this review may be to erosion rate increases during the same timescales. Lastly, we discuss the importance of glacial and periglacial processes on Late Cenozoic relief and erosion rate changes, and stress the importance of frost shattering and glacial erosion at mid- and high-latitudes.

Event layers in the Japanese Lake Suigetsu ‘SG06’ sediment core: description, interpretation and climatic implications

Event layers in lake sediments are indicators of past extreme events, mostly the results of floods or earthquakes. Detailed characterisation of the layers allows the discrimination of the sedimentation processes involved, such as surface runoff, landslides or subaqueous slope failures. These processes can then be interpreted in terms of their triggering mechanisms. Here we present a 40 ka event layer chronology from Lake Suigetsu, Japan. The event layers were characterised using a multi-proxy approach, employing light microscopy and μXRF for microfacies analysis. The vast majority of event layers in Lake Suigetsu was produced by flood events (362 out of 369), allowing the construction of the first long-term, quantitative (with respect to recurrence) and well dated flood chronology from the region. The flood layer frequency shows a high variability over the last 40 ka, and it appears that extreme precipitation events were decoupled from the average long-term precipitation. For instance, the flood layer frequency is highest in the Glacial at around 25 ka BP, at which time Japan was experiencing a generally cold and dry climate. Other cold episodes, such as Heinrich Event 1 or the Late Glacial stadial, show a low flood layer frequency. Both observations together exclude a simple, straightforward relationship with average precipitation and temperature. We argue that, especially during Glacial times, changes in typhoon genesis/typhoon tracks are the most likely control on the flood layer frequency, rather than changes in the monsoon front or snow melts. Spectral analysis of the flood chronology revealed periodic variations on centennial and millennial time scales, with 220 yr, 450 yr and a 2000 yr cyclicity most pronounced. However, the flood layer frequency appears to have not only been influenced by climate changes, but also by changes in erosion rates due to, for instance, earthquakes.