scholarly journals Vegetation and climate effects on soil production, chemical weathering, and physical erosion rates

2021 ◽  
Author(s):  
Mirjam Schaller ◽  
Todd Alan Ehlers
Keyword(s):  
Chemical Weathering ◽  
Mediterranean Climate ◽  
Annual Precipitation ◽  
Mean Annual Precipitation ◽  
Weathering Rates ◽  
Erosion Rates ◽  
Denudation Rates ◽  
Soil Production ◽  
Physical Erosion ◽  
Global Data

Abstract. Weathering of bedrock to produce regolith is essential for sustaining life on Earth and global biogeochemical cycles. The rate of this process is influenced not only by tectonics, but also by climate and biota. Here we investigate these interactions with new observations of soil production, chemical weathering, and physical erosion rates from the large climate and vegetation gradient of the Chilean Coastal Cordillera (26° to 38° S). These findings are compared to a global compilation of published data from similar settings. The four Chilean study areas span (from North to South): arid (Pan de Azúcar), semi-arid (Santa Gracia), mediterranean (La Campana) and temperate humid (Nahuelbuta) climate zones. We test the hypotheses that: 1) soil production as well as chemical weathering rates increase with increasing mean annual precipitation; 2) physical erosion rates stabilize as vegetation cover increases; and 3) the contribution of chemical weathering to total denudation is constant over the climate gradient.We find observed soil production rates range from ~7 to 290 t/(km2 yr) and are lowest in the sparsely vegetated and arid North, increase southward toward the vegetated mediterranean climate, and then decrease further South in the temperate humid zone. This trend is discussed and compared with global data from similar catchments underlain by granitic lithologies. Calculated chemical weathering rates range from zero in the arid North to a high value of 211 t/(km2 yr) in the mediterranean zone. Chemical weathering rates are comparable in the semi-arid and temperate humid zones (~20 t/(km2 yr). Physical erosion rates are low in the arid zone (~11 t/(km2 yr)) and increase towards the South (~ 40 t/(km2 yr)). Combined total chemical weathering and physical erosion rates indicate that denudation rates are lowest in the arid North and highest in the Mediterranean climate zone. The contribution of chemical weathering to total denudation rates increases and then decreases with increasing mean annual precipitation from North to South. The observation that the calculated chemical weathering rates in the southernmost location, with the highest mean annual precipitation and the highest chemical index of alteration, are not the highest of all four study areas is found to be consistent with the global data analysis.

Chemical weathering and physical erosion rates along a vegetation and climate gradient, Chilean Coastal Cordillera (26° – 38°S)

2020 ◽  
Author(s):  
Mirjam Schaller ◽  
Todd A. Ehlers
Keyword(s):  
Chemical Weathering ◽  
Annual Precipitation ◽  
Mean Annual Precipitation ◽  
Weathering Rates ◽  
Coastal Cordillera ◽  
Erosion Rates ◽  
Denudation Rates ◽  
Chemical Index ◽  
Chemical Index Of Alteration ◽  
Physical Erosion

<p>Chemical weathering and physical erosion are important processes shaping topography, producing soils, and providing nutrients for life.  The rates of these processes are influenced not only by tectonics, but also by climate and biota.  The Chilean Coastal Cordillera from 26° to 38°S is a natural laboratory to investigate chemical weathering and physical erosion rates over different climatic settings.  From North to South, climate changes from arid (Pan de Azúcar), semi-arid (Santa Gracia), Mediterranean (La Campana) to temperate humid (Nahuelbuta).  Here we present chemical weathering and physical erosion rates based on published and new in situ-produced cosmogenic nuclides and immobile elements published from soil pedon depth profiles in the four study areas.</p><p>Calculated chemical weathering rates range from zero in Pan de Azúcar to an high value of 211 t/(km<sup>2</sup> yr) in La Campana.  Chemical weathering rates are comparable in Santa Gracia and Nahuelbuta (~20 t/(km<sup>2</sup> yr).  Physical erosion rates are low in Pan de Azúcar (~11 t/(km<sup>2</sup> yr)) and increase towards the South (~ 40 t/(km<sup>2</sup> yr)).  Combined chemical weathering and physical erosion rates indicate that denudation rates are lowest in Pan de Azúcar and highest in La Campana.  The contribution of chemical weathering to total denudation rates is increasing and then decreasing with increasing mean annual precipitation from North to South.  The observation that the calculated chemical weathering rates in the southernmost location with the highest mean annual precipitation and the highest chemical index of alteration are not the highest of all four study areas is evaluated and discussed.   We investigate possible influence of precipitation and vegetation on chemical weathering and physical erosion rates.</p>

Patchy bedrock explained: Tectonic fracture control on landscape evolution patterns in south-Central Chile 

2021 ◽  
Author(s):  
Emma Lodes ◽  
Dirk Scherler ◽  
Hella Wittmann ◽  
Renee Van Dongen
Keyword(s):  
Chemical Weathering ◽  
Landscape Evolution ◽  
Tectonic Deformation ◽  
Fracture Density ◽  
Rock Fracturing ◽  
Central Chile ◽  
Erosion Rates ◽  
Denudation Rates ◽  
South Central

<p>Rock fracturing induced by tectonic deformation is thought to promote faster denudation in more highly fractured areas by lowering grain size and directing the flow of water. That the density and pattern of fractures in a landscape play a role in controlling erosion and landscape evolution has been known for over a century, but not until recently do we have tools, like cosmogenic nuclides, to quantify erosion rates in places with varying fracture densities. In the Nahuelbuta Range in south-central Chile, we observed that >30-m thick regolith exists next to patches of unweathered bedrock. We hypothesize that the density of fractures dictates the pace and patterns of chemical weathering, regolith conversion, and erosion in the Nahuelbuta Range. To test this, we used in situ cosmogenic <sup>10</sup>Be to obtain denudation rates from amalgamated samples of bedrock, corestones and soils, and measured fracture density and orientation, as well as hillslope boulder size in several sites in the Nahuelbuta Range. We found that more highly fractured areas indeed have higher denudation rates than less fractured areas, and that bedrock denudation rates are ~10 m/Myr while soil denudation rates are ~30 m/Myr, suggesting that soil-covered areas may be sites of higher fracture density at depth. Fractures have orientations that match mapped faults across the Nahuelbuta range, and thus are considered to be tectonically-induced. In addition, both fracture and fault orientations match the orientation of streams incising the range, suggesting that fractures control stream channel orientation by weakening bedrock and thus directing flow.</p>

(U-Th-Sm)/He dating of supergene Fe duricrusts in NE French Guiana: implications of a multiproxy approach

2020 ◽  
Author(s):  
Beatrix Heller ◽  
Silvana Bressan Riffel ◽  
Cécile Gautheron ◽  
Thierry Allard ◽  
Guillaume Morin ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
French Guiana ◽  
X Ray Diffraction ◽  
X Ray ◽  
Weathering Processes ◽  
Erosion Rates ◽  
Large Dispersion ◽  
Icp Ms ◽  
Physical Erosion ◽  
Geochemical Analyses

<p>Laterites are developing under intense chemical weathering and low physical erosion rates. Despite their large extension at the Earth’s surface, there is still a lack of time constraints for their formation, evolution and relation with climatic change. Nevertheless, several chronological studies show that they represent a geological record at least all along the Cenozoic Era. Indeed, laterite samples often contain several coexisting generations of iron oxides and oxyhydroxides that indicate successive weathering processes due to the dissolution of previously formed phases followed by reprecipitation. This study focuses on the condition and chronology of weathering in Northeastern French Guiana which generated pedogenic iron crusts on Paleoproterozoic mafic and intermediate rocks. It offers the opportunity to document the evolution of this part of the Guyana Shield, known as a tectonically stable area since the Cretaceous. The two sampling sites, Kaw and Baduel, are paleosurfaces at 300m and 100m elevations, respectively, that have been dated previously by paleomagnetism, providing Eocene ages for both sites, albeit with some substantial uncertainties and dispersion [1].</p><p>Since the duricrust (top layer) of the lateritic profile is enriched in hematite and goethite, we aim to date those mineral phases using the (U-Th-Sm)/He method. Older ages are from Oligocene and Miocene epochs for the Kaw and Baduel sites, respectively, with a large dispersion in the age values, as expected from the presence of several generations of Fe-minerals. Identification of petrological relationship between these different generations is hindered by their intimate mixing. In order to overcome this difficulty and to identify the episodes of weathering and mineral precipitation, we coupled a number of mineralogical and geochemical analyses, namely through powder and single grain X-ray diffraction, energy dispersive X-ray spectrometry (SEM-EDS) and solution- and LA-ICP-MS. Data on formation ages of secondary iron phases will be discussed by reference to literature, in terms of geodynamic and paleoclimatic forcing.</p><p>[1] Théveniaut, H., and Freyssinet, P. (2002): Timing of lateritization on the Guiana Shield: synthesis of paleomagnetic results from French Guiana and Suriname. Palaeogeography, Palaeoclimatology, Palaeoecology (178) 91-117</p>

scholarly journals High natural erosion rates are the backdrop for present-day soil erosion in the agricultural Middle Hills of Nepal

2015 ◽  
Vol 3 (3) ◽  
pp. 363-387 ◽  
Author(s):  
A. J. West ◽  
M. Arnold ◽  
G. AumaÎtre ◽  
D. L. Bourlès ◽  
K. Keddadouche ◽  
...  
Keyword(s):  
Land Use ◽  
Soil Erosion ◽  
Soil Loss ◽  
Mass Wasting ◽  
Catchment Scale ◽  
Erosion Rates ◽  
Denudation Rates ◽  
Soil Production ◽  
The Himalaya

Abstract. Although agriculturally accelerated soil erosion is implicated in the unsustainable environmental degradation of mountain environments, such as in the Himalaya, the effects of land use can be challenging to quantify in many mountain settings because of the high and variable natural background rates of erosion. In this study, we present new long-term denudation rates, derived from cosmogenic 10Be analysis of quartz in river sediment from the Likhu Khola, a small agricultural river basin in the Middle Hills of central Nepal. Calculated long-term denudation rates, which reflect background natural erosion processes over 1000+ years prior to agricultural intensification, are similar to present-day sediment yields and to soil loss rates from terraces that are well maintained. Similarity in short- and long-term catchment-wide erosion rates for the Likhu is consistent with data from elsewhere in the Nepal Middle Hills but contrasts with the very large increases in short-term erosion rates seen in agricultural catchments in other steep mountain settings. Our results suggest that the large sediment fluxes exported from the Likhu and other Middle Hills rivers in the Himalaya are derived in large part from natural processes, rather than from soil erosion as a result of agricultural activity. Catchment-scale erosional fluxes may be similar over short and long timescales if both are dominated by mass wasting sources such as gullies, landslides, and debris flows (e.g., as is evident in the landslide-dominated Khudi Khola of the Nepal High Himalaya, based on compiled data). As a consequence, simple comparison of catchment-scale fluxes will not necessarily pinpoint land use effects on soils where these are only a small part of the total erosion budget, unless rates of mass wasting are also considered. Estimates of the mass wasting contribution to erosion in the Likhu imply catchment-averaged soil production rates on the order of ~ 0.25–0.35 mm yr−1, though rates of mass wasting are poorly constrained. The deficit between our best estimates for soil production rates and measurements of soil loss rates supports conclusions from previous studies that terraced agriculture in the Likhu may not be associated with a large systematic soil deficit, at least when terraces are well maintained, but that poorly managed terraces, forest, and scrubland may lead to rapid depletion of soil resources.

scholarly journals Rapid response of silicate weathering rates to climate change in the Himalaya

2021 ◽  
Author(s):  
Anthony Dosseto ◽  
Nathalie Vigier ◽  
Renaud Joannes-Boyau ◽  
Ian Moffat ◽  
Tejpal Singh ◽  
...  
Keyword(s):  
Climate Change ◽  
Carbon Dioxide ◽  
Atmospheric Carbon Dioxide ◽  
Chemical Weathering ◽  
Tight Coupling ◽  
Weathering Rates ◽  
Fluvial Terraces ◽  
Physical Erosion ◽  
Atmospheric Carbon ◽  
Earth’S Climate

Chemical weathering of continental rocks plays a central role in regulating the carbon cycle and the Earth’s climate (Walker et al., 1981; Berner et al., 1983), accounting for nearly half the consumption of atmospheric carbon dioxide globally (Beaulieu et al., 2012). However, the role of climate variability on chemical weathering is still strongly debated. Here we focus on the Himalayan range and use the lithium isotopic composition of clays in fluvial terraces to show a tight coupling between climate change and chemical weathering over the past 40 ka. Between 25 and 10 ka ago, weathering rates decrease despite temperature increase and monsoon intensification. This suggests that at this timescale, temperature plays a secondary role compared to runoff and physical erosion, which inhibit chemical weathering by accel-erating sediment transport and act as fundamental controls in determining the feedback between chemical weathering and atmospheric carbon dioxide.

scholarly journals Lithologic, tectonic, and climatic controls on chemical weathering, soil production, and erosion in New Zealand

2020 ◽  
Author(s):  
Claire Lukens ◽  
Kevin Norton ◽  
Dennis Dahms ◽  
Eron Raines
Keyword(s):  
Spatial Patterns ◽  
Chemical Weathering ◽  
Large Fraction ◽  
Southern Alps ◽  
Published Data ◽  
Surface Erosion ◽  
Temperature Threshold ◽  
Production Rates ◽  
Erosion Rates ◽  
Soil Production

Over geologic timescales, chemical weathering in mountain landscapes may play an important role in regulating atmospheric CO2. Understanding the feedbacks between climate, tectonics, erosion rates, biota, and weathering has been a recent focus of research, but disentangling these complex relationships remains a challenge. One area of particular interest has been the potential for a kinetic limit to weathering and soil production. Studies in New Zealand's Southern Alps were among the first to clearly exceed proposed kinetic limits on soil production and demonstrate thresholds in the influence of precipitation on chemical weathering. Here we present a new dataset that addresses chemical weathering, soil production rates, and surface erosion rates, measured across an altitudinal transect in the Tararua Range on New Zealand's North Island. The transect spans a kilometer in relief, and receives 3.5-5.5 m of annual precipitation. Underlying bedrock comprises silty and sandy members of the same Cretaceous Greywacke, but subtle lithologic changes correspond to abrupt shifts in soil production rates and total weathering. Total weathering across the transect is roughly invariant for each lithology and reflects near-complete depletion of weatherable species, consistent with a previously proposed threshold in the influence of precipitation. However, spatial patterns in weathering differ markedly in saprolite and in soils. Deep weathering in saprolite decreases with elevation and makes up a large fraction of the total weathering. This pattern suggests that climate may influence saprolite weathering, even where the total weathering is supply-limited. Spatial patterns in saprolite and total weathering do not correlate with an abrupt vegetation transition from dense forest to alpine tussock, which may suggest that biota are more strongly affected by a temperature threshold or more complex biogeochemical cycling. We contrast these results with new and previously published data from the Southern Alps, which have a similar climate but experience rapid tectonic uplift. There, the fresh supply of minerals to soils provided by uplift and erosion may enable much faster weathering and soil production rates. Taken together, these observations suggest a strong lithologic and tectonic control on soil production and weathering rates in humid climates.

The convexity of carbonate hillslopes: the influence of climate, chemical weathering and dust flux

2020 ◽  
Author(s):  
Matan Ben-Asher ◽  
Itai Haviv ◽  
Onn Crouvi ◽  
Josh J Roering ◽  
Ari Matmon
Keyword(s):  
Mass Balance ◽  
Carbonate Rocks ◽  
Chemical Weathering ◽  
Airborne Lidar ◽  
Annual Rainfall ◽  
Soil Thickness ◽  
Denudation Rates ◽  
Soil Production ◽  
Hillslope Evolution ◽  
Dust Flux

<p>Convex soil-covered hillslopes are ubiquitous in various tectonic and climatic settings and are often modeled based on a mass balance relating hillslope convexity to regolith transport and soil production. In order to account for chemical weathering of carbonate rocks and dust input to the regolith, two fluxes that are commonly neglected in settings with silicate-dominated bedrock,  we modify this mass balance.</p><p>We studied 7 study sites in carbonate rocks across an Eastern Mediterranean gradient in the mean annual rainfall (250 to 900 mm yr<sup>-1</sup>) and dust flux (150 to 40 g m<sup>-2</sup> yr<sup>-1</sup>). Combining cosmogenic <sup>36</sup>Cl-derived hilltops denudation rates with an estimate of the regolith chemical depletion and dust fraction based on immobile elements, we predict the hillslope curvature and compare our predictions with observations based on high-resolution airborne LiDAR.</p><p>Our results demonstrate that soft carbonates (chalk) experience faster denudation rates relative to resistant dolo-limestone. However, the harder carbonates are more prone to chemical weathering, which systematically constitutes around half of their total denudation.  Soil production rates exhibit a humped dependency on soil thickness, with an apparent maximum at a depth of 8-16 cm.</p><p>The observed hillslope curvature vary as function of rainfall and dust flux with a minimum at sub-humid sites with intermediate rainfall of  500-600 mm/yr. The predicted curvature based on our new mass balance is not far from the observed curvature, illustrating the prominent effects of dust flux and chemical weathering on hillslope morphology.  Our model also implies that drier sites in the south probably experienced a more complex history of regolith production due dust flux fluctuations.</p><p>By incorporating dust flux and chemical weathering to the classic hillslope evolution model we identify a complex relation between hillslope curvature, soil production, and climate. These two fluxes are not unique to carbonate bedrock and should be incorporated in hillslope evolution models.</p>

scholarly journals Supplemental Material: The convexity of carbonate hilltops: 36Cl constraints on denudation and chemical weathering rates and implications for hillslope curvature

2020 ◽  
Author(s):  
Matan Ben-Asher
Keyword(s):  
Steady State ◽  
Numerical Modelling ◽  
Chemical Weathering ◽  
Annual Rainfall ◽  
State Table ◽  
Weathering Rates ◽  
Denudation Rates ◽  
Soil Creep ◽  
Mean Annual Rainfall ◽  
Study Sites

Figure S1: 36Cl denudation rates vs. mean annual rainfall of samples categorized by hillslope position and samples types; Figure S2: fd and CDF vs. mean annual rainfall, derived from immobile elements; Figure S3: Values of soil creep efficiency (K) vs. mean annual rainfall, estimated from numerical modelling and steady state, table with coordinates of study sites location; Figure S4: Photographs of hard dolo-limestone and soft chalk rocks; Figure S5: Mean hillslopes slope vs. mean relief.

A theoretical model coupling chemical weathering rates with denudation rates

Geology ◽  
2009 ◽  
Vol 37 (2) ◽  
pp. 151-154 ◽  
Author(s):  
Emmanuel J. Gabet ◽  
Simon M. Mudd
Keyword(s):  
Theoretical Model ◽  
Chemical Weathering ◽  
Model Coupling ◽  
Weathering Rates ◽  
Denudation Rates
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